KR102376086B1 - Liquid hydride-based autothermal hydrogen and electric power generator - Google Patents

Abstract

The present specification provides a liquid hydride-based autothermal hydrogen and power generator, comprising: one or more reactors including a liquid-phase hydride-based catalyst; and a hydrogen fuel cell; wherein the reactant supplied to the one or more reactors undergoes a dehydrogenation reaction to convert it to hydrogen (H ₂ ), and the product containing the hydrogen is discharged from the reactor to at least a part of it as a hydrogen fuel cell Disclosed is an autothermal hydrogen and power generating device that is supplied.

Description

Liquid hydride-based autothermal hydrogen and power generator

Disclosed herein is an autothermal hydrogen and power generating device based on liquid hydride.

Hydrogen continues to attract attention as a clean energy carrier because it can store sufficient energy from renewable energy sources such as solar and wind through water electrolysis. In particular, hydrogen has not only a high energy-to-weight density (about 33 kWh/kg), but also the advantage of being able to produce water, an environmentally friendly by-product when used with a polyelectrolyte fuel cell (PEMFC). Because renewable energy production is highly dependent on location and seasonal changes, controllable and efficient hydrogen storage technologies are important to meet geographic and temporal differences between hydrogen supply and demand.

However, hydrogen gas has an extremely low volumetric energy density, and thus, in the current technology, it is stored in a compressed form (300 bar H ₂ , 20 g H ₂ /L). In this regard, the technology of storing hydrogen in the form of liquid chemicals has received particular attention in high-capacity storage and long-distance transport.

One of the candidates, formic acid (HCOOH, FA), is a stable liquid at ambient temperature and can be prepared through oxidative conversion of biomass feedstocks. As shown in Formula 1, the dehydrogenation reaction has received considerable attention as a promising hydrogen storage material (4.4 wt%, 53 g H ₂ /L) because it has mild conditions.

[Formula 1]

HCOOH (l) → CO ₂ (g) + H ₂ (g)

△ _r H ^o (kJ/mol) = 31.2 △ _r G ^o (kJ/mol) = -32.9

The dehydrogenation reaction for hydrogen and carbon dioxide is thermodynamically favorable at room temperature and water conditions, but the dehydrogenation reaction is also favorable for water and carbon monoxide as shown in the following formula (2). Therefore, this reaction must be suppressed for application to PEMFC.

[Formula 2]

HCOOH (l) → H ₂ O (l) + CO (g)

△ _r H ^o (kJ/mol) = 28.7 △ _r G ^o (kJ/mol) = -12.9

In addition, it has been reported that the palladium-based nanocatalyst is the most efficient catalyst for H ₂ production from formic acid (FA), and additives such as formate are often added to improve the H ₂ production yield in this dehydrogenation reaction.

In contrast, formate (MHCO ₂ , M=Na, K, NH ₄ ) is a H ₂ storage material (1.2-1.6 wt %, 20-28 gH ₂ /L) as the conjugate base of formic acid. Formate is a non-toxic solid material at room temperature and has been shown to be thermodynamically superior in reversible H ₂ storage and release at ambient temperature and pressure as shown in formula (3).

[Formula 3]

NaHCO ₂ (aq) + H ₂ O (l) ↔ NaHCO ₃ (aq) + H ₂ (g)

△ _r H ^o (kJ/mol) = 20.5 △ _r G ^o (kJ/mol) = 0.7

Formic acid is a promising substitute for formic acid because it forms a reversible energy cycle with CO ₂ electrochemical reduction by excess renewable energy without the need for additional acidification with formic acid. Since Sasson et al. first reported using sodium formate as a hydrogen carrier (Non-Patent Document 1), a catalyst for efficient formic acid dehydrogenation has been developed. For example, the Ru-based or Ir-based homogeneous catalyst reported by Beller, Laurenczy, Olah, and Joo (Non-Patent Document 2-5) exhibited scalability as well as excellent reactivity for reversible hydrogen storage and release.

However, in the development of formate-based dehydrogenation systems for portable or mobile applications, the problem of catalyst separation from the homogeneous formate reaction mixture remains to be resolved.

On the other hand, it seems that the heterogeneous catalyst can be used in a portable power generation system, and among many heterogeneous catalysts, Pd nanoparticles supported on a carbon-based support are known as one type of efficient dehydrogenation catalyst. However, there are no studies related to the integration of the system with the optimized reaction conditions of these catalysts.

a) H. Horvath, G. Papp, R. Szabolcsi, A. Kath, F. Joo, ChemSusChem 2015, 8, 3036-3038; b) G. Papp, J. Csorba, G. Laurenczy, F. Joo, Angew. Chem. Int. Ed. 2011, 50, 10433-10435. H. Wiener, Y. Sasson, J. Blum, J. Mol. Catal. 1986, 35, 277-284. A. Boddien, F. Gδrtner, C. Federsel, P. Sponholz, D. Mellmann, R. Jackstell, H. Junge, M. Beller, Angew. Chem. Int. Ed. 2011, 50, 6411-6414. K. Sordakis, A. F. Dalebrook, G. Laurenczy, ChemCat Chem 2015, 7, 2332-2339. J. Kothandaraman, M. Czaun, A. Goeppert, R. Haiges, J.-P. Jones, RB May, GKS Prakash, GA Olah, ChemSusChem 2015, 8, 1442-1451.

a) H. Horvath, G. Papp, R. Szabolcsi, A. Kath, F. Joo, ChemSus Chem 2015, 8, 3036-3038; b) G. Papp, J. Csorba, G. Laurenczy, F. Joo, Angew. Chem. Int. Ed. 2011, 50, 10433-10435.

Embodiments of the present invention are intended to produce hydrogen from liquid hydride, which is a hydrogen storage material, in the form of a liquid chemical substance in order to safely store hydrogen (gas) having an extremely low volumetric energy density at room temperature and normal pressure.

Embodiments of the present invention are to solve the problem of low utility because dehydrogenation of liquid hydride requires an endothermic reaction, and waste heat of a fuel cell is low-grade waste heat with a low temperature.

In one embodiment of the present invention, there is provided an autothermal hydrogen and power generating device based on liquid hydride, comprising: at least one reactor including a catalyst based on liquid hydride; and a hydrogen fuel cell, wherein the reactant supplied to the one or more reactors undergoes a dehydrogenation reaction to convert it to hydrogen (H ₂ ), and a product containing hydrogen is discharged from the reactor to at least partly be converted to a hydrogen fuel cell A supplied, autothermal hydrogen and power generating device is provided.

In one embodiment, the product discharged from the reactor may be directly supplied to the hydrogen fuel cell.

In one embodiment, some of the product discharged from the reactor may be recycled to one or more reactors.

In one embodiment, the autothermal hydrogen generator may include two or more reactors.

In one embodiment, in the reactor, the dehydrogenation reaction may be performed at a temperature below the vaporization point of the reactants.

In one embodiment, the reactant includes a formate compound, and in the reactor, the dehydrogenation reaction may be performed at a temperature in the range of 40 to 100 °C.

In one embodiment, the autothermal hydrogen and power generating device may further include a heat exchange device for transferring the heat generated in the hydrogen fuel cell to the reactor.

In one embodiment, the autothermal hydrogen and power generating device may further include a catalyst reactivation device for recycling the liquid hydride-based catalyst by treating it with deionized water.

In one embodiment, after deionized water is treated in the catalyst reactivation device, nitrogen (N ₂ ) treatment may be performed to recycle the catalyst.

In one embodiment, the reactant may include liquid hydride at a concentration ranging from 0.1 to 10M.

In one embodiment, the reactant may include a formate compound of one or more of ammonium formate, sodium formate, and potassium formate.

In one embodiment, the liquid hydride-based catalyst may include a support and a metal supported on the support.

In one embodiment, the metal may be nanoparticles having a diameter range of 2.0 to 3.0 nm.

In one embodiment, the liquid hydride-based catalyst may have a metal loading amount in the range of 1 to 10 wt% based on the total weight of the catalyst.

In one embodiment, the liquid phase hydride based catalyst may have a dispersion in the range of 10 to 50% as measured by CO chemisorption.

In one embodiment, the purity of hydrogen discharged from the membrane reactor may be 99.97% or more.

In one embodiment, hydrogen may be additionally supplied to the hydrogen fuel cell.

In one embodiment of the present invention, there is provided a method for generating hydrogen and power through the above-described autothermal hydrogen and power generating device.

Autothermal hydrogen and power generating device according to an embodiment of the present invention can have excellent dehydrogenation reaction efficiency by controlling factors such as an optimal formate concentration, reaction temperature, and catalyst metal loading amount.

The device for generating autothermal hydrogen and power according to an embodiment of the present invention provides heat necessary for the dehydrogenation reaction by transferring heat generated from the fuel cell to the reactor, thereby improving the operating efficiency of the entire system without a separate external heat source. , which can be effective in portable hydrogen generation and power generation systems.

1 shows a flowchart of a liquid hydride-based autothermal hydrogen generator according to an embodiment of the present invention.
2 is a graph showing a comparison of gas emissions according to the dehydrogenation reaction by varying the concentration of NaHCO ₂ .
3a is a graph showing a comparison of gas emission according to the dehydrogenation reaction by varying the Pd metal loading in the dehydrogenation catalyst, and FIG. 3b is a comparison showing the H ₂ yield according to the dehydrogenation reaction by varying the Pd metal loading. It is a graph.
4A to 4D show dehydration with different Pd metal loadings of 1 wt.% (FIG. 4A), 3 wt.% (FIG. 4B), 5 wt.% (FIG. 4C), and 10 wt.% (FIG. 4D), respectively. The STEM image of the digestion catalyst is shown.
5 is a graph showing a comparison of gas emission according to the dehydrogenation reaction by changing the temperature of the carbonization reaction.
6 shows the results of plotting an ln( _{ko obs} ) versus 1/T graph from the results obtained by varying the dehydrogenation reaction temperature.
7 is a graph showing a comparison of gas emissions in the dehydrogenation reaction according to the cation effect of formate (Na, K, NH ₄ ).
8 is a graph showing the gas chromatography results of the NH ₄ HCO ₂ dehydrogenation reaction.
9a to 9c are graphs showing comparison of in situ pH measurement results and gas emissions of NH ₄ HCO ₂ (FIG. 9a), NaHCO ₂ (FIG. 9b), and KHCO ₂ (FIG. 9c).
10 is a graph showing the results of measuring the iTOFm value by recycling the catalyst of the formate dehydrogenation reaction up to 5 cycles.
11a and 11b are graphs showing the results of measuring iTOFm values by recycling the catalyst for formate dehydrogenation reaction up to 5 cycles, and comparing the results with or without nitrogen treatment during the reactivation treatment.
Figures 12a to 12c are, while recycling the catalyst for dehydrogenation reaction up to 5 cycles, NaHCO ₂ (Fig. 12a), KHCO ₂ (Fig. 12b), NH ₄ HCO ₂ (Fig. 12c) IR spectroscopy from the gas discharged from the dehydrogenation reaction It is a graph showing a comparison of the detection result of CO ₂ through.
13 is a graph showing a comparison of gas emission when the catalyst of the formate dehydrogenation reaction is reacted with O ₂ .
14A and 14B show the nitrogen adsorption/desorption curves of the Pd/C catalyst before use (FIG. 14A) and the 5-cycle regeneration catalyst (FIG. 14B), and FIG. 14C is a comparison of gas emissions in the dehydrogenation reaction of the catalyst before and after BET measurement It is the graph shown.
15a and 15b show the gas emission from the dehydrogenation reaction after mixing the Pd/C catalyst with the formate (FIG. 15a), and the bicarbonate (FIG. 15b) solution at different stirring times of 140 minutes, 274 minutes, and 1,114 minutes. It is a graph showing comparison.
16A and 16B show comparison STEM images of the Pd/C catalyst before use ( FIG. 16A ) and the Pd/C catalyst regenerated for 5 cycles ( FIG. 16B ).
FIG. 17 is a comparison of gas emissions from a dehydrogenation reaction using a Pd/C catalyst, a Pd/C catalyst treated with CO/Ar, and a Pd/C catalyst treated with CO/Ar and then washed and filtered. It is a graph.
18 shows a thermally integrated dehydrogenation fuel cell system.
19 illustrates temperature changes of a fuel cell and a reactor with time and power output values of the fuel cell in a fuel cell system according to an embodiment of the present invention.
20a to 20d show IV curves applying externally fed H ₂ and H ₂ fed from a reactor of a system according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The embodiments of the present invention disclosed in the text are illustrated for the purpose of explanation only, and the embodiments of the present invention may be embodied in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention can make various changes and can have various forms, and the embodiments are not intended to limit the present invention to a specific disclosed form, and all changes, equivalents or substitutes included in the spirit and scope of the present invention should be understood as including

The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Term Definition

As used herein, "conversion" is defined as the flow rate of liquid hydroxide converted to nitrogen and hydrogen per volume feed rate of liquid hydride supplied to the reactor.

Autothermal hydrogen generator

In one embodiment of the present invention, there is provided an autothermal hydrogen and power generating device based on liquid hydride, comprising: at least one reactor including a catalyst based on liquid hydride; and a hydrogen fuel cell, wherein the reactant supplied to the one or more reactors undergoes a dehydrogenation reaction to convert it to hydrogen (H ₂ ), and a product containing hydrogen is discharged from the reactor to at least partly be converted to a hydrogen fuel cell A supplied, autothermal hydrogen and power generating device is provided.

In one embodiment, the product discharged from the reactor may be directly supplied to the hydrogen fuel cell. The hydrogen generator may not require a separate process and/or equipment for increasing the purity of hydrogen by directly supplying the produced hydrogen to the fuel cell, thereby preventing a decrease in the efficiency of the entire system.

In one embodiment, some of the product discharged from the reactor may be recycled to one or more reactors. Through this, the unreacted material (eg, formate-based reactant) included in the product recycled to the reactor may undergo dehydrogenation, and the overall hydrogen yield may be improved.

In one embodiment, the autothermal hydrogen and power generating device may include two or more reactors. For example, the autothermal hydrogen and power generating device may include two reactors. Specifically, the plurality of reactors may be operated sequentially, for example, the second reactor may be purged and filled during operation while hydrogen is generated from the first reactor. A plurality of reactors can be used to continuously operate the hydrogen and power generating device, and through this, hydrogen can be continuously generated.

In one embodiment, in the reactor, the dehydrogenation reaction may be performed at a temperature below the vaporization point of the reactants. When carried out at a temperature above the vaporization point of the reactants, water may vaporize and other byproducts may be produced by the resulting material.

For example, when formate is included as the reactant, the dehydrogenation reaction may be performed in the reactor at a temperature in the range of 40 to 100 °C. Specifically, the dehydrogenation reaction may be carried out at a temperature in the range of 30 to 80 °C or at a temperature in the range of 60 to 80 °C. When the dehydrogenation reaction temperature is less than 40 ° C, hydrogen generation may not occur due to low reactivity, and if it is more than 100 ° C, water may be vaporized and other by-products may be produced by the produced material, for example, produced at a temperature greater than 100 ° C. More carbon dioxide can be produced by the bicarbonate.

In one embodiment, the autothermal hydrogen and power generating device may further include a heat exchange device for transferring the heat generated in the hydrogen fuel cell to the reactor. For example, the heat exchange device circulates cooling water to exchange heat. Specifically, the cooling water is circulated through a fuel cell stack and then the circulated cooling water is introduced into the reactor to transfer heat energy.

In one embodiment, the autothermal hydrogen and power generating device may further include a catalyst reactivation device for recycling the liquid hydride-based catalyst by treating it with deionized water. The catalyst may be reactivated for one cycle or more through the catalyst reactivation device. In general, as the number of reactivation cycles increases, the activity of the catalyst tends to decrease, but when a specific formate-based reactant is used, the reduction in catalyst reactivity can be minimized. For example, potassium formate (PF) may have a smaller decrease in catalytic activity according to an increase in the number of reactivation cycles compared to other formate reactants.

On the other hand, when the autothermal hydrogen and power generating device includes two or more reactors, the catalyst reactivation device may sequentially treat the catalysts included in the plurality of reactors with deionized water to be recycled.

In one embodiment, after deionized water is treated in the catalyst reactivation device, nitrogen (N ₂ ) treatment may be performed to recycle the catalyst. When the catalyst is recycled by treating with nitrogen (N ₂ ), it may help to remove impurities that may be attached to the recovered catalyst, and not only iTOFm but also H ₂ yield may be improved in the dehydrogenation reaction.

In one embodiment, the reactant may include liquid hydride at a concentration ranging from 0.1 to 10 M. If the concentration range is less than 1 M, the yield of hydrogen generation may be as low as, for example, about 48%, and if it is more than 10 M, the yield of hydrogen generation may reach 100%, but for example, bicarbonate as a product may be precipitated. On the other hand, the liquid hydride reactant may be diluted while being introduced into the reactor, and thus a hydride solution of high concentration may be injected.

In one embodiment, the reactant may include a formate compound of one or more of ammonium formate, sodium formate, and potassium formate.

In one embodiment, the formate-based catalyst may include a support and a metal supported on the support. Specifically, the support is a carbon support such as ketjen black (ketjen black), carbon black (vulcan carbon), or activated carbon (activated carbon); and a metal oxide support such as alumina or silica, and at least one of zeolite, wherein the metal comprises at least one of Pd, Pt, Ni, PdAu, PdAg, and PdNi. may include

In one embodiment, the metal supported in the formate-based catalyst may be present in the form of nanoparticles, for example, may have a diameter range of 2.0 to 3.0 nm, preferably, a diameter range of 2.0 to 2.2 nm. In the case of having the nanoparticle diameter range, high reactivity may be exhibited during the dehydrogenation reaction of liquid hydride, and if the particle diameter becomes larger, the reactivity may be reduced.

In one embodiment, the liquid hydride-based catalyst may have a metal loading amount in the range of 1 to 10 wt% based on the total weight of the catalyst. When the metal loading amount is less than 1% by weight, the conversion rate of hydrogen generation from the liquid hydride may be low, and when the metal loading amount is more than 10% by weight, the metal may not be efficiently used in the reaction.

In one embodiment, the liquid phase hydride based catalyst may have a dispersion in the range of 10 to 50% as measured by CO chemisorption. The degree of dispersion can be in the same tendency as the initial mass activity of the catalyst. When it has a dispersion degree in the above range, it may have a high conversion rate from the liquid hydride.

In one embodiment, the purity of hydrogen discharged from the reactor may be 99.97% or more. In particular, the hydrogen generator according to an embodiment of the present invention can obtain high-purity hydrogen from the reactor, and can directly supply hydrogen produced to the fuel cell without going through a separate filtration device. For example, the ammonium formate dehydrogenation reaction product gas discharged from the reactor may include ammonia as an impurity, and the ammonia discharged from the reactor may be less than 2%.

In one embodiment, hydrogen may be additionally supplied to the hydrogen fuel cell. Specifically, hydrogen may be additionally supplied to the fuel cell using a separate external supply device, thereby further improving the power generation efficiency of the fuel cell.

Meanwhile, in one embodiment of the present invention, there is provided a method for generating hydrogen and power through the above-described autothermal hydrogen and power generating device.

Example

Hereinafter, the configuration and effect of the present invention will be described in more detail by way of examples. However, these examples are provided for the purpose of illustration only to help the understanding of the present invention, and the scope and scope of the present invention are not limited by the following examples.

material

Palladium supported on carbon (Pd/C; loading 1 wt% 205672, lot no. MKBW6956V; 3 wt% 237515, lot no. MKBR8734V; 5 wt% 205680; 10 wt% 205699, lot no. MKCF0394), sodium Sodium bicarbonate (ACS reagent, ≧9.7%), ammonium formate (≧9.995% trace metal basis) were purchased from Sigma-Aldrich. Sodium formate (ACS reagent) and ammonium bicarbonate (99%, for analysis) were purchased from Acros Organics. Potassium formate (99%) was purchased from Alfa Aesar. Potassium bicarbonate was purchased from Daejeong Chemical. All reagents were used as such without further purification.

Catalyst Characterization Methods

The particle size of the catalyst (Pd/C) was analyzed by high hallucinogenic dark field image-scanning transmission electron microscopy (HAADF-STEM) and transmission electron microscopy (TEM; Talos F200X, FEI).

The particle size distribution of the catalyst was analyzed by counting more than 200 particles.

The specific surface area of the catalyst was measured at 77 K using a nitrogen adsorption instrument (Micrometrics ASAP 2000). Prior to analysis, samples were pretreated at 80° C. under vacuum for 18 hours.

The Pd content of the catalyst was determined using inductively coupled plasma-light emission spectra (ICP-OES) (Varian 720ES, Agilent). CO pulsed chemisorption was performed in Belcat-M (BEL, Japan) to quantify the amount of CO chemisorbed on both new and used Pd/C catalysts. The catalyst was reduced under 10% H ₂ /He flow at 100° C. for 0.5 h, and then cooled to room temperature under He atmosphere. Then, CO pulses (0.0896 cm ³ per pulse) were injected until the eluted peak area of successive pulses became constant. The amount of Pd/C used for CO pulsed chemisorption was 30 mg. The value of the Pd dispersion was deduced assuming an average CO:Pd ratio of 1.

Pd 3d X-ray photoelectron spectroscopy (XPS) spectra were acquired using a K-alpha spectrometer (ThermoFischer Scientific) equipped with a monochromatic Al Kα X. - source (1486.6 eV). Energy correction was applied to all spectra by adjusting the binding energy of C1 at 284.5 eV. Pd 3d X-ray photoelectron spectroscopy (XPS) spectra were acquired using a K-alpha spectrometer (ThermoFischer Scientific) equipped with a monochromatic Al Kα X-ray source (1486.6 eV).

Catalytic dehydrogenation of formate

In the catalytic dehydrogenation of formate according to an embodiment of the present invention, a glass reactor containing Pd/C (1.25 mg of Pd) was purged with nitrogen and placed in an oil bath at 80°C. After adding a preheated aqueous formate solution to the reaction vessel, the reaction was initiated by stirring at a constant speed of 800 rpm. The volume of the gas produced was measured using an automatic gas burette system, which was connected directly to the reactor for real-time volume measurement.

In a further experiment, a portion of the gas mixture produced during formate dehydrogenation was collected using an airtight syringe, and the compositional ratio of CO ₂ :H ₂ was analyzed through gas chromatography (GC). The GC was calibrated with a known concentration of CO ₂ : H ₂ prior to use and a Model 7890A instrument (Agilent Technologies) equipped with a TCD detector and column (J&W Zeolite 5 Å Packed Column) was used.

To detect ammonia produced from ammonium formate dehydrogenation, the gaseous product was either collected in a Tedlar bag connected to the reactor or fed directly to the GC along with a carrier gas. The gas compositions of H ₂ and NH ₃ were analyzed using a gas chromatograph equipped with a TCD detector and calibrated prior to use of two columns (J&W HP-PLOT Molesieve GC column, 19091P-MS4; J&W PoraPLOT amine GC column, CP7591). did The obtained H ₂ :CO ₂ :NH ₃ ratio was calculated based on the values determined from H ₂ :NH ₃ and H ₂ :CO ₂ .

calculation method

V _H2 is initially calculated using the gas volume released based on the reaction (MCO ₂ + H ₂ O → MCO ₃ + H ₂ ) and further corrected by the CO ₂ :H ₂ ratio determined by GC. The amount of H ₂ was calculated using the following formula.

[Equation 1]

moles of hydrogen (H ₂ ), n H ₂ = P(V _H2 )/(RT)

where P is atmospheric pressure, V _H2 is the volume of H ₂ produced by the reaction, R is the gas constant, and T is room temperature (293 K).

The initial mass activity, turnover frequency (iTOFm) reported here is a TOF value calculated based on the moles of Pd of the catalyst as well as the rate during the first 10 minutes, which is calculated from the following equation.

[Equation 2]

The initial specific activity turnover frequency (iTOF _s ) reported here is a calculated TOF value based on the rate during the initial 10 min and the number of surface Pd sites on the catalyst, which is calculated from the following equation.

[Equation 3]

where D is the degree of dispersion of Pd atoms located on the surface of the support, which is obtained by CO chemisorption. The units of iTOFm and iTOF are both expressed as h ^-1 .

Preparation Example: Thermal integrated dehydrogenation system using formate solution

A heat-integrated reaction system comprising two semi-batch reactors (R1 and R2) and a water-cooled 180W class fuel cell stack (CNL Energy, Korea) was prepared. Referring to the overall process flow diagram of Figure 1,

At the bottom of each reactor, a filter was installed to allow gas and liquid to flow for the purpose of purging while blocking the catalyst powder, and the flow controller unit is equipped with a pure nitrogen gas (99.9995 % N ₂ ; Shinyang) that can selectively flow into each reactor. Oxygen Corporation) to control the flow rate.

A formate solution as a reactant was fed to the top of the reactor using a liquid pump. The gas produced in the reactor was passed through a mass flow meter, partly fed to the fuel cell and partly recycled to the reactor.

Mass flow controllers (MFC2, MFC3) were used to supply hydrogen (99.9995% H2; Shinyang Oxygen Co., Ltd.) and air to the anode and cathode of the hydrogen fuel cell, respectively.

To transfer waste heat generated in the fuel cell, coolant was circulated through the fuel cell stack using a liquid pump and then circulated to R1 or R2, where the flow direction was controlled by a solenoid valve. When the cooling water entered the reactor, small heat exchangers (HEX1 and HEX2) located at the bottom of the reactor heated the DI water or reactant solution in the reactor.

The specific development sequence is as follows. First, R1 filled with water and Pd (3 wt%)/C was heated to the desired reaction temperature (65 °C to 80 °C) using electric heaters (HT1 and HT2). The water required to reach the tip of the temperature sensor was The reactor was filled, therefore, a high concentration of formate solution was injected as it was diluted when it was introduced into the reactor.

Since potassium formate exhibits a solubility of 14.5M at 20 °C, a potassium formate solution (14M, 5mL min ^{- 1} ) was then fed to the reactor using a liquid pump to initiate the formate dehydrogenation reaction. When the reaction started, product gas was supplied to the fuel cell to generate electricity while dissipating heat through the coolant.

The heated coolant from the fuel cell stack is passed through a heat exchange unit at R2 to heat the reactor to perform formate dehydrogenation, which is carried out upon completion of the reaction at R1. After R2 started the reaction and produced enough hydrogen to run the fuel cell, R1 was purged for the next reaction cycle.

Test Example 1: Dehydrogenation reaction according to change in reactant (NaHCO2) concentration

Dehydrogenation of sodium formate (NaHCO ₂ , SF) according to the concentration change was performed. Specifically, a total of 10 mmol of SF was dissolved at various concentrations of formate solutions of 0.5M, 1M, 2M, 5M, and 7M, respectively, with Pd (3 wt%)/C catalyst at 80 °C, and at each concentration, 10 mmol of NaHCO ₂ (aq) was dehydrogenated by reacting 42 mg of Pd(3 wt)/C(1.25 mg of Pd) at 80°C. On the other hand, it is known that the solubility limit of SF at 20 °C is 8.4M.

The total volume of the emitted gas is shown in FIG. 2, and the corrected H ₂ volume based on the CO ₂ :H ₂ ratio using GC, iTOFm and the H ₂ yield in each concentration of the solution is shown in Table 1.

density 0.5 M 1M 2M 5M 7M H ₂ : CO ₂ ratio 85:15 90:10 81:19 80:20 86:14 H ₂ (mL, corrected) 116 169 164 200 235 iTOF _m (h ^-One ) 1,070 1,760 2,150 2,840 2,610 H ₂ transference number (%) 48 70 68 83 98

As a result, in the case of the 7M solution, 98% H2 yield was achieved, and it was confirmed that 2,610h ^-1 of iTOFm was obtained at 80 °C.

Experimental Example 2: Dehydrogenation reaction according to metal loading amount and particle size

In order to test the effect according to the metal loading of the Pd/C catalyst, NaHCO ₂ (aq, 7 M, 2.0 mL) was dehydrogenated

As can be seen in Figure 3a, the mass activity of the catalyst decreased in the order of 3 wt%> 1 wt%> 5 wt%> 10 wt%.

On the other hand, the H2 yield was initially calculated based on the total volume of the emitted gas (Fig. 3a), and was further corrected based on the CO ₂ :H ₂ ratio through GC (Fig. 3b). As a result, the yield of H ₂ was confirmed to be 92% (3% by weight Pd), 76% (1% by weight Pd), 53% (5% by weight Pd) and 28% (10% by weight Pd), respectively. In particular, for the 3 wt% Pd/C catalyst, an initial mass active TOF (3,200 h ⁻¹ , Table 2) and dehydrogenation rate (30,060 mmol H ⁻¹ g (Pd) ⁻¹ , initial 10 min) were observed. .

In addition, in order to investigate the change in the reactivity of Pd/C according to the amount of surface Pd, CO chemisorption analysis was performed to measure the Pd dispersion of the searched catalyst. As shown in Table 2 below, the Pd dispersion showed a tendency to agree well with the initial mass activity of the catalyst. In particular, the highest Pd dispersion of 46% was observed in the Pd (3 wt%)/C catalyst, and this catalyst showed the highest activity among the searched catalysts.

1 wt.% 3 wt.% 5 wt.% 10 wt.% H ₂ + CO ₂ (mL) 314 384 220 117 Dispersion (%) 27 46 25 19 H ₂ (mL, corrected) 254 311 178 95.7 H ₂ yield (%) 76 92 53 28 Average particle size (nm) 2.32 ± 0.58 2.04 ± 0.25 2.17 ± 0.51 2.47 ± 0.70 Mass activity (iTOF) _m , h ^-One ) 2,640 3,200 1,710 1,170 Inactive (iTOF _s , h ^-One ) 9,760 6,950 6,860 6,160

Meanwhile, to investigate the reactivity dependence on the size of Pd nanoparticles, STEM images were taken to determine the particle size distribution. The Pd nanoparticles were homogeneously dispersed on the carbon support, and the particle size distribution obtained by counting 200 or more nanoparticles from the STEM image is shown in FIG. 4 .

As a result, it was observed that Pd nanoparticles having a size range of 2.0-2.2 nm generally exhibited the highest reactivity during FA dehydrogenation, and decreased reactivity in larger size particles.

In addition, in the case of formate dehydrogenation, the size of the Pd active sites used in this study was maintained within 2.04-2.47 nm (Table 2), whereas Pd (3 wt%)/C had the smallest size and narrow size distribution. showed the highest iTOFm.

Experimental Example 3: Dehydrogenation reaction according to temperature change

For the dehydrogenation reaction at various temperatures, NaHCO ₂ (7 M, 2.0 mL) was reacted with 42 mg of Pd (3 wt%)/C (1.25 mg of Pd) at a temperature of 30, 40, 60, and 80 °C, respectively ( Fig. 5, Table 3).

30 ℃ 40 ℃ 60 ℃ 80 ℃ CO ₂ + H ₂ (mL) 71 109 239 384 H ₂ : CO ₂ 92:8 95:5 94:6 81:19 H ₂ (mL, corrected) ^b 66 104 224 311 H ₂ transference number (%) 20 31 67 92

In addition, kob(s ⁻¹ ) at each temperature was calculated as the slope of the plot of time versus ln([SF] ₀ /[SF]) with an initial value up to 3 min. From the calculated values, a plot of ln(k _obs ) versus 1/T was obtained, and it was confirmed that it had an apparent activation energy (Ea) of 40.0 kJ/mol ( FIG. 6 ). It was confirmed that these activation energy values were within the range of formate dehydrogenation Ea reported in literature (Table 4).

catalyst Ea (kJ/mol) Pd/mpg-C ₃ N ₄ 52.6 Pd/TiO ₂ 37.0±2 Pd (10 wt.%)/C 49.0±2 [{RuCl ₂ -(mtppms) ₂ } ₂ ]
Monosulfonated triphenylphosphine 41.0±2

Experimental Example 4: Cationic effect of formate on dehydrogenation (Na, K, NH4)

By comparing three formate sources of sodium formate (SF), potassium formate (PF) and ammonium formate (AF), the effect according to the cation of formate was confirmed. Each formate solution (7M, 2.0 mL) was added to a dehydrogenation reactor containing a Pd (3 wt %)/C (Pd 1.25 mg) catalyst at 80 ° C., and the amount of emitted gas was shown in FIG. shown. Table 5 also shows the total volume of gas and the yield of H ₂ based on the gas composition analyzed using GC.

NaHCO ₂ (SF) KHCO ₂ (PF) NH ₄ HCO ₂ (AF) V _gas (mL) 384 304 443 Gas rate (%) H ₂ / CO ₂
81 of 19 H ₂ / CO ₂
82/18 H ₂ / CO ₂ / NH ₃
77/22/2 H ₂ (mL, corrected) ^b 311 250 339 H ₂ transference number (%) 92 74 100 iTOF _m (h ^-One ) 3,200 3,410 6,190

In Table 5, in the case of PF, H ₂ yield was 74%, which was lower than that of SF, and it was confirmed that the generated CO ₂ :H ₂ ratio was the same as that of SF. In particular, it was confirmed that AF was dehydrogenated at the fastest rate (58,200mmol H ₂ h ⁻¹ g(Pd ^{) −1} for the first 10 minutes) among the three formate sources.

In addition, in order to monitor whether ammonia is produced through the AF dehydrogenation reaction, an on-line GC was connected to a gas burette system using N ₂ (20 mL/min) as a carrier gas and additional measurements were made. As a result, ammonia was not observed during the first GC run (6 min) but progressively ammonia was observed during the second (12 min) and third (18 min) runs of GC, and the H ₂ content as the reaction slowed down with the GC run. It was confirmed that this gradually decreased, and it was confirmed that 2% of ammonia from the entire reformed gas was generated in the AF dehydrogenation process (FIG. 8). It was not clear whether ammonia was not observed at the beginning of the reaction because ammonia was mainly produced as ammonium bicarbonate or because it was observed after the gas was saturated with aqueous solution. These results indicate that additional adsorbents are required to remove ammonia for fuel cell applications in AF dehydrogenation systems.

Meanwhile, in-situ pH measurements were performed for SF, PF and AF dehydrogenation (1M, 10 mL) at 80 °C using Pd (3 wt%)/C to investigate the CO ₂ ratio from the reformed gas. Specifically, in-situ pH measurement of the reaction was performed in a modified glass reactor with four necks. The pH electrode was calibrated with a buffer solution before every reaction. A pH electrode was placed on the neck of the reactor prior to addition of the reaction solution. The reactor containing the Pd (3 wt %)/C catalyst was purged with nitrogen and placed in an oil bath at 80°C. Then, the reactant solution (1M, 10 mL) preheated at 80° C. was added to the reactor and stirred at a speed of 800 rpm. As the dehydrogenation reaction proceeded, the pH change was measured and recorded in real time (FIG. 9).

As a result, the initial pH (6.51) of the AF solution was the lowest among the three formate sources, and the pH increased to 7.9 at the end of the reaction. As can be seen from the low initial pH (6.5), since a high CO ₂ content is observed from the low initial pH of the FA and SF mixture, AF has a larger source of protons due to the NH ₄ ⁺ cations and has a high CO ₂ production. it can be seen that In addition, the FA and SF mixtures produced faster gas than pure SF, which is consistent with the results obtained by AF. That is, it can be seen that both the FA and AF solutions have a proton source, thereby accelerating the dehydrogenation reaction.

Experimental Example 5: Effect of formate cations on catalyst recyclability

In order to evaluate the effect of formate cations on catalyst stability on catalyst recycling, catalyst recycling experiments were performed. When the dehydrogenation reaction for Pd (3 wt%)/C was completed, the spent catalyst was recovered through filtration and washed with a large amount of deionized water. The filtered catalyst was then dried in a vacuum oven at 80° C. before use in the next cycle. For the high temperature treatment, the dried catalyst was further treated at 200° C. for 2 hours with a nitrogen flow of 50 mL/min. The dehydrogenation reaction - recycling of the spent catalyst was repeated 5 times, and the iTOFm value of the recycled catalyst is shown in FIG. 10 .

As a result, the catalytic activity decreased with every cycle, and AF showed the fastest decrease in reactivity among all formate sources. PF showed a reactivity pattern similar to that of SF, but the decrease in reactivity was the smallest among formate sources. PF produced the highest H ₂ yield at up to 5 cycles and AF produced the lowest H ₂ yield.

In addition, when the recovered catalyst is further treated with N ₂ at 200 ° C. after each cycle, it helps to remove impurities that may be attached to the recovered catalyst, so that not only iTOFm but also H ₂ yield is improved in the SF dehydrogenation reaction It was confirmed (FIG. 11).

In addition, when the recovered catalyst was passed with a flow of N ₂ at 200 ° C., CO ₂ was detected from the emitted gas through IR spectroscopy (FIG. 12). The detected carbon dioxide can be produced from the pores when the desorbed bicarbonate species on the catalyst surface or the bicarbonate is decomposed into CO ₂ at high temperature. It can be seen that the amount of CO ₂ released from SF dehydrogenation is much higher than that released from PF. This is because the solubility of KHCO ₃ in water is higher than that of NaHCO ₃ , and it can be seen that filtration and washing of the catalyst is required to effectively remove KHCO ₃ .

On the other hand, an oxidation method through air has been proposed as one of the effective regeneration methods of the Pd catalyst after the PF dehydrogenation reaction, but it was confirmed that the O ₂ treatment (2%) at 200 ° C. was not very effective for catalyst regeneration (Fig. 13). ).

Experimental Example 6: Catalyst Deactivation Analysis

In order to investigate the potential metal leaching effect of the used formate catalyst, the Pd content of the catalyst before use and after 5 cycles of use was measured using ICP-OES, respectively. The metal content of Pd (3 wt %)/C increased from 3.06% of the catalyst before use to 3.74% of the catalyst after 5 cycles of use, indicating that metal leaching is not the main cause of deactivation, but decomposition of the carbon support occurs during the reaction. seems to be because

In addition, in order to investigate the fouling effect of catalyst pores, which has been pointed out as one of the main causes of catalyst deactivation in recent dehydrogenation reactions, the BET surface area of the catalyst before use and after 5 cycles of use was compared. As a result of measuring the BET surface area, the catalyst before use and after 5 cycles of use, the catalyst before use (SBET = 852 m ² g ^-1 ) in both the micropore and mesopore regions of the catalyst after 5 cycles of use (SBET = 973 m ² ) g ^{- 1} ), it was confirmed that the surface area did not decrease.

Although inactivation through formate or fouling of pores from the produced bicarbonate may occur during the reaction, formate or bicarbonate may also be desorbed during pretreatment (40 μmHg vacuum for 18 h at 80 °C) for BET measurement. there is. In addition, after measuring the BET surface area, it was confirmed that the catalyst did not fully recover the catalyst reactivity in the formate dehydrogenation test after 5 cycles of use (Table 6, FIG. 14 ).

S _BET (m ² g ^-One ) S _Micro (m ² g ^-One ) S _Meso (m ² g ^-One ) before reaction 852.4 558.1 294.3 after reaction 979.3 597.4 381.9

Next, in order to investigate the poisoning effect from formate or bicarbonate, SF (aq, 7M, 2.0 mL) was initially stirred with Pd (3 wt%)/C at room temperature for 140 min, 274 min and 1,114 min. , and then the stirred mixture was dehydrogenated at 80 °C.

As shown in FIG. 15A , in all cases, the SF solution was dehydrogenated at room temperature with a yield of 19% H ₂ , but it can be seen that the amount of emitted gas is smaller when stirred at room temperature for a longer period of time. These results indicate that catalyst poisoning occurred by formate or bicarbonate.

To determine whether catalyst poisoning was due to formate or bicarbonate exposure, the Pd/C catalyst was pretreated with NaHCO ₃ (aq, 3 mmol, 0.5 mL) at room temperature with different treatment times of 140, 274 and 1,114 minutes. . The reaction mixture was then dehydrogenated at 80° C. after addition of SF (aq, 7M 2.0 mL).

As shown in FIG. 15B , it was observed that the gas volume decreased during the bicarbonate treatment, but the catalyst poisoning effect by the bicarbonate was confirmed to be lower than that of formate. In particular, Pd/C pretreated with NaHCO ₃ (aq) for more than 140 minutes showed almost the same dehydrogenation activity as SF (Fig. 15b), similar to the results obtained after stirring Pd/C with SF for 140 minutes at room temperature. do (Fig. 15a, yellow line).

These results suggest that the inhibitory effect of formate on dehydrogenation reactivity is because formate anion has a higher binding affinity for Pd compared to bicarbonate.

In addition, a potential factor for catalyst deactivation is the agglomeration of metals during formate dehydrogenation. In this regard, a change in the Pd particle size was confirmed through STEM analysis.

Through STEM measurement, comparison was made for Pd (3 wt%)/C catalyst before use and after 5 cycles of dehydrogenation, and the particle sizes were 2.04 ± 0.25 nm (before use) and 2.74 ± 1.77 nm (5 cycles). After use), it was confirmed that the catalyst particles were agglomerated after the dehydrogenation reaction (FIG. 16). In addition, it was confirmed that the Pd dispersity decreased to 14% after 5 cycles of reaction through the CO chemisorption experiment. The particle size and dispersion of the catalyst after the reaction were similar to those of Pd (10 wt%)/C before use, as well as the iTOFm values obtained (Table 2). Therefore, an increase in particle size and a decrease in dispersibility according to the cycle may be one of the major inactivation factors in the formate dehydrogenation reaction.

Finally, CO poisoning experiments were performed. A Pd (3 wt%)/C catalyst was treated with 5% CO/Ar for 1 hour (30 mL/min) and then reacted with SF (aq, 7M 2.0 mL) at 80°C. Immediate inactivation was reduced to iTOFm of 518 h ^-1 , which is much lower than iTOFm of 3,200 h ^-1 of the catalyst before use, and the catalyst reactivity was partially restored to iTOFm 1,530 h ^-1 through washing and filtration. was confirmed (FIG. 17).

However, as demonstrated through GC analysis, CO poisoning may be excluded from the main deactivation factor because CO gas was not provided in the SF dehydrogenation experiment.

Experimental Example 7: Power generation through a thermally integrated dehydrogenation fuel cell system

In order to prove that hydrogen produced through the formate dehydrogenation described above can be directly used in a fuel cell, a system including a dehydrogenation reactor and a fuel cell was integrated in the preparation example ( FIGS. 1 and 18 ). Potassium formate i) showed better H ₂ yield at high concentration, potassium formate showed the greatest solubility in water, and ii) potassium formate showed high H ₂ yield upon catalyst recycling. It was chosen for the extinguishing fuel cell system.

The heat generated in the fuel cell is transferred to the heat exchanger device of the reactor through the adiabatic coolant line, and it is expected that the waste heat generated in the fuel cell can be coupled to the dehydrogenation reaction. This improves overall system efficiency by enabling thermal neutralization of the entire system without the need for an external heat supply such as an electric heater.

About 18% of the waste heat is generated from the fuel cell, which can only be used as the enthalpy of formate dehydrogenation. In fact, more than 18% of the waste heat energy is required to maintain the reaction temperature, thereby compensating for the heat loss in the reactor.

For example, to ensure that the temperature of the reactor is maintained by the heat released from the fuel cell stack, the fuel cell generated 53 W of power using an external H ₂ (> 99.999% pure) source. The temperature and power output of the fuel cell are shown in FIG. 19 .

19 the reactor reaches a temperature high enough for the formate dehydrogenation reaction. It can be seen that when the reaction starts, the temperature is slightly lowered, but the reaction rate does not change significantly. Here, the PEMFC can measure the total gas flow and determine the heat required to produce ~650 mL/min using GC analysis of the gas sample in the product flow. Theoretically, if the formate provided to the reactor is dehydrogenated to 100%, theoretically the enthalpy of the dehydrogenation reaction requires a power of 9.2W, which is covered by the heat emitted from the fuel cell, but in practice the theoretical value This results in less power consumption because it shows a lower conversion rate compared to .

Thereafter, in order to operate the fuel cell using the hydrogen generated in the reaction, pure hydrogen provided externally and the gas generated from the reactor were supplied to operate the fuel cell, and IV curves were compared.

From FIG. 20A , it can be confirmed that the performance of the fuel cell is similar in both the case of supplying hydrogen from the outside and the case of supplying hydrogen obtained from formate. A fuel cell was operated using the product prepared from the reactor of the preparation example, and when the gas emission reached ˜800 sccm ( FIG. 20B ), the gas generated in the reactor was delivered to the fuel cell, where the emission opened the stack. The circuit voltage was gradually increased by loading to 8A (Fig. 20c). It was then possible to generate ~50 W of power over 20 minutes, enough to heat the reactor to provide sufficient enthalpy. The system operated without an external heat source and the reactor temperature was maintained within a range ( FIG. 20D ).

The embodiments of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can improve and change the technical idea of the present invention in various forms. Accordingly, such improvements and modifications will fall within the protection scope of the present invention as long as they are apparent to those of ordinary skill in the art.

Claims (18)

A liquid hydride-based autothermal hydrogen and power generator, comprising:
at least one reactor comprising a liquid phase hydride based catalyst; hydrogen fuel cell; and a heat exchange device;
The reactant supplied to the one or more reactors undergoes an endothermic dehydrogenation reaction to convert it to hydrogen (H ₂ ), and the product containing the hydrogen is discharged from the reactor and at least a portion is supplied to a hydrogen fuel cell,
The heat exchanger transfers the heat generated in the hydrogen fuel cell to the reactor,
wherein the reactant comprises a formate compound of at least one of ammonium formate, sodium formate, and potassium formate;
The liquid hydride-based catalyst includes a support, and a metal supported on the support, wherein the metal loading amount is in the range of 1 to 10% by weight based on the total weight of the catalyst, autothermal hydrogen and power generating device. The method of claim 1,
The product discharged from the reactor is directly supplied to a hydrogen fuel cell, autothermal hydrogen and power generating device. The method of claim 1,
and a portion of the product discharged from the reactor is recycled to one or more reactors. According to claim 1,
The autothermal hydrogen generating device comprises two or more reactors, autothermal hydrogen and power generating device. According to claim 1,
In the reactor, the dehydrogenation reaction is performed at a temperature below the vaporization point of the reactants, autothermal hydrogen and power generating device. The method of claim 1,
The reactant comprises a formate compound,
In the reactor, the dehydrogenation reaction is carried out at a temperature in the range of 40 to 100 ℃, autothermal hydrogen and power generating device. delete According to claim 1,
The autothermal hydrogen and power generating device further comprises a catalyst reactivation device for recycling the liquid hydride-based catalyst by treating it with deionized water. 9. The method of claim 8,
After deionized water treatment in the catalyst reactivation device, nitrogen (N ₂ ) treatment to recycle the catalyst, autothermal hydrogen and power generating device. The method of claim 1,
wherein the reactant comprises liquid hydride at a concentration ranging from 0.1 to 10M. delete delete The method of claim 1,
The metal is nanoparticles having a diameter range of 2.0 to 3.0 nm, autothermal hydrogen and power generating device. delete The method of claim 1,
wherein the liquid hydride based catalyst has a dispersion in the range of 10 to 50% as measured by CO chemisorption. The method of claim 1,
Autothermal hydrogen and power generating device, characterized in that the purity of the hydrogen discharged from the reactor is 99.97% or more. The method of claim 1,
An autothermal hydrogen and power generating device for additionally supplying hydrogen to the hydrogen fuel cell. 18. A method for generating hydrogen and power using the autothermal hydrogen and power generating device of any one of claims 1 to 6 and 8 to 10, 13, and 15 to 17.

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