GB2400973A - Production of components for electrochemical cell assemblies - Google Patents

Abstract

A process for the production of fuel cell or other electrochemical cell components in plate form in particular BIPOLAR plates comprises the following steps: <SL> <LI>(a) treating a metal sheet to modify at least its interfacial resistance and/or corrosion resistance with respect to the fuel cell or other electrochemical cell environment; and <LI>(b) following such treatment introducing features into the metal sheet in a repeating pattern by the application of mechanical force to the sheet; and <LI>(c) dividing or separating the metal sheet into a plurality of individual plates each provided with a said feature or features. </SL>

Description

MP100706-WO 1 2400973

PRODUCTION OF COMPONENTS FOR ELECTROCHEMICAL

CELL ASSEMBLIES

This invention relates to the production of components in the form of plates for use in electrochemical cell assemblies, including fuel cell stacks and water eleckolysers.

In fuel cell stacks, e.g. PEM based fuel cell stacks, components in the form of plates may play a major role in the operation of the stack. For instance, the bipolar plates, through the flow field, act as the primary distribution medium for the input and exit fluids while providing the means of electrical contact and conduction from cell to cell. In addition to their functionality, the bipolar plates can occupy a significant proportion of the stack volume and account for a large proportion of the stack cost. The ideal bipolar plate would therefore have high electrical bulk conductivity, have low interracial electrical resistance, be resistant to the corrosive environment within the fuel cell, be thin and be of low cost.

Typically, bipolar plates for fuel cell stacks are manufactured using mass production techniques and are produced in the following forms: machined or moulded graphite composite plates, embossed flexible graphites or etched or stamped metal plates. For those applications requiring high volumetric power density and gravimetric power densities (e.g. automotive, consumer electronics), a preferred solution is a metal system (e.g. stainless steel plates), coated with a suitable coating to increase interracial conductivity and reduce the corrosion rate.

In addition, those fuel cell technologies operating at elevated temperatures (e.g. > 250 C) also require the use of metallic bipolar plates or interconnects. Such high temperature fuel cell technologies include solid oxide and molten carbonate fuel cells (SOFCs and MCFCs respectively).

MP 1 00706-WO 2 It is known from EP-A-1237215 to produce metallic separator plates for polymer electrolyte cells by forming a thin noblemetal layer on the metal base of the separator plate, compression working the layer to reduce its thickness and eliminate pin-holes therein and thereafter using a forming operation to introduce surface features into the separator plate. Prior to the mechanical operation, the plate is subjected to heat treatment to relieve work hardening introduced by the compression step.

From JP-A-2002373673, it is also known to provide the metal substrate (e.g. stainless steel) of a fuel cell separator plate with a cladding or coating comprising molybdenum so that the surface of the separator substrate material is covered by the cladding or coating. The molybdenum layer is then subjected to nitriding (e.g. gas phase nitriding) to achieve good corrosion resistance with respect to sulphuric acid together with improved electrical conductivity.

The present invention, at least in some aspects thereof, addresses the requirement for low cost production of electrochemical cell components, e. g. fuel cell components, in plate form while securing good corrosion resistance and interracial electrical resistance.

According to one aspect the present invention there is provided a process for the production of electrochemical cell components, e.g. fuel cell components, in plate form comprising the following steps: (a) treating a metal sheet to modify at least its interracial resistance and/or corrosion resistance with respect to the fuel or other electrochemical cell environment; and (b) following such treatment introducing a feature or features into at least one treated major face of the metal sheet in a repeating pattern by the application of mechanical force to the sheet; and MP 1 00706-WO 3 (c) dividing or separating the metal sheet into a plurality of individual plates each constituting a said component provided with said feature or features.

A feature of the process of the invention is that the features introduced by mechanical force are introduced into the stock material, e.g. metal sheet unwound from a coil, before the stock material is divided up into individual cell components. Moreover, in a preferred aspect of the invention, step (a) involves modification of the surface of the stock material rather than the application of a coating or cladding material to the stock material thereby obviating the need to subject the Heated stock material to a compression operation with consequent work hardening and reducing the risk that could otherwise arise of the separate coating or cladding layer being disrupted or breached during the application of mechanical force to introduce said features into the substrate material. Also, the stock material is usually one which, prior to step (a) being performed, does not carry any cladding or coating on at least the surface or surfaces to be treated in step (a).

Treatment step (a) typically involves modifications in interracial resistance and/or corrosion resistance which enhance the performance of a fuel cell stack or other electrochemical cell assembly (such as a water electrolyser) incorporating such components. For instance, the treatment step may comprise reducing the interracial resistance and/or increasing the corrosion resistance associated with the components.

Following division, the plates so formed may be used in the assembly of one or more fuel cell stacks or other electrochemical cell assemblies. Division may comprise a metal stamping operation for example.

MP 1 00706-WO 4 The features may comprise flow field features such as grooving, porting and/or features such as apertures for accommodating components such as tie rods used in compressing or clamping the cell components together. Some features may be introduced into the metal sheet or resulting plate components subsequent to step (b) or step (c).

Steps (a) and (b) at least may be carried out as part of an integrated treatment and mechanical forming process in which a stock material is subjected to steps (a) and (b) on a production line. Step (c) may also be part of the integrated production line.

Steps (b) and (c) may be carried out in succession, viz. step (b) followed by step (c), or they may be carried out substantially simultaneously.

Step (a) may involve the application of a coating to the metal sheet and/or the modification of the bulk material of the sheet at the surface thereof such that the properties and/or composition of the sheet in a surface layer thereof differ from the bulk material properties and/or composition of the metal prior to such treatment.

The treatment effected in step (a) may be such that the resulting enhancement in terms of cell operation is not disrupted, at least not to any significant extent, by the mechanical operation carried out in step (b).

Thus, for example, where features in the form of flow field patterns are introduced into the metal sheet, the treatment of step (a) may be such that the coating or surface layer created by such treatment is not breached at least over the active region of the plate, the active region being that part of the surface that is exposed to the corrosive environment prevailing in the assembled cell stack or assembly in operation. In the case of features in the form of porting introduced as MP100706-WO 5 apertures, the apertures will of course penetrate through the thickness of the resulting plate and, as such, will penetrate the coating or surface layer produced by the treatment of step (a); however, the porting in the resulting plates will usually be formed in non-active areas which are not subject to the corrosive conditions prevailing in the fuel cells or other electrochemical cells.

The mechanical operation of step (b) typically introduces said features by mechanical forming techniques such as metal pressing and/or metal embossing and/or metal stamping or punching. As mentioned above, steps (b) and (c) may be carried out successively or simultaneously.

For example, the mechanical operation may involve the introduction by a metal pressing or embossing technique of a flow field pattern into the sheet metal on one or both major faces thereof and/or the introduction by a mechanical metal removal technique, such as stamping or punching, of porting (e.g. inlet and/or outlet apertures for passage of fluids used in a fuel cell for instance).

If desired, following step (b) a further treatment may be applied to the metal sheet and/or the individual plate components resulting from step (c) . Such further treatment may comprise the application of a coating to the metal sheet and/or the modification of the bulk material of the sheet or plate component at the surface thereof such that the properties and/or composition of the sheet in a surface layer thereof differ from the bulk material properties and/or composition of the metal prior to such treatment. Such further treatment may comprise specific performance enhancements such as reducing interracial resistance and/or nereasmg Corrosion resistance.

Because such further treatment is carried out after step (b), it need not necessarily be capable of withstanding the mechanical pressures and stresses imparted during step (b).

MP 1 00706-WO 6 Prior to the step (a), the metal sheet may be subjected to a cleaning treatment' e.g. degreasing.

Prior to step (b), it may be necessary to treat the metal sheet to facilitate the application of mechanical force to the sheet, for instance, a lubricating agent may be used. In event of using such an agent, it may be necessary to carry out a further cleaning step, e.g. decreasing, to remove the agent after the desired formations have been introduced into the metal sheet.

The metal sheet may be initially in coiled form and the invention may be carried out in a substantially continuous production process. For example, the sheet may be drawn from the coil and fed along a path in which it traverses a number of stations in which at least steps (a), (b) and (c) are performed.

Conveyance of the sheet metal may be by rollers. Movement of the sheet may be arrested in order to carry out step (a), (b) and/or (c). Step (b) may involve a single operation (e.g. the introduction of flow field and porting features in one operation) or it may comprise a number of operations carried out in sequence (e.g. formation of one type of feature or features such as flow field features followed by the separate formation of another feature or features such as porting).

The metal sheet is desirably one which, prior to being subjected to process steps of the present invention, comprises a metal substrate without any coating or cladding material (such as molybdenum) applied thereto.

The components produced may comprise any one of a number of plates that are normally to be found in a fuel cell stack or other electrochemical cell assembly, in particular any metal plate which conducts electricity and/or fluids whether bipolar or monopolar. Examples include but are not necessarily limited MP 1 00706-WO 7 to bipolar plates, current collector plates, separator plates and edge collector plates.

According to another aspect of the present invention there is provided a bipolar plate fabricated from two separate halves (separate anode and cathode plates) joined together, e.g. by brazing or welding. Also within the scope of the invention is a cell stack or assembly including bipolar plates fabricated in this manner.

In the case of such bipolar plates, it is envisaged that the process defined above and further disclosed hereinafter may be used to produce the separate halves which may be subsequently joined together. The advantage of such an arrangement is that the two halves may, before they are joined, have different treatments (e.g. reduction in interracial resistance and/or corrosion resistance) applied to at least the faces which are exposed in the end product. At least one such treatment may involve a process as disclosed in our prior International Patent Application No. WO 02/13300 or European Patent Application No. 03250707.1, the entire contents of which are incorporated herein by this reference.

In the process of the present invention, the metal sheet may comprise a steel, stainless steel, titanium or titanium alloy, nickel or a nickel alloy (especially a high nickel alloy), aluminium or aluminium alloy for example.

Step (a) may have the effect of"upgrading" the metal from a low grade material to a higher grade material in terms of the properties that are important for use in a cell stack or assembly. For instance, the surface region of a carbon steel may be upgraded to a a composition similar to a stainless steel equivalent, e.g a 316 stainless steel.

MP 100706-WO 8 Step (a) may comprise the deposition of material on to the surface of the metal sheet and/or the variation of the surface layer composition by material addition or removal from the surface region of the metal sheet, in all cases by chemical or other techniques. It is preferred that step (a) is carried out in such a way that the composition or properties of the surface layer is or are varied, compared with the bulk material, rather than by application of a separate layer to the metal sheet by deposition, cladding or other technique which results in the production of a distinct layer on that surface of the metal sheet to be subjected to the mechanical operation of step (b). Thus, in the preferred process, step (b) is performed directly on the metal sheet surface which has been treated in step (a) rather than indirectly through a distinct layer of coating material or cladding material applied to that surface of the metal sheet.

For instance, step (a) may be an electrolytic treatment step such as that described in our prior International Patent Application No. WO 02/13300 or European Patent Application No. 03250707.1, the entire contents of which are incorporated herein by this reference. Both of these prior disclosures give examples of suitable metals that may be used in the present invention for the production of plate components for use in fuel cell stack cells or other electrochemical cell assemblies. This technique may be used to adjust the balance of constituents in the surface region in such a way as to enhance the interracial electrical resistance without necessarily detrimentally affecting the corrosion resistance of the metal sheet. Interfacial resistance as referred to herein is measured using the method disclosed in WO 02/13300.

Thus, step (a) may be performed by treating the metal sheet (stainless steel or otherwise) with an electrical current while contacted by an electrolyte under conditions which reduce the interracial resistance and/or increase the corrosion resistance associated with the surface of the bulk material forming the sheet metal.

MP100706-WO 9 The electrolyte may include at least one acid selected from the group comprising sulphuric acid, hydrochloric acid, nitric acid, chromic acid, oxalic acid and phosphoric acid, e.g. at least sulphuric acid. s

The treatment effected in step (a), whether carried out using an electrical current in the presence of electrolyte as stated above or otherwise, preferably results in a reduction of the interracial resistance of said surface by a factor of at least 5% compared with the interracial resistance prevailing prior to said lO treatment. Typically the reduction may be at least 15%, e.g. at least 25% and often at least 40%.

Step (a) may alternatively (or additionally) comprise the introduction or integration of additives in the form of elements (e.g. metal elements) or compounds into the bulk material at the surface region thereof so as to alter the composition of this region compared with the bulk material. This may for instance be effected by implantation techniques, e.g. metal ion implantation, or by surface alloying techniques, e.g. laser surface alloying (LSA), nitriding, or by vacuum techniques such as sputtering, or molecular beam deposition.

We do not however exclude the possibility that step (a) may be implemented by for example a plating method, such as electroplating or electroless plating, or chemical vapour deposition which results in the production of a distinct layer over the metal sheet.

Typically surface alloying is effected using one or more high density energy beams, e.g. a laser beam or an electron beam, or suitable heating sources, e.g. a plasma torch, to produce localized melting at the surface of the bulk material in order to allow alloying of the additive(s) with the bulk material.

Relative motion between the metal sheet and the beam(s) or heating source(s) MPl00706-WO 10 may be produced such that the beam(s) may be scanned or swept across the surface to be treated (i.e. the surface of an individual plate or the surface of a metal sheet to be subsequently divided up into a plurality of plates), e.g. in a rastering motion in the presence of the additive(s).

Usually the metal sheet will be horizontally orientated during conveyance through one or more steps of the process.

Where LSA is used in step (a), the rate and effectiveness of surface alloying can be determined by factors such as the power output ofthe laser used, the manner in which the laser beam is scanned relative to the surface being treated (e.g. raster rate) and pulse time. 1 he pulse time for instance affects the depth of the melt and the rate of cooling of the alloy.

The additive(s), e.g. nickel, may be applied as a powder, thin foil or a deposit, e.g. by electroplating, on the metal surface so that, after LSA, the additive is integrated into the surface region of the substrate metal to produce a homogeneous surface region, leaving no significant residue on the substrate.

It is also envisaged that the treatment of step (a) may involve electrochemical modification of a passive layer on the metal sheet, e.g. by plating and alternating the current anodically and cathodically. According to the potential chosen preferential dissolution of elements may occur at the metal surface. In this way, it is envisaged that a passive layer with good corrosion resistance and electrical conductivity may be secured. Where passive layer modulation produces a porous passive layer, it is contemplated that other elements may be incorporated into the passive layer, for instance ruthenium, to improve corrosion resistance and/or electrical conductivity properties.

MP 1 00706-WO The process of the invention may be applied to the production of plate components for use in various types of fuel cells, e. g. alkaline fuel cells, polymer electrolyte fuel cells, direct methanol fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, and intermediate temperature solid oxide fuel cells.

According to further aspect of the present invention there is provided a component in or for an electrochemical cell assembly such as a fuel cell stack, the component being a metal plate the bulk material of which is modified at at least one surface thereof by integration of at least one additive into the bulk material to form a surface region comprising a modified layer of the bulk material which is exposed and has superior interracial resistance and/or corrosion resistance compared with that of the untreated plate.

A feature of the invention is that the modified layer conferring superior interracial resistance and/or corrosion resistance is a surface region of the substrate material produced by integration of additive(s) into the substrate material so that the modified layer is exposed and is not covered by a distinct cladding or coating material comprising a phase from which the substrate material is absent.

The additive(s) may have been integrated into the surface region by surface alloying, e.g. laser surface alloying, before or after any feature or features are introduced by the application of mechanical force or otherwise into at least one major face of the plate.

The plate may have been produced by division from a sheet of the bulk material.

MP100706-WO 12 Thus, for instance, the modification may comprise reduced interracial resistance and/or increased corrosion resistance.

A component in accordance with this aspect of the invention may but S need not necessarily be produced by a process of the invention as disclosed herein.

The layer so produced may be provided on at least one major face of the plate.

The layer created by integration of additive(s) into the bulk material may be such that it is sufficiently robust to retain its integrity and hence the enhancement(s) it confers when surface features (e.g. flow field features) are mechanically pressed into the surface provided with the layer.

The modified layer may be at least 0.001 microns thick, e.g. from about 0.002 to about 20 microns in thickness.

The bulk material may be a steel alloy which normally would be considered unsuitable for use in the corrosive environment prevailing within a fuel cell stack or other electrochemical cell assembly during operation, e.g. a carbon steel. The additive(s) introduced into the bulk material may be selected so as to upgrade the surface region of the bulk material to allow use of the plate in a cell stack or assembly. For example, additive introduction into the surface region of the bulk material may upgrade the steel, to a stainless steel equivalent to or similar to a more corrosion resistant material such as a 316, 349 or 904 stainless steel.

The bulk material may, if desired, be a stainless steel alloy, titanium or a titanium alloy, nickel or a nickel alloy, aluminium or an aluminium alloy. In the MP100706-WO 1 3 case where the bulk material is a stainless steel for example, additive introduction may be effective to upgrade the stainless steel from one grade to a superior grade for the purposes ofthe present invention. For instance, a 316 stainless steel may be upgraded, in the surface region, to a stainless steel S equivalent to or similar to a 904 stainless steel equivalent.

The additive may be an element, e.g. a metal element, or a compound, e.g. a metal compound. Where it is desired to upgrade to a stainless steel equivalent or a higher grade stainless steel equivalent, the additive(s) may comprise nickel and/or chromium or compounds thereof.

The invention will now be described further by way of example only with reference to the accompanying drawings, in which: Figure 1 is a flow diagram of one embodiment of the process of the invention; and Figure 2 is an exploded perspective view showing components of a PEM fuel cell stack.

Referring to the flow diagram of Figure 1, in a typical production line, metal sheet M, e.g. 316 or 316L stainless steel, is unwound from a coil C thereof and, at a first work station S 1, is degreased or cleaned using a solvent such as acetone, iso-propanol, trichloroethylene, or an alkaline based aqueous system.

Further downstream, at work station S2, the sheet is subjected to a coating or other treatment to enhance fuel cell performance in terms of interracial and/or corrosion resistance, such treatment being one which results in a coating or surface layer on one or both sides of the sheet which is sufficiently robust to withstand the subsequent stages of processing. In accordance with the invention, the metal sheet is treated in work station S2 in such a way as to enhance the MPI 00706-WO 14 surface conductivity (i.e. reduce interracial resistance), preferably without reducing the corrosion resistance and, in some cases, increasing the corrosion resistance of the metal. This treatment may comprise the electrolytic process as disclosed in International Patent Application No. WO 02/13300 or European Patent Application No. 03250707.1, or it may be one of the other treatments described hereinbefore, preferably one which involves modification of a surface region of the metal sheet as opposed to one which involves formation or provision on the metal sheet of a layer distinct from the bulk material of the metal sheet.

At work station S3, the sheet has sets of features introduced into one or both treated major surfaces by the application of mechanical force imparted by appropriate tooling which may be carried by one or more rotating rollers arranged so that the sheet passes through the nip between the rollers. Each set of features may serve as flow distribution channels and/or porting for fluids for a bipolar or other plate to be incorporated into an electrochemical cell assembly such as a fuel cell stack. If necessary, the different features may be introduced by separate operations, in which case station S3 may comprise two or more sub stations. The fluids may be (but are not limited to) hydrogen, air, oxygen, water and/or methanol. An example of such a flow field pattern is shown in Figure 2 to be described below. At work station S4, the sheet is divided into a smaller pieces each forming a plate provided with a set of fluid flow channels on one or each major face, each plate being dimensioned and configured for use in the fuel cell.

In a modification, work stations S3 and S4 may be replaced by a single work station in which the features are introduced into the metal sheet and the sheet is divided into individual fuel cell plates in a single operation.

MP 100706-WO 15 In another variation, the opposite faces of the metal sheet may be subjected to the enhancement treatment to differing extents, in which case work station S2 may be appropriately adapted to effect this.

Referring now to Figure 2, one application of the present invention is in the production of a fuel cell stack comprising ion-permeable membranes 31 and 32 which have cathode electrodes 33 and 34 respectively and anode electrodes (not shown), bonded to each of their major surfaces. Each membrane 31, 32 and its associated anode and cathode forms a fuel cell unit. A bipolar separator plate 35, provided with surface features 36, is disposed between ion-permeable membranes 31 and 32 in contact with the electrode surfaces thereof. Terminal plates 37 and 38, provided with tabs 39 and 40 for delivering electric current generated in the cell stack to an external circuit, are disposed adjacent membranes 31 and 32 respectively. In Figure 2, only one bipolar separator plate 35 is shown. In practice, there will usually be a plurality of bipolar separator plates each associated with adjacent pairs of fuel cell units.

In the stack, membrane 31 is held firmly between terminal plate 37 and bipolar plate 35 so as to form an oxidant gas chamber 41 and a fuel gas chamber 42. In like manner, membrane 32 is held firmly between terminal plate 38 and bipolar plate 35 so as to form an oxidant gas chamber 43 and a fuel gas chamber 44. Hydrogen fuel is supplied to the anodes in the fuel gas chambers 42 and 44 via fuel gas inlet conduit 45 and by-products removed via conduit 46. Oxidant gas is supplied to cathodes 33 and 34 in the oxidant gas chambers 41 and 43 via oxidant gas inlet conduit 47 and by-products removed via conduit 48. Openings 49 and 50 located in opposite corners of membranes 31 and 32 are aligned with hydrogen gas inlet and outlet conduits 45 and 46 and with openings S 1 and 52 in bipolar plate 35 to facilitate passage of hydrogen fuel gas into the fuel chambers 42 and 44 and to remove by-products therefrom.

MP100706-WO 16 Openings, not shown, and openings 53 located in opposite corners of membranes 31 and 32 are aligned with oxidant inlet and outlet conduits 47 and 48 and with opening 54 and another not shown in bipolar plate 35 to facilitate passage of oxidant gas into the oxidant chambers 41 and 43 and to remove by- products therefrom.

End plates 37 and 38, membranes 31 and 32 and bipolar plate 35 are each provided with a plurality of openings 55 through which assembly tie-rods 56 (one only of which is illustrated in part) pass and engage with nuts 56A so that the fuel cell units and bipolar separator plates are clamped between the end plates 37 and 38. Though not illustrated, sealing gaskets will be interleaved with the membrane carrying plates 31 and 32, the bipolar plates 35 and the end plates 37 and 38 to seal the active interior of the fuel cell stack.

The end plates 37, 38 and/or the bipolar plate 35 are made of for examplesteel, stainless steel or nickel alloy which has been treated in accordance with the process of the invention so that the interracial resistance between these plates and the adjacent membranes 31 is significantly reduced. In addition, the conduits and also the tabs 39 and 40 may be made of stainless steel or nickel alloy treated in this way. In the case of the end plates 37, 38 only those faces which are presented towards the interior of the fuel cell stack need be treated in practice.

However, for simplicity of treatment, the entire surface of the end plates may be so treated, including the borders which are not actually directly exposed to the interior of the fuel cell stack, and hence the strongly reducing/oxidising and high temperature conditions prevailing during operation of the fuel cell stack.

It will be understood that the various plate components in the fuel cell stack of Figure 2 will have been produced by the process described with reference to Figure 1. After the metal sheet has been treated to reduce the interracial and/or increase the corrosion resistance properties at at least one MP 1 00706-WO 17 major face of the sheet, an array of surface features such as those depicted by reference numeral 36 are impressed into the sheet metal. Also, features corresponding to the openings 51, 55 and other apertures in the plates 35, 37 and 38 may be introduced into the metal sheet prior to its division into individual plates.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features disclosed herein andlor shown in the drawings whether or not particular emphasis has been placed on such feature or features.

Claims (27)

MP l 00706-WO 1 8 CLAIMS

1. A process for the production of electrochemical cell components, e.g. fuel cell components, in plate form comprising the following steps: (a) treating a metal sheet to modify at least its interracial resistance and/or corrosion resistance with respect to the fuel or other electrochemical cell environment; and (b) following such treatment introducing a feature or features into at least one treated major face of the metal sheet in a repeating pattern by the l O application of mechanical force to the sheet; and (c) dividing or separating the metal sheet into a plurality of individual plates each constituting a said component provided with said feature or features.

2. A process as claimed in Claim 1 in which following division, the plates so formed are used in the assembly of one or more fuel cell stacks or other electrochemical cell assemblies.

3. A process as claimed in Claim l or 2 in which steps (a) and (b) at least are carried out as part of an integrated treatment and mechanical forming process in which a stock material is subjected to steps (a) and (b) on a production line.

4. A process as claimed in any one of Claims l to 3 in which step (a) involves the application of a coating to the metal sheet and/or the modification of the bulk material of the sheet at the surface thereof such that the properties and/or composition of the sheet in a surface layer thereof differ from the bulk material properties and/or composition of the metal prior to such treatment.

5. A process as claimed in any one of the preceding claims in which the metal sheet is initially in coiled form.

MPl00706-WO 19

6. A process as claimed in any one of the preceding claims, being a substantially continuous production process.

7. A process as claimed in any one of the preceding claims in which the components produced comprise metal plates which conduct electricity and/or fluids.

8. A process as claimed in any one of the preceding claims in which the metal sheet comprises a steel, stainless steel, titanium, a titanium alloy, nickel, a high nickel alloy, aluminium or aluminium alloy.

9. A process as claimed in any one of the preceding claims in which step (a) has the effect of upgrading the metal from a low grade material to a higher grade I S material.

10. A process as claimed in any one of the preceding claims in which step (a) comprises the introduction of material into or removal of material from the surface region of the bulk material forming the metal sheet without leaving the bulk material covered with a distinct and separate layer of coating or cladding material and in which step (b) is performed on the so treated exposed surface region.

11. A process as claimed in any one of the preceding claims in which step (a) comprises the introduction of elements or compounds into the bulk material at the surface region thereof so as to alter the composition and/or properties of this region compared with the bulk material.

12. A process as claimed in any one of the preceding claims in which step (a) comprises the use of metal ion implantation, surface alloying (optionally laser MP100706-WO 20 surface alloying), vacuum techniques or electrochemical modification of a passive layer on the metal sheet.

13. A process as claimed in any one of Claims 1 to l l in which step (a) is performed by treating the metal sheet with an electrical current while contacted by an electrolyte under conditions which reduce the interracial resistance associated with said surface.

14. A process as claimed in Claim 13 in which the electrolyte includes at least one acid selected from the group comprising sulphuric acid, hydrochloric acid, nitric acid, chromic acid, oxalic acid and phosphoric acid.

15. A process as claimed in Claim 13 or 14 in which the electrolyte includes sulphuric acid.

16. A process as claimed in Claim 13, 14 or 15 in which the interracial resistance of the stainless steed is reduced by a factor of at least 5% compared with the interracial resistance prevailing prior to said treatment.

17. A process as claimed in any one of the preceding claims in which step (a) is performed on a stock material comprising a non-coated or non-clad base material.

18. A process as claimed in any one of the preceding claims in which, prior to step (a), the surface or surfaces of the metal sheet to be treated is free of any cladding or coating material.

l9. A fuel cell or other electrochemical cell incorporating at least one metal plate treated by the process claimed in any one of the preceding claims.

MP100706-WO 21

20. A fuel cell as claimed in Claim 19, being selected from the group comprising: alkaline fuel cells, polymer electrolyte fuel cells, direct methanol fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, and intermediate temperature solid oxide fuel cells.

21. A component in or for an electrochemical cell assembly such as a fuel cell stack, the component being a metal plate the bulk material of which is modified at at least one surface thereof by integration of at least one additive into the bulk material to form a surface region comprising a modified layer of the bulk I O material which is exposed and has superior interracial resistance and/or corrosion resistance compared with that of the untreated plate.

22. A component in or for an electrochemical cell assembly such as a fuel cell stack, the component being a plate comprising a metal which is selected from the group comprising steel, stainless steel, titanium, a titanium alloy, nickel, a high nickel alloy, aluminium or aluminium alloy and which is modified at at least one surface thereof by integration of at least one additive into the bulk material to form a surface region comprising a modified layer of the bulk material and has superior interracial resistance and/or corrosion resistance compared with that of the untreated plate.

23. A component as claimed in Claim 21 or 22 in which the bulk material comprises a stainless steel.

24. A component as claimed in Claim 23 in which the bulk material comprises a 316 stainless steel.

25. A component as claimed in any one of Claims 21 to 24 in which said surface region has been produced by surface alloying, preferably laser surface alloying.

MP100706-WO 22

26. A component as claimed in any one of Claims 21 to 24, being one produced by the process of any one of Claims 1 to 17.

27. A bipolar plate fabricated from two separate halves (separate anode and cathode plates) joined together, e.g. by brazing or welding, each half being produced by the process of any one of Claims 1 to 17.