Valence-variable thiospinels for ampere-scale water electrolysis

Abstract

Oxygen electrochemistry plays a key role in industrial hydrogen fuel production from water electrolysis, but the slow kinetics of the anodic oxygen evolution reaction (OER) at large current density restricts the commercialization of such energy devices. Here, we design a new class of valence-variable metal-modified CuCo₂S₄ thiospinels, termed as v-M–CuCo₂S₄/NF (v-M = Mn, V, Cr), to achieve large-current-density OER performance. The introduction of valence-variable metals (v-M) can promote the generation of a special oxyhydroxide-like active phase with a contractive interatomic Co–Co distance, which breaks the limit of the inherent linear scaling relationship and causes the OER on v-M–CuCo₂S₄/NF to follow a more efficient oxide path mechanism. Therefore, v-M–CuCo₂S₄/NF, taking Mn–CuCo₂S₄/NF as a representative, delivers low overpotentials of 255 and 378 mV to achieve large current densities of 500 and 1500 mA cm⁻² in alkaline electrolytes. The optimal catalyst shows a large mass activity of 3000 A g_metal⁻¹ and a high turnover frequency of 16 500 h⁻¹ at a low overpotential of 378 mV (1500 mA cm⁻²), tens of times larger than commercial RuO₂/NF. The design principle provides some hints for optimizing abundant spinel materials as large current density OER catalysts.