A cobalt-yttria heterointerface on nitrogen- and sulphur-doped carbon as a durable electrocatalyst for metal–air batteries and overall water electrolysis

Abstract

The development of an efficient, cost-effective trifunctional electrocatalyst is critical for advancing next-generation energy conversion and storage technologies. A trifunctional electrocatalyst comprising a heterointerface of cobalt–yttria nanoparticles embedded in nitrogen- and sulphur-codoped reduced graphene oxide was synthesised via a hydrothermal, mechanochemical, and pyrolytic approach. Electrochemical studies demonstrate that the Co–Y₂O₃ heterointerface in heteroatom-doped carbon exhibits outstanding oxygen reduction reaction (ORR) activity with an onset potential of 0.97 V and a half-wave potential of 0.85 V in alkaline media, rivalling commercial Pt/C. Additionally, it shows superior performance in the oxygen evolution and hydrogen evolution reactions (E₁₀ = 1.54 V for the OER and η₁₀ = 228 mV for the HER). The exceptional bifunctional activity (ΔE = 0.69 V) arises from the synergistic effects of the Y₂O₃ and Co species in the heterojunctions, as well as N & S heteroatom doping, as evidenced by comparative studies with control samples. The practical applicability was validated in both liquid- and solid-state rechargeable zinc-air batteries, where it delivered higher energy densities (782 mW h g_Zn⁻¹) and ultrahigh stability (>1400 hours), outperforming the Pt/C + RuO₂ benchmark combination. The post-mortem analysis confirms the strong stabilisation of cobalt nanoparticles by yttria and the retention of their heterostructures. The results suggest that it is a highly promising non-noble metal-based catalyst for sustainable electrochemical energy devices.