A trifunctional electrocatalyst of multi-component metal sulfide for methanol-assisted zinc-air batteries with enhanced energy efficiency

To address the low energy efficiency of zinc-air batteries (ZABs), this work proposes a novel methanol-assisted ZAB (M-ZAB). The battery employs the multi-component metal sulfide as the cathode, where the cathodic charging reaction of oxygen evolution reaction (OER) is replaced by the methanol oxidation reaction (MOR). The multi-component metal sulfide is synthesized by converting the medium-entropy alloy of NF-CoFeNiCuAl into the corresponding sulfide (NF-CoFeNiCuAl-S) through a simple hydrothermal method. NF-CoFeNiCuAl-S retains the high OER/MOR activity of NF-CoFeNiCuAl while exhibiting significantly improved oxygen reduction reaction (ORR) catalytic performance. NF-CoFeNiCuAl-S demonstrates the OER and MOR potentials of 1.49   V and 1.372   V at 100   mA   cm⁻², respectively, and an ORR potential of 0.66   V at 10   mA   cm⁻². Aqueous and flexible ZABs based on NF-CoFeNiCuAl-S achieve the peak power densities of 210.3 and 180.6   mW   cm⁻², respectively, along with excellent cycling stability. Compared to traditional ZABs without methanol in the electrolyte, M-ZAB shows a reduction in the charge-discharge voltage gap by 471   mV (@100   mA   cm -2 ) and an improvement in energy efficiency by 14%.