Selection criteria for current collectors for highly efficient anode-free Zn batteries

Considerable efforts have been invested in replacing standard metallic Zn anodes with diverse conductive substrates in pursuit of higher energy density, durability, and cost-effectiveness in aqueous Zn-based batteries. Despite substantial progress in the development of anode-free Zn systems, there is still a major gap in our fundamental knowledge of how the physicochemical parameters of the substrate (current collector) impact the efficiency of the reversible Zn electrodeposition process. Of particular interest are the interactions between the Zn cations, the accompanied water molecules, and the foreign substrates. As both Zn deposition and hydrogen evolution processes occur at similar potential ranges, the performance of the anode-free cells will be dictated by the catalytic nature of the electrified substrates and the chemistry of their passivation. In this study, we conduct thorough examinations of four prominent current collectors: copper, nickel, titanium, and graphite foils. Using a systematic approach that includes electrochemical investigations supplemented by refined X-ray diffraction analysis and in situ techniques such as online electrochemical mass spectrometry (OEMS) and electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), we uncover the critical role of these current collectors in the reversible Zn electroplating process. According to our findings, graphitic foils provide significantly more efficient electrodeposition of Zn in mildly acidic electrolyte solutions. This work provides comprehensive investigations of reversible zinc metal electrodeposition on various metallic and nonmetallic substrates and describes the main factors influencing the coulombic efficiency of the process.