Specific adsorption induced electric double layer on gallium-based liquid metal electrode

Abstract

Gallium-based liquid metal (GBLM) has been identified as a promising electrode material in flexible aqueous batteries, which are widely employed in wearable electronic devices. The electrode–electrolyte interface has significant effects on battery performance, but its molecular-level structure remains elusive. This work, for the first time, attempts to unravel electric double layer (EDL) at the interface between GBLM electrode and aqueous electrolyte through density functional theory (DFT) calculation and ab initio molecular dynamic (AIMD) simulation. It is found that such EDL structure origins from the specific adsorption of gallates (e.g. Ga(OH)4− and H2GaO3−) on GBLM (e.g. eutectic gallium-indium alloy), and these gallates build up the inner Helmholtz layer (IHL), attracting a diffusion layer with opposite charges. Further, the adsorption properties of gallates and the capacitive behavior of EDL are analyzed, in which the charging of GBLM electrode is systematically considered. The results manifest that the excess negative charge on GBLM surface interferes with the adsorbed gallates and amplifies the interface potential change across EDL. The proposed EDL structure contributes to deep understandings of the electrochemical processes occurring at electrode–electrolyte interface in GBLM aqueous batteries.