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, dendritic growth of the anode as well as expensive cathode electrocatalysts with limited stability and durability in alkaline medium during prolonged operation. Thus, exploratory researches are essential to replace these platinum-group noble metal catalysts with other stable transition metal oxide. In this work, we demonstrate a 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 electrocatalytic activity for ORR and OER compared to the undoped material, by modulating the electronic structure and elevating the metal valence states. The optimized composition, Fe₀.₀₃CuCo₂S₄ exhibits outstanding bifunctional activity with an oxygen reduction reaction (ORR) onset potential of 0.89 V vs RHE, a half-wave potential (E₁/₂) 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 Fe₀.₀₃CCS as the air cathode delivers a peak power density of 82 mW cm⁻² and a specific capacity of 780 mAh gZn⁻¹. The battery demonstrates excellent cycling stability, maintaining performance over 200 cycles (75 hours) at 5 mA cm⁻² with 20-minute charge–discharge intervals. Under depth of discharge study for extended charge–discharge durations (up to 6-hour 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.