Method for treating a structural component of an electrochemical cell and coated structural component

Abstract

The present invention relates to a method for treating a structural component of an electrochemical cell. The structural component comprises a substrate metal layer having an oxide layer on at least a portion of a surface of the substrate metal layer. The method comprises subjecting at least said portion of the surface to a first physical vapor deposition process using an etching metal, wherein the first physical vapor deposition process is a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE) process operated under conditions effective to remove at least part of the oxide layer and to form an interfacial layer comprising the substrate metal and the etching metal, and subsequently subjecting at least said portion of the surface to a second physical vapor deposition process using a coating metal, operated under conditions effective to form a coating metal layer. The invention further relates to coated structural components obtainable by the method and to electrochemical cells comprising such coated structural components.

Description

[0001] Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0002] - 1 -

[0003] Method for Treating a Structural Component of an Electrochemical Cell and Coated Structural Component

[0004] Technical Field

[0005] The present invention relates to a method for treating a structural component of an electrochemical cell , preferably for coating at least a portion of a surface of the structural component , such as a porous transport layer or a bipolar plate , and to a coated structural component obtainable by the method .

[0006] Technical Background

[0007] Electrochemical cells , such as fuel cells and electrolyzer cells , typically comprise several structural components formed from metallic materials . Examples of such structural components include porous transport layers ( PTLs ) , bipolar plates and flow field plates . These components are often exposed to corrosive environments and are required to exhibit both high electrical conductivity and long-term stability under operating conditions .

[0008] To improve the corrosion resistance and electrochemical performance of such structural components , it is known to provide coatings comprising noble metals , such as platinum . However, the metallic substrate of the structural component typically comprises a native oxide layer on at least a portion of its surface . The presence of this oxide layer can adversely af fect the adhesion and durability of subsequently applied coatings . In particular, coatings deposited on top of an oxide layer may delaminate

[0009] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0010] -2- during operation or show increased interfacial resistance.

[0011] For instance, Proton Exchange Membrane (PEM) water electrolysis is considered one of the most promising technologies for the production of hydrogen by splitting water. PEM water electrolyzers comprise a solid polymer electrolyte that conducts protons, separates produced gases, and insulates the electrodes. The porous transport layer (PTL) is a crucial component in various electrochemical devices including PEM water electrolyzers as it plays multiple functions including facilitating the movement of water / gas to / from the catalyst layer and providing good electrical conductivity. Commercially available porous transport layers are typically made of porous titanium, stainless steel or carbon. Titanium has excellent corrosion resistance and good electrical conductivity, whereas carbon-based materials and stainless steel are less expensive alternatives, though they do not offer the same level of corrosion resistance as titanium. The porous transport layer affects the overall performance of a PEM electrolyzer, such as minimizing ohmic losses. The PTL can be coated with protective metals such as platinum group metals to improve its durability by preventing its oxidation and to enhance its conductivity. The coating can be achieved using various methods including physical vapor deposition (PVD) , electroplating, and thermal deposition.

[0012] The drawback with all methods involving noble metal coatings in structural components, especially coatings with platinum group metals, is the relatively high amount of platinum group metals needed to be deposited on the structural component, such as a PTL, to ensure its

[0013] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0014] - 3 - durability. Typically, a load in a range of at least 2-5 grams per square meter of platinum group metal is required. Additionally, the coatings obtained by those methods, especially electroplating and thermal deposition, do not provide adequate uniformity, adhesion, and conductivity.

[0015] The structural component, such as a PTL, is usually subjected to cleaning and native oxide layer removal before the deposition of the protective metals on its surface.

[0016] This results in better adhesion of the protective layer and improved durability of the structural component. Native oxide layer removal can be done using plasma etching including argon (Ar) plasma etching.

[0017] The drawback of the argon plasma etching is that the native oxide layer is not entirely removed. Consequently, the obtained coated structural component may not have sufficient uniformity, adhesion and durability.

[0018] Jose Antonio Antonio Santiago Varela et al. (2024, ECS Meet. Abstr. MA2024-01, 1814) describes the use of high power impulse magnetron sputtering (HiPIMS) to thin platinum coatings onto components of PEM water electrolyzers.

[0019] CN 117364121 A describes a multilayer coating for anode materials, such as bipolar plates or gas diffusion layers, in PEM water electrolysis hydrogen production, comprising a bottom oxide layer, an intermediate metal nitride layer, and a surface layer of precious metal particles. The coating is applied to stainless steel or titanium alloy substrates to enhance corrosion resistance

[0020] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0021] - 4 - and conductivity while reducing precious metal content . Preparation involves substrate pretreatment , followed by deposition of layers via heat treatment , magnetron sputtering, vacuum plasma spraying, arc plasma deposition, or chemical vapor deposition .

[0022] Summary of the Invention

[0023] It is an obj ect of the present invention to provide an improved method for treating a structural component of an electrochemical cell , which method allows at least part of an oxide layer present on a metallic substrate of the structural component to be removed and replaced by an interfacial layer that promotes strong adhesion and low interfacial resistance of a subsequently applied coating . It is a further obj ect to provide coated structural components of electrochemical cells exhibiting improved durability and electrochemical performance while allowing for a reduced noble metal loading, especially a reduced loading of platinum group metals .

[0024] The Applicant has now found a method for treating a structural component of an electrochemical cell comprising a substrate metal layer . In a first step, the structural component is subj ected to a first physical vapor deposition process using an etching metal , speci fically a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE ) process . The HiPIMS-MIE process is operated under conditions ef fective to remove at least part of the oxide layer and to form an interfacial layer comprising the substrate metal and the etching metal , which produces a structural component with improved adhesion properties and

[0025] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0026] - 5 - reduced oxygen content. Subsequently the structural component is subjected to a second physical vapor deposition process using a coating metal, operated under conditions effective to form a coating metal layer.

[0027] The second physical vapor deposition process is preferably a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process, which produces a coated structural component with improved uniformity and conductivity. The Applicant has surprisingly found that using a HiPIMS-D process for the deposition of a coating metal layer or using a HiPIMS-MIE process for the removal of native oxide layer and for the deposition of an interfacial layer and leads to maintaining the interfacial contact resistance (ICR) , performance and durability of the structural component, even with reduced amount of the metal deposited on the component. Specifically, the method of the present invention allows for reducing the noble metal loadings, specifically the platinum group metal loadings in the coating without sacrificing the performance and durability of the structural component.

[0028] These and other objects and advantages of the present invention will become obvious from the following detailed description .

[0029] Brief Description of the Figures

[0030] Figure 1 shows a schematic representation of the method according to Example 2 of the present invention.

[0031] Figure 2 shows a schematic representation of the direct-current magnetron sputtering (DCMS) process

[0032] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0033] - 6 - according to Comparative Examples 1 and 2 .

[0034] Figure 3 shows a schematic representation of the High- Power Impulse Magnetron Sputtering (HiPIMS ) process according to Examples 1 and 2 of the present invention .

[0035] Figure 4 shows schematic cross section representations of coated porous transport layers , wherein Figure 4a shows a PTL obtained according to Comparative Example 1 , Figure 4b shows a PTL obtained according to Comparative Example 2 , Figure 4c shows a PTL obtained according to Example 1 of the invention and Figure 4d shows a PTL obtained according to Example 2 of the invention .

[0036] Detailed Description of the Invention

[0037] A first obj ect of the present invention therefore relates to a method for treating a structural component of an electrochemical cell , which comprises :

[0038] - providing a structural component comprising a substrate metal layer having an oxide layer on at least a portion of a surface of the substrate metal layer,

[0039] - subj ecting at least said portion of the surface of the substrate metal layer to a first physical vapor deposition process using an etching metal , wherein the first physical vapor deposition process is a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE ) process operated under conditions ef fective to remove at least part of the oxide layer and to form an interfacial layer comprising the substrate metal and the etching metal , and

[0040] - subsequently subj ecting at least said portion of the surface to a second physical vapor deposition process using a coating metal , operated under conditions ef fective to

[0041] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0042] - 7 - form a coating metal layer .

[0043] In the context of the present invention, the term " structural component of an electrochemical cell" denotes any component which in operation contributes to electrical conduction and / or mechanical support in the electrochemical cell . Examples of such components include porous transport layers , bipolar plates and flow field plates . The structural component may be made entirely of a metallic material or may be a composite material , for example a metal-polymer , a metal-ceramic or a metal-carbon composite . It is only required that , on at least a portion of its surface , the structural component comprises a substrate metal layer . The substrate metal layer may be formed by or be integral with the bulk metallic material of the structural component , or it may be provided as a metallic layer on a non-metallic or composite body . Typical substrate metals used for such structural components include titanium and titanium alloys , stainless steels or nickel-based alloys for example as porous transport layers in electrolyzer cells , for bipolar plates or flow field plates . The substrate metal layer is typically prone to oxidation under ambient and / or processing conditions and is therefore usually covered by a native or grown oxide layer prior to carrying out the method of the invention . The native oxide layer may have a thickness of 1 to 10 nm .

[0044] In the first treatment step of the method, at least the portion of the surface of the substrate metal layer that is to be coated is exposed to the HiPIMS-MIE process using the etching metal . The HiPIMS-MIE process is a physical vapor deposition process in which a target

[0045] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0046] - 8 - comprising the etching metal is sputtered in a pulsed high- power magnetron discharge so as to generate a flux of energetic metal ions . During the HiPIMS-MIE process , the structural component is negatively biased such that positively charged ions of the etching metal are accelerated towards the surface of the substrate metal layer . The energetic etching metal ions interact with the oxide layer and the underlying substrate metal and thereby remove at least part of the oxide layer from the surface .

[0047] Without wishing to be bound by theory, it is believed that the bombardment of the surface by energetic etching metal ions leads not only to sputter removal of oxygen from the oxide layer but also to mixing of atoms of the etching metal with atoms of the substrate metal in a near-surface region of the substrate metal layer . As a result , an interfacial layer is formed which comprises both substrate metal and etching metal and, optionally, any remaining oxide . This interfacial layer can be regarded as a graded region in which the concentration of etching metal decreases and the concentration of substrate metal increases with depth into the substrate metal layer . The HiPIMS-MIE process parameters , such as pulse voltage , pulse duration, duty cycle , working gas pressure and substrate bias , are selected such that a desired degree of oxide removal and a desired thickness of the interfacial layer are obtained .

[0048] In the HiPIMS-MIE process , large negative bias voltages are applied to the substrates to achieve etching ef fects and ion implantation during treatment . Negative bias voltages in HiPIMS-MIE process are generally between

[0049] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0050] - 9 -

[0051] 100 and 1500 V, preferably in a range of 400 to 1400 V and more preferably in a range of 500 to 1200 V, again depending on the materials used and desired ion implantation depth . By substrate biasing at high voltages , the sputtering yield at the substrate side is increased and the net deposition rate is reduced . Film growth ceases as the average yield approaches unity, which is for most elements at energies in the range of 400 eV and 1400 eV, and the surface is etched as the energy is increased even further . Metal ion etching is technologically used in the pre-deposition step in order to remove contaminants and reduce the oxide scale of the substrate , generating a gradual interface to the subsequent metal deposition .

[0052] For the purpose of the present invention, the native oxide layer is named interfacial layer after the complete or partial removal of oxygen . The etching metal atoms replace the oxygen atoms in the interfacial layer for an implantation depth in a range of 1 to 10 nm during the removal of native oxides .

[0053] For the purposes of the present invention, the expression "remove at least part of the oxide layer" covers the formation of an oxygen-depleted interfacial layer in which the oxygen atoms originally present in the native oxide are replaced or displaced by atoms of the etching metal , while maintaining the overall surface integrity of the structural component . The expression refers to a process in which the oxide compounds present on the surface of the structural component are chemically and / or physically reduced, displaced, or thinned by energetic ion bombardment during the HiPIMS-MIE process . The extent of

[0054] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0055] - 10- oxide removal is controlled by the bias voltage and ion energy. In the invention, the oxide layer originally having a thickness of about 2-10 nm under atmospheric exposure is partly or fully eliminated, depending on the applied parameters. When the expression "at least part" is used, it encompasses both a partial removal, in which residual oxygen or oxide fragments remain within the interfacial region, provided that the oxygen concentration is reduced by at least 30 % compared with the untreated surface. Partial removal is typically achieved when the substrate bias voltage is at the lower range of the HiPIMS-MIE operating window (e.g., 400-600 V) , resulting in an oxygen- reduced interfacial layer still containing some oxide species. Complete removal occurs when the bias voltage and ion flux are higher (e.g., 800-1200 V) , generating a substantially metallic interface.

[0056] In the subsequent second treatment step of the method, at least the same portion of the surface is subjected to the second physical vapor deposition process using the coating metal. The second physical vapor deposition process may, for example, be a HiPIMS deposition process or another magnetron sputtering process, and is operated under conditions effective to deposit the coating metal on the interfacial layer and thereby form the coating metal layer. In one embodiment, the coating metal layer is thus formed directly on the interfacial layer, i.e. on a surface in which the oxide content has been reduced and which contains both substrate metal and etching metal. This configuration provides improved adhesion of the coating metal layer and reduced interfacial resistance compared with coatings deposited directly on an oxide layer.

[0057] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0058] - 11 -

[0059] By combining the HiPIMS-MIE step and the subsequent coating step in the above manner, the method of the invention enables controlled removal of at least part of the oxide layer and its replacement by an interfacial layer comprising the etching metal and the substrate metal , followed by deposition of the coating metal layer on this interfacial layer . This results in coated structural components which exhibit improved electrochemical performance and long-term stability under the operating conditions of electrochemical cells .

[0060] In some embodiments , the HiPIMS-MIE process is operated under conditions ef fective not only to form the interfacial layer but also to form an etching metal layer on the structural component , adj acent to the interfacial layer . In such embodiments , the treatment time and / or the ion flux of the etching metal during the HiPIMS-MIE process are selected such that , after the oxide layer has been substantially removed and the interfacial layer comprising substrate metal and etching metal has been formed, further etching metal is deposited and accumulates at the surface . This results in a substantially continuous etching metal layer which is enriched in, or substantially composed of , the etching metal and which overlies the interfacial layer .

[0061] The etching metal layer may have a thickness comprised between 1 and 30 nm, preferably comprised between 1 and 20 nm, more preferably in a range of 1 to 10 nm .

[0062] Without wishing to be bound by theory, it is believed that at shorter treatment times or lower ef fective ion

[0063] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0064] - 12 - doses , the energetic etching metal ions predominantly contribute to oxygen removal and atomic mixing within a near-surface region of the substrate metal layer, thereby forming the interfacial layer . At longer treatment times or higher ef fective ion doses , once a desired degree of oxide removal and mixing has been achieved, the continued arrival of etching metal ions at the surface leads to net growth of the etching metal layer on top of the interfacial layer .

[0065] The HiPIMS-MIE process parameters , such as target power, pulse duration, duty cycle , working-gas pressure and substrate bias , may be selected within typical HiPIMS operating windows known to the skilled person and adj usted such that the desired degree of oxide removal and the desired thickness of the interfacial layer and the etching metal layer are obtained . For example , suitable treatment times may be in the range of a few seconds up to several minutes , depending on the material of the substrate metal layer, the selected etching metal and the applied ion flux .

[0066] The presence of the etching metal layer between the interfacial layer and the subsequently applied coating metal layer can further improve the adhesion and corrosion resistance of the coated structural component . In addition, the etching metal layer can act as a di f fusion barrier or protective underlayer for the coating metal , while still providing low contact resistance due to the underlying interfacial layer comprising both substrate metal and etching metal .

[0067] In some embodiments , the etching metal used in the HiPIMS-MIE process is selected from niobium, chromium,

[0068] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0069] - 13 - aluminum, tungsten, titanium or a combination thereof , preferably niobium or titanium, more preferably niobium . These metals are capable of forming stable interfacial regions with typical substrate metals used for structural components of electrochemical cells , such as titanium or stainless steels . During the HiPIMS-MIE treatment , atoms of the etching metal are mixed with atoms of the substrate metal in the near-surface region of the substrate metal layer and thereby contribute to the formation of the interfacial layer . The selected etching metals exhibit a favorable combination of sputtering behavior, reactivity and corrosion resistance under the operating conditions of electrochemical cells . In particular, niobium and titanium are able to form interfacial layers that provide low contact resistance and high stability, for example under acidic conditions as encountered in polymer electrolyte membrane electrolyzers and fuel cells . Chromium, aluminum and tungsten can also be used as etching metals , for example to form interfacial layers on stainless-steel or nickel-based alloy substrates . A "combination" of etching metals may comprise , for example , an alloy target containing two or more of the above metals or a cosputtering arrangement in which two or more etching metals are sputtered simultaneously or sequentially during the HiPIMS-MIE process .

[0070] In embodiments in which the substrate metal layer does not comprise titanium and the etching metal layer is titanium, the interfacial layer preferably comprises less than 70 atomic % titanium, so that atoms of the substrate metal constitute at least 30 atomic % of the metallic species present in the interfacial layer . This allows

[0071] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0072] - 14 - distinguishing the interfacial layer from the etching metal layer . When the substrate metal is titanium and the etching metal is also titanium, the etching metal layer cannot be distinguished from the substrate layer but may still be distinguishable from the interfacial layer as long as residual oxides remain present .

[0073] In some embodiments , the coating metal used in the second physical vapor deposition process is selected from platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof , preferably platinum . These metals , in particular the noble metals of the platinum group and gold, are well known for their high corrosion resistance and good electrical conductivity under the operating conditions of electrochemical cells . Platinum is especially preferred as the coating metal , for example for use in polymer electrolyte membrane electrolyzers and fuel cells , owing to its excellent stability and low contact resistance when in contact with typical electrolyte environments and catalyst layers .

[0074] The coating metal layer may consist essentially of a single coating metal , such as platinum, or may comprise a combination of two or more of the above metals . A "combination" may, for example , be provided by depositing an alloy of two or more coating metals from a single alloy target , by co-sputtering from two or more separate targets , or by forming a multilayer structure in which di f ferent coating metals are deposited sequentially . The choice of coating metal or combination of coating metals can be adapted to the speci fic application requirements , for

[0075] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0076] - 15 - example in terms of corrosion resistance , contact resistance and cost .

[0077] In some embodiments , the second physical vapor deposition process used to form the coating metal layer is a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process . In a HiPIMS-D process , a target comprising the coating metal is sputtered in a pulsed high- power magnetron discharge so as to generate a flux of sputtered species with a high degree of ioni zation . The structural component is arranged in the coating chamber such that at least the portion of the surface to be coated is exposed to the plasma and to the ioni zed coating metal species . The use of HiPIMS-D for depositing the coating metal layer allows improved control over the energy and directionality of the arriving coating metal species , for example by applying an appropriate substrate bias during the HiPIMS pulses . As a result , dense and well-adhering coating metal layers with a controlled microstructure can be obtained . In particular, HiPIMS-D can be used to promote preferred crystal orientations of the coating metal , for example of platinum, and to minimi ze the formation of defects and porosity in the coating metal layer . This contributes to low contact resistance , high corrosion resistance and improved durability of the coated structural component under the operating conditions of electrochemical cells . The HiPIMS-D process utili zes extremely high-power densities in short pulses at low duty cycle for the deposition of thin films .

[0078] For the purposes of the present invention, a High- Power Impulse Magnetron Sputtering deposition (HiPIMS-D)

[0079] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0080] - 16 - process is a method for physical vapor deposition of thin films which is based on magnetron sputter deposition and operated in a pulsed mode . The power of each pulse can be in the range from 0 . 1 kW to 1 MW and is preferably within the range from 10 kW to 1 MW for typical target areas conventionally used in sputtering devices . The pulses can have a duration in the range of less than a hundred microseconds up to hundreds of microseconds and the intervals between pulses can range from hundreds of microseconds up to hundreds of milliseconds , and in special cases up to seconds . A magnetic field is arranged at the surface of a target , the magnetic field having a conventional magnetron configuration . The target is a usually stationary obj ect from which material is to be sputtered in order to be deposited onto a substrate . A gas which is chosen so that it can be ioni zed is supplied to the chamber containing the target . A negative voltage is applied between an anode and a cathode in the chamber, the cathode being the target and the anode being, for example , parts of the walls of the chamber . An electric discharge then occurs between the anode and the cathode , producing electrons which are trapped in the magnetic field by the cooperation of the electric field produced by the applied voltage . Thus , an extremely high absolute level of pulsed electric power, or equivalently an extremely high level of power density in the generated electric pulses , is provided to the sputtering device . This is accomplished using electric pulses directed to the cathode which have an extremely high power density relative to the area of the cathode . In the discharge , very high currents and high current densities occur . This high power level permits the production of a nearly fully ioni zed plasma in the vicinity

[0081] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0082] - 17- of the cathode, for example for current densities up to about 10 A / cm2and applied voltages up to about 3 kV. The high ionization can be achieved in a pressure range of about 10-5to 10-1mbar.

[0083] In the HiPIMS-D process, a negative bias voltage in the range of 10 to 400 V is applied to the substrate, depending on the materials used and the desired coating density. Preferably, a negative bias voltage in the range of 50 to 150 V is applied to the substrate in the HiPIMS-D process. In contrast to the HiPIMS-MIE process described above, in which relatively high negative bias voltages can be applied to the structural component in order to promote intense ion bombardment and sputter removal of material from the surface, the HiPIMS-D process is generally operated at lower negative bias voltages. In the HiPIMS-D step, the substrate bias is selected such that the energy of the arriving ions is sufficient to densify the growing coating metal layer and to tailor its microstructure, but not so high as to cause excessive resputtering of the deposited material. The preferred bias range of 50 to 150 V in the HiPIMS-D process is therefore typically lower than the bias voltages used in the HiPIMS-MIE process.

[0084] Advantageously, the thickness of the coating metal layer is comprised between 1 and 100 nm, preferably comprised between 2 and 50 nm, more preferably comprised between 5 and 25 nm.

[0085] In some embodiments, the method further comprises a third physical vapor deposition process using a second metal, different from the coating metal and the etching

[0086] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0087] - 18 - metal, operated under conditions effective to form a second metal layer on the coating metal layer. In such embodiments, after formation of the coating metal layer in the second physical vapor deposition process, the structural component remains in the coating chamber or is transferred to a further coating chamber and is subjected to the third physical vapor deposition process. The second metal is deposited onto the coating metal layer so as to form the second metal layer which overlies the coating metal layer. The second metal layer can, for example, act as a protective top layer, a contact layer or a functional layer adapted to specific operating conditions of the electrochemical cell.

[0088] The second metal may be selected from platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof, preferably platinum. The use of metals from this group allows the properties of the surface of the coated structural component to be tailored, for example in terms of corrosion resistance, contact resistance and interaction with adjacent components such as catalyst layers or membranes. A "combination" of second metals may be provided, for example, by depositing an alloy of two or more metals from a single alloy target, by co-sputtering from multiple targets or by forming a multilayer stack comprising two or more different second metals.

[0089] Any suitable type of physical vapor deposition, such as DCMS, can be used for forming the second metal layer. Preferably, however, the third physical vapor deposition process is a High-Power Impulse Magnetron Sputtering

[0090] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0091] - 19 - deposition (HiPIMS-D) process . In such cases , the same HiPIMS power supply and coating chamber equipment as used for the second physical vapor deposition process may be employed, with appropriate adj ustment of the target material and process parameters . The use of HiPIMS-D for depositing the second metal layer enables dense and welladhering second metal layers with controlled microstructure and thickness to be obtained on the underlying coating metal layer . The thickness of the second metal layer may be selected according to the desired function of the layer and the speci fic application requirements of the electrochemical cell .

[0092] In certain embodiments , the first treatment step using HiPIMS-MIE can be preceded by subj ecting the structural component to a pre-treatment process to remove contaminants or debris . The pre-treatment process may involve washing the substrate in isopropyl alcohol ( IPA) and deioni zed water ( DI H20) to remove organic contaminants , particles , and ionic residues in a simple , low-cost , and ef fective manner . In addition or alternatively, the pre-treatment process may involve plasma assisted etching such as argon plasma assisted etching . In this preferable step, the native oxides and other contaminants including organic contaminants are removed at a thickness or penetration in a range of 1 to 2 nm .

[0093] According to another aspect of the invention, there is provided a coated structural component of an electrochemical cell . The coated structural component comprises a substrate metal layer, an interfacial layer formed on at least a portion of a surface of the substrate

[0094] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0095] - 20 - metal layer, wherein the interfacial layer comprises substrate metal and an etching metal , and a coating metal layer formed on the interfacial layer . The substrate metal layer may be part of a structural component as defined herein, for example a porous transport layer, a bipolar plate or a flow field plate made from a metallic or composite material and comprising the substrate metal layer on at least a portion of its surface .

[0096] The interfacial layer is formed in a near-surface region of the substrate metal layer and comprises a mixture of atoms of the substrate metal and atoms of the etching metal . Without wishing to be bound by theory, the interfacial layer can be regarded as a graded region in which the concentration of etching metal decreases and the concentration of substrate metal increases with depth into the substrate metal layer . The interfacial layer preferably has a reduced oxide content compared with the oxide layer originally present on the substrate metal layer, and provides an improved interface for the coating metal layer formed thereon . The coating metal layer is formed directly on the interfacial layer and may comprise , for example , a noble metal such as platinum, as described in connection with the method aspect of the invention .

[0097] In preferred embodiments , the interfacial layer is obtainable by subj ecting at least a portion of the surface of the substrate metal layer to a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE ) process using the etching metal . The HiPIMS-MIE process is operated under conditions ef fective to remove at least part of an oxide layer present on the substrate metal layer prior to

[0098] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0099] - 21 - the HiPIMS-MIE process and to form the interfacial layer comprising substrate metal and etching metal . In particular, energetic ions of the etching metal generated in the HiPIMS-MIE process bombard the surface of the substrate metal layer, assist in removing oxygen from the oxide layer and promote atomic mixing between the etching metal and the substrate metal in the near-surface region .

[0100] The etching metal in the interfacial layer may be selected from niobium, chromium, aluminum, tungsten, titanium or a combination thereof , preferably niobium or titanium, more preferably niobium . These etching metals are capable of forming stable interfacial regions with typical substrate metals used for structural components of electrochemical cells and can provide low contact resistance and high corrosion resistance under the operating conditions of such cells . A combination of etching metals may be present in the interfacial layer, for example when an alloy target containing two or more etching metals is used in the HiPIMS-MIE process or when two or more etching metals are sputtered sequentially or simultaneously during the treatment .

[0101] In some embodiments , the coating metal of the coating metal layer is selected from platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof , preferably platinum . These metals , in particular the noble metals of the platinum group and gold, are known for their high corrosion resistance and good electrical conductivity under typical operating conditions of electrochemical cells . Platinum is especially preferred as the coating metal owing to its excellent stability and

[0102] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0103] -22- low contact resistance when in contact with, for example, acidic electrolytes and catalyst layers in polymer electrolyte membrane electrolyzers and fuel cells. The coating metal layer may consist essentially of a single coating metal, such as platinum, or may comprise a combination of two or more metals from the above group, for example in the form of an alloy or a multilayer stack.

[0104] In preferred embodiments, the coating metal layer comprises platinum having crystal structures Pt

[0111] and Pt

[0200] , wherein the ratio Pt

[0200] : Pt

[0111] is less than 0.04, preferably less than 0.02. The ratio Pt

[0200] : Pt

[0111] may be determined, for example, from X-ray diffraction (XRD) measurements of the coating metal layer by comparing the intensities of the diffraction peaks corresponding to the Pt

[0200] and Pt

[0111] planes. It is believed that a low Pt

[0200] : Pt

[0111] ratio indicates a strong preferred orientation of the platinum crystallites in the

[0111] direction and correlates with a dense, fine-grained microstructure of the coating metal layer. Such a microstructure is advantageous in terms of contact resistance and corrosion resistance under electrochemical operating conditions. Other PVD methods, such as DCMS, yield higher Pt

[0200] : Pt

[0111] ratios, typically higher than 0.05.

[0105] In some embodiments, the coating metal layer is obtained via a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process as described herein. The use of HiPIMS-D for depositing the coating metal layer allows the energy and ionization state of the arriving coating metal species to be controlled, for example by adjusting

[0106] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0107] -23 - the pulse parameters and the substrate bias. This promotes the formation of dense and well-adhering coating metal layers with a controlled crystal orientation, in particular platinum layers exhibiting a low Pt

[0200] : Pt

[0111] ratio as described above. Coating metal layers obtained via HiPIMS-D therefore provide coated structural components with low contact resistance and high durability in electrochemical cells .

[0108] In further embodiments, the coated structural component comprises a second metal layer on top of the coating metal layer, wherein the second metal is different from the coating metal and the etching metal. The second metal layer overlies the coating metal layer and may be provided, for example, as a protective top layer, a contact layer or a functional layer adapted to specific operating conditions of the electrochemical cell. By appropriate choice of the second metal, the surface properties of the coated structural component, such as corrosion resistance, contact resistance and interaction with adjacent components (for example catalyst layers or membranes) , can be tailored independently of the underlying coating metal layer.

[0109] The second metal may be selected from platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof. A combination of second metals may be present, for example when an alloy of two or more metals from this group is deposited, when two or more second metals are co-sputtered from separate targets or when a multilayer stack comprising two or more different second metals is formed. The second metal is selected such that it is different from both the coating

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[0111] -24- metal and the etching metal, thereby allowing the properties of the second metal layer to be adjusted independently of the composition of the interfacial layer and the coating metal layer.

[0112] In some embodiments, the second metal layer is obtained via a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process. In such embodiments, the same type of HiPIMS coating equipment as used for depositing the coating metal layer can be employed, with a suitable target comprising the second metal. The use of HiPIMS-D for depositing the second metal layer enables dense and well-adhering second metal layers with controlled microstructure and thickness to be formed on the coating metal layer. This contributes to a robust multilayer coating architecture in which the interfacial layer, the coating metal layer and the second metal layer together provide low contact resistance, high corrosion resistance and improved durability of the coated structural component under the operating conditions of electrochemical cells.

[0113] In some embodiments, the second metal layer is platinum, more preferably platinum having crystal structures Pt

[0111] and Pt

[0200] , and wherein the ratio Pt

[0200] : Pt

[0111] is less than 0.04, preferably having a thickness comprised between 1 and 100 nm.

[0114] In certain embodiments, the structural component is selected from a porous transport layer, a bipolar plate or a flow field plate.

[0115] For the purposes of the present invention, a porous

[0116] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0117] -25 - transport layer is a porous and electrically conductive layer suitable for use in electrochemical devices, including polymer electrolyte membrane (PEM) water electrolyzers and fuel cells. The porous transport layer may have a thickness comprised between 50 and 1000 micrometers, preferably comprised between 100 and 500 micrometers. The porosity of the porous transport layer may be comprised between 20% and 90%, preferably comprised between 25% and 60%, where the porosity is defined as (Volume of Voids / Total Volume) x 100 and may be measured by mercury intrusion porosimetry. The electrical conductivity of the porous transport layer may be comprised between 1 and 100 S / cm, preferably comprised between 10 and 60 S / cm. The porous transport layer is typically formed from a metallic material, such as titanium or a titanium alloy, or from a composite material including a metallic phase, and comprises at least on a portion of its surface the substrate metal layer as defined herein.

[0118] Advantageously, the porous transport layer or at least the native oxide layer of the porous transport layer comprises a material selected from porous titanium (Ti) , porous nickel (Ni) , porous stainless steel (SS) or a combination thereof, preferably titanium. The porous transport layer can be made of a planar or a mesh substrate of the same materials (Ti, Ni, and SS) .

[0119] For the purposes of the present invention, a bipolar plate is an electrically conductive plate configured to be arranged between adjacent electrochemical cells in a cell stack. Each major surface of the bipolar plate can form an electrode-facing surface of a respective cell. The bipolar

[0120] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0121] - 26 - plate typically comprises at least one flow field structure with channels , ribs and / or openings for distributing reactants and / or coolant across the electrode surfaces , and additionally provides mechanical support and sealing functions within the stack . The bipolar plate may be formed from a metallic material , such as stainless steel , titanium or a nickel-based alloy, or from a composite material comprising a metallic substrate layer, and comprises at least on a portion of its surface the substrate metal layer which is treated and coated in accordance with the invention .

[0122] For the purposes of the present invention, a flow field plate is an electrically conductive component comprising a structured flow- field surface with channels , ribs , apertures and / or porous regions configured to guide a fluid stream, such as a reactant gas , liquid water or coolant , to and / or from an electrode of the electrochemical cell . The flow field plate may be provided as a separate component or may be integrated with another structural component , for example with a bipolar plate or a current collector . The flow field plate may be made from a metallic material , such as stainless steel , titanium or a nickel- based alloy, or from a composite material that includes a metallic substrate layer . In all cases , at least a portion of the surface of the flow field plate comprises the substrate metal layer on which the interfacial layer and the coating metal layer according to the invention are formed .

[0123] According to a further aspect of the invention, there is provided an electrochemical cell comprising any of the

[0124] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S . p . A. , Nano4Energy S . L . N . E .

[0125] - 27 - coated structural components described herein . The electrochemical cell may be configured, for example , as a polymer electrolyte membrane ( PEM) water electrolyzer cell , a PEM fuel cell , a regenerative fuel cell , or another type of electrochemical cell in which metallic structural components are exposed to corrosive environments and are required to provide good electrical conductivity and longterm stability . The electrochemical cell typically comprises at least one anode , at least one cathode and an ion-conducting electrolyte arranged between the anode and the cathode . The electrolyte may be provided, for example , in the form of a polymer electrolyte membrane . One or more of the coated structural components according to the invention is arranged in electrical contact with one of the electrodes .

[0126] In some embodiments , the coated structural component is a porous transport layer arranged between the electrode and a flow field plate or bipolar plate , for example an anode-side porous transport layer in a PEM water electrolyzer cell . In other embodiments , the coated structural component is a bipolar plate or a flow field plate forming part of the current-collecting and flowdistribution structure of the cell . The coated structural component provides a low-resistance electrical connection between the associated electrode and an external current collector or adj acent cell , while at the same time exhibiting improved corrosion resistance under the operating conditions of the electrochemical cell . The presence of the interfacial layer comprising substrate metal and etching metal , the coating metal layer and, where present , the second metal layer, contributes to stable

[0127] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0128] -28- interfacial contact and reduced degradation over time. The invention thus enables electrochemical cells with improved efficiency and durability, especially under demanding operating conditions such as high current densities, elevated temperatures and corrosive electrolytes. The electrochemical cell may be used as a single cell or as part of a stack comprising a plurality of electrochemical cells connected in series or in parallel. In a cell stack, coated structural components according to the invention may be provided in some or all of the cells, for example as coated bipolar plates and / or coated porous transport layers, thereby improving the overall electrical performance and service life of the stack.

[0129] In one embodiment, the electrochemical cell is an electrolyzer or fuel cell, preferably proton exchange membrane (PEM) water electrolyzer comprising a coated structural component of the present invention in the form of a coated porous transport layer. A PEM water electrolysis cell may comprise an electrolyte membrane, an anode, and a cathode, a gas diffusion layer for the cathode, a porous transport layer (PTL) for the anode, a cathode bipolar plate, and an anode bipolar plate.

[0130] In the present patent application, all the operating conditions reported in the text must be understood as preferred conditions even if not expressly declared.

[0131] For the purposes of the present patent application the term "to comprise" or "to include" also comprises the term "to consist of" or "essentially consisting of".

[0132] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0133] -29-

[0134] For the purposes of the present patent application the definitions of the ranges always comprise the extreme values unless otherwise specified.

[0135] Examples

[0136] The following examples are provided for illustrative purposes only of the present invention and must not be understood as limiting the scope of protection defined by the appended claims. In the examples, the coated structural component is a coated porous transport layer (PTL) .

[0137] Figure 2 shows a schematic representation of a direct- current magnetron sputtering (DCMS) system 20 as used in the Comparative Examples. The system 20 comprises substrate fixturing 21 holding various PTLs 22. In a pre-treatment chamber 23, the substrate is subjected to an argon plasma etching process while the substrate is biased at - 450 V, DC-pulsed at 150 kHz. In a magnetron sputtering chamber 24, a coating material source 25 is provided. The DCMS process operates with a constant power density of about 1.25 W / cm2and the substrate bias voltage is -150 V.

[0138] Figure 3 shows a schematic representation of a high- power impulse magnetron sputtering (HiPIMS) system 30 according to the invention. The system 30 comprises substrate fixturing 31 holding various PTLs 32. In a pretreatment chamber 33, the substrate is subjected to an argon plasma etching process while the substrate is biased at - 450 V, DC-pulsed at 150 kHz. In a magnetron sputtering chamber 34, a HiPIMS-MIE process followed by a HiPIMS-D process are carried out. A Nb-MIE source 35 and a Pt

[0139] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0140] -30- coating material source 36 are provided. In contrast to DCMS, HiPIMS applies short, high-power pulses to the target, generating a dense, highly ionized plasma containing metal ions. Magnetron power is at 7.5 W / cm2(avg) , 100 ps pulse length at a rate of 500 Hz for HiPIMS-

[0141] MIE and at 1.25 W / cm2(avg) , 50 ps pulse length at a rate of 200 Hz for HiPIMS-D platinum deposition. During HiPIMS- MIE, the substrate is biased at about - 600 V, promoting energetic ion bombardment, at least partial sputter-etching of native oxides, and metal ion implantation. During HiPIMS-D, the bias voltage is reduced to about -150 V to favor net film growth. The pulsed operation produces extremely high instantaneous power densities — up to 7.5 W / cm2for metal-ion etching and 1.25 W / cm2for platinum deposition— resulting in dense and adherent coatings with finely controlled morphology and thickness.

[0142] Figure 4 summarizes the comparative examples and the examples according to the invention.

[0143] Fig. 4a: coated porous transport layers 40a obtained according to Comparative Example 1 comprising a substrate 41, a reduced oxide layer 42 obtained by Ar etching, and a DCMS coating metal layer 43 having a thickness of 100 nm;

[0144] Fig. 4b: coated porous transport layers 40b obtained according to Comparative Example 2, comprising a substrate 41, a reduced oxide layer 42 obtained by Ar etching, and a DCMS coating metal layer 44 having a thickness of 10 nm;

[0145] Fig. 4c: coated porous transport layers 40c obtained according to Example 1 of the invention, comprising a substrate 41, an interfacial layer 45 obtained by HiPIMS- MIE, an etching metal layer 46 obtained by HiPIMS-MIE and a DCMS coating metal layer 47 having a thickness of 10 nm;

[0146] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0147] - 31 - and

[0148] Fig. 4d: coated porous transport layers 40d obtained according to Example 2 of the invention comprising a substrate 41, an interfacial layer 45 obtained by HiPIMS- MIE, an etching metal layer 46 obtained by HiPIMS-MIE and a coating metal layer 48 obtained by HiPIMS-D having a thickness of 10 nm.

[0149] Example 1 according to the present invention (HiPIMS-MIE then DCMS) .

[0150] Example 1 of the method of the present invention starts with a porous transport layer or a substrate having a native oxide layer. The substrate is made of porous titanium. Native oxide layer has a thickness in a range of 2 and 10 nm at normal atmospheric conditions.

[0151] The substrate is subjected to argon plasma assisted etching. The native oxides (TiOx) and any surface contaminants are removed at a thickness or penetration in a range of 1 to 2 nm.

[0152] Afterwards, the porous titanium substrate is subjected to a HiPIMS-MIE process. Niobium is used as an etching metal. Initially, the native oxides (TiOx) are removed at a thickness or penetration in a range of 1 to 10 nm and at the same time niobium is implanted into the porous titanium substrate at an implantation depth in a range of 1 to 10 nm. Then, niobium is no longer implanted but rather starts to build up on top of the substrate forming a layer having a thickness in a range of 1 to 20 nm.

[0153] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0154] -32-

[0155] The substrate is lastly subjected to protective metal deposition. The direct-current magnetron sputtering (DCMS) process is used for the deposition of platinum. The thickness of the protective metal is around 10 nm, and the Pt load is 0.2 g.m-2.

[0156] Example 2 according to the present invention (HiPIMS-MIE then HiPIMS) .

[0157] Example 2 of the method of the present invention can be represented by Figure 1 which starts in step a) with a porous transport layer (PTL) 10 or a substrate 11 having a native oxide layer 12. The substrate 11 is made of porous titanium. Native oxide layer 12 has a thickness in the range of 2 and 10 nm at normal atmospheric conditions.

[0158] In step b) the PTL or substrate is subjected to argon plasma assisted etching. The native oxides (TiOx) are partially removed and any surface contaminants are removed, yielding a reduced native oxide layer 13 having a thickness in a range of 1 to 2 nm.

[0159] Afterwards, in step c) , the porous titanium substrate 11 is subjected to a HiPIMS-MIE process. Niobium is used as an etching metal. Initially, the native oxides (TiOx) are removed at a thickness or penetration in a range of 1 to 10 nm and at the same time niobium is implanted into the porous titanium substrate at an implantation depth in a range of 1 to 10 nm, yielding an interfacial layer 14 on the substrate. Then, in step d) , niobium is no longer implanted but rather starts to build up on top of the substrate forming an etching metal layer 15 having a

[0160] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0161] - 33 - thickness in a range of 1 to 20 nm.

[0162] In step e) , the substrate is lastly subjected to protective metal deposition. In this case, High-Power Impulse Magnetron Sputtering Deposition (HiPIMS-D) is used for the deposition coating metal layer 16 (or second metal layer) of platinum. The thickness of the protective coating metal layer is around 10 nm, and the Pt load is 0.2 g.m-2.

[0163] Comparative Example 1 (DCMS - high Pt loading)

[0164] Comparative example 1 starts with a porous transport layer or a substrate having a native oxide layer. The substrate is made of porous titanium. Native oxide layer has a thickness in a range of 2 and 10 nm at normal atmospheric conditions.

[0165] The substrate is subjected to argon plasma assisted etching. The native oxides (TiOx) are partially removed and any surface contaminants are removed yielding a reduced native oxide layer at a thickness in a range of 1 to 2 nm.

[0166] The substrate is lastly subjected to protective metal deposition. The direct-current magnetron sputtering (DCMS) process is used for the deposition of platinum. The thickness of the protective metal is around 100 nm, and the Pt load is 2 g.m-2.

[0167] Comparative Example 2 (DCMS - low Pt loading)

[0168] Comparative example 2 starts with a porous transport layer or a substrate having a native oxide layer. The

[0169] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0170] -34- substrate is made of porous titanium. Native oxide layer has a thickness in a range of 2 and 10 nm at normal atmospheric conditions.

[0171] The substrate is subjected to argon plasma assisted etching. The native oxides (TiOx) are partially removed and any surface contaminants are removed yielding a reduced native oxide layer at a thickness in a range of 1 to 2 nm.

[0172] The substrate is lastly subjected to protective metal deposition. The direct-current magnetron sputtering (DCMS) process is used for the deposition of platinum. The thickness of the protective metal is around 10 nm, and the Pt load is 0.2 g.m-2.

[0173] Operating conditions

[0174] Argon etching

[0175] Argon etching is conducted using the operating conditions as follows. Substrate is biased at 450V, DC- Pulsed 150 kHz. This results in a power comprised between 0.1 to 0.2W / cm2. Ar pressure in the low-pressure range of 4xl0“3mbar. The process last for around 10 minutes without heating .

[0176] Nb HiPIMS-MIE

[0177] This step provides enhanced adhesion. MIE reduces the oxide thickness at titanium interface and improves contact between surface and Pt coating deposition.

[0178] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0179] - 35 -

[0180] Magnetron generates energetic ions with HiPIMS working at high current densities compared to conventional DCMS .

[0181] The operating conditions are as follows:

[0182] - The substrate is negatively biased and collects the positive metal niobium (Nb) ions,

[0183] - Ar pressure is set at 4xl0“3mbar.

[0184] - The average power density of 7.5 W / cm2is applied and distributed in pulses of 100 ps width and 500 Hz repetition frequency. This results in a peak current density of 0.75 A / cm2.

[0185] - Bias voltage to the substrate: DC mode, Arc control management is essential to withstand bias current higher than 10 A.

[0186] - Substrate is biased at 600V.

[0187] - No extra heating is applied.

[0188] - HiPIMS peak current around 0.75A / cm2guarantees the formation of Nb ions.

[0189] Negative voltage bias controls the energy of the arriving ions. Higher negative bias voltage increases metal ion etching rate and prevents the formation of oxides.

[0190] Pt HiPIMS:

[0191] The aim of this step is obtaining a denser and finegrained Pt coating with enhanced finishing at ultra-low loading. The emission of secondary electrons in intrinsic Pt is lower as compared to Nb. Therefore, lower current densities are obtained even when higher voltages are applied.

[0192] The operating conditions are as follows:

[0193] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0194] -36-

[0195] - Ar pressure 4xl0-3mbar.

[0196] - An average power density of 1.25W / cm2is applied and distributed in pulses of 50 ps width and 200 Hz repetition frequency. This results in a peak current density of 0.15 A / cm2.

[0197] - Substrate is biased at 150 V without heating.

[0198] Pt DCMS

[0199] Platinum deposition is conducted under the following operating conditions in Direct Current magnetron sputtering .

[0200] - Ar pressure 4x10-3mbar.

[0201] - A constant power density of 1.25W / cm2is applied which results in a current density of 2.27xl0-3A / cm2.

[0202] - Substrate is biased at 150 V without heating.

[0203] Characterization studies

[0204] Ohmic decay over time for the PTL of the examples 1 and 2 according to the invention and comparative examples 1 and 2 were conducted.

[0205] Electrochemical cell

[0206] Cell Hardware

[0207] 25 cm2fuel cell technologies hardware is used. The cathode is flow f ield / bipolar plate (BPP) - graphite, triple serpentine (Fuel Cell Technologies) , while the anode is flow field / BPP - Ti, platinized, parallel channel (sputter coated, 100 nm thickness) . A gasketing made of

[0208] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0209] -37- polytetraf luoroethylene (PTFE) is used.

[0210] Operating Conditions

[0211] The 25cm2cell is operated at 60 °C using ultra-pure water (>2 megaohm (MQ) ) with the flow rate of 300 mL / min under atmospheric pressure. Water is fed to the anodic side only.

[0212] MEA Configuration:

[0213] Standard catalyst coated membranes (CCMs) are made using the methods known in the art. In the electrochemical tests reported herein, the membrane of the MEA was a proton exchange membrane of the perfluorosulfonic acid type, specifically a Nafion™ 117 membrane, although other PEM membranes known in the art can likewise be used.

[0214] Anode Catalyst - Ir Black, 2mg / cm2.

[0215] Anode (PTL) - Porous Ti (sintered powder) , PVD Pt coating .

[0216] Cathode Catalyst - 50wt% Pt / C, 0.5mg / cm2Pt.

[0217] Cathode (gas diffusion layer (GDL) ) - Carbon Paper, 5% wet-proofed .

[0218] Test Protocol

[0219] The test is run with constant current, at a current density of 4A / cm2(100A with 25cm2active area) . Intermittently, an electrochemical impedance spectroscopy (EIS ) / Polarization protocol is performed to gain an understanding of any voltage decay taking place. This is

[0220] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0221] - 38 - done with the intent to separate out contributions from ohmic, kinetic, and mass transport losses. For the PTL protective coating, of interest for this invention, the key performance indicator (KPI) is the ohmic contribution, which can be extracted using the high frequency resistance (HFR) from the EIS data. Multiplying this value (ohms) by the operating current (100A) gives us the ohmic contribution in Volts. Furthermore, due to expected variability in cell builds, the main KPI for this testing is the decay in ohmic contribution (final - initial) .

[0222] The ohmic decay values are reported in the Table 1 below .

[0223] Polarization - 0 - 4A / cm2, 500mA / s scan rate.

[0224] Galvanostatic Electrochemical Impedance Spectroscopy (GEIS) - 2.5A, 20 kHz to 0.1Hz, 100mA amplitude. ( Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) equivalent at ~1.45V) .

[0225] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0226] -39-

[0227] Table 1: Ohmic Decay Over Time Results The results show that:

[0228] - with standard DCMS process, the benchmark sample (comparative example 1) , has an ohmic decay (in 500hrs of testing) of 38 pV / hr.

[0229] - Lowering the Pt loading to 10 nm, using the same DCMS process (comparative example 2) , increases the ohmic decay to 86 pV / hr.

[0230] - keeping the loading at 10 nm, but introducing the HiPIMS-MIE (Nb) step (Example 1) , there is a

[0231] M / 66050-PCT2 (414PCT-GEN) Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.

[0232] -40- significant improvement in the ohmic degradation, surpassing that of the benchmark sample (comparative example 1) by 12 pV / hr, and by comparative example 2 by 62 pV / hr. - Example 2 introduces the HiPIMS Pt Deposition step, as well as the HiPIMS-MIE step, and shows further improvement of the ohmic degradation to 0 pV / hr in the first 500 hrs tested.

[0233] - These results show clear, incremental improvement enabled by both the HiPIMS-MIE step and HiPIMS Pt deposition step to minimize Pt loading, while maintaining / improving stability of the ohmic contribution (main indicator for protective coating functionality) .

[0234] M / 66050-PCT2 (414PCT-GEN)

Claims

Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.-41 -Claims1. A method for treating a structural component of an electrochemical cell, the method comprising:- providing a structural component comprising a substrate metal layer having an oxide layer on at least a portion of a surface of the substrate metal layer,- subjecting at least said portion of the surface of the substrate metal layer to a first physical vapor deposition process using an etching metal, wherein the first physical vapor deposition process is a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE) process operated under conditions effective to remove at least part of the oxide layer and to form an interfacial layer comprising the substrate metal and the etching metal, and- subsequently subjecting at least said portion of the surface to a second physical vapor deposition process using a coating metal, operated under conditions effective to form a coating metal layer.

2. The method according to claim 1, wherein the HiPIMS- MIE process is operated under conditions effective to form an etching metal layer on the structural component, adjacent to the interfacial layer.

3. The method according to one of claims 1 or 2, wherein the etching metal is selected from a group consisting of niobium, chromium, aluminum, tungsten, titanium or a combination thereof, preferably niobium or titanium, more preferably niobium.M / 66050-PCT2 (414PCT-GEN)Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.-42-4. The method according to any one of claims 1 to 3, wherein the coating metal is selected from a group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof, preferably platinum.

5. The method according to any one of the preceding claims, wherein the second physical vapor deposition process is a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process.

6. The method according to any one of the preceding claims, wherein the method further comprises a third physical vapor deposition process using a second metal, different from the coating metal and the etching metal, operated under conditions effective to form a second metal layer on the coating metal layer.

7. The method according to claim 6, wherein the second metal is selected from a group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof, preferably platinum.

8. The method according to one of claims 6 or 7, wherein the third physical vapor deposition process is a HiPIMS-D process.

9. A coated structural component of an electrochemical cell comprising:- a substrate metal layer,- an interfacial layer formed on at least a portionM / 66050-PCT2 (414PCT-GEN)Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.-43 - of a surface of the substrate metal layer, wherein the interfacial layer comprises substrate metal and an etching metal, and- a coating metal layer formed on the interfacial layer .

10. The coated structural component of claim 9, wherein the interfacial layer is obtained via a High-Power Impulse Magnetron Sputtering metal-ion etching (HiPIMS-MIE) process using the etching metal, operated under conditions effective to remove at least part of an oxide layer present on the substrate metal layer prior to the HiPIMS-MIE process, and effective to form the interfacial layer.

11. The coated structural component of one of claims 9 or 10, wherein the etching metal is selected from a group consisting of niobium, chromium, aluminum, tungsten, titanium or a combination thereof, preferably niobium or titanium, more preferably niobium.

12. The coated structural component of any one of claims9 to 11, wherein the coating metal is selected from a group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof, preferably platinum.

13. The coated structural component of any one of claims 9 to 12, wherein the coating metal layer comprises platinum having crystal structures Pt [111] andPt [200] , wherein the ratio Pt [ 200 ] : Pt [ 111 ] is less than 0.04, preferably less than 0.02.M / 66050-PCT2 (414PCT-GEN)Industrie De Nora S.p.A. , Nano4Energy S.L.N.E.-44-14. The coated structural component of any one of claims 9 to 13, wherein the coating metal layer is obtained via a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process.

15. The coated structural component of any one of claims 9 to 14, further comprising a second metal layer on top of the coating metal layer, wherein the second metal is different from the coating metal and the etching metal .

16. The coated structural component of claim 15, wherein the second metal is selected from a group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium, gold, silver, tantalum and a combination thereof .

17. The coated structural component of one of claims 15 or 16, wherein the second metal layer is obtained via a High-Power Impulse Magnetron Sputtering deposition (HiPIMS-D) process.

18. The coated structural component of any one of claims 9-17, wherein the structural component is selected from the group consisting of a porous transport layer, a bipolar plate or a flow field plate.

19. Electrochemical cell comprising the coated structural component of any one of claims 9 to 18.M / 66050-PCT2 (414PCT-GEN)

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