Polyoxometalate-Decorated MWCNTs as High-Performance Electrocatalysts for Oxygen Reactions

The ongoing and significant growth in global energy demand makes it crucial to develop new, cost-effective, high-quality materials on a large scale to serve as effective electrocatalysts (ECs) in clean energy storage and conversion devices. Among these, fuel cells (FCs) and water splitting devices have emerged as promising candidates. However, their application has been constrained by the reliance on noble metal-based electrocatalysts. In oxygen reactions, specifically O₂ reduction (ORR) and evolution (OER), conventional electrocatalysts are based on noble metals and their oxides, including Pt, Pd, RuO₂, and IrO₂. However, in addition to being scarce and expensive, these materials have poor stability under operating conditions. For this reason, the practical application of these technologies requires the development of efficient electrocatalysis for these processes, which has prompted a recent search for new, cost-effective, and highly active electrocatalysts. Polyoxometalates (POMs) have been proposed as a potential alternative to traditional electrocatalysts, offering a cost-effective solution with high efficiency.

This work involves the preparation of two hybrids based on Dawson Sandwich-type polyoxometalates and multi-walled carbon nanotubes doped with melamine (CoNi3@MWCNT_N8 and NiCo3@MWCNT_N8). The two electrocatalysts exhibited excellent electrocatalytic performance in OER in an alkaline medium (0.1 M KOH), with maximum current densities of 86.70 and 68.32 mA cm 2 and overpotential values of 0.45 and 0.49 V vs. RHE. Furthermore, the two electrocatalysts showed favorable performance in ORR in the same electrolyte, with diffusion limiting current densities of -2.98 and -2.33 mA cm-2 and potential onset values of 0.82 and 0.78 V vs. RHE.