Reunderstanding aqueous Zn electrochemistry from interfacial specific adsorption of solvation structures

H Yang and D Chen and RZ Zhao and GY Li and H Xu and L Li and X Liu and GS Li and DL Chao and W Han, ENERGY & ENVIRONMENTAL SCIENCE, 16, 2910-2923 (2023).

DOI: 10.1039/d3ee00658a

Although sulfate- and sulfonate-based electrolytes have been widely used in the study of aqueous zinc-ion batteries (AZIBs), discrepancies in the faradaic reaction kinetics of cation interfacial chemistry including in Mn2+ redox reactions and Zn deposition are observed in these two systems, the mechanism of which is still unclear. Herein, through focusing on the electrolyte solvation structure, we constructed a specific adsorption model involving the coexistence of anions, cations, and water molecules at the electrode/electrolyte interface. Distinguished from the traditional investigation of isolated adsorbed particles, we demonstrate that the specific adsorption model enables a rational explanation of the reaction difference of cations with different solvation structures at the electrode/electrolyte interfaces (EEIs). Specifically, owing to the more intense adsorption of active solvated Mn2+ near the inner Helmholtz plane, the deposition reaction of Mn species is enhanced in a sulfate-based electrolyte, resulting in a stronger capacity increase and fluctuation in comparison with sulfonate electrolytes. Similarly, the more rapid Zn2+ deposition kinetics in the sulfate-based electrolyte can be attributed to its strong adsorption behavior at the EEI. Furthermore, as validation of the as-proposed model, a sulfate/sulfonate hybrid electrolyte system is proposed, in which the optimized adsorption behavior at the EEI gives it synergistic improvement both in terms of capacity and cycling stability for aqueous Zn-Mn cells. This work provides rationale for understanding the interfacial electrochemistry in various aqueous electrolyte systems from the view of the adsorption behavior of the solvation structure.

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