Dimeric Co(II) Complexes as Excellent Electrocatalysts Toward Efficient Hydrogen and Oxygen Evolution Reactions and Electrochemical Water Splitting

In this study, two Co(II) dimeric complexes have been reported. Interestingly, the synthesized complexes exhibit significant electrochemical water splitting activity for hydrogen and oxygen evolution reactions (OER) in alkaline medium. However, chlorobenzoate-based complex is superior to bromobenzoate-based complex in regard to bifunctional activity.

Abstract

Production of sustainable green hydrogen is a topic of global interest. Electrochemical water splitting is considered as a highly promising method for generating hydrogen from water using renewable electrical energy without causing environmental pollution. Now, electrocatalysts with decent performance are used for the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in alkaline water electrolysis. In this study, we report the synthesis of two such Co(II)-based dimeric complexes [Co₂(4-Clbz)₂(4-nvp)₂] (1); and [Co₂(4-Brbz)₂(4-nvp)₂] (2) {H4-Clbza = 4-chlorobenzoic acid; H4-Brbza = 4-bromobenzoic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine} acting as efficient bifunctional catalysts for water splitting. The water oxidation activity of complexes 1 and 2 exhibit Tafel slope equivalent to 35 and 44 mV dec⁻¹, respectively, for HER whereas the Tafel slope is equivalent to 183 and 188 mV dec⁻¹ respectively for complexes 1 and 2 for OER in alkaline medium. Hence, from the above findings it can be concluded that both the complexes show magnificent bifunctional activity, making them highly promising catalysts for efficient overall water splitting. However, complex 1 exhibits better catalytic activity as compared to 2, requiring a lower cell voltage of 1.60 V to achieve a current density of 10 mA cm⁻².

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