Supported catalyst

Abstract

A method for the preparation of a supported catalyst comprising an electrocatalyst on a nitrogen-functionalized carbon support. The method comprises providing an electrocatalyst on a carbon support; and then incorporating nitrogen into the carbon support to provide the supported catalyst. Nitrogen may be incorporated by exposing the electrocatalyst to gaseous nitrogen.

Description

[0001] SUPPORTED CATALYST

[0002] Field

[0003] The present specification relates to a method for the manufacture of a supported catalyst, in particular, a supported catalyst comprising an electrocatalyst on a nitrogen-functionalized carbon support. The supported catalyst may be employed in an electrochemical device such as a fuel cell or electrolyser.

[0004] Background

[0005] Carbon supports have been modified with nitrogen for use in fuel cells. Zhou, Y. et al. (Energy Environ. Sci. 3,1437-1446 (2010)) is a review article that describes enhancement of Pt and Pt-alloy fuel cell catalyst activity and durability via nitrogen-modified carbon supports.

[0006] Orfanidi et al. (Journal of The Electrochemical Society, 164 (4) F418-F426 (2017)) reports that by introducing nitrogen containing surface groups, it was shown that the ionomer distribution in the cathodic electrode can be optimized to decrease mass transport related voltage losses at high current density. The method of preparation is said to closely follow Jansen et al. (R. J.J. Jansen and van Bekkum, Carbon, 32, 1507 (1994)). Jansen et al. describes amination and ammoxidation of activated carbons by oxidizing carbon with nitric acid and then subjecting the oxidized carbon to ammonia and ammonia / oxygen gas mixtures at temperatures between 200 and 420°C.

[0007] Ott et al. (Nat. Mater. 19, 77-85 (2020)) describes ionomer distribution control in porous carbon supported catalyst layers for proton exchange membrane fuel cells. Pre-oxidized carbon is ammonolysed in a tube furnace under ammonia flow at 200, 400 or 600°C to generate the N-functionalized carbon support.

[0008] Pimped et al. (Journal of Power Sources, Volume 507, 30 September 2021 , 229971) reports that N-functional groups interact strongly with phosphoric acid, controlling the phosphoric acid distribution in the electrode. The method of manufacture is said to follow Orfanidi et al. (above).

[0009] Ott et al. (J. Electrochem. Soc. 2022 169) describes N-functionalization of pre-oxidized carbon via ammonia at 200, 600 and 800°C and investigates the underlying mechanism for the performance enhancement associated with nitrogen modified carbon supports.

[0010] The present invention provides a new method to produce a supported catalyst comprising an electrocatalyst on a nitrogen-functionalized carbon support.

[0011] Summary According to a first aspect of the invention there is provided a method for the preparation of a supported catalyst, the method comprising:

[0012] (i) providing an electrocatalyst on a carbon support; and

[0013] (ii) incorporating nitrogen into the carbon support to provide the supported catalyst, the supported catalyst comprising an electrocatalyst on a nitrogen-functionalized carbon support.

[0014] The resulting supported catalyst is suitable for use in a fuel cell or electrolyser.

[0015] The method of the invention employs an electrocatalyst on a carbon support as its starting material, i.e., carbon may be catalysed so that it supports an electrocatalyst (e.g. electrocatalyst particles) on its surface and / or in its pores; and then the carbon support (carrying the electrocatalyst) is N-functionalized to yield an electrocatalyst on a N- functionalized carbon support (see Figure 1a).

[0016] In contrast, the known method (e.g. Jansen et al.) employs carbon as its starting material; then oxidizes carbon with nitric acid; N-functionalizes the oxidized carbon; and subsequently catalyses the N-functionalized carbon to yield an electrocatalyst on a N-functionalized carbon support (see Figure 1b).

[0017] The method of the invention does not require (and suitably does not comprise) a pre-oxidation step. Having fewer steps may be more efficient and / or economical than the conventional method. In addition, pre-oxidation may be associated certain disadvantages. For example, pre-oxidation may be hazardous (e.g., where concentrated nitric acid is employed). Pre- oxidation may also affect the porosity of the carbon support (e.g. cause pores to collapse), reducing the surface area available to support the electrocatalyst. Hence, the method of the invention can allow more catalyst to be located in pores of the support.

[0018] The ability to N-functionalize carbon carrying an electrocatalyst is unexpected. Conventional methods require pre-oxidation of the carbon (without electrocatalyst) to promote the subsequent N-functionalization. The examples show that N-functionalization of a “fresh” carbon black (i.e. no oxidation or catalysation) is unsuccessful. The inventors have determined that the pre-oxidation can be avoided by catalysing before N-functionalization. Without being bound by theory the inventors propose that that the presence of the electrocatalyst “activates” the carbon support, allowing N-functionalization to proceed.

[0019] According to a second aspect of the invention there is provided a supported catalyst produced or producible by the method of the first aspect, the supported catalyst comprising an electrocatalyst on a N-functionalized carbon support. It will be appreciated that the method of manufacture may be determined by analysing the supported catalyst product. In particular, it may be possible to determine whether N- functionalization took place before or after catalysation due to the distribution of electrocatalyst and N-functionalization in the carbon support. Catalyst (e.g. Pt particles) is present on the surface and / or in the pores of the support. Without being bound by theory, the inventors propose that the method of the invention leads to a higher proportion of catalyst in the pores, relative to the surface, as compared to the known method (Fig 1 b). Various techniques are available to investigate the location of the catalyst on the support. For example, the catalyst can be incorporated into an electrochemical device and then tested under wet and dry conditions. Since the N-functionalization is being catalysed by the electrocatalyst, it is expected that there will be a greater amount of N-functionalization around the electrocatalyst particles, e.g. the N-functionalization will be concentrated around the catalyst rather than evenly distributed. Various techniques are available to investigate the relative location of the catalyst and the N-functionalization. For example, samples could be assessed by TEM (transmission electron microscopy).

[0020] According to a third aspect of the invention there is provided a catalyst layer comprising the supported catalyst of the invention, and optionally an ionomer.

[0021] According to a fourth aspect of the invention there is provided a catalyst-coated membrane (CCM) comprising the catalyst layer of the invention disposed on an electrolyte (e.g. ionconducting) membrane. The electrolyte membrane may have a first face and an opposing second face and the catalyst layer may be located on the first face or the second face.

[0022] According to a fifth aspect of the invention there is provided a gas diffusion electrode comprising the catalyst layer of the invention disposed on a gas diffusion layer.

[0023] According to a sixth aspect of the invention there is provided a decal comprising the catalyst layer of the invention and a decal transfer substrate.

[0024] Detailed description

[0025] Providing an electrocatalyst on a carbon support

[0026] Step (i) requires “providing an electrocatalyst on a carbon support” and may be understood as “providing a precursor, the precursor comprising an electrocatalyst on a carbon support”. The precursor (electrocatalyst on a carbon support) may be a commercially available supported catalyst. For example, platinum on carbon black catalysts are available under the HiSPEC™ brand (Johnson Matthey). Alternatively, the method of invention may comprise an initial step of catalysing carbon to yield the precursor (the electrocatalyst on the carbon support). For example carbon (e.g. carbon black) can be reacted with a platinum salt (e.g. Pt nitrate, F^PtCU or I^PtCk) and the platinum can be reduced to yield Pt nanoparticles on the surface and pores of the carbon.

[0027] Incorporating nitrogen into the carbon support

[0028] Incorporating nitrogen into the carbon support may be described as N-doping, N- functionalizing or N-modifying.

[0029] Typically, incorporating nitrogen into the carbon support comprises exposing the carbon support (and the associated electrocatalyst on its surface and / or in its pores) to ammonia (NH3). The reaction may take place at standard ambient temperature and pressure (SATP, 25°C, 100 kPa).

[0030] The carbon support may be exposed to a flow of (gaseous) ammonia. For example, the carbon support may be exposed to ammonia at a flow rate of (i) at least 200ml / min; and / or (ii) 800ml / min or less. The carbon support may be exposed to ammonia for a period of two hours or more; four hours or more; or 6 hours or more; and / or the carbon support may be exposed to ammonia for a period of 24 hours or less; 12 hours or less; or 6 hours or less.

[0031] The carbon support may be exposed to ammonia (e.g. a flow of ammonia) at a temperature of 200°C or more, 400°C or more, 500°C or more, 600°C or more, 700°C or 800°C or more and / or the carbon support may be exposed to ammonia (e.g. a flow of ammonia) at a temperature of 1100°C or less, 1000°C or less, 900°C or less, 800°C or less, 700°C or less, 600°C or less, 500°C or less, 400°C or less, or 200°C or less.

[0032] The carbon support may be exposed to ammonia at a temperature of from 500 to 1000°C, such as 500 to 800°C or 550 to 750°C. This temperature range promotes the formation of a lattice having both carbon atoms and nitrogen atoms, which is preferred.

[0033] The carbon support may be exposed to ammonia at a temperature of from 200 to 400°C. This temperature range promotes the formation of NHx surface groups.

[0034] Acid treatment

[0035] The method can optionally comprise a step of modifying the nitrogen incorporated into the nitrogen-functionalized carbon support. The step can comprise changing (preferably increasing) the ratio of pyrrolic N species to pyridinic N species that is incorporated into the nitrogen-functionalized carbon support. Such a step can enable the properties of the supported catalyst to be tuned. The method of the invention may comprise a subsequent acid treatment step to modify the N-functionalized carbon support. Acid treatment may comprise treatment with a mineral acid such as sulphuric acid (H2SO4) and may lead to the N- functionalized carbon support comprising oxidized N species togetherwith reduced N species. Acid treatment allows the ratio of these species to be tuned as desired. For example, the optional acid treatment can tune the ratio of pyrrolic N species to pyridinic N species present in the N-functionalized carbon. The inventors have determined that the level of N- functionalization is maintained following acid treatment, as shown in the examples.

[0036] Electrocatalyst

[0037] The electrocatalyst is on the carbon support prior to N-functionalization. The electrocatalyst is typically in the form of nanoparticles. The electrocatalyst is suitably selected from

[0038] (i) the platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium);

[0039] (ii) gold or silver;

[0040] (iii) a base metal;

[0041] (iv) or an alloy or mixture comprising one or more of these metals or their oxides.

[0042] The preferred electrocatalyst metal is platinum, which may be alloyed with other precious metals or base metals. A base metal is tin or a transition metal which is not a noble metal. A noble metal is a platinum group metal (platinum, palladium, rhodium, ruthenium, iridium or osmium), gold or silver. Suitable base metals include copper, cobalt, nickel, zinc, iron, titanium, molybdenum, vanadium, manganese, niobium, tantalum, chromium and tin. Preferred base metals are nickel, cobalt, and chromium. More preferred base metals are nickel and cobalt.

[0043] Preferably, the electrocatalyst comprises platinum, palladium, rhodium, ruthenium, iridium and / or osmium.

[0044] The electrocatalyst may be a reduced single metal electrocatalyst, such as a Pt catalyst.

[0045] The electrocatalyst may comprise an alloy, such as a binary alloy. In particular, the alloy may comprise PtaXb wherein the ratio of a to b is in the range of and including 10:1 to 1 :2.5, optionally 5: 1 to 1 :2.5; and wherein X is Co, Ni, Y, Gd, Sc or Cu. Preferably X is Co or Ni and most preferably Ni.

[0046] The exact electrocatalyst used will depend on the reaction it is intended to catalyse and its selection is within the capability of the skilled person.

[0047] The loading of electrocatalyst (e.g. electrocatalyst particles) on the carbon support is suitably 10-90wt%, such as 15-75wt%, preferably 20 to 60wt% of the weight of resulting supported electrocatalyst. Carbon support

[0048] The carbon support is typically a particulate carbon support.

[0049] Suitable carbons typically include those from the carbon black family, such as oil furnace blacks, extra-conductive blacks, acetylene blacks and graphitised versions thereof. Exemplary carbons include Ketjenblack™ EC-300J and Cabot Vulcan® XC72R. Additionally, carbons specifically designed for fuel cell applications such as those described in WO2013 / 012894 may be used.

[0050] The carbon support is preferably a particulate carbon black, which is optionally graphitized on its surface.

[0051] Nitrogen-functionalized carbon support

[0052] The N-functionalized carbon support may be described as an N-doped carbon support. N- functionalization requires N atoms to be incorporated into the carbon support and encompasses a number of different N species, as described in Jansen et al. (R.J.J. Jansen and van Bekkum, Carbon, 32, 1507 (1994)) and Ott et al. (Nat. Mater. 19, 77-85 (2020)).

[0053] The N-functionalized carbon support may comprise graphitic N species; quaternary N species; pyrrolic N species; and / or pyridinic N-species. Graphitic N species correspond to graphite with a neutral N atom taking the place of a carbon atom in a 6 membered ring. Quaternary N species are positively charged, and an example is shown in figure 2 (dashed diamond).

[0054] Pyrrolic N species are based on pyrrole C4H4NH, and examples are shown in figure 2 (dashed circle). Pyridinic N-species are based on pyridine C5H5N, and examples are shown in figure 2 (dashed square).

[0055] The N-functionalized carbon support may comprise a carbon lattice (grid) that comprises carbon atoms and nitrogen atoms, and optionally hydrogen atoms and / or oxygen atoms. Preferably the carbon lattice comprises pyridine units and / or pyrrole units.

[0056] Figure 2 also illustrates nitroso N species (-N=O), which may be present in small quantities. The N-functionalized carbon support may comprise surface N in an amount of <2.0 wt.%, suitably <1.0 wt.%, suitably <0.8 wt.%, as determined by XPS. The N-functionalized carbon support may comprise surface N in an amount of at least 0.1 wt.%, preferably at least 0.3 wt.%, as determined by XPS. The N-functionalized carbon support may comprise surface N in an amount in a range comprising any combination of the aforementioned upper and lower limits.

[0057] Catalyst ink and catalyst layer The method may comprise further steps to incorporate the supported catalyst of the invention into a catalyst layer. The supported catalyst may be formulated into an ink. The ink may comprise the supported catalyst, an ionomer and a dispersant.

[0058] The ink may be deposited to form a wet catalyst layer, which is then dried (to remove the dispersant) and annealed to form the catalyst layer. The ink may be deposited (i) onto a decal transfer substrate; (ii) onto an ion-conducting (e.g., electrolyte) membrane, i.e. direct deposition; or (iii) onto another catalyst layer.

[0059] The ratio of ionomer to N-functionalized carbon support (in the ink or catalyst layer) may be 0.1 to 2.0, optionally 0.2 to 1.0 or 0.5 to 1.5.

[0060] The N-functionalized carbon support may constitute from 20 to 80wt%, optionally 35 to 55wt%, of the catalyst layer.

[0061] Ionomer

[0062] The ionomer is an ion-conducting polymer such as a proton-conducting polymer or an anion- conducting polymer (e.g., a hydroxyl anion-conducting polymer). The ionomer is preferably a proton-conducting polymer. Examples of suitable proton-conducting polymers include perfluorosulphonic acid ionomers (e.g. Nation® (E.l. DuPont de Nemours and Co.), Aciplex® (Asahi Kasei), Aquivion™ (Solvay Speciality Polymers), Flemion® (Asahi Glass Co.), or ionomers based on a sulphonated hydrocarbon such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others. Examples of suitable anion-conducting polymers include A901 made by Tokuyama Corporation and Fumasep FAA from FuMA-Tech GmbH.

[0063] Electrolyte membrane

[0064] The electrolyte membrane comprises an ion-conducting polymer. The ion-conducting polymer is suitably a proton-conducting polymer. Preferred ion-conducting polymers are partially- or fully-fluorinated sulphonic acid polymers e.g. perfluorinated sulphonic acid polymers. For example, the ion-conducting polymer may be based on a perfluorinated sulphonic acid material such as Nation® (Chemours Company), Aquivion® (Solvay Specialty Polymers), Flemion® (Asahi Glass Group) and Aciplex® (Asahi Kasei Chemicals Corp.). Alternatively, the ion-conducting materials may be based on a sulphonated hydrocarbon polymer, such as those available from FuMA-Tech GmbH as the fumapem® P, E or K series of products, JSR Corporation, Toyobo Corporation, and others.

[0065] Catalyst-coated membrane (CCM)

[0066] The invention also resides a CCM obtainable or obtained by the method of the invention. The CCM comprises an electrolyte membrane and a catalyst layer, wherein the electrolyte membrane has a first face and an opposite second face and the catalyst layer is located on the first face.

[0067] The catalyst layer may comprise cracking defects covering an area of less than 8 % of the total area of the catalyst layer when measured after applying a strain of 30 % to the catalyst- coated membrane.

[0068] Brief description of the Figures

[0069] Figure 1 is a schematic diagram to compare the method of the invention (Fig 1 A) to a prior art method (Fig 1 B).

[0070] Figure 2 shows examples of types of N-functionalization.

[0071] Figure 3 shows XPS signals for 50% Pt / N-EC300j, N-functionalized catalyst prepared with N- EC300j according to known method; 50% Pt / PostN-EC300j, N-functionalized catalyst prepared by post-functionalization of 50% Pt / EC300j; and 50% Pt / PostN-EC300j AT, N- functionalized catalyst prepared by acid modification of 50% Pt / PostN-EC300j

[0072] EXAMPLES

[0073] 1 . Carbon activation with nitric acid

[0074] An amount not higher than 120g of the desired carbon black material (EC300j Ketjenblack carbon) was transferred to a glass reactor with a vessel not bigger than 20 L, preheated at 75°C. 42mL of 70% nitric acid per g of carbon support were added slowly. The mixture was stirred for 1h at 75°C at reflux conditions using a condenser. After the reaction time the mixture was left to cool at room temperature, filtered, cleaned with demineralized water and dried in a vacuum oven. The resulting material is referred as activated carbon (0-EC300j). Activated carbons by this method present higher levels of O on their surface and low levels of N in form of NOT, confirmed by XPS. This type of N is unstable and will be easily removed. See table below for amount of N.

[0075] 2. NH3 treatment of activated carbon

[0076] An amount not bigger than 40g of the activated carbon (produced in 1 .) was placed in a tube furnace. The furnace was then purged with Ar overnight. After the purging the material was placed under a flow of 360ml / min of 100% NH3 and heated to 600°C at 10° C / min before a 5 h dwell. After the treatment the material was allowed to cool to room temperature. The flow was switched back to Ar below 200°C and allowed to cool. The resulting material was referred as N functionalized carbon (N-EC300j) contains a mixture of pyridinic and pyrrolic N species on the surface confirmed by XPS. See table below for amount of N. 3. NH3 treatment of fresh carbon

[0077] An amount not bigger than 40g of EC300j Ketjenblack carbon was placed in a tube furnace. The furnace was then purged with Ar overnight. After the purging the material was placed under a flow of 360ml / min of 100% NH3 and heated to 600°C at 10° C / min before a 5 h dwell. After the treatment the material was allowed to cool to room temperature. The flow was switched back to Ar below 200°C and allowed to cool. The resulting material does not present N functional groups on its surface. No N can be detected by XPS or CHN techniques.

[0078] 4. Synthesis of 50% Pt EC300j

[0079] The Pt was deposited on the material as described in the patent WO2013045894A1 using EC300j Ketjenblack carbon as carbon support:

[0080] The carbon support material was dispersed in water using a shear mixer. The slurry was transferred to a beaker, fitted with temperature and pH probes and two feed inlet tubes connected to a pH control unit. The Pt salt (Pt nitrate or K2PtCk ) was added in an amount sufficient to give a nominal loading of 50wt% Pt. NaOH was added to maintain the pH between 5.0 and 7.0 (final pH). The slurry was stirred, and once hydrolysis was complete, formaldehyde was added to reduce the Pt. Once the reaction was complete, the catalyst was recovered by filtration and washed on the filter bed. No N is detected by XPS.

[0081] 5. Synthesis of 50% Pt / N-EC300j

[0082] The Pt was deposited on the material as described in the patent WO2013045894A1 using N- EC300j (N functionalized carbon black from 2.) as carbon support:

[0083] The N-functionalized carbon support material (from 2.) was dispersed in water using a shear mixer. The slurry was transferred to a beaker, fitted with temperature and pH probes and two feed inlet tubes connected to a pH control unit. The Pt salt (Pt nitrate or K2PtCk ) was added in an amount sufficient to give a nominal loading of 50wt% Pt. NaOH was added to maintain the pH between 5.0 and 7.0 (final pH). The slurry was stirred, and once hydrolysis was complete, formaldehyde was added to reduce the Pt. Once the reaction was complete, the catalyst was recovered by filtration and washed on the filter bed.

[0084] This material keeps the N functionalization of the support and same type of N. The amount of N is reduced to half as expected for a 50% weight Pt catalyst with a functionalized support. See table below for amount of N.

[0085] 6. Example 1, synthesis of 50%Pt / PostN-EC300j An amount not bigger than 40g of 50%Pt / EC300j catalyst was placed in a tube furnace. The furnace was then purged with Ar overnight. After the purging the material was placed under a flow of 360ml / min of 100% NH3 and heated to 600°C at 10° C / min before a 5 h dwell. After the treatment the material was allowed to cool to room temperature. The flow was switched back to Ar below 200°C and allowed to cool. Once at temperature the flow was changed to N2 and small bleed of air were successively added before exposing the material to atmosphere.

[0086] This material, referred as 50%Pt / PostN-EC300j, presents the same amount of N than 50%Pt / N-EC300j but a more reduced N species. This can be modified by acid treatment.

[0087] 7. Example 2, acid modification of N species

[0088] An amount not higher than 100g of the desired 50%Pt / PostN-EC300j (from 6) was transferred to a glass reactor with a vessel not bigger than 5 L. 80mL of 0.5M H2SO4 solution per g of catalyst were added slowly. The mixture was stirred for 24h at 80°C at reflux conditions using a condenser. After the reaction time the mixture was left to cool at room temperature, filtered, cleaned with demineralized water and dried in a vacuum oven.

[0089] This material, referred as 50%Pt / PostN-EC300j AT, presents the same amount of N than 50%Pt / PostN-EC300j but a more oxidated N species, comparable to 50%Pt / N-EC300j.

[0090] SUMMARY

[0091] RESULTS

[0092] XPS (X-ray photoelectron spectroscopy) is a surface specific elemental analysing technique that involves bombarding a sample in an ultra-high vacuum environment with x-rays of sufficient energy to cause the ejection of electrons from the atoms that constitute the sample. Ultra-high vacuum conditions are necessary for two reasons; (i) to allow the ejected electrons to reach the detector without loss of energy through collisions and (ii) to keep the surface free from absorbed species. The ejected electrons are measured for their kinetic energies from which it is possible to calculate their binding energies from the following equation: - EK = hv- EB - f

[0093] Where EK is the kinetic energy, hv is the energy of the radiation, EB is the binding energy and f is the work function of the spectrometer.

[0094] The binding energy in turn can be correlated to the element of origin, not only the element but also the electronic shell (s, p, d, f) that the electron came from. The electrons are also counted and the intensity can be used to provide a quantitative analysis of the elements detected. Scanning over a range of binding energies, typically 0 to 1100 eV, provides a spectrum that displays intensity as a function of binding energy that can be processed to identify and quantify the elements detected. The binding energy of a particular element can also indicate the oxidation state of that element. In some cases, e.g. sulphur, this can be readily seen from the broad scan but in most instances a high-resolution scan over a narrow binding energy range must be performed. This results in a spectral envelope that can be resolved into the individual components.

[0095] X-ray photoelectron spectroscopy (XPS) data were collected with a Thermo Scientfic NEXSA with a base pressure of 5E-10 mbar. The radiation was produced using a monochromatic aluminium Ka source with a 400 x 800 urn elliptical spot size. A dual mode (electrons and argon ions) flood gun was used for charge compensation; modified Schofield sensitivity factors were used during quantification using Avantage software. Samples were prepared using a powder holder plate consisting of wells which the powder was contained in - no carbon tape was used in these studies.

[0096] Surface weight % of C, O, N and Pt by XPS

[0097] Referring to the table above, it can be seen that 50%Pt / PostN-EC300j (N-functionalization after catalysation) achieves the same N content (0.6%) as 50%Pt / N-EC300j (N- functionalization before catalysation). Acid treatment (50%Pt / PostN-EC300j AT) is employed to modify the ratio of N and O as desired. Figure 3 compares the XPS signals for 50% Pt / N-EC300j; 50% Pt / PostN-EC300j (example 1); and 50% Pt / PostN-EC300j AT (example 2) and shows different types of N-functionalization: Pyridinic (A); Pyrrolic (B); quaternary (C); graphitic (D); NO2'(E); and NOT(F). It can be seen that pyridinic (A) and pyrrolic (B) dominate.

Claims

Claims1. A method for the preparation of a supported catalyst comprising an electrocatalyst on a nitrogen-functionalized carbon support, the method comprising:(i) providing an electrocatalyst on a carbon support; and(ii) incorporating nitrogen into the carbon support to provide the supported catalyst, the supported catalyst comprising the electrocatalyst on the nitrogen-functionalized carbon support.

2. The method of claim 1 , wherein incorporating nitrogen into the carbon support comprises exposing the carbon support to gaseous ammonia.

3. The method of claim 2, wherein the carbon support is exposed to ammonia at a temperature of 200°C or more; and / or 1100°C or less.

4. The method of claim 3, wherein the carbon support is exposed to ammonia at a temperature of from 500 to 1000°C, optionally from 500 to 800°C.

5. The method of any one of the preceding claims, comprising an initial step of catalysing carbon to yield the electrocatalyst on the carbon support.

6. The method of any one of the preceding claims, comprising a subsequent acid treatment step to modify the N-functionalized carbon support.

7. The method of any one of the preceding claims, wherein the electrocatalyst comprises electrocatalyst particles on a particulate carbon support.

8. The method of any one of the preceding claims, wherein the electrocatalyst comprises platinum, palladium, rhodium, ruthenium, iridium and / or osmium.

9. The method of claim 8, wherein the electrocatalyst comprises PtaXb wherein the ratio of a to b is in the range of and including 10:1 to 1:2.5, optionally 5:1 to 1:2.5; and wherein X is Co, Ni, Y, Gd, Sc or Cu.

10. The method of any one of the preceding claims wherein the electrocatalyst constitutes 10-90wt% of resulting supported electrocatalyst.

11. A supported catalyst produced or producible by the method of any one of the preceding claims, the supported catalyst comprising an electrocatalyst on a N-functionalized carbon support.

12. A catalyst layer comprising the supported catalyst of claim 11 , and optionally an ionomer.

13. A catalyst-coated membrane comprising the catalyst layer of claim 12 disposed on an electrolyte membrane.

14. A gas diffusion electrode comprising the catalyst layer of claim 12 disposed on a gas diffusion layer.

15. A decal comprising the catalyst layer of claim 12 disposed on a decal transfer substrate.

16. A membrane electrode assembly comprising the catalyst layer of claim 12, the catalyst- coated membrane of claim 13 or the gas diffusion electrode of claim 14.

17. An electrochemical device, such as a fuel cell or electrolyser comprising the membrane electrode assembly of claim 16.

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