Transient Potential Amplification in Dynamically Operated Electrochemical Systems

Electrochemical technologies underpin hundreds of billions of dollars in industrial value and are increasingly operated under dynamic voltage switching in systems ranging from flow batteries to continuous electrolyzers. Yet the true electrode energetics during such operation remain largely unresolved because absolute potentials are poorly understood in two-electrode devices. Here we resolve electrode potentials operando using a reference-assisted five-channel method and uncover an alternating-current-driven potential excursion (APEX), a transient amplification of electrode potential that can exceed the steady-state value by up to threefold and reach 4.2 V versus the standard hydrogen electrode. We show that APEX arises from spatiotemporal coupling between voltage switching, electrolyte flow and electric-double-layer dynamics, which transiently accesses otherwise inaccessible electrochemical reaction regimes. In a flow-through electrochemical reactor, this phenomenon enables rapid and sustained mineralization of diverse organic chemicals under mild operating voltages with long-term mineralization rate stability (>80%) exceeding 500 h. Our findings reveal a hidden energetic dimension in dynamically operated electrochemical systems and provide a framework for interpreting and designing voltage-switching electrochemical technologies.