Catalytic activity of graphene–cobalt hydroxide composite for oxygen reduction reaction in alkaline media

Abstract

The electrocatalysis of graphene–cobalt hydroxide (Co(OH) 2) composite towards oxygen reduction reaction (ORR) in 0.1 M KOH is studied with Co(OH) 2/graphene-modified glassy carbon (GC) electrode using cyclic and rotating ring-disk electrode voltammetry. The electrode is prepared by casting of graphene suspension on GC electrode and subsequent electrodeposition of Co(OH) 2 from Co(NO 3) 2 solution. A characteristic interlaced nanowalls morphology is observed for Co(OH) 2 with scanning electron microscopy. Raman spectra demonstrate the microstructure of graphene changes during electrochemical treatment in nitrate solutions, which has a great impact on its catalysis towards ORR. At GC electrode, two reduction processes both attributed to 2-electron reduction are recorded for ORR. The presence of Co(OH) 2 on GC electrode results in larger peak current without obvious potential shift due to its good catalytic activity towards the disproportionation of intermediates. Graphene not only increases the peak current and shifts the peak potential in the positive direction, but also leads to further reduction of HO 2 − at the second step. After electrochemical treatment in nitrate solutions, graphene is activated to catalyze the disproportionation of HO 2 − effectively, and its cooperation with Co(OH) 2 enables reduction of O 2 to OH − at lower overpotential. Graphene–Co(OH) 2 composite is a potential electrode material for air cathodes in alkaline electrolyte electrochemical systems.