Proton Conduction in Oxides Via Electrochemical Proton Injection and Proton–Electron Spillover

Proton conduction in oxides (PCOs) is traditionally explained by hydration-based equilibrium models, which assume sufficient proton uptake from moisture or hydrogen. However, this static hydration-based framework fails under real operating conditions of proton ceramic fuel cells, where proton injection and field-driven dynamic processes dominate. This disconnection has led to an underestimation of proton concentration and mobility, also limiting the development of advanced PCOs. Here, we establish a distinct fundamental and experimental framework based on electrochemical proton injection (EPI) and proton–electron spillover, which are dynamic processes enabling an enhanced proton transport both in bulk and across grain boundary domains. Supported by in situ electrochemical impedance spectroscopy and the distribution of relaxation time, we demonstrate that EPI surpasses the conductivity ceiling imposed by the hydration-limited models. This urgent correction restores the true basis of proton transport and suggests a transformative strategy for designing next-generation oxide electrolytes for electrochemical energy devices.