Porous Nickel‐Coated Steel Anodes for Alkaline Water Electrolysis: Corrosion Resistance

Anodes for alkaline water electrolysis made by sintering porous nickel coatings to mild steel substrates have produced low oxygen evolution overpotentials. Despite the porosity of the nickel coatings, the anodes display a high degree of corrosion resistance in at 80°C. The present work shows that the anodes are stabilized by nickel‐iron alloy formed at the steel substrate surface. The results of metallographic, electron microprobe, and scanning electron microscope studies of the nickel‐iron alloy formation are presented. The alloy is formed by diffusion during the sintering operation which binds the porous coating to the substrate. Rapid grain boundary diffusion produces nickel‐rich veins in the steel, from which bulk diffusion proceeds into the grains, broadening the alloy formation region. The partial contact between the coating and the substrate results in areas of higher nickel concentration directly below the nickel‐steel contact areas.