GB2515174A - Electrochemical apparatus and method - Google Patents
Electrochemical apparatus and method Download PDFInfo
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- GB2515174A GB2515174A GB1407126.0A GB201407126A GB2515174A GB 2515174 A GB2515174 A GB 2515174A GB 201407126 A GB201407126 A GB 201407126A GB 2515174 A GB2515174 A GB 2515174A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/42—Measuring deposition or liberation of materials from an electrolyte; Coulometry, i.e. measuring coulomb-equivalent of material in an electrolyte
Abstract
An electrochemical apparatus comprises an electrically conductive diamond electrode 2 configured to have a surface 4 which is disposed in contact with a solution 6 in use and a surface 8 which does not contact the solution in use; electrical contacts 10 configured to apply a voltage to the electrically conductive diamond electrode to perform an electrochemical process on the solution; and a heater 12 configured to apply pulsed heating to the surface 8 which does not contact the solution whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the diamond electrode from the surface which does not contact the solution. The heater 12 may be a laser or electrical resistance heater in contact with the surface not contacting the solution.
Description
ELECTROCHEMICAL APPARATUS AND METHOD
Field of Invention
The present invention relates to electrochemical apparatus and methodology. In particular, embodiments of the present invention provide suitable apparatus and methodology for performing electro-deposition and/or electrochemical sensing using heated electrodes.
Background of Invention
It is known that heating an electrochemical system can be beneficial for certain electro-deposition and electrochemical sensing applications. For example, Wildgoose et al. [Electroanalysis, 16, No. 6 (2004)j provide a review of the art in the field of high-temperature electrochemistry. It is reported that the promotion of mass transport at high-temperatures, through diffusion or convection, often results in increased current signals and this increase benefits electroanalytical measurements by lowering detection limits, It is also reported that high temperatures can usefully enhance the sensitivity of electrochemical systems with slow kinetics.
A variety of techniques for heating an electrochemical system are described by Wildgoose et al. and these are broadly split into two groups: isothermal heating in which the entire electrochemical cell, including the electrodes and the solution being analysed, is heated to a constant temperature; and non-isothermal heating in which localized heating is applied to the electrode and the region of solution near the electrode, Methods of isothermal heating are described as including: an autoclave; a high temperature high pressure cell; a water bath; a hot air gun; a resistive metal wire heater wrapped around the electrochemical cell; and a high-temperature wall-jet cell. Methods of non-isothermal heating are described as including: resistive metal electrodes, such as metal wire electrodes and metal micro-disc electrodes, heated via application of an electric current; microwave radiation; and radio frequency radiation. It is further described that non-isothermal heating methods may comprise either continuous heating such that the temperature remains constant over a period of time or pulsed heating utilizing temperature jumps to enhance signal-to-background ratios and of particular use for redox systems with slow kinetics. The latter pulsed heating approach is known as temperature pulse voltammetry (TPV). Nearly all the examples in the review paper appear to :i.
utilize metal electrodes, such as gold or platinum electrodes, although towards the end of the review paper it is reported that a microwave irradiation technique has been used for lead (Pb) detection using boron doped diamond electrodes [see Y. C. Tsai et a!., Electroanalysis, t3, 313 (2001)].
A number of further publications also disclose the use of microwave irradiation of boron doped diamond electrodes including: M A Ghanem, H Hanson et al, "Microwave-enhanced electro-deposition and stripping of palladium at boron-doped diamond electrodes", Talanta, 72, pp 66-7t (2007); and M A Ghanem, R G Compton et al, "Microwave activation of electrochemical processes: High temperature phenol and triclosan electro-oxidation at carbon and diamond electrodes", Electrochim Acta, 53, pp 1092-1099 (2007).
Other non-isothermal heating techniques known in the art include the use of focused laser beams or ultrasound as mentioned by Ghaemi et al, [Journal of Power Sources 125, 256-266 (2004).
Akkermans et al, [Electroanalysis, II, 1191 (1999)] described a laser activated voltammetry technique in which a 10Hz pulsed Nd:YAG laser, frequency doubled to operate at 532 nm, is focussed on platinum and gold disk electrodes. It is described that an enhancement in mass transport is observed as a function of laser intensity in the thermoelastic region where light energy absorbed by the metal is insufficient to cause localized melting or vaporization but does lead to a partial thinning of the diffusion layer thickness through surface heating/vibration. This leads to sigmoidal shaped voltammograms whilst maintaining a clean, reproducible electrode surface.
Qiu et al, [Analytical Chemistry Vol. 72, No, 1 (2000)] also disclose the use of laser activated voltammetry but in this case on glassy carbon and boron-doped diamond electrodes.
The technique uses a pulsed Nd-YAG 532 nm laser, with laser pulses having a width of approximately 10 ns and a frequency of 0 Hz. Laser intensities averaged over the full electrode area were typically in a range 0.1 to 0.8 Wcm'2. The described technique uses laser ablation of deposited species as a means of aiding selective detection of multiple different species deposited on glassy carbon and boron-doped diamond electrodes. This methodology is effectively a selective in-situ cleaning process. A key feature of this process is that the laser is applied to the deposited species on the front sensing surface of the electrode after deposition to selectively ablate deposited species from the electrode and aid detection during electrochemical stripping. The technique is compared with standard heating of the electrodes and it is concluded that merely heating the electrode does not show the same ifmnctionality as laser ablation.
A number of recent patent application relating to electrochemical sensors comprising boron doped diamond electrodes also mention the possibility of heating the boron doped diamond electrodes. For example, W02012/126802 discloses a band electrode structure for boron doped diamond electrodes and suggests that the diamond based electrochemical band sensor may comprise two spaced apart boron doped diamond electrodes with a layer of semi-conductive boron doped diamond disposed therebetween to form a sandwich type stmcture configured to heat the semi-conductive boron doped diamond layer and thus raise the temperature of the sensing surface. It is described that one or more such heating elements may be provided within the diamond electrochemical sensor and configured to raise the temperature of the sensing surface sufficiently to clean the sensing surface by increasing the rate of chemical degradation and removal ("burning off') of contaminants adhered to the sensing surface, It is also disclosed that the one or more heating elements may be configured to vary the temperature of the sensing surface to a target value and maintain a specific tcmpcraturc for a prcdctcrmincd pcriod of timc. W02012/156307 and W02012/156203 also disclose diamond based electrochemical sensor configurations and suggest that a heater may be provided within the electrochemical sensor for in-situ deaning and/or for changing the temperature of the sensing electrode to alter mass transport, reaction kinetics, and alloy formation. It is described that heating during stripping voltammetry can aid in increasing peak signals, Furthermore, heating during deposition can aid formation of better alloys and can also increase mass transport, shortening deposition times and/or increasing deposition.
Accordingly, it is suggested that in certain arrangements configured to detect very low concentrations of chemical species in solution a heater may be provided within the electrochemical sensor for heating the sensing electrode to increase deposition to within the detection limits. It is fhrther suggested that the use of diamond material for the sensing electrode is useful in this regard as diamond material can be heated and cooled very quickly.
it is an aim of certain embodiments of the present invention to provide a method and apparatus for performing electro-deposition and/or electrochemical sensing with increased sensitivity and/or selectivity, particularly for very low concentrations of chemical species, It is a fbrther aim to achieve the aforementioned goal while providing a system which is applicable to a wide range of different chemical species. Yet a further aim of certain embodiments is to achieve the aforementioned goals while providing a system which is compact, robust, and easy to use,
Summary of Invention
According to a first aspect of the present invention there is provided an electrochemical apparatus comprising: an electrically conductive diamond electrode configured to have a surface which is disposed in contact with a solution in use and a surface which does not contact the solution in use; an electrical contact configured to apply a voltage to the electrically conductive diamond electrode to perform an electrochemical process on the solution; and a heater configured to apply pulsed heating to the surface which does not contact the solution whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the electrically conductive diamond electrode from the surface which does not contact the solution to the surface which is disposed in contact with the solution.
According to a second aspect of the present invention there is provided an electrochemical method comprising: applying a voltage to an electrically conductive diamond electrode to perform an electrochemical process on a solution in contact with a surface of the electrically conductive diamond electrode; and applying pulsed heating to the electrically conductive diamond electrode via a surface of the electrically conductive diamond electrode which is not in contact with the solution, whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the electrically conductive diamond electrode from the surface which does not contact the solution to the surface which is in contact with the solution.
Brief Description of the Drawings
For a better understanding of the present invention and to show how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode and a pulsed laser focused on a rear surface of the electrically conductive diamond electrode; Figure 2 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode and a pulsed laser focused on a side surface of the electrically conductive diamond electrode; Figure 3 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode embedded within an electrically insulating diamond support and a pulsed laser focused on the electrically insulating diamond support; Figure 4 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode and an electrical resistance heater disposed on a rear surface of the electrically conductive diamond electrode; Figure 5 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode and an electrical resistance heater disposed on a side surface of the electrically conductive diamond electrode; Figure 6 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode embedded within an electrically insulating diamond support and an electrical resistance heater disposed on a rear surface of the electrically insulating diamond support; Figure 7 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode embedded within an electrically insulating diamond support and an electrical resistance heater embedded within the electrically insulating diamond support on a rear surface of the electrically conductive diamond electrode; Figure 8 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode embedded within an electrically insulating diamond support and electrical resistance heaters disposed on side walls of the electrically insulating diamond support adjacent to the electrically conductive diamond electrode; Figure 9 illustrates an electrochemical apparatus comprising an electrically conductive diamond electrode and a pulsed laser focused on an absorption layer on rear surface of the electrically conductive diamond electrode; Figure 10 illustrates an electrochemical method in which cyclic voltammetry is performed by imposing a potential staircase on the diamond electrode whilst a laser is shone intermiftently onto a rear surface of the diamond electrode; Figure 1] illustrates results of the electrochemical method showing electrochemical current (raw data shown) plotted versus applied potential and comparing results with and without laser heating; Figure 12 illustrates an expanded view of current versus potential data when applying laser pulsed heating; Figure 13 illustrates a series of current versus potential plots at different laser powers; and Figure 14 illustrates how peak current increases with laser power.
Detailed Description
Pulsed heating of electrochemical sensors in known in the art as outlined in the background section of this specification. However, all prior art methods of pulse heating electrochemical sensing electrodes comprise application of heat directly to the sensing surface of the electrochemical sensing electrode. For example, in resistive metal electrodes, such as metal wire electrodes and metal micro-disc electrodes, pulsed heating is achieved via application of a pulsed electric current through the electrodes, including at the sensing surface, and this can lead to unwanted Faradaic effects at the sensing surface, Non-contact pulsed heating methods described in the art, such as pulsed lasers or pulsed microwaves, are also directed onto the sensing surface of the electrode. In some instances this is desirable, For example, a pulsed laser may be used to selectively ablate chemical species deposited on the sensing surface as described by Qui et al. However, in most instances it is undesirable to interfere directly with the sensing surface and/or the chemical species deposited thereon by, for example, ablating the species off the sensing surface. Furthermore, directing a pulsed laser through the solution overlying the sensing surface is problematic due to absorption of laser energy within the solution leading to heating of the solution and generating convection currents which can adversely affect electrochemical performance at the sensing surface. In contrast, the present inventors have recognized that it is desirable to heat the sensing surface of the electrode without unduly changing the temperature of the bulk solution causing convection currents.
Embodiments of the present invention are based on the realization that when using an electrically conductive diamond sensing electrode, the extremely high thermal conductivity of the diamond material allows rapid and accurate heating and cooling of the sensing surface even if pulsed heating is not applied directly to the sensing surface of the conductive diamond sensing electrode. Pulsed heating may be applied to a non-sensing surface of the electrically conductive diamond sensing electrode, such as a rear surface of the electrically conductive diamond sensing electrode or to a diamond support material in which the diamond sensing electrode is disposed, and due to the extremely high thermal conductivity of the diamond material heat will be rapidly transferred to the sensing surface of the diamond sensing electrode. It is considered that such a pulsed heating configuration has a number of advantages over prior art arrangements including one, several, or all of the following: (1) as the pulsed healing is not applied directly to the sensing surface then the sensing surface and/or chemical species deposited thereon are not adversely affected by the pulsed heating, e.g. species are not ablated from the sensing surface and the electrical and physical structure of the sensing surface is not unduly adversely affected/damaged; (2) as the pulsed heating is not applied through the solution overlying the sensing surface then absorption within the solution leading to heating of the solution and generation of convection currents which can adversely affect electrochemical performance at the sensing surface is avoided; (3) diamond is hard, inert, and has a low thermal expansion coefficient in addition to its high thermal conductivity allowing aggressive pulse heating sequences to be applied while retaining dimensional, structural, and chemical stability; (4) electrically conductive diamond material can be fabricated with an extremely wide potential window, a high degree of electrochemical reversibility, and with a low capacitance and this functionality in combination with the pulsed heating method as described herein will allow a wide range of chemical species to be detected at unprecedented levels of sensitivity and selectivity; (5) by applying the pulsed heating to a non-sensing surface of the diamond electrode this enables the sensor configuration to be made more compact, robust, and easy to use by allowing the heater to be mounted at the rear of the sensing electrode rather than, for example, opposite the sensing surface and directed through the solution being analysed; (6) the very high thermal conductivity of diamond material allows heat to be rapidly transferred to the sensing surface of a diamond electrode even when pulsed heating is not directly applied to the sensing surface and also allows the sensing surface to rapidly cool after application of a heating pulse; (7) data indicates that while continuous heating of a diamond electrode does not significantly improve electrochemical performance due to adverse convection, pulsed heating of a diamond electrode via a non-sensing surface of the diamond electrode has been found to improve diamond's electrochemical sensing perfbrmance; (8) it has been found that pulsed heating can be controlled to allow heating of the sensing surface of the diamond electrode without initiating substantial gas bubble formation at the sensing surface of the diamond electrode which can adversely affect electrochemical performance, particularly if the sensing surface of the diamond electrode is made highly smooth which aids in avoiding gas bubble formation; (9) pulsed heating of diamond electrodes to improve sensing potentially allows the use of lower quality diamond material in certain applications while achieving a sensing performance equivalent to a higher quality diamond material thereby saving costs; and (10) pulsed heating may be used to separate and distinguish between two overlapping electrochemical signals from two different reactions which have different surface kinetics.
S
A number of possible configurations for implementing the present invention are possible as illustrated in Figure 1 to 9 and outlined in more detail below, Common features are denoted by common reference numerals.
All electrochemical apparatus configurations share the following common features: an electrically conductive diamond electrode 2 configured to have a surface 4 which is disposed in contact with a solution 6 in use and a surface 8 which does not contact the solution 6 in use; an electrical contact 10 configured to applying a voltage to the electrically conductive diamond electrode 2 to perform an electrochemical process on the solution 6; and a heater 12 configured to apply pulsed heating to the surface 8 which does not contact the solution 6 whereby the surface 4 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 from the surface 8 which does not contact the solution 6 to the surface 4 which is disposed in contact with the solution 6.
In one configuration the electrically conductive diamond electrode is configured to have a front surface which is disposed in contact with the solution in use and a rear surface disposed on an opposite side of the electrically conductive diamond electrode to the front surface, and wherein the heater is configured to apply pulsed heating directly onto the rear surface of the electrically conductive diamond electrode. Figure 1 illustrates a first example in which a heater 12 comprises a laser configured to emit a pulsed laser beam onto a rear surface 8 of an electrically conductive diamond electrode 2. A surface 4 of the electricafly conductive diamond electrode 2 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 from the rear surface 8 which does not contact the solution 6 to the surface 4 which is disposed in contact with the solution 6. An electrical contact 10 is disposed on the rear surface 8 of the electrically conductive diamond electrode. The electrical contact 10 can be patterned to leave a window through which the laser beam can be focussed directly onto the rear surface 8 of the electrically conductive diamond electrode 2.
In another configuration, the electrically conductive diamond electrode is configured to have a front surface which is disposed in contact with the solution in use, a rear surface disposed on an opposite side of the electrically conductive diamond electrode to the front surface, and a side surface disposed between the front and rear surfaces, and the heater is configured to apply pulsed heating directly onto the side surface of the electrically conductive diamond electrode. Figure 2 illustrates an example of such a configuration in which a heater 12 comprises a laser configured to emit a pulsed laser beam onto a side surface 14 of an electrically conductive diamond electrode 2. A surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 from the side surface 14 which does not contact the solution 6 to the surface 4 which is disposed in contact with the solution 6, An electrical contact 10 is disposed on the rear surface 8 of the electrically conductive diamond electrode 2.
In yet another configuration the electrically conductive diamond electrode is mounted within an electrically insulating diamond support, and the heater is configured to apply pulsed heating to the electrically insulating diamond support whereby the surface which is disposed in contact with thc solution in usc is hcatcd via thcrmal conduction through thc clcctrically insulating diamond support to the surface which does not contact the solution and from the surface which does not contact the solution through the electrically conductive diamond electrode to the surface which is disposed in contact with the solution in use. Figure 3 illustrates an example of such a configuration in which an electrically conductive diamond electrode 2 is mounted within an electrically insulating diamond support 16. A heater 12 comprises a laser configured to apply pulsed heating to the electrically insulating diamond support t6 whereby a surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with a solution 6 in use is heated via thermal conduction through the electrically insulating diamond support 16 to a surface 18 which does not contact the solution 6 and from the surface 18 which does not contact the solution 6 through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. One or more electrical contacts 10 are provided through the electrically insulating diamond support 16 to a rear surface 18 of the electrically conductive diamond electrode 2.
The electrical contacts tO can be formed by vias in the electrically insulating diamond support 16.
Figure 4 illustrates another example in which the heater comprises an electrical resistance heater 12 configured to provide a pulsed current through a resistive element which is disposed on, or adjacent to, a surface 8 of the electrically conductive diamond electrode 2 which does not contact a solution 6. In the illustrated configuration, the electrical resistance heater 12 is disposed on a rear surface 8 of the electrically conductive diamond electrode 2.
In use a surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. An electrical contact 10 is also disposed on the rear surface 8 of the electrically conductive diamond electrode. The electrical contact 10 can be patterned to leave a window in which the electrical resistance heater 12 is disposed on the rear surface 8 of the electrically conductive diamond electrode 2. The resistive heater element may be formed of a metallic material or of an alternative material such as a semiconductive diamond material.
Figure 5 illustrates another example in which the heater comprises an electrical resistance heater 12 configured to provide a pulsed current through a resistive element which is disposed on, or adjacent to, a side surface 14 of the electrically conductive diamond electrode 2 which docs not contact a solution 6. In usc a surfacc 4 of thc clcctrically conductivc diamond electrode 2 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. An electrical contact 10 is also disposed on the rear surface 8 of the electrically conductive diamond electrode.
Figure 6 illustrates another example in which an electrically conductive diamond electrode 2 is mounted within an electrically insulating diamond support 6. A heater 12 comprises an electrical resistance heater configured to apply pulsed heating to the electrically insulating diamond support 16 whereby a surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with a solution 6 in use is heated via thermal conduction through the electrically insulating diamond support 16 to a surface 18 which does not contact the solution 6 and from the surface 18 which does not contact the solution 6 through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. One or more electrical contacts 10 are provided through the electrically insulating diamond support 16 to a rear surface 8 of the electrically conductive diamond electrode 2. The electrical contacts 10 can be formed by vias in the electrically insulating diamond support 16, Figure 7 illustrates another example in which an electrically conductive diamond electrode 2 is mounted within an electrically insulating diamond support 16. A heater 12 comprising an electrical resistance heater is also embedded within the electrically insulating diamond support 16 and contacts a rear surface 18 of the electrically conductive diamond electrode 2.
The heater 12 is configured to apply pulsed heating to the electrically conductive diamond electrode 2 whereby a surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with a solution 6 in use is heated via thermal conduction through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. One or more electrical contacts 10 are provided through the electrically insulating diamond support 16 to a rear surface 18 of the electrically conductive diamond electrode 2. The electrical contacts 10 can be formed by vias in the electrically insulating diamond support I 6.
Figure 8 illustrates yet another example in which an electrically conductive diamond electrode 2 is mounted within an electrically insulating diamond support 16. One or more heaters 12 are disposed on side surfaces of the electrically insulating diamond support 16 adjacent to the electrically conductive diamond electrode 2. The heaters 12 are configured to apply pulsed heating to the electrically conductive diamond electrode 2 via the electrically insulating diamond support 16 whereby a surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with a solution 6 in use is heated via thermal conduction through the electrically insulating diamond support 16 and through the electrically conductive diamond electrode 2 to the surface 4 which is disposed in contact with the solution 6. An electrical contact 10 is provided through the electrically insulating diamond support 16 to a rear surface 18 of the electrically conductive diamond electrode 2.
Figure 9 illustrates another example which is similar to that illustrated in Figure 1. The configuration comprises a heater 12 in the form of a laser configured to emit a pulsed laser beam. An absorption layer 20 is provided on a rear surface 8 of an electrically conductive diamond electrode 2 for absorbing the laser light and heating the electrically conductive diamond electrode 2. An example of an absorption layer 20 is a region of boron-doped diamond material. A surface 4 of the electrically conductive diamond electrode 2 which is disposed in contact with the solution 6 is heated via thermal conduction through the electrically conductive diamond electrode 2 from the rear surface 8 which does not contact the solution 6 to the surface 4 which is disposed in contact with the solution 6. An electrical contact 10 is disposed on the rear surface 8 of the electrically conductive diamond electrode.
The electrical contact 10 can be patterned to leave a window through which the laser beam can be focussed directly onto the rear surface 8 of the electrically conductive diamond electrode 2.
In the configuration illustrated in Figure 9 the absorption layer 20 is disposed on the rear surface 8 of the electrically conductive diamond electrode 2. However, in a modified arrangement the absorption layer 20 may be disposed on a side surface of the electrically conductive diamond electrode 2 (in a configuration similar to that illustrated in Figure 2).
Alternatively, the electrically conductive diamond electrode 2 may be embedded in an electrically insulating diamond support and the absorption layer 20 can be disposed on a rear surface 8 of the electrically insulating diamond support (in a configuration similar to that illustrated in Figure 3). The absorption layer 20 can be fabricated from any material which absorbs laser light at the operating frequency of the laser in use. A further modification is to rcplacc thc lascr light sourcc with a flash lamp focusscd onto thc absorption laycr 20 (c.g. via a concave mirror) with the absorption layer being fabricated from a material which absorbs light from the flash light in use.
While a range of diamond electrode and heater configurations have been described above, it is envisaged that other configurations may be provided. For example, the diamond electrodes may be provided in the form of a microelectrode array comprising fluid channels with one or more electrically conductive diamond electrodes therein as described in W02007]07844.
Alternatively, the diamond electrodes may be provided in the form of a microelectrode array comprising pins or projections of electrically conductive diamond at a planar surface as described in W02005W 2894, In yet another alternative the diamond electrodes are formed as a series of elongate bands as described in W02012126802. Further still, the diamond electrode configuration may also be provided in conjunction with a diamond reference electrode as described in W02012156203. However the diamond electrodes and heater elements are configured, a key feature is that the apparatus is configured to apply pulsed heating indirectly to an electrochemically active surface of the diamond electrodes via thermal conduction through the diamond material of the electrode structure, The electrically conductive diamond material used in embodiments of the present invention may be single crystal or polycrvstalline diamond material, e.g. single crystal or polycrvstalline diamond material fabricated using a chemical vapour deposition technique.
Electrically conductive diamond material is typically fabricated by doping the diamond material with boron during synthesis. For example, the electrically conductive diamond material may comprise a boron content ofat least I x 1018 boron atoms cm3, I x I9 boron atoms cm3, I x 1020 boron atoms cm3, 2 x 1020 boron atoms cm3, 3 x 1020 boron atoms cm3, x to2° boron atoms cm3, 7 x 1020 boron atoms cm3, 9 x 1020 boron atoms cm3, 1 x 1021 boron atoms cm3, or 3 x 1021 boron atoms cm3, Furthermore, the electrically conductive diamond material may comprise a boron content of no more than 7 x 1021 boron atoms cm3, 6 x tO21 boron atoms cm2, 5 x 1021 boron atoms cm3, 4 x 1021 boron atoms cm3, 3 x 1021 boron atoms cm3, 2 x 1021 boron atoms cm3, or I x tO21 boron atoms cm3. For example the boron content of the electrically conductive diamond material may be in a range I x 20 -i 21 -3 20 -3 21 boron atoms cm to 7 x 10 boron atoms cm, 2 x 10 boron atoms cm to 5 x 10 boron atoms cm3, 4 x 1020 boron atoms cm3 to 3 x 1021 boron atoms cm3, or 8 x 1020 boron atoms cm3 to I x tO21 boron atoms cm3.
The aforementioned configurations and materials can be utilised in an electrochemical method comprising: applying a voltage to an electrically conductive diamond electrode to perform an electrochemical process on a solution in contact with a surface of the electrically conductive diamond electrode; arid applying pulsed heating to the electrically conductive diamond electrode via a surface of the electrically conductive diamond electrode which is not in contact with the solution, whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the electrically conductive diamond electrode from the surface which does not contact the solution to the surface which is in contact with the solution.
The pulsed heating may be applied before, during, or after the application of the voltage.
Parameters for the pulsed heating may be optimized to achieve increased electrochemical sensitivity and/or selectivity. In this regard, data indicates that while continuous heating of a diamond electrode does not significantly improve electrochemical performance due to adverse convection, pulsed heating of diamond electrodes has been found to improve diamonds electrochemical sensing performance.
Figure 10 illustrates a basic example of the methodology in which cyclic voltammetry is performed by imposing a potential staircase on the diamond electrode, whilst a laser is shone intermittently onto a rear face of the diamond electrode which is not in contact with the solution being analysed. In the illustrated example, laser pulses are applied with a pulse length of 10 ms and a frequency of 10 Hz.
Figure 11 illustrates results of the electrochemical method showing electrochemical current (raw data shown) p'otted versus applied potential and comparing results with and without laser heating while Figure 12 illustrates an expanded view of current versus potential data when applying laser pulsed heating. It is clear that the indirect pulsed laser heating as described herein increases the observed electrochemical current.
Figure t3 illustrates a series of current versus potential plots at different laser powers while Figure 14 illustrates how peak current changes with laser power.
From the aforementioned data it is clear that an increase in electrochemical current is observed with laser-heating, and this increase in electrochemical current increases with increasing laser power. Higher rates of mass transport are responsible for the observed enhancement, Furthermore, the peak potential shifts towards 0 V with laser-heating. This is likely due to an increased rate of kinetics for the electrochemical reaction as the energy barrier is easier to overcome at higher temperatures.
Various parameters of the pulsed heating may be optimized for a particular electrode size and geometry and/or end application including pulse frequency, pulse length, power, and power density relative to the diamond electrode area. It should be noted that the optimum value for these parameters will vary according to the diamond electrode size and geometry.
Accordingly, for a particular electrode size and geometry the parameters for the pulse heating can be varied to find an optimum set of conditions for optimized electrochemical performance, In this regard, the present inventors have identified a number of parameters which are independent of any specific electrode geometry and which can be readily tested as a means for optimizing the specific pulsed heating parameters previously mentioned, For example, the embodiments of the present invention may be configured to meet one, several, or all of the following characteristics: (i) The heater should be configured to emit heat pulses which do not damage the electrically conductive diamond electrode. Excessive heating may cause graphitization and/or ablation of the diamond material and thus the heat pulse parameters should be selected to ensure that the electrically conductive diamond material is not damaged in use.
Furthermore, hydrogen terminated diamond material is less stable to pulsed heating than oxygen terminated diamond material. Accordingly, oxygen terminated electrically conductive diamond material is preferred for use in embodiments of the present invention.
(ii) The heater is preferably configured to emit heat pulses which do not initiate a significant flux of bubbles from the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use. Continuous heating or heating with long pulses can lead to bubble formation and this detrimentally affects the thnctional performance of the diamond electrode, The bubbles can be detected visually and/or via noise introduced into a voltammogram signal as a result of bubble formation. It has been found that the application of relatively short heat pulses can avoid bubble formation while still effectively heating the working surface of the diamond electrode. Further still, the provision of a diamond electrode having a smooth working surface can also aid in preventing bubble formation during pulsed heating. As such, the surface of the electrically conductive diamond electrode which is disposed in contact with the solution may have a flatness variation of no more than 10 tm, 5 tm, 1 j.tm, 500 nm, or 100 nm and/or a surface roughness Ra of no more than 50 nm, 3Onm, 15 nm, 10 nm, ors nm, (iii) The heater is preferably configured to emit heat pulses which heat the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use but do not significantly change a temperature of the solution at a location outside a diffusion layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode, If the bulk of the solution is excessively heated then convection currents arise reducing electrochemical performance. Ideally, heating is limited to a surface region of the diamond electrode.
(iv) The heater is preferably configured to emit heat pulses which decrease a thickness of a diffusion layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode. It has been found that heating a diamond electrode in accordance with embodiments of the present invention can reduce the thickness of the diffusion layer and thus increase electrochemical performance.
(v) The heater is preferably configured to emit heat pulses which create a change in temperature T at the surface of the electrically conductive diamond electrode which is sufficient to significantly increase the reaction kinetics of a target reaction and increase sensitivity of the electrochemical apparatus. that is, AT »= x, where x may be equal to, for example, 10°C, 50°C, 100°C, 200°C, 300°C, or 500°C.
(vi) Due to the high thermal conductivity of diamond material it is possible to achieve relatively large changes in temperature at the surface of the electrically conductive diamond electrode over a short time period t. That is AT/t? y, where y may be equal to, for example, 5°CW1, 10°Cs1, 20°Cs', 300CsA, or 50°Cs1.
The electrochemical apparatus as described herein may be configured to perform a range of electro-deposition and/or electrochemical sensing applications including, for example, electro-deposition and stripping voltammetry or in fuel cell applications where the surface of the diamond electrode is functionalized with catalyst particles. Furthermore, the heater configurations as described herein may be utilized in a combined electro-deposition and spectroscopic sensing methodology as described in W02012/156307 to increase the sensitivity of this technique, particularly at low concentrations of target chemical species.
While this invention has been particularly shown and described with reference to certain embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.
Claims (20)
- Claims An electrochemical apparatus comprising: an electrically conductive diamond electrode configured to have a surface which is disposed in contact with a solution in use and a surface which does not contact the solution in use; an electrical contact configured to apply a voltage to the electrically conductive diamond electrode to perform an electrochemical process on the solution; and a heater configured to apply pulsed heating to the surface which does not contact the solution whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the electrically conductive diamond electrode from the surface which does not contact the solution to the surface which is disposed in contact with the solution.
- 2. An electrochemical apparatus according to claim I, wherein the heater comprises a laser configured to emit a pulsed laser beam onto, or adjacent to, the surface of the electrically conductive diamond electrode which does not contact the solution.
- 3. An electrochemical apparatus according to claim 1, wherein the heater comprises an electrical resistance heater configured to provide a pulsed current through a resistive element which is disposed on, or adjacent to, the surface of the electrically conductive diamond electrode which does not contact the solution.
- 4. An electrochemical apparatus according to claim 3, wherein the resistive element is formed of a metallic material.
- 5. An electrochemical apparatus according to claim 3, wherein the resistive element is formed of a semiconductive diamond material,
- 6. An electrochemical apparatus according to any preceding claim, wherein the heater is configured to emit heat pulses which do not damage the electrically conductive diamond electrode.
- 7, An electrochemical apparatus according to any preceding claim, wherein the heater is configured to emit heat pulses which do not initiate a significant flux of bubbles from the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use.
- 8. An electrochemical apparatus according to any preceding claim, wherein the heater is configured to emit heat pulses which heat the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use but do not significantly change a temperature of the solution at a location outside a difftision layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode.
- 9. An electrochemical apparatus according to any preceding claim, wherein the heater is configured to emit heat pulses which decrease a thickness of a diffusion layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode.
- 10. An electrochemical apparatus according to any preceding claim, wherein the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use has a flatness variation of no more than 10 tm.
- 11. An electrochemical apparatus according to any preceding claim, wherein the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use has a surface roughness Ra of no more than 50 nm.
- 12. An electrochemical apparatus according to any preceding claim, wherein the surface of the electrically conductive diamond electrode which is disposed in contact with the solution in use has an oxygen termination.
- 13. An electrochemical apparatus according to any preceding claim, wherein the electrically conductive diamond electrode is configured to have a front surface which is disposed in contact with the solution in use and a rear surface disposed on an opposite side of the electrically conductive diamond electrode to the front surface, and wherein the heater is configured to apply pulsed heating directly onto the rear surface of the electrically conductive diamond electrode.
- 14. An electrochemical apparatus according to any one of claims 1 to 12, wherein the electrically conductive diamond electrode is configured to have a front surface which is disposed in contact with the solution in use, a rear surface disposed on an opposite side of the electrically conductive diamond electrode to the front surface, and a side surface disposed between the front and rear surfaces, and wherein the heater is configured to apply pulsed heating directly onto the side surface of the electrically conductive diamond electrode.
- 15. An electrochemical apparatus according to any one of claims I or 12, wherein the electrically conductive diamond electrode is mounted within an electrically insulating diamond support, and wherein the heater is configured to apply pulsed heating to the electrically insulating diamond support whereby the surface which is disposed in contact with the solution in use is heated via thermal conduction through the electrically insulating diamond support to the surface which does not contact the solution and from the surface which does not contact the solution through the electrically conductive diamond electrode to the surface which is disposed in contact with the solution in use.
- 16. An electrochemical method comprising: applying a voltage to an electrically conductive diamond electrode to perform an electrochemical process on a solution in contact with a surface of the electrically conductive diamond electrode; and applying pulsed heating to the electrically conductive diamond electrode via a surface of the electrically conductive diamond electrode which is not in contact with the solution, whereby the surface which is disposed in contact with the solution is heated via thermal conduction through the electrically conductive diamond electrode from the surface which does not contact the solution to the surface which is in contact with the solution.
- 17. An electrochemical method according to claim 6, wherein the pulsed heating is set such that heat pulses do not damage the electrically conductive diamond electrode.
- 18, An electrochemical method according to claim 6 or 17, wherein the pulsed heating is set such that heat pulses do not initiate a significant flux of bubbles from the surface of the electrically conductive diamond electrode which is disposed in contact with the solution.
- 19. An electrochemical method according to any one of claims 16 to 18, wherein the pulsed heating is set such that the surface of the electrically conductive diamond electrode which is disposed in contact with the solution is heated but the solution at a location outside a diffusion layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode does not significantly change in temperature.
- 20. An electrochemical method according to any one of claims 16 to 19, wherein the pulsed heating decreases a thickness of a diffusion layer of the solution disposed adjacent the surface of the electrically conductive diamond electrode.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB1307680.7A GB201307680D0 (en) | 2013-04-29 | 2013-04-29 | Electrochemical apparatus and method |
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| Publication Number | Publication Date |
|---|---|
| GB201407126D0 GB201407126D0 (en) | 2014-06-04 |
| GB2515174A true GB2515174A (en) | 2014-12-17 |
| GB2515174B GB2515174B (en) | 2015-06-24 |
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| GBGB1307680.7A Ceased GB201307680D0 (en) | 2013-04-29 | 2013-04-29 | Electrochemical apparatus and method |
| GB1407126.0A Expired - Fee Related GB2515174B (en) | 2013-04-29 | 2014-04-23 | Electrochemical apparatus and method |
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| GBGB1307680.7A Ceased GB201307680D0 (en) | 2013-04-29 | 2013-04-29 | Electrochemical apparatus and method |
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| WO (1) | WO2014177433A1 (en) |
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| GB201603680D0 (en) | 2016-03-03 | 2016-04-20 | Ucl Business Plc | Device |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5777372A (en) * | 1995-03-01 | 1998-07-07 | Kabushiki Kaisha Kobe Seiko Sho | Diamond film biosensor |
| JP2007040796A (en) * | 2005-08-02 | 2007-02-15 | Okutekku:Kk | Working electrode and electrochemical measuring device using the same |
| JP2007086037A (en) * | 2005-09-26 | 2007-04-05 | Horiba Ltd | Diamond electrode and surface reformation method |
| WO2007107844A1 (en) * | 2006-03-17 | 2007-09-27 | Element Six Limited | Microelectrode array |
| GB2491018A (en) * | 2011-05-18 | 2012-11-21 | Element Six Ltd | Electrochemical deposition and spectroscopic analysis using diamond electrodes |
| GB2491005A (en) * | 2011-05-18 | 2012-11-21 | Element Six Ltd | Electrochemical sensor with diamond electrodes |
-
2013
- 2013-04-29 GB GBGB1307680.7A patent/GB201307680D0/en not_active Ceased
-
2014
- 2014-04-23 WO PCT/EP2014/058211 patent/WO2014177433A1/en active Application Filing
- 2014-04-23 GB GB1407126.0A patent/GB2515174B/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5777372A (en) * | 1995-03-01 | 1998-07-07 | Kabushiki Kaisha Kobe Seiko Sho | Diamond film biosensor |
| JP2007040796A (en) * | 2005-08-02 | 2007-02-15 | Okutekku:Kk | Working electrode and electrochemical measuring device using the same |
| JP2007086037A (en) * | 2005-09-26 | 2007-04-05 | Horiba Ltd | Diamond electrode and surface reformation method |
| WO2007107844A1 (en) * | 2006-03-17 | 2007-09-27 | Element Six Limited | Microelectrode array |
| GB2491018A (en) * | 2011-05-18 | 2012-11-21 | Element Six Ltd | Electrochemical deposition and spectroscopic analysis using diamond electrodes |
| GB2491005A (en) * | 2011-05-18 | 2012-11-21 | Element Six Ltd | Electrochemical sensor with diamond electrodes |
Non-Patent Citations (1)
| Title |
|---|
| QUI, F. et al; "Laser activation voltammetry: Selective removal of reduced forms of methyl viologen deposited on glassy carbon and boron doped diamond electrodes", Anal. Chem., 2000, Vol 72, No 11, pp2362-2370 * |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2014177433A1 (en) | 2014-11-06 |
| GB2515174B (en) | 2015-06-24 |
| GB201407126D0 (en) | 2014-06-04 |
| GB201307680D0 (en) | 2013-06-12 |
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