Insight into the Effects of Current Collectors and In Situ Ni Leaching in High‐Voltage Aqueous Supercapacitors

Abstract The limited 1.23 V of electrochemical stable window hinders the energy output of aqueous supercapacitors. Good stability of current collectors toward high operation voltage closely determines whether the voltage window of aqueous supercapacitors can be further improved. Here, the electrochemical stability of representative current collectors in aqueous electrolytes in terms of intrinsic response toward oxygen/hydrogen evolution side reaction and capacitance contribution are decoupled detailedly. The lowest response to the occurrence of electrolyte decomposition and negligible capacitance contribution are presented for Ti mesh, along with a high & stable electrochemical window up to 3.61 V in neutral electrolyte and accurate evaluation of the electrochemical performance of electrode. The experimental verification in 21 m LiTFSI confirms that the Ti mesh can indeed work at a record high voltage up to 2.6 V. Operando Raman, ex situ atomic force microscopy, X‐ray photoelectron spectroscopy, and self‐built electrolyte decoupling system further reveal the process of Ni leaching and generation of Ni(OH)₂ new species in promising neutral electrolyte for commonly used Ni foam current collector. This work supplies theoretical support for the choice of current collectors in high‐voltage aqueous supercapacitors and the design of catalysts, and intrinsic activity decoupling in the electrocatalytic conversion of small molecules related to aqueous electrolytes.