In Situ Raman Study of Amorphous and Crystalline Ni-Co Alloys for the Alkaline Oxygen Evolution Reaction

Amorphous Ni79.2-xCoxNb12.5Y8.3 (x = 0, 5 at.%) alloys were synthesized using cryogenic mechanical alloying and evaluated as catalyst for the oxygen evolution reaction (OER) in alkaline media using cyclic voltammetry and Tafel measurements. Electrochemical testing showed that the amorphous alloys possessed lower Tafel values for the OER compared to crystalline Ni and Ni95Co5. Anodic cycling of amorphous Ni74.2Co5Nb12.5Y8.3 resulted in a lower onset potential for the OER and decreased Tafel values while no changes were observed for amorphous Ni79.2Nb12.5Y8.3 and crystalline Ni95Co5. Pairing of in situ confocal Raman spectroscopy with anodic cycling showed that the amorphous Ni74.2Co5Nb12.5Y8.3 alloy formed reversible hydrous Co surface species instead of irreversible CoO2 typically seen on crystalline NiCo alloys in KOH. The formation of hydrous Co surface species upon cycling was also accompanied by increased formation of β-NiOOH leading to enhanced catalytic performance of amorphous Ni74.2Co5Nb12.5Y8.3 alloy over the amorphous Ni79.2Nb12.5Y8.3 and the crystalline counterparts.