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The electrochemical behavior of a sputtered film of carbon and nickel, of approximate stoichiometry NiC 3 , is presented. This film is quite passive in hot sulfuric acid solution. The material also displays considerable electrocatalytic activity toward the hydrogen reaction, both anodically and cathodically. The electrocatalyst is passivated by the carbon component after dissolution of some of the surface nickel. The remaining surface nickel, entrapped by carbon, provides electrocatalytic activity comparable with that of pure polycrystalline nickel.The hydrogen oxidation reaction in alkaline fuel cells is carried out efficiently on nickel metal electrocatalysts. 1,2 This is due to the high intrinsic electrocatalytic activity of nickel and an appropriate thermodynamic stability region in base electrolyte. The Ni/NiO equilibrium potential is 0.110-0.116 V above the hydrogen equilibrium potential. 3 Anodic oxidation of hydrogen is thus possible in alkaline electrolyte on the native metal surface. The Ni/Ni͑II͒ equilibrium line falls below that of hydrogen at pH values below 4, ruling out nickel metal as an acidic electrolyte electrocatlyst. 3 Despite unfavorable thermodynamics, several materials containing nickel have shown promising results as acidic electrolyte electrocatalysts. Combinations of nickel, carbon, and tantalum and/or tungsten have shown electrocatalytic activity and excellent passivity in acidic electrolyte. 4-8 Nickel alloys have been investigated for hydrogen evolution electrocatalytic activity in acidic electrolyte. 9,10 In order for the nickel to catalyze the hydrogen electrode reaction in acidic electrolyte, it must be passive against corrosion. Nickel is normally passivated against corrosion by an oxide film, either NiO or Ni͑OH͒ 2 , which covers the surface. 3,11,12 Ni shows a region of active dissolution in the absence of an oxide film according to Tafel's equation up to 0.4 V above the hydrogen equilibrium potential in sulfuric acid. 13,14 Above this potential at room temperature a degree of passivation occurs by formation of a metastable oxide film, although passive current densities may remain quite high. 14 At higher temperatures even this passivation is expected to be more difficult. At potentials appropriate for efficient anodic oxidation of hydrogen ͑Ͻ0.4 overpotential͒, nickel is unable to form a passivating oxide in sulfuric acid. It is therefore unsuitable for use as an anode in acidic fuel cells.It would nevertheless be useful to be able to design a nickelbased electrocatalyst for use in acidic fuel cells, and it is to this end that the present work was approached. We demonstrate below that a sputtered nickel-carbon film can be made passive at low anodic hydrogen overpotential in hot sulfuric acid solution and retain electrocatalytic activity toward hydrogen provided the carbon content is high. ExperimentalElectrocatalyst synthesis.-The electrocatalyst investigated here was made as a thin film by magnetron sputtering. The films were fabricated by simultaneous deposition from two 35 ...

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Tungsten carbide is an interesting non-noble metal anode electrocatalyst that can be passivated against corrosion in acidic electrolytes for use in low-temperature fuel cells. The structure of nanocrystalline WC passivated in 1.5 M H2SO4 at 65 °C was studied using synchrotron extended X-ray absorption fine structure spectroscopy and compared with the as-prepared material. Changes in the average local structure are noted that correspond to the development of an oxide phase in the material. This is most likely to be present as a WIV-oxide phase on the surfaces of the particles.