Stabilizing Zn metal anodes by 4-hydroxybenzaldehyde as the H* scavenger

The conventional wisdom of Zn metal anodes suggests avoiding the hydrogen evolution reactions (HER) in aqueous electrolytes since it leads to H2 production, irregular by-product precipitation, and then the quick failure of batteries. However, the HER process is thermodynamically inevitable during cycling, especially when water is the main solvent. Herein, we propose a novel H* scavenger strategy to properly utilize the HER process instead of blocking it. By coupling experimental and theoretical analysis, we reveal the positive role of 4-hydroxybenzaldehyde (HB) additives, which consume the H* produced by the Volmer step and thus suppress the Heyrovsky or Tafel step of HER. The former produces a uniform organic/inorganic solid electrolyte interphase (SEI), while the latter eliminates H2 gas production. As a consequence, HB additives enable a stable cycle life of 120 h at 30 mA cm-2 with a depth of discharge (DOD) of 51.3 % in Zn|Zn symmetric cells and an average Coulombic efficiency of 99.8 % at 2 mA cm-2 for 2460 cycles in Zn|Cu half cells. The versatility of this H* scavenger strategy is also demonstrated by extending it to other zinc salts and electrolyte additives.