Fe-doped CuCo2S4 thiospinel as a high-performance oxygen electrocatalyst for rechargeable all-solid-state zinc–air batteries

Abstract

The commercial viability of rechargeable zinc–air batteries (ZABs) is hindered by their poor round-trip efficiency, the dendritic growth of the anode and expensive cathode electrocatalysts with limited stability and durability in alkaline media during prolonged operation. Thus, exploratory research studies are essential to replace these platinum-group noble metal catalysts with other stable transition metal oxides. In this work, we demonstrate the facile one-step hydrothermal synthesis of Fe-doped CuCo₂S₄ thiospinels. Both experimental and theoretical analyses confirm that Fe incorporation into the CuCo₂S₄ lattice markedly enhances its electrocatalytic activity for the ORR and OER compared with the undoped material by modulating the electronic structure and elevating the metal valence states. The optimized composition, Fe_0.03CuCo₂S₄, exhibits outstanding bifunctional activity with an oxygen reduction reaction (ORR) onset potential of 0.89 V vs. RHE, a half-wave potential (E_1/2) of 0.80 V vs. RHE, and an oxygen evolution reaction (OER) overpotential of 330 mV at 10 mA cm⁻², resulting in a low bifunctional voltage gap (ΔE) of 0.76 V. Furthermore, a prototype ZAB assembled using Fe_0.03CCS as the air cathode delivers a peak power density of 82 mW cm⁻² and a specific capacity of 803.4 mA h g_Zn⁻¹. The battery demonstrates excellent cycling stability, maintaining performance over 200 cycles (75 hours) at 5 mA cm⁻² with 20 minutes charge–discharge intervals. During the depth of discharge study for extended charge–discharge durations (up to 6 hours cycles), the ZAB retains impressive stability for over 50 hours. This study highlights a promising strategy for designing efficient bifunctional electrocatalysts, paving the way for practical applications in next-generation zinc–air batteries.