Decoding pH-dependent electrocatalysis through electric field models and microkinetic volcanoes

The impact of electrolyte pH on electrocatalytic reactions has long been recognized, yet its underlying mechanisms remain a subject of active debate. This perspective explores how pH influences reaction activity and mechanisms at the computationally affordable atomic scale. Traditional interpretations attribute pH effects to changes described by the computational hydrogen electrode (CHE) model and the Nernst equation. However, recent advances have uncovered more complex interfacial interactions involving electric fields, including dipole moments (μ), polarizability (α), and the potential of zero charge (PZC). We summarize recent progress on how pH influences surface states and reaction mechanisms across various typical electrocatalytic processes, including the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂RR), and nitrate reduction reaction (NO₃RR). By integrating experimental observations with theoretical models and computational simulations, researchers are beginning to unravel the multifaceted role of pH in electrocatalysis. Furthermore, several key theoretical frameworks have been developed to date to predict reaction activity and elucidate underlying mechanisms, such as the reversible hydrogen electrode (RHE)-referenced Pourbaix diagram and the pH-dependent microkinetic volcano model. Understanding these pH-driven effects is essential for designing catalysts that operate efficiently across diverse electrochemical environments, ultimately contributing to the development of sustainable energy technologies.