Realizing the Kinetic Origin of Hydrogen Evolution for Aqueous Zinc Metal Batteries

The commercialization of zinc metal batteries (ZMBs) for large-scale energy storage is hindered by challenges such as dendrite formation, the hydrogen evolution reaction (HER), and passivation/corrosion, which lead to poor stability of zinc metal anodes. HER is a primary contributor to this instability, and despite efforts to enhance ZMB cyclability, a significant knowledge gap remains regarding the origin of HER in these systems. Prior works, based primarily on theoretical calculations with minimal experimental support, suggest that HER originates from Zn²⁺-solvated water. For the first time, by employing scanning electrochemical microscopy (SECM), and electrochemical mass spectrometry (ECMS), in real-time the inherently intertwined nature of Zn electrodeposition and H₂ liberation is revealed, both exhibiting the same onset potential in voltammetry. The findings show that water molecules surrounding Zn²⁺ ions undergo reduction simultaneously during Zn²⁺ deposition. Additionally, ECMS conducted under chronopotentiometric/galvanostatic conditions at battery-relevant current densities elucidates why elevated electrolyte concentrations enhance the prolonged cyclability of ZMBs. Understanding the origin of HER opens avenues for developing high-performance, reliable aqueous ZMBs, addressing key challenges in their commercialization and advancing their technological capabilities.