The Electrochemical Interface As a Reactive Environment to Re-Synthesize Electrode Surface Chemistry Using the Dissolution-Redeposition Dynamics

Abstract

The electrode-electrolyte interface governs the efficiency and life time of almost all electrochemical reactions. Essentially, this interface, as a geometrically confined environment, allows many interfacial reactions occurring and provides a versatile toolbox of tailoring electrode surface chemistry under operating conditions. Here, through synchrotron spectroscopic, microscopic, and imaging characterizations, using the electrochromic tungsten trioxide (WO3) in an acidic electrolyte as the research platform, we reveal that the performance degradation is related to electrode material morphology evolution, phase transformation, and charge heterogeneity. We experimentally demonstrate that WO3 dissolution and redeposition across the electrochemical interface trigger all these evolutions. The redeposition process provokes the in situ crystal growth, inducing the evolution from the semicrystalline WO3 to the single-crystalline, nanoflake-shaped, proton-trapped tungsten trioxide di-hydrate (H x WO3·2H2O). Importantly, as a ubiquitous phenomenon, transition metal dissolution will form the diffusion layer at the interface. We have established a novel experimental design to probe and understand how the dissolved transition metal species evolve in the diffusion layer. The thickness of the diffusion layer is up to tens of micrometers, and the local electronic structure of dissolved species varies with the distance from the electrode surface. Furthermore, this dynamic dissolution and redeposition feature can be manipulated to regulate the chemical composition and crystal structure of the electrode surface as well as the overall electrochemical performance. Foreign cations (e.g., Ti4+), either added as electrolyte additives or dissolved from surface coatings, can rapidly participate in the electrode dissolution-redeposition process and facilitate the establishment of the dissolution-redeposition equilibrium, thereby alleviating W net dissolution, modulating the electrode morphology, and improving the Coulombic efficiency and cycling stability during long-term electrochemical reactions. Therefore, our systematic study demonstrates that it is feasible to exploit the intertwined dissolution-redeposition kinetics between oxide surface coatings and electrodes in aqueous electrolytes to extend control over electrochemical interfacial reactions. Electrode surface chemistry can be re-synthesized in terms of regulating the dynamic structural evolution of electrode surface and the correlatively developing speciation at the interface, which highlights the significance of more fundamental investigations at the electrode-electrolyte interfaces.