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

Abstract

Amorphous Ni 79.2-x Co x Nb 12.5 Y 8.3 (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 Ni 95 Co 5. Anodic cycling of amorphous Ni 74.2 Co 5 Nb 12.5 Y 8.3 resulted in a lower onset potential for the OER and decreased Tafel values while no changes were observed for amorphous Ni 79.2 Nb 12.5 Y 8.3 and crystalline Ni 95 Co 5. Pairing of in situ confocal Raman spectroscopy with anodic cycling showed that the amorphous Ni 74.2 Co 5 Nb 12.5 Y 8.3 alloy formed reversible hydrous Co surface species instead of irreversible CoO 2 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 Ni 74.2 Co 5 Nb 12.5 Y 8.3 alloy over the amorphous Ni 79.2 Nb 12.5 Y 8.3 and the crystalline counterparts.