Coating of Ni on Fe (oxy)hydroxide: Superior Catalytic Activity for Oxygen-Involved Reaction During Water Splitting

Transition-metal-based oxides based on Ni, Co, and Fe have recently been studied as efficient electrocatalysts for oxygen evolution reaction (OER), however, they are still Ni- or Co-rich although Fe is tens to hundreds of times cheaper than Ni or Co and the second most earth-abundant metal behind Al. In this paper, we tried to develop an efficient Fe-rich OER electrocatalyst by coating a thin layer of Ni(oxy)hydroxide on a porous Fe (oxy)hydroxide electrodeposited on a substrate of carbon paper (CP). Due to the Ni/Fe contact with a large area on the surface, the clear interplay between Fe and Ni ions is observed through the X-ray photoelectron spectra, which demonstrates the partial charge transfer between them. When comparing with those of pure Fe (oxy)hydroxide/CP, pure Ni (oxy)hydroxide/CP, and traditional NiFe (oxy)hydroxide/CP, the as-prepared product of Ni (oxy)hydroxide/Fe (oxy)hydroxide/CP exhibits the best OER performance with a low overpotential of 223 mV at 10 mA cm –2, a small Tafel slope of 32.5 mV dec –2, and a super stability of above 100 h continuous testing under 50 mA cm –2 . Such double-layer hierarchical architecture not only provides an enlarged surface area with sufficient active sites for the redox reactions but also possesses improved intrinsic OER activity due to the interaction between the metal ions. Moreover, the Fe-rich (oxy)hydroxide also processes good catalytic activity for hydrogen evolution reaction after dynamically self-optimizing, making it an efficient bifunctional catalyst with 1.53 V to drive 10 mA cm –2 under basic solution in two-electrode measurements.