Cobalt-nickel sandwich-type Dawson polyoxometalates as bifunctional OER/ORR electrocatalysts: the influence of metal arrangement.

The rising global need for sustainable energy has intensified research into environmentally friendly energy conversion technologies, such as fuel cells and electrochemical water splitting devices. The efficiency of these technologies is strongly influenced by the activity of electrocatalysts that enable the oxygen reduction (ORR) and evolution (OER) reactions. Noble metal-based electrocatalysts, including Pt, Pd, RuO2 and IrO2, are widely regarded as benchmark materials for these reactions due to their excellent electrocatalytic activity; nevertheless, their high cost, scarcity and limited long-term stability have prompted the development of alternatives. Polyoxometalates (POMs) have attracted considerable interest as a versatile class of materials, owing to their adjustable structures, redox properties and potential to serve as efficient and economically viable catalysts. In this research, we investigate two sandwich-type Dawson POM clusters containing cobalt and nickel ([CoNi3(As2W15O56)2]16- and [NiCo3(As2W15O56)2]16-) but with different spatial arrangements. The prepared electrocatalysts exhibited notable OER activity in alkaline media, achieving maximum current densities of 86.70 and 68.32 mA cm-2 with corresponding overpotential values of 0.45 and 0.49 V vs. RHE, respectively. The electrocatalysts also demonstrated promising activity towards the ORR, with diffusion-limiting current densities of -2.98 and -2.33 mA cm-2 and onset potentials of 0.82 and 0.78 V vs. RHE, respectively. This paper provides evidence suggestive of an influence of the metal centre position within the POM framework on the ORR/OER electrochemical performance and reinforces the potential of these hybrid materials as cost-effective and sustainable bifunctional electrocatalysts for next-generation energy devices.