Critical factors to inhibit water-splitting side reaction in carbon-based electrode materials for zinc metal anodes

Zinc metal anodes (ZMA) have high theoretical capacities (820 mAh g⁻¹ and 5855 mAh cm⁻³) and redox potential (−0.76 V vs. standard hydrogen electrode), similar to the electrochemical voltage window of the hydrogen evolution reaction (HER) in a mild acidic electrolyte system, facilitating aqueous zinc batteries competitive in next-generation energy storage devices. However, the HER and byproduct formation effectuated by water-splitting deteriorate the electrochemical performance of ZMA, limiting their application. In this study, a key factor in promoting the HER in carbon-based electrode materials (CEMs), which can provide a larger active surface area and guide uniform zinc metal deposition, was investigated using a series of three-dimensional structured templating carbon electrodes (3D-TCEs) with different local graphitic orderings, pore structures, and surface properties. The ultramicropores of CEMs are the determining critical factors in initiating HER and clogging active surfaces by Zn(OH)₂ byproduct formation, through a systematic comparative study based on the 3D-TCE series samples. When the 3D-TCEs had a proper graphitic structure with few ultramicropores, they showed highly stable cycling performances over 2000 cycles with average Coulombic efficiencies of ≥99%. These results suggest that a well-designed CEM can lead to high-performance ZMA in aqueous zinc batteries.