Universal Approach to Direct Spatiotemporal Dynamic in-situ Optical Visualization of On-Catalyst Water Splitting Electrochemical Processes

Abstract

Electrochemical reactions are the unrivaled backbone of next generation energy storage, energy conversion and healthcare devices. However, the in-situ real-time visualization of electrochemical reactions, which can shed light on various critical unknown insights on the electrochemical processes, still remains the bottleneck for fully exploiting their intrinsic potential. In this work, for the first time, a universal approach to the direct spatiotemporal-dynamic in-situ optical visualization of pH based as well as specific byproduct based electrochemical reactions is performed. As a highly relevant and impactful example, the in-operando optical visualization of on-catalyst water splitting processes is performed under neutral water/seawater conditions. pH based visualization are performed using a water-soluble fluorescent pH probe HPTS (8-hydroxypyrene-1,3,6-trisulfonicacid), known for its exceptional optical capability of detecting even the tiniest environment pH changes, thus allowing the unprecedented “spatiotemporal” real-time visualization at the cathode and anode. The successful experimental investigations embarked here, allowed us to reach several yet unveiled deeper insights into the spatiotemporal water splitting processes and their practical modulation for potentially improving the applicability and efficiency of water splitting devices. As a result, we were able to unprecedentedly reveal that at a critical cathode-to-anode distance, a continuous bulk-electrolyte “self-neutralization” phenomenon can be achieved during the water splitting process, leading to the practical realization of enhanced additive-free neutral water splitting. Furthermore, we experimentally unveiled that at increasing electrolyte flow rates, a swift and severe inhibition of the concomitantly forming acidic and basic ‘fronts’, developed at anode and cathode compartments is observed, thus acting as a continuous on-catalysts “buffering” mechanism that allows for a remarkably enhanced water splitting process. Furthermore, to demonstrate the universal applicability of this elegant strategy which is not limited to pH changes, the technique was extended to visualization of specific electrochemical process by the use of reaction product-specific fluorophore. For the purpose, N-(4-butanoic acid) dansylsulfonamide (BADS) fluorophore was successfully explored to in-situ visualize the formation of hypochlorite/ chlorine at the anode during electrolysis of sea water. Thus, a unique experimental tool that allow real-time spatiotemporal visualization and simultaneous mechanistic investigation of complex electrochemical processes in developed that can be universally extended to various fields of research.