WO2010094113A1 - Ammonia electrolyzer - Google Patents

Abstract

There is provided an ammonia electrolyzer comprising at least one electrolysis cell, said electrolysis cell comprising at least one anode compartment housing an anolyte; at least one cathode compartment housing a catholyte; a plurality of anodes connected in parallel and submerged within the anolyte, the anodes comprising an anode catalyst; and a plurality of cathodes connected in parallel and submerged within the catholyte, the cathodes comprising a cathode catalyst, wherein the application of an electric potential between the anodes and the cathodes activates electrolysis.

Description

TITLE OF THE INVENTION

AMMONIA ELECTROLYZER

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional application serial No. 61/153999, filed on February

20, 2009, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an ammonia electrolyzer. More specifically, the present invention relates to a system for the continuous generation of hydrogen via the electrolysis of ammonia.

BACKGROUND OF THE INVENTION

[0003] Fuel cell technology, particularly hydrogen fuel cell technology, for power generation has been recognized as an environmentally friendly alternative to traditional energy sources such as fossil fuels and has garnered a worldwide interest as a renewable clean energy supply. However, the use of hydrogen as fuel for fuel cells is pervaded with problems related to its transportation, storage and safety. Several on-site hydrogen production methods have been considered, for example via steam reforming of natural gas or hydrocarbons, water electrolysis, methanol reforming or dissociation of ammonia. However, current production methods of hydrogen, such as water electrolysis, are often inefficient and expensive.

[0004] Ammonia, with a storage capacity of 17.6 wt% hydrogen and 1.7 times as much hydrogen than liquefied hydrogen for a given volume, is a very interesting hydrogen carrier. Ammonia has thus been targeted as an alternative carrier and source of hydrogen for fuel cell applications notably due to the advantages it demonstrates over hydrogen. For instance, ammonia is easily liquefiable at ambient temperatures making it an ideal candidate for transportation and storage. It is also readily procurable and provides attractive economies of scale. In addition, it exudes a pungent odour detectable by humans. Also, since it is the second most produced chemical in the world, safety procedures for its handling and use are already in place in most countries. Lastly, the decomposition of ammonia via electrolysis in an alkaline media during low overpotential electro-oxidation is environmentally friendly as the nitrogen and water by-products pose little impact to the environment.

[0005] With an adequate infrastructure in place, the challenges related to exploiting the benefits of ammonia for hydrogen production via electrolysis of ammonia reside in its efficient conversion into hydrogen for stationary and mobile applications employing hydrogen fuel cell or genset technology.

[0006] A method for generation of hydrogen is the electro oxidation (electrolysis) of ammonia in an alkaline medium at room temperature, which was proposed by Gerischer and Mauerer in 1969 [H. Gerischer, A. Mauerer,

J. Electroanal. Chem. 25 (1970) 421- 443]. These authors also proposed a mechanism for the oxidation of ammonia on platinum, which was supported in a study by differential electrochemical mass spectrometry [J.F.E.

Gootzen, A.W. Wonders, W. Visscher, R.A. van Santen, J.A.R. van Veen, Electrochim. Acta 43 (1998) 1851].

[0007] A source of inefficiency for this method however is catalyst poisoning. While efficiencies as high as

70% can be attained through back conversion of hydrogen from ammonia via electrolysis, when such conversion endures over a longer period of time, the maximum value of conversion efficiency tends to decline due to the slow deactivation of an electrolyzer's anode. This slow deactivation can be explained by understanding the electro-oxidation mechanism at the anode. Although, there have been several mechanisms proposed for the ammonia oxidation on aclive sites of catalysts, a recent study by electrochemical mass spectrometry supported the following mechanism proposed by Gerischer and Mauerer [H. Gerischer, A. Mauerer, J. Electroanal. Chem. 25 (1970) 421- 443],

NH₃,ads + OH- → NH₂,ads + H₂O + e- [2]

NH₂,ads + OH^" → NHads + H₂O + e- [3]

NH_Xlads + NH_y,ads → N₂H_x+y,ads [4]

N₂H_x+y,_ads + (x + y)OH- → N₂ + (x + y)H₂O +(x + y)e^" [5]

NHads + OH- → Nads + H₂O + e- [6] where x = 1 or 2, y = 1 or 2.

[0008] It has been observed that at low current densities, the dehydrogenation of surface amine limits the overall rate of the reaction. Similarly, at higher current densities, the recombination of adsorbed nitrogen also limits the reaction rate. Thus, when demand for higher generated energy from an electrolyzer is attained by operating an electrolyzer at higher current densities, the adsorbed nitrogen formed at the above step 6 tends to block the active sites of the catalyst and reduce the catalyst's effectiveness through an effect known as catalyst poisoning (see also K. Endo, K. Nakamura, T. Miura, Electrochim. Acta 49 (2004) 2503-2509 and Vitse et al. Journal of Power Source, 143 (2005) 18-26).

[0009] In 2004, Endo et al. significantly reduced the poisoning of the electrode by alloying the platinum catalyst with iridium, ruthenium or nickel [K. Endo, Y. Katayama, T. Miura, Electrochim. Acta 49 (2004) 1635]. This bimetallic system leads to enhanced electrochemical activity for oxidation of ammonia in alkaline media. [0010] Other inefficiencies tend to arise in commercial scale electrolysis cells. During the electrolysis of ammonia, the amount of electrical energy that must be added is equivalent to the change in Gibbs free energy of the reaction plus the losses in the system. This electrical energy corresponds to the energy requirement for a standalone electrolysis cell without any additional components. In a commercial scale electrolysis cell, there are three key sources of electrical losses: overpotential; polarizalion; and resistance. Overpotential losses are due to the slowness in the rate of the reaction-taking place at the catalyst surface. The overpotential losses are found to be much higher at the anode than at the cathode and the activity of the anode catalyst thus limits the rate of the electrochemical reaction. Polarization losses are caused by the slowness of the essential ions to reach the aclive surface of the catalyst in the cell. Essentially, ions need to able to reach the active catalyst sites on the electrode plate. Anything that hinders the movement of ions will create a situation whereby there are not enough ions present at the electrode to deliver higher current densities. There is a competition with adsorbed ions needing to move away from the electrode sites when the fresh ions move in. If this is not influenced by natural convection, external energy has to be supplied to manifest the change. The loss of extra energy is termed as polarization losses. Finally, resistive losses occur when a current passes through any resistance, such as electrode rods, substrate plates, etc. Keeping the resistance low can minimize these losses. With all the losses taken into account, the electrical input is larger than the enthalpy change of the reaction, so some energy is released as waste heat.

[0011] Although, only small amounts of catalyst are typically electroplated on the electrode plates, the usual catalyst materials (e.g., platinum, ruthenium, etc.) are expensive and they can represent a substantial fraction of the overall cost of an electrolyzer. For instance, the reduction of ammonia at the anode can be achieved using a platinum alloy catalyst, while the cathode electrode typically contains a platinum catalyst for the reduction of water. Considering the increasing costs of the noble metals, catalyst use should be as efficient as possible. [0012] Electrodes prepared by electroplating of abovementioned bimetal catalysts over the surface of a metallic substrate were disclosed in US 2005/0211569 and WO 2007/047630 [also see Botte et al. Journal of the Electrochemical Society, 153 (10) A1894-1901 (2006) and Vitse et al. Journal of Power Source, 143 (2005) 18- 26]. These different multi-metallic catalysts were prepared by electroplating a substrate for both for the oxidation of ammonia and reduction of water. The substrates were a metal mesh, a metal foil or a metal sponge. The alloy catalyst was electrochemically deposited on the surface of the electrode plates by electro-deposition. [0013] Many other electrodes for the electrolysis of ammonia are known in the art. Non-limiting examples include those disclosed or referred to in the following documents: Endo et al. Electrochimica Acta 50 (2005) 2181-2185; Endo et al. Electrochimica Acta 49 (2004) 2503-2509; Wang et al. J. Phys. Chem. B 2005, 109, 7883-7893; Katan et al. J. Electrochem. Soc. 110, 9, 1022-1023; Sasaki et al. J. Electrochem Soc. 117, 6, 758- 762; and Zhou et al. International Journal of Hydrogen Energy 33 (2008) 5897-5904. [0014] Electrodes for many other applications are also known in the art. Non-limiting examples of electrodes for polymer electrolyte fuel cells include that disclosed or referred to in the following documents: US 4,876,115; US 2005/0260117; Natarajan et al. Journal of Electrochemical Society, 156 (2) B210-B215 (2009); Natarajan et al., Journal of the Electrochemical Society 154(3) B310-B315 (2007); and Natarajan et al. Electrochimica Acta 52 (2007) 3751-3757. Non-limiting examples of electrodes for the decomposition of ammonia include those disclosed in Yin et al. Applied Catalysis A: General 277 (2004) 1-9; Kim et al. Electrochimica Acta 50 (2005) 4356-4364 and Dietrich et al. Surface Science 352-354 (1996) 138-141. The chemical reaction and mechanism involved in polymer electrolyte fuel cells and decomposition of ammonia are different from those involved in the electrolysis (i.e. oxidation) of ammonia.

[0015] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. SUMMARY OF THE INVENTION

[0016] In accordance with the present invention, there is provided an ammonia electrolyzer comprising at least one electrolysis cell, said electrolysis cell comprising at least one anode compartment housing an aπolyte; at least one cathode compartment housing a catholyte; a plurality of anodes connected in parallel and submerged within the anolyte, the anodes comprising an anode catalyst; and a plurality of cathodes connected in parallel and submerged within the catholyte, the cathodes comprising a cathode catalyst, wherein the application of an electric potential between the anodes and the cathodes activates electrolysis.

[0017] In embodiments, the ammonia electrolyzer comprises a plurality of electrolysis cells connected in parallel.

[0018] In embodiments, the anode compartment and the cathode compartment are separated by an anionic exchange membrane.

[0019] In embodiments, the anode compartment and the cathode compartment are separated by a salt bridge compartment. In specific embodiments, the salt bridge compartment is filled with a saturated KCI solution.

[0020] In embodiments, the anodes are substantially parallel to each other. In embodiments, the cathodes are substantially parallel to each other.

[0021] In embodiments, the anodes and cathodes are electrically connected to an electrode switch matrix comprising a first plurality of relay switches electrically connected to the anodes and the cathodes, whereby the anodes and the cathodes can be selectively activated or deactivated by the closing or opening of the relay switches. In more specific embodiments, the ammonia electrolyzer further comprises a catalyst replenisher comprising a second plurality of relay switches electrically connected to the first plurality of relay switches of the switch matrix and a monitor to monitor the catalyst poisoning of the anodes, wherein when the monitor detects a poisoned anode catalyst, the catalyst replenisher reverses the electrical polarity applied to the poisoned anode and selectively isolates a cathode corresponding to the poisoned anode to reduce adsorbed nitrogen at the poisoned anode catalyst..

[0022] In embodiments, the ammonia electrolyzer further comprises an catholyte management system for controlling the concentration and level of the catholyte. In embodiments, the catholyte management system comprises a pH regulator for monitoring and maintaining the concentration of KOH within an operation range by adding KOH as needed. In embodiments, the catholyte management system comprises a fluid level regulator to monitor and maintain the level of anolyte within an operation range by adding water and KOH as needed.

[0023] In embodiments, the ammonia electrolyzer further comprises an anolyte management system for controlling the concentration and level of the anolyte. In embodiments, the anolyte management system comprises a pH regulator for monitoring and maintaining the concentration of KOH within an operation range by adding KOH as needed. In embodiments, the anolyte management system comprises a fluid level regulator to monitor and maintain the level of anolyte within an operation range by adding water, KOH and ammonia as needed. In embodiments, the anolyte management system comprises an ammonia regulator for monitoring and maintaining the concentration of ammonia within an operation range by adding ammonia to the anolyte by adding ammonia as needed. In embodiments, the anolyte management system comprises a water removal system for removing excess water in the anolyte.

[0024] In embodiments, the ammonia electrolyzer further comprises a cooling system for regulating the temperature of the ammonia electrolyzer.

[0025] In embodiments, the anolyte comprises 5 to 25 wt% ammonia in a 0.5M to 7M aqueous KOH solution.

In embodiments, the catholyte is a 0.5M to 7M aqueous KOH solution. [0026] In embodiments, the anodes and the cathodes comprises a solid solution painted, pressed and sintered on a substrate, the solid solution being a solid solution of a supported electrocatalyst and polytetrafluoroethyleπe, the supported electrocatalyst comprising the anode catalyst and the cathode catalyst, respectively, in the form of particles supported on a high surface area support material in the form of particles.

[0027] In embodiments, the support material is a carbon-based support material such as carbon black, carbon nanotubes, carbon nanofibers, and carbon nanostructures. In other embodiments, the support material is a metal oxide-based support material, such as indium (IV) oxide, titanium dioxide or titanium dioxide nanotubes.

[0028] In embodiments, the anode catalyst is platinum combined with iridium, ruthenium and/or nickel. In embodiments, the cathode catalyst is platinum or nickel.

[0029] In embodiments, the substrate is: a reinforcing net of metal cloth, a perforated metal sheet wherein perforations occupy between about 15% and about 45% of the volume of the perforated metal sheet, or a rough metal sheet. In more specific embodiments, the rough metal sheet is produced by acid etching or by sandblasting. In embodiments, the metal in the metal cloth, perforated metal sheet or rough metal sheet is nickel, aluminium, ferritic steels, carbon steels, stainless steel or titanium.

[0030] In embodiments, the substrate is a type 316 stainless steel woven cloth of between about 10 and about 400 mesh or a type 304 stainless steel woven cloth of between about 10 and about 400 mesh.

[0031] There is also provided a method of replenishing the catalyst of a poisoned electrode anode of a multielectrode ammonia electrolyzer anode, the method comprising individually monitoring the catalyst poisoning of each electrode anode; and reversing the polarity of an electric potential applied to the poisoned electrode anode and selectively isolating an electrode cathode corresponding to the poisoned electrode anode, wherein reversing the polarity reduces catalyst poisoning...

[0032] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the appended drawings:

[0034] Figure 1 shows a schematic diagram of an apparatus for the continuous generation of hydrogen via electrolysis of ammonia;

[0035] Figure 2 shows an embodiment of a multielectrode electrolysis cell illustrating a horizontal arrangement of electrode plates;

[0036] Figure 3 shows an embodiment of a multielectrode electrolysis cell illustrating a vertical arrangement of electrode plates;

[0037] Figure 4 shows an embodiment of a multielectrode electrolysis cell illustrating a vertical arrangement of electrode plates;

[0038] Figure 5 shows an embodiment of a multielectrode electrolysis cell illustrating a vertical and horizontal arrangement of electrode plates; [0039] Figure 6 shows an exemplary embodiment of peripheral components to a multielectrode electrolysis cell illustrating a gas processing system;

[0040] Figure 7 shows an exemplary embodiment of peripheral components to a multielectrode electrolysis cell illustrating an ammonia refill component and management of excess ammonia for cogeneration with a fuel cell system;

[0041] Figure 8 shows an embodiment of peripheral components to a multielectrode electrolysis cell illustrating an ammonia refill component and management of excess ammonia for cogeneration with an ammonia genset;

[0042] Figure 9 shows an exemplary embodiment of peripheral components to a multielectrode electrolysis cell illustrating an electrode switch matrix with a catalyst repleπisher component;

[0043] Figure 10 shows an exemplary embodiment of peripheral components to a multielectrode cell illustrating a switch mode power supply connection with the electrolyzer and cogeneration with a fuel cell system;

[0044] Figure 11 shows an embodiment of peripheral components to a multielectrode cell illustrating switch mode power supply connection with the electrolyzer and cogeneration with an ammonia genset;

[0045] Figure 12 shows a cross-sectional and a side view of an embodiment of an ammonia electrolysis cell body with a salt bridge (SB) compartment;

[0046] Figure 13 shows a high-resolution transmission electron microscopy images of a supported electrocatalyst according to an embodiment of the invention;

[0047] Figure 14 shows a high-resolution transmission electron microscopy images of a supported electrocatalyst according to an embodiment of the invention;

[0048] Figure 15 shows the particle size distribution of the platinum nanoparticles on the carbon nanostructure support in a supported electrocatalyst according to an embodiment of the invention;

[0049] Figure 16 is an X-ray diffractogram of a supported electrocatalyst according to an embodiment of the invention; and

[0050] Figure 17 is an X-ray diffractogram of a supported electrocatalyst according to another embodiment of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0051] The current invention allows increasing the efficiency of the catalyst employed for the electrochemical reaction by correspondingly increasing the available active catalyst surface area per unit weight of catalyst through the use of a multielectrode assembly cell configuration. Furthermore, the present invention provides a scaled-up design of an ammonia electrolyzer cell and the necessary peripheral components required for a continuous and large scale generation of hydrogen by compensating for the deficiency of reactants due to continuous operation of the electrolyzer and the replenishing of poisoned catalysts.

[0052] The present invention is illustrated in further details by the following non-limiting examples.

[0053] Referring now to Figure 1 , and in accordance with an illustrative embodiment of the present invention, an electrolyzer for the continuous and large scale generation of hydrogen via the electrolysis of ammonia, or a hydrogen delivery system for a fuel cell or genset, generally referred to using the reference numeral 10, will now be described. The apparatus for a hydrogen delivery system 10 according to the present invention comprises an electrolysis cell 12, a switched-mode power supply unit 14, or SMPS, an electrode switch matrix 16, a catalyst replenisher 18, an electrolyte management system 20, a safe anode gas processing system 22 and a safe gas cathode gas processing system 24, and a programmable control system 26.

[0054] Still referring to Figure 1, and in addition to Figures 2, 3, 4, and 5, the electrolysis cell 12 of the ammonia electrolyzer 10 comprises a multi-electrode cell arrangement 28 housed within the electrolysis cell body 30. The electrolysis cell body 30 is fabricated by injection molding or machining, preferably using polymeric materials such as polytetrafluoroethylene, polychlorotrifluoroethylene, polyamide, high density polypropylene and polyvinylchloride or metals such as aluminum, carbon steels, ferritic steels and stainless steel, or other like materials with high corrosion resistance to ammonia. The electrolysis cell body 30 comprises at least two compartments, an anolyte compartment 32 containing an anode 34 and a catholyte compartment 36 containing a cathode 38 with the anolyte compartment 30 and catholyte compartment 34 being separated by an anion- selective membrane 40 or by a salt bridge filled, for example, with a saturated solution of KCI. The anion- selective membrane 40 is also known in the art as an anion-exchange membrane or strongly basic anion permeable membrane.

[0055] The anolyte compartment 32 is charged with ammonia in an aqueous solution of basic electrolyte, such as potassium hydroxide (KOH), and the catholyte compartment 36 is charged with the same concentration of basic electrolyte used at the anolyte. The anode and cathode are filled with anodic electrolyte solution (anolyte) and cathodic electrolyte solution (catholyte), respectively. In particular, the anolyte consists of 5 to 25 wt% (e.g. 5, 10, 15, 20, 25 wt%) ammonia dissolved in a 0.5 M to 7 M (e.g. 0.5, 0.55, 0.6, 0.65, 0.7 M) aqueous solution of KOH. The catholyte is an aqueous solution of KOH at a concentration range from 0.5 M to about 7 M (e.g. 0.5, 1, 2, 3, 4, 5, 6, 7 M. In other embodiments disclosed in this invention, the anolyte is an aqueous solution of 0.5M to 7M KOH(e.g. 0.5, 0.55, 0.6, 0.65, 0.7 M) and 2.93 M to 14.67 M (e.g. 2.93, 3.93, 4.93, 5.93, 6.93, 7.93, 8.93, 9.93, 10.93, 11.93, 12.93, 13.93, 14.67 M) of ammonium hydroxide whereas, the catholyte is an aqueous solution of KOH at a concentration range between 0.5 M and 7 M (e.g. 0.5, 1, 2, 3, 4, 5, 6, 7 M). Further, a salt bridge is filled with a saturated solution of KCI with concentration greater than or equal to 4.6 M. The alkalinity of the electrolyte at both the electrode compartments are maintained with a pH variation of not more than 0.5.

[0056] Still referring to Figure 1 , a DC power supply employing either a rectifying element such as a selenium or silicon rectifier or a DC-to-DC converter is used to supply power to the electrolytic cell 12 required for the electrolysis of ammonia. The power source may be a battery or a fuel cell stack 101 or an ammonia genset 102 connected to the electrolytic cell 12 through a switched-mode power supply unit 14, which is an electronic power supply unit incorporating a switching regulator. The SMPS 14 employs either a DC-to-DC converter 15, when a fuel cell 101 or a battery is used as a power source or a rectifying element 17 when a hydrogen genset 102 is used as a power source. [0057] Now referring to Figure 2 through to Figure 5, multielectrode cell arrangements 28 housed within anolyte compartments 32 and catholyte compartments 36 of an electrolysis cell 12 and comprising electrode substrates 42 are described. In the basic operation of an ammonia electrolyzer, an anolyte is oxidized to nitrogen in an anolyte chamber, and water in the catholyte is reduced to hydrogen in a catholyte chamber. [0058] The inventors believe that on a pilot scale, the rate of hydrogen production is directly proportional to a group of factors including: the availability of the reactants; the overpotential of the electrodes; the current density measured in mAcnr² or Acm² for a given cell size; and the specific surface area of the catalyst. The influence of temperature and pressure on the rate of the reaction due to optimization and simple control of these factors, regardless of the size of the electrolysis cell, is ignored. During scale up, the variation in the electrode overpotential and the losses associated with it are assumed to be negligible. In such a case, the inventors believe that the only significant factor contributing to a higher production rate of hydrogen is the active surface area of the catalyst and that using a supported electrocatalyst can increase the rate of hydrogen production. [0059] In one illustrative embodiment, the electrode substrates 42 forming the anode 34 and cathode 38 of the electrolysis cell 12 are coated with supported electrocatalysts as part of a multielectrode arrangement 28 to increase the surface area of the supported electrocatalyst at the electrodes 42 and correspondingly increase the rate of hydrogen production. In particular, each electrode substrate 42 is coated on both of its surface sides with supported electrocatalyst layers to significantly reduce the overall size and cost of the electrolysis cell 12. Electrode substrates 42 prepared with high active surface area effectively reduce the number of electrodes in large-scale ammonia electrolysis for continuous generation of hydrogen.

[0060] Still referring to Figure 2 through Figure 5, the multielectrode cell arrangements 28 comprise a plurality of anode-forming electrode substrates 42 with or without the support of a metal rod or a tube 44 and a plurality of cathode-forming electrode substrates 42 similarly with or without the support of a metal rod or a tube 44. Each anode-forming electrode substrate 42 further comprises a wire lead 46 which exits the anolyte compartment 32 through a metal tube in the electrolysis cell body 30 and each cathode-forming electrode substrates 42 similarly comprises a wire lead 46 which exits the catholyte compartment 34 through a metal tube in the electrolysis cell body 30. These wire leads 46 are connected in a series arrangement to a programmable electrode switch matrix 16, as shown in Figure 9, which interconnects the working electrode substrates 42 of the anolyte compartment 32 and catholyte compartment 36. Various embodiments of a multielectrode cell arrangement 28 according to the present invention are depicted in Figure 2 through Figure 5. In particular, Figure 2 depicts a multielectrode cell arrangement 28 showing a horizontal arrangement of electrode substrates 42. Figures 3 and 4 depict multielectrode cell arrangements 28 showing vertical arrangement of electrode substrates 42. Figure 5 depicts a multielectrode cell arrangement 28 illustrating a combination of vertical and horizontal arrangement of electrode substrates 42.

[0061] The hydrogen required by power generating devices 100 such as fuel cells 101 and hydrogen gensets 102 may be greater than what can be produced by simple electrolysis cells. For the large scale production of hydrogen, the electrolysis cell 12 may be equipped with components for its continuous operation as described herein below in exemplary embodiments.

[0062] The following examples illustrate the influence of various parameters on scaling-up the laboratory scale electrolysis cell to pilot or commercial scale. The mathematical forms of equations shown below comparing some of these factors are based on the results observed by the inventors during the study of a laboratory scale system. Moreover, the losses included in these equations indicate the total losses that incur during the continuous run of an electrolyzer. Since the electrode compartments are fitted with cooling conduits with a temperature control system, resistance losses and catalyst activation improvements due to temperature increases are considered to be negligible. Furthermore, the volume of the electrolyzer is limited to the type of application. Therefore, there is a volume for the electrolysis cell beyond which the dimensions of the electrodes cannot be altered.

[0063] As part of a first example of an ammonia electrolyzer, which supplies hydrogen for a fuel cell or a genset, it is assumed that the flow rate of hydrogen required for operating a fuel cell system or a genset at its maximum power is x slpm (standard liters per minute). The maximum power generated by the fuel cell and hydrogen genset is given by f W and h W, respectively. The power required to operate the control components in the apparatus is denoted as cc W. The bench, pilot and commercial sizes are denoted as b /(liters), s / and c /, respectively. The available geometrical area of electrode assembly in each electrode compartment is denoted as bi cm², Si cm² and ci cm² for bench, pilot and commercial scale, respectively. With an operating voltage of op V and current densities at £>₂ Acm ², S₂ Acm ² and C₂ Acm ² on the electrode assembly, the rate of hydrogen production is given as fo slpm, S3 slpm and C3 slpm, respectively. The losses (/ W) incurred during the continuous run are mainly contributed by the group comprising overpotential losses, resistance losses and polarization losses. During cogeneration of the electrolyzer with a genset, the losses incurred for the conversion of AC current into DC current in SMPS is given as s W. To compare the role of active sites during scale-up, the higher activity of catalysts at elevated temperatures is assumed to be negligible. The scaling up of the specific surface area of the electrode from bi cm² to ci cm² is reflected in higher rate of hydrogen production {C3 slpm » b^ slpm). With the usage of a single electrolyzer cell, the limitations of the apparatus in simpler equation is given as follows,

[0064] The flow rate of hydrogen produced in a commercial scale electrolyzer volume with single electrode is given by,

C3 slpm « X slpm

[0065] The power generated by the fuel cell stack to run the apparatus is much lesser than the power consumed by the apparatus, f W « (op V x C₂ Acm ²) + (cc W) + I W

[0066] Similarly, the power generated by the genset does not meet the level to operate the electrolyzer and its components, h W « (op V x C₂ Acm-²) + (cc W) + I W + s W [0067] However, the fuel cell stack or hydrogen genset can be designed to operate with the hydrogen produced from the single electrode apparatus. The profit energy level (PEL) is defined as the state of the system in which the electrolyzer produces enough hydrogen to run a power generation device, the power of which is sufficient enough to run the electrolyzer and its components. Simply, at PEL, during cogeneration with a fuel cell system, f W = (ci cm² x op V x C₂ Acrτv²) + (cc W) + I W or with the genset, h W = (ci cm² x op V x C₂ Acnr²) + (cc W) + 1 W + s W that is used for an end application. Additionally, the power generated by the devices is not high enough to run the electrolyzer with its control components.

[0068] As a second example, to avoid the limitations of the above mentioned apparatus, a multitude of semi- commercial size electrolyzers are installed to generate a hydrogen flow high enough to achieve the required profit energy. The supported electrodes from each cell are connected in parallel to each another, wherein the power supply is a standard potentiostat. However, the installation of components for monitoring and controlling every single electrolysis cell increases the installation cost of the apparatus and it eventually becomes less efficient to operate due to much higher energy consumption.

[0069] In this second example, let us assume that 'n' electrolyzer cells are connected in parallel with the potentiostat to supply one of the power generating devices with maximum fuel injection. In such a case the cost of the apparatus increases along with the power required for operating every single component in the additional cells. With the usage of 'n' electrolyzer cells, the limitations of the coupled system in simpler equation is given as follows,

[0070] The continuous flow of hydrogen produced in a commercial scale electrolyzer volume with single electrode is given by,

C3 slpm = X slpm

[0071] The power generated by the fuel cell system to operate the apparatus is higher than the power consumed by the electrolyzer and its components, f W » nx[(ci cm² x op V x C₂ Acnr²) + (cc W) + 1 W]

[0072] Similarly, a part of the power generated by the genset is sufficient enough to operate the electrolyzer and its components, h W > nx[(ci cm² x op V x C₂ Acπr²) + (cc W) + I W] + s W

[0073] Considering the higher efficiency of the fuel cell stack than the hydrogen combustion genset, the former generates more power than the latter. Even though, the setup described in the second embodiment extends beyond the PEL, considering the cost and the extra energy requirement, this design is labeled as expensive and inefficient.

[0074] Any amount of energy that is available to run a stationary or mobile application is termed as profit energy. In the first example, the hydrogen produced by the apparatus is not sufficient enough to run either the fuel cell system or a genset [0075] The support components for the large scale and continuous generation of hydrogen via the electrolysis of ammonia are herein below described. These components include a catalyst replenisher component 18, an electrolyte management system 20, an anode gas processing system 22 and a cathode gas processing system 24, a programmable control system 26 in addition to a coolant circulation system and an ammonia refill component 48. A programmable control system 26 comprising either a computer or a PLC monitors and controls all such support components for a large scale continuous generation hydrogen delivery system 10.

[0076] With referral to Figure 6, an exemplary gas-liquid processing system 52 for the large scale continuous generation of hydrogen from an electrolysis cell 12 comprising at least a water trap 54, a moisture trap or desiccators 56, a relief valve 58, a backfire prevention device 60, a buffer tank 62 and a differential pressure regulator 64 is described along with the interconnections between the electrolysis cell 12 and gas-liquid separation mechanism 66 comprising a nitrogen outlet 50 and a hydrogen outlet 51 connected with gas-liquid separating means for nitrogen and a gas-liquid separation means for hydrogen. These gas outlets are situated at the upper part of the anolyte compartment 32 and catholyte compartment 36. The gas outlet of each electrolytic compartment is connected on the outside to a gas-liquid separation device 66. However, gas-liquid separation device 66 may not remove all the moisture content in the exit gas streams. A gas dessicator 56 may therefore be needed to trap the moisture from the gas stream output of the gas-liquid separation device 66. The ends of the dry gas output from the gas dessicator 56 are connected to a differential pressure regulator control valve 64 and pressure relief valves 58. The pressure relief valve 58 is set to regulate the pressure inside the anolyte compartment 32 and catholyte compartment 36, when the modulus value of pressure difference is between 0.5 psi and 15 psi (e.g. 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, 15.0 psi). The pressure relief valves 58 used in this embodiment is a variable pressure set valve, which is monitored and operated by the programmable control system 26.

[0077] The pressure difference between the two electrolytic compartments is maintained between about 5 psi and about 15 psi (e.g. 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 psi). The thickness of anion-selective membranes 40 used in this embodiment ranges between 0.1 and 0.2 mm (e.g. 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 mm). As a thinner anion-selective membrane 40 results in higher anionic conductivity with minimum resistance to the overall electrochemical reaction, an anion-selective membrane 40 of such low thickness used for this purpose may be damaged even at pressure differences as low as about 15 psi. The method employed in this embodiment to secure the membrane against harmful pressure differences involves the use of a pressure relief valve 58 and a buffer tank 62. The differential pressure regulator control valve 64 is monitored and controlled by the programmable control system 26. When the difference in pressure exceeds the tolerable range, the pressure relief valves 58 lowers the gas pressure inside the catholyte compartment 36 by releasing the gas to the buffer tank 62. A backfire prevention system 62 has its inlet connected to exit tubing of the above mentioned buffer tank 62 and the outlet of which is connected to the fuel processing unit 68 on the energy conversion device 100. [0078] With referral to Figure 1, an exemplary water circulation system for the large scale continuous generation of hydrogen from an electrolysis cell 12 comprises a source of liquid coolant and circulation conduits over the electrode compartments of the electrolysis cell 12 and a circulation pump for pumping the liquid coolant through the liquid coolant conduit. Each of the two cell electrode compartments has a temperature-sensing switch as part of the cell temperature control mechanism. The water circulation system prevents system overheating mainly caused by electrical energy losses from overpotential, polarization and resistance during electrolysis. Since during the operation of the electrolytic cell its temperature will gradually increase, the cooling system will be automatically turned on when the temperature is in excess of approximately 3O⁰C for example. By controlling the temperature in this manner, overheating is prevented and cell operation stoppage due to cell overheating is avoided. In operation, the system temperature is regulated by the programmable control system 26 regulating the temperature of the electrolytic solution to a range of 10⁰C to 60°C (e.g. 10, 20, 30, 40, 50, 60 °C)which activates the circulation pump when the temperature of the electrolytic solution crosses a set point level. The coolant liquid is pumped through the circulation conduits until the temperature falls back into the operation range. The coolant liquid is selected from the group consisting of water and automotive antifreeze (glycol/water mixture).

[0079] In another embodiment, a water circulation system is integrated with a hydrogen genset 102. Operating an irrigation pump can flush a part of the water through the conduits to maintain the temperature of the electrode solutions. This integration will minimize the cost and power requirement related to the installation of an additional pump to the cooling system. The cooling effect of the running water from the irrigation pump also assists in precipitating moisture out of the generated gases and limits the vapor pressure of ammonia by cooling the anode compartment. Thus, continuous operation for the production of high purity grade of hydrogen can be achieved with higher efficiency.

[0080] With referral to Figure 7 in addition to Figure 1 , an exemplary electrolyte management system 20 for the monitoring and control of the concentration of anolyte and catholyte as part of the large scale continuous generation of hydrogen from an electrolysis cell 12 comprising a pH regulator 70, a source of anhydrous ammonia 72, fluid level regulators 80 and ammonia refill components 48 is described. In operation, the electrolyte management system 20 maintains a desired level of ammonia and water in the anolyte compartment 32 and catholyte compartment 36. In particular, a porous tipped sparger tube bubbles anhydrous ammonia into the anolyte solution if the concentration of ammonium hydroxide in the solution drops between 0.05M and 2M (e.g. 0.05, 0.25, 0.45, 0.65, 0.85, 1.05, 1.25, 1.45, 1.65, 1.85, 1.95, 2.00 M) until the concentration level of ammonium hydroxide falls within the desired operation range. Furthermore, a pH regulator component 70, such as an ammonium hydroxide sensor, periodically monitors for changes in the pH level of the electrolyte with reference to a set point. When the pH drops below the threshold value, the preinstalled KOH refill component 48 adds alkalinity to the corresponding electrolyte to maintain the concentration of the electrolytic solution in the desired operating range. In particular, a basic salt (KOH) is added to the electrolytic solution when the pH drops between 0.1 and 2.5 (e.g. 0.1, 0.4, 0.7, 1.0, 1.3, 1.6, 1.9, 2.2, 2.5 pH) from the set point value. In one particular embodiment, an exemplary ammonia refill component 48 for the large scale continuous generation of hydrogen for cogeneration in a fuel cell system is illustrated in Figure 7. In yet another embodiment, an exemplary ammonia refill component 48 for the large scale continuous generation of hydrogen for cogeneration ammonia genset is illustrated in Figure 8.

[0081] With referral to Figure 9 in addition to Figure 1, an exemplary catalyst repleπisher 18 for reducing the adsorbed nitrogen poisoning at the anode active sites in the catalyst layer as part of a large scale conlinuous generation of hydrogen from an electrolysis cell 12 comprising a standard DC power source 14, and at least one reference electrode 76 immersed in anolyte solution of the anolyte compartment 32 and sealed airtight within the electrolysis cell body 30 is described. The reference electrode 76 used in one embodiment is a standard hydrogen electrode with its standard electrode potential declared to be zero at any operating temperature of the electrolyzer and is selected from a group consisting of reversible hydrogen electrodes, standard calomel electrodes and silver/silver chloride reference electrodes. To replenish the active sites on the catalyst, a catalyst replenishing component 18 periodically monitors each electrode substrate 42 to estimate the degree of catalyst poisoning. If the overpotential of the poisoned electrode 42 exceeds the threshold limit the catalyst replenishing component 18 reverses the polarity of the potential applied to a deactivated anodic electrode with reference to the standard reference electrode 76 or to its corresponding cathodic electrode. Reversal of the polarity of the poisoned electrode aids the reduction of adsorbed nitrogen species into intermediate forms of dehydrogenated ammonia and eventually to ammonia upon further reduction.

[0082] The operation of the catalyst replenisher 18 is now described in detail. Prior to first run of the electrolyzer 10, the potential difference between each electrode 42 and the reference electrode 76 is recorded as standard reduction potential or set point for the above-mentioned electrode 42. At any instance, the evaluation of the degree of poisoning due to adsorbed nitrogen of an electrode 42 requires a subject electrode 42 to be disconnected from the electrode switch matrix 16. The isolation of a poisoned electrode 42 is made possible by the electrode split wire leads 46 connection to the electrode switch matrix 16. The extent of catalyst poisoning is then determined by measuring the difference between the standard reduction potential and the reduction potential of the subject electrode 42 measured during the time of analysis. The toleration limit, or the threshold value, for catalyst poisoning is set between 0.01V and 0.5V (e.g. 0.01, 0.11, 0.21, 0.31, 0.41, 0.5 V) as a positive deflection from the standard overpotential and is dependant on how close the application wants to run the electrolyzer to the limiting current density. When the degree of poisoning exceeds the set threshold value, the polarity of the working electrode 42 and the reference electrode 76 is reversed. The reversal of polarity is accomplished through a series of catalyst replenisher relay switches 78 as illustrated in Figure 9. A periodic pulse ranging between 0 V and 1 V (e.g. 0, 0.2, 0.4, 0.6, 0.8, 1.0 V) ranging for a period of time between five seconds and fifteen minutes (e.g. 0.12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 min) is applied by either electrode in the form of a combination of sine, square, triangle and saw tooth waves. When the applied current density drops within the toleration range of steady-state value, the periodic anodic pulse is interrupted and the reduction potential of the corresponding electrode 42 is measured. With the addition of new active sites on the electrode 42, the reduction potential should be higher than the measured value of the poisoned electrode. If the reduction potential of the reactivated electrode is more than the threshold value, the regeneration cycle is repeated. This reduction of the adsorbed nitrogen poisoning at the anode active sites in the catalyst layer operating will allow the electrolyzer 10 to produce hydrogen at higher efficiencies.

[0083] The catalyst replenisher 18 takes advantage of the electrode switch matrix 16 which is now described with referral to Figure 9. In one embodiment, wire leads 46, in particular a plurality of anode wire leads 80 and a plurality of cathode wire leads 82 electrically connected to each electrode 42 are connected to electrode switch matrix relay switches 84 operated by the control system 26. The electrode switch matrix 16 connects in series these parallel electrodes 42 to meet the hydrogen requirement to maintain higher operating efficiency in the apparatus. In addition to aiding in the reduction of adsorbed nitrogen poisoning at the anode active sites in the catalyst layer, the electrode switch matrix 16 is also controlled by the control system 26 to activate a number of electrodes 42 within a multielectrode cell arrangement 28 based on one or more determinative factors such as the desired rate of hydrogen generation, the availability of electrical energy and the activity of the electrode 42. Electrode switch matrix relay switches 84 are opened to deactivate an electrode 42 or closed to activate an electrode 42.

[0084] In another particular embodiment, as exemplified in Figure 10 and Figure 11, a hydrogen delivery system 10 to supply hydrogen to a fuel cell 101 or a genset 102 is illustrated. In this particular embodiment, the electrical energy required for the electrolysis of ammonia is supplied via SMPS 14 by either a fuel cell 101 or a hydrogen genset 102. The power source for the electrolysis cell 12 is shown in Figure 10 and Figure 11 for cogeneration with a fuel cell 101 and genset 102, respectively. At any instance, if the power required by the end application is less than the maximum operational power, the demand for profit energy from the power conversion devices decreases and so does the hydrogen required to run these devices. Therefore, the electrical energy that must be added to the electrolysis cell 12 equals the change in Gibbs free energy of the reaction to produce limited flow of hydrogen plus the losses in the system. The electrode connections are switched to selective series connection by the electrode switch matrix 16, thus operating the electrolysis cell 12 with the dynamic variations of electrical energy supplied by either a fuel cell 101 or a hydrogen genset 102. For example, consider an electrolysis cell 12 embodiment wherein ten anode 34 substrates and ten cathode 38 substrates are immersed in anolyte and catholyte solutions, respectively. As mentioned earlier, a wire lead 46 from each electrode substrate 42 is connected to the electrode switch matrix 16, which is controlled by a programmable control system 26. Depending on the electrical energy available to the electrolysis cell 12 from the switched-mode power supply unit 14 and the hydrogen required by the power conversion device to generate profit energy, the programmable control system 26 activates the required number of parallel electrodes 42 in series via the relay modules 84, such as diode switches, which are connected to each wire lead 46 from the electrodes 42. For instance, if a series connection of just six parallel electrodes 42 via electrode switch matrix 16 can stabilize the profit energy without compromising the efficiency of the apparatus, the other four parallel electrodes 42 comprising in the electrolysis cell 12 remain deactivated until such a time as a demand for higher profit energy arises. In this sense, the independent wiring system on each catalyst-coated electrode substrate 42 allows the end user to configure the electrode switch matrix 16 based on the different variables.

[0085] The electrodes 42 can be any electrode known to the skilled person to be useful for the electrolysis of ammonia. This includes electrodes disclosed in US 2005/0211569; WO 2007/047630; Botte et al. Journal of the

Electrochemical Society, 153 (10) A1894-1901 (2006); Vitse et al. Journal of Power Source, 143 (2005) 18-26;

Endo et al. Electrochimica Acta 50 (2005) 2181-2185; Endo et al. Electrochimica Acta 49 (2004) 2503-2509;

Wang et al. J. Phys. Chem. B 2005, 109, 7883-7893; Katan et al. J. Electrochem. Soc. 110, 9, 1022-1023;

Sasaki et al. J. Electrochem Soc. 117, 6, 758-762; and Zhou et al. International Journal of Hydrogen Energy 33

(2008) 5897-5904.

[0086] In an embodiment of the invention, the electrodes 42 comprise a solid solution painted, pressed and sintered on a substrate, the solid solution being a solid solution of a supported electrocatalyst and polytetrafluoroethylene. The supported electrocatalyst comprises a catalyst supported on a support material.

[0087] In embodiments, the solid solution comprises between about 60 wt% and 95 wt% (e.g. 65, 70, 75, 80,

85, or 90 wt%) of the supported electrocatalyst and between about 5 wt% to about 40 wt% (e.g. 5, 10, 15, 20, 25,

30, 35, 40 wt%) of polytetrafluoroethylene (based on the total weight of the solid solution). The polytetrafluoroethylene (i.e. Teflon™) acts as a binder to attach the supported electrocatalyst on the surface of the substrate. Changing the supported electrocatalyst/polytetrafluoroethylene raϋo influences the mechanical stability, porosity and electrical conductivity of the electrode and thus allows tailoring and optimization.

[0088] The support material should be durable under operating conditions and environment. The support material is in the form of particles and is thus a high surface area material. The electrochemical activity of the electrode is typically improved by using high surface area support materials.

[0089] Non limiting examples of support materials include carbon-based support materials such as carbon black, carbon nanotubes, carbon nanofibers, and carbon nanostructures. Some of these can provide surface areas as high as 3000 m²g-¹. In embodiments, the surface area of the carbon-based support materials ranges between about 75 m² g ¹ and about 3000 m² g-'.

[0090] In embodiments, the support material is a carbon naπostructure material (CNS) as defined in US

2005/260117, which is incorporated herein by reference.

[0091] Non limiting examples of support materials also include metal oxide-based support materials such as iridium (IV) oxide, titanium dioxide and titanium dioxide nanotubes. Some of these can provide surface areas as high as 500 m²g-¹. In embodiments, the size of the metal oxide-based support materials particles ranges from about 20 to about 200 nm and their specific surface areas ranges from about 10 to about 500 m²g-¹.

[0092] The catalyst is also in the form of particle and is thus a high surface area material. The electrochemical activity of the electrode is typically improved by using catalysts with reduced particle size. In fact, building nano-sized catalyst particles on the support material increases the number of active sites available for electrochemical reaction.

[0093] The catalyst material is typically platinum or nickel alone or combined with iridium, ruthenium, and/or nickel. For example, when the electrode is the anode, the catalyst can be a binary alloy comprising (A) platinum and (B) iridium or ruthenium or a ternary alloy comprising platinum, iridium and ruthenium. This typically enhances the electrochemical activity of the electrode and reduces active site poisoning by adsorbed nitrogen atoms. When the electrode is the cathode, the catalyst is platinum or nickel, which reduces water into hydrogen.

The weight percentage of these catalysts in the supported electrocatalyst typically ranges from about between 10 to about 80 wt% (e.g. 10, 15, 20, 25, 30, 35, 40, 4550, 55, 60, 65, 70, 75 or 8Q wt% based on the total weight of the supported electrocatalyst). The catalyst particles size typically ranges from about 1.5 rim to about 50 nm

(e.g. 1.5 , 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50 nm).

[0094] In embodiments, the atomic percentage of platinum ranges from about 50 at% to about 100 at% (e.g.

50, 60 70, 80, 90 or 100 at%) while the atomic percentage of iridium or ruthenium is from about 50 at% to about

0 at% (e.g. 50, 40, 30, 20, 10 or 0 at%). In more specific embodiments, the atomic percentage of platinum ranges from about 90 at% to about 100 at%, while the atomic percentage of ruthenium ranges from 10 at% to about 0 at%.

[0095] The substrate should be resistant to ammonia and be electrically conductive. In embodiments, the substrate can be a reinforcing net of metal cloth, a perforated metal sheet wherein perforations occupy between about 15% and about 45% (e.g. 15, 20, 25, 30, 35, 40, or 45 %) of the volume of the perforated metal sheet, or a rough metal sheet. Such rough metal sheet can be produced by acid etching or by sandblasting. This increases the geometrical surface area substrate, thus enhancing the electrochemical activity of the resulting electrode.

[0096] When the electrode is the anode, the metal in the metal cloth, perforated metal sheet or rough metal sheet may be, in embodiments, nickel, aluminium, ferritic steels, carbon steels, stainless steel or titanium. When the electrode is the anode, the metal in the metal cloth, perforated metal sheet or rough metal sheet may be, in embodiments, nickel, aluminum, ferritic steels, stainless steel, nickel or titanium.

[0097] In embodiments, the substrate is a type 316 stainless steel woven cloth of between about 10 and about 400 mesh or a type 304 stainless steel woven cloth of between about 10 and about 400 mesh.

[0098] In embodiments, the catalyst loading on the electrode substrate is between about 0.2 mg cm² and about 50 mg cπr²(e.g. 1, 5, 10, 25, 40, or 50%).

[0099] The above electrode typically has good conductivity and permeability to electrolyte and gas. It is rather durable and has a high electrochemical activity, i.e. the oxidation of ammonia at anode and the reduction of water at cathode is enhanced. The use of such an electrode with increased available active catalyst surface area per weight unit of catalyst is a rather efficient use of expensive noble metals.

[00100] The above electrode can be prepared by hot pressing, followed by sintering of the solid solution. This solid solution can be prepared by impregnation of the polytetrafluoroethylene with the catalyst.

[00101] More specifically, the electrode can be prepared by

(a) mixing the supported electrocatalyst, the polytetrafluoroethylene (in the form of a powder) and an organic solvent by ball milling or magnetic stirring thereby producing the solid solution;

(b) drying the solid solution thereby producing an ink; (c) painting the ink on the substrate;

(d) drying the painted substrate;

(e) repeating painting step (c) and drying step (d) until a desired loading of supported electrocatalyst is achieved;

(f) hot-pressing; and

(g) sintering.

[00102] The solid solution produced by the above mixing is homogenous.

[00103] In embodiments, drying step b) comprises evaporating about 95% of the solvent from the solid solution prepared at step a). In embodiments, the solid solution is dried between about 60⁰C and about 110⁰C over a period of about 30 min to about 3 h.

[00104] In embodiments, the painted substrate is dried in an oven, for example at a temperature of about 120

⁰C.

[00105] In embodiments of the hot-pressing step, the ink is preheated at a temperature between about 300⁰C and about 400⁰C and is pressed with a pressure ranging from about 500 psi to about 2500 psi for about 10 min to about 45 min. In embodiments, the electrodes are hot-pressed at 140 °C and 800 psi.

[00106] In embodiments, the sintering is carried out under an atmosphere comprising about 80% to about 90% argon and about 10% to about 20% hydrogen at a temperature ranging from about 300°C to about 400⁰C for about 10 min to about 5h.

[0100] Electrolyzer

[0101] An ammonia electrolyzer system was built. It comprised an anolyte compartment 32 and a catholyte compartment 36 (50 cm³ each) separated by a salt-bridge compartment 86 as shown in Figure 12. In this figure, the anolyte compartment 32 and catholyte compartment 36 are separated by a salt bridge compartment 86. An anode gas outlet 88, an anolyte inlet 90, a cathode gas outlet 92 and a catholyte inlet 94 allowed introducing anolyte and catholyte in the anolyte compartment 32 and a catholyte compartment 36 and allowed the produced gases to exit the compartments. The gases were produced at the anode 34 electrode plate and at the cathode

38 electrode plate, which were powered through an anode electrical feedthrough 96 and a cathode electrical feedthrough 98. The anolyte compartment 32 and a catholyte compartment 36 and the salt bridge compartment

86 were separated by air tightly sealed ion exchange membranes 40.

[0102] The anode and cathode compartments were filled with an anodic electrolyte solution (45 ml, anolyte) and a cathodic electrolyte solution (45 ml, catholyte), respectively. The anolyte consisted of 5 M of ammonium hydroxide solution dissolved in 1 M aqueous solution of KOH. The catholyte was a 1 M aqueous solution of KOH.

The salt bridge was filled with a saturated KCI solution.

[0103] An electrical power source was connected to the electrodes, which were dipped inside their respective solution. When a minimum current density of 20 mA cm ² was applied, hydrogen appeared at the cathode and nitrogen appeared at the anode. Assuming ideal Faradic efficiency, the generated amount (moles) of hydrogen is thrice that of nitrogen, and both are proportional to the total electrical charge sent through the solution. Electrolysis of ammonia requires excess energy in the form of over potential to overcome various activation barriers. Without the excess energy, the electrolysis of ammonia occurs very slowly if at all. The current density was raised to a maximum of 115 rtiA cm², where the maximum hydrogen rate of 80 seem was measured using an Aalborg hydrogen flow meter. The hydrogen was fed to a 20 W fuel cell stack to generate electric energy.

[0104] Electrodes

[0105] The anode electrode matrix was composed of two electrodes, each of them were coated and sintered with a solid solution of Pt-Ru catalyst supported on proprietary carbon nanostructure material (CNS) and 1% amorphous tetrafluoropolymer solution (Teflon™). The carbon nanostructure material (CNS) was produced according to the teachings of US 2005/260117.

[0106] The cathode electrode matrix was composed of two electrodes, each of them were coated and sintered with a Pt catalyst supported on the same proprietary carbon nanostructure material (CNS) and Teflon™.

[0107] The catalyst loading on the cathode Ni substrate was 0.5 mg cm². The ratio of supported electro catalyst to Teflon™ was 5:2 (weight of solids). A homogeneous ink of electro catalyst (100 mg) and Teflon™ (dry weight, 40 mg) was prepared by magnetically stirring the mixture for 24 h. As prepared ink was painted on a 5 crrv² nickel substrate until a catalyst loading of 0.5 mg cm-² was achieved for all the electrodes. Then, the electrodes were hot-pressed and sintered in a 10% hydrogen and 90% argon atmosphere at 250⁰C for 5h.

[0108] Preparation of the supported electrocatalyst

[0109] A Pt-Ru electrocatalyst was prepared as follows: 400 mg of surface functionalized carbon nanostructures were suspended in 40 ml of ethylene glycol (EG) solution and stirred for 30 min. Then, 6.5 ml of

H₂PtCI₆ (10 wt% Pt) and 6.5 ml of RuCI₃ (10 wt% Ru) were added dropwise to the mixture.

[0110] The pH of the solution was adjusted above 13 by appropriate addition of NaOH in EG solution. A precipitate (instead of a metallic colloidal solution) will result if pH goes below 12.

[0111] The amount of added water controls the size of the formed intermediates metal hydroxide or platinum hydroxyl acetate clusters, which is subsequently reduced to obtain colloidal metal.

[0112] Reflux was carried out in an oil bath at 140 "C for 3 h to completely reduce the platinum and ruthenium and to prevent water escape. The electro catalyst supported on CNS was filtered, washed and dried overnight at 120 ⁰C under dry nitrogen.

[0113] A Pt only electrocatalyst was prepared in a manner similar to this Pt-Ru electrocatalyst except that the

RuCb was omitted.

[0114] Characterization of the supported electrocatalyst

[0115] Figures B and C shows high-resolution transmission electron microscopy images of the supported electro catalyst containing platinum only at different scales. These figures clearly show the presence of smaller platinum nanoparticles on the surface of CNS.

[00107] Figure 15 shows the particle size distribution of the platinum nanoparticles on the carbon nanostructure support in the electro catalyst containing platinum. Most of the platinum nanoparticles were 3 to 6 nm in size. [00108] Figure 16 is an X-ray diffractogram showing nanoparticles of platinum supported on the carbon nanostructures.

[0116] Figure 17 is an X-ray diffractogram showing nanoparlicles of platinum and ruthenium supported on the carbon nanostructures.

[0117] Ammonia electrolysis

[0118] Table 1 shows the power consumption, hydrogen mass flow and hydrogen mass flow per watt of the ammonia electrolyzer. The data for the comparative water electrolyzer are from Narayanan et al. NASA Tech.

Briefs 26 (2002) 19.

Table 1 : Power consumption and hydrogen yield comparison between a typical water electrolyzer and our ammonia electrolyzer.

[0119] Significant current densities >110 mA cm^" were obtained during electrolysis testing at the relatively low metal loading used (0.5 mgPt/sq.cm). High H2 flow rates (> 50 seem) were also obtained.

[00109] Herein, "about" means plus or minus 5% of the numerical value it qualifies.

[00110] Although the present invention has been described hereinabove by way of specific embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.

REFERENCES

[00111] The content of the documents below is herein incorporated by reference in their entirety:

[00112] US 7,141 ,675;

[00113] US 2005/0211569;

[00114] US 4,876,115;

[00115] US 2005/0260117;

[00116] WO 2007/047630;

[00117] Botte et al. Journal of the Electrochemical Society, 153 (10) A1894-1901 (2006);

[00118] Dietrich et al. Surface Science 352-354 (1996) 138-141;

[00119] Endo, K. Nakamura, T. Miura, Electrochim. Acta 49 (2004) 2503-2509;

[00120] Endo et al. Electrochimica Acta 50 (2005) 2181-2185;

[00121] Endo et al. Electrochimica Acta 49 (2004) 2503-2509;

[00122] Endo et al. Electrochim. Acta 49 (2004) 1635; [00123] Gerischer et al. J. Electroanal. Chem. 25 (1970) 421- 443;

[00124] Gootzen et al. Electrochim. Acta 43 (1998) 1851;

[00125] Katan et al. J. Electrochem. Soc. 110, 9, 1022-1023;

[00126] Kim et al. Electrochimica Acta 50 (2005) 4356-4364;

[00127] Narayanan et al. NASA Tech. Briefs 26 (2002) 19;

[00128] Natarajan et al. Journal of Electrochemical Society, 156 (2) B210-B215 (2009);

[00129] Natarajan et al., Journal of the Electrochemical Society 154(3) B310-B315 (2007);

[00130] Natarajan et al. Electrochimica Acta 52 (2007) 3751-3757;

[00131] Sasaki et al. J. Electrochem Soc. 117, 6, 758-762;

[00132] Vitse et al. Journal of Power Source, 143 (2005) 18-26;

[00133] Wang et al. J. Phys. Chem. B 2005, 109, 7883-7893;

[00134] Yin et al. Applied Catalysis A: General 277 (2004) 1-9; and

[00135] Zhou et al. International Journal of Hydrogen Energy 33 (2008) 5897-5904.

Claims

CLAIMS:

1. An ammonia electrolyzer comprising at least one electrolysis cell, said electrolysis cell comprising: at least one anode compartment housing an anolyte; at least one cathode compartment housing a catholyte; a plurality of anodes connected in parallel and submerged within the anolyte, the anodes comprising an anode catalyst; and a plurality of cathodes connected in parallel and submerged within the catholyte, the cathodes comprising a cathode catalyst, wherein the application of an electric potential between the anodes and the cathodes activates electrolysis.

2. The ammonia electrolyzer of claim 1 comprising a plurality of electrolysis cells connected in parallel.

3. The ammonia electrolyzer of claim 1 or 2 wherein the anode compartment and the cathode compartment are separated by an anionic exchange membrane.

4. The ammonia electrolyzer of claim 1 or 2 wherein the anode compartment and the cathode compartment are separated by a salt bridge compartment.

5. The ammonia electrolyzer of claim 4 wherein the salt bridge compartment is filled with a saturated KCI solution.

6. The ammonia electrolyzer of any one of claims 1 to 5, wherein the anodes are substantially parallel to each other.

7. The ammonia electrolyzer of any one of claims 1 to 6, wherein the cathodes are substantially parallel to each other.

8. The ammonia electrolyzer of any one of claims 1 to 7, wherein the anodes and cathodes are electrically connected to an electrode switch matrix comprising a first plurality of relay switches electrically connected to the anodes and the cathodes, whereby the anodes and the cathodes can be selectively activated or deactivated by the closing or opening of the relay switches.

9. The ammonia electrolyzer of claim 7 further comprising a catalyst replenisher comprising a second plurality of relay switches electrically connected to the first plurality of relay switches of the switch matrix and a monitor to monitor the catalyst poisoning of the anodes, wherein when the monitor detects a poisoned anode catalyst, the catalyst replenisher reverses the electrical polarity applied to the poisoned anode and selectively isolates a cathode corresponding to the poisoned anode to reduce adsorbed nitrogen at the poisoned anode catalyst.

10. The ammonia electrolyzer any one of claims 1 to 9 further comprising a catholyte management system for controlling the concentration and level of the catholyte.

11. The ammonia electrolyzer of claim 10, wherein the catholyte management system comprises a pH regulator for monitoring and maintaining the concentration of KOH within an operation range by adding KOH.

12. The ammonia electrolyzer of claim 10 or 11 , wherein the catholyte management system comprises a fluid level regulator to monitor and maintain the level of anolyte within an operation range by adding water and KOH.

13. The ammonia electrolyzer any one of claims 1 to 12 further comprising an anolyte management system for controlling the concentration and level of the anolyte.

14. The ammonia electrolyzer of claim 13, wherein the anolyte management system comprises a pH regulator for monitoring and maintaining the concentration of KOH within an operation range by adding KOH.

15. The ammonia electrolyzer of claim 13 or 14, wherein the anolyte management system comprises a fluid level regulator to monitor and maintain the level of anolyte within an operation range by adding water, KOH and ammonia.

16. The ammonia electrolyzer of any one of claims 13 to 15, wherein the anolyte management system comprises an ammonia regulator for monitoring and maintaining the concentration of ammonia within an operation range by adding ammonia.

17. The ammonia electrolyzer of any one of claims 13 to 16, wherein the anolyte management system comprises a water removal system for removing excess water in the anolyte.

18. The ammonia electrolyzer of any one of claims 1 to 17 further comprising a cooling system for regulating the temperature of the ammonia electrolyzer.

19. The ammonia electrolyzer of any one of claims 1 to 18 wherein the anolyte comprises 5 to 25 wt% ammonia in a 0.5M to 7M aqueous KOH solution.

20. The ammonia electrolyzer of any one of claims 1 to 19 wherein the catholyte is a 0.5M to 7M aqueous KOH solution.

21. The ammonia electrolyzer of any one of claims 1 to 20, wherein the anodes and the cathodes comprises a solid solution painted, pressed and sintered on a substrate, the solid solution being a solid solution of a supported electrocatalyst and polytetrafluoroethylene, the supported electrocatalyst comprising the anode catalyst and the cathode catalyst, respectively, in the form of particles supported on a high surface area support material in the form of particles.

22. The ammonia electrolyzer of claim 21, wherein the support material is a carbon-based support material such as carbon black, carbon nanotubes, carbon nanofibers, and carbon nanostructures.

23. The ammonia electrolyzer of claim 21, wherein the support material is a metal oxide-based support material, such as iridium (IV) oxide, titanium dioxide or titanium dioxide nanotubes.

24. The ammonia electrolyzer of any one of claims 21 to 23, wherein the anode catalyst is platinum combined with iridium, ruthenium and/or nickel.

25. The ammonia electrolyzer of any one of claims 21 to 24, wherein the cathode catalyst is platinum or nickel.

26. The ammonia electrolyzer of any one of claims 21 to 25, wherein the substrate is:

^■ a reinforcing net of metal cloth,

^■ a perforated metal sheet wherein perforations occupy between about 15% and about 45% of the volume of the perforated metal sheet, or

■ a rough metal sheet.

27. The ammonia electrolyzer of claim 26, wherein the rough metal sheet is produced by acid etching or by sandblasting.

28. The ammonia electrolyzer of claim 26 or 27, wherein the metal in the metal cloth, perforated metal sheet or rough metal sheet is nickel, aluminium, ferritic steels, carbon steels, stainless steel or titanium.

29. The ammonia electrolyzer of claim 26, wherein the substrate is a type 316 stainless steel woven cloth of between about 10 and about 400 mesh or a type 304 stainless steel woven cloth of between about 10 and about 400 mesh.

30. A method of replenishing the catalyst of a poisoned electrode anode of a multielectrode ammonia electrolyzer anode, the method comprising:

(a) individually monitoring the catalyst poisoning of each electrode anode; and

(b) reversing the polarity of an electric potential applied to the poisoned electrode anode and selectively isolating an electrode cathode corresponding to the poisoned electrode anode, wherein reversing the polarity reduces catalyst poisoning..