Understanding H₂ evolution electrochemistry to minimize solvated water impact on zinc anode performance

Abstract

H2 evolution is the reason for poor reversibility and limited cycle stability with Zn metal anodes, and impedes practical application in aqueous zinc ion batteries (AZIB). Here we demonstrate for the first time, using combined gas chromatography experiment and computation, that H2 evolution primarily originates from solvated water, rather than free water without interaction with Zn2+ . We evidence, using linear sweep voltammetry (LSV) in salt electrolytes that H2 evolution occurs at a more negative potential than zinc reduction because of high overpotential against H2 evolution on Zn metal. We test our hypothesis and confirm, using glycine additive to reduce solvated water, that H2 evolution and "parasitic" side reactions are suppressed on the Zn anode. We evidence that this electrolyte additive suppresses H2 evolution, reduces corrosion and gives a uniform Zn deposition in Zn|Zn and Zn|Cu cells when compared with bare ZnSO4 electrolyte. We demonstrate Zn|PANI (highly conductive polyaniline) full cells exhibit boosted electrochemical performance in 1 M ZnSO4 -3 M glycine electrolyte and, a high reversible capacity of 100 mAh g-1 in a practical Zn|PANI pouch cell. We conclude that this new understanding of electrochemistry of H2 evolution can be used for design of relatively low-cost and safe AZIB for practical large-scale energy storage. Findings will be of immediate benefit in electrolyte design for high performance rechargeable batteries and therefore of wide interest to researchers and manufacturers. This article is protected by copyright. All rights reserved.