Brønsted Acid Site-Mediated Proton Injection and Redistribution Regulate Phosphoric Acid Electrochemical Interfaces

Molecular control of the proton environment in phosphoric acid (PA) based electrochemical interfaces is critical for efficient proton transport and oxygen reduction reaction (ORR), yet effective strategies for actively regulating this environment remain limited. Here, we show that Brønsted acid sites (BASs) in HY zeolite function as solid-state proton regulating centers that directly participate in and reorganize the interfacial PA hydrogen bond network. By combining ab initio molecular dynamics (AIMD) simulations, free energy calculations, variable-temperature diffuse reflectance infrared Fourier transform spectroscopy (VT-DRIFTS), and electrochemical measurements, we reveal a BAS-mediated proton injection and redistribution mechanism. The framework BAS proton transfers to an adjacent PA molecule, generating an excess proton defect that dynamically redistributes among neighboring PA molecules through hydrogen-bond-assisted proton hopping. The potential of mean force (PMF) along δ01 reveals a favorable free energy change for BAS to PA1 proton transfer (–0.122 eV), while density functional theory (DFT) calculations show lower electronic energies for representative PA-associated configurations, with PA2 exhibiting the lowest energy. AIMD simulations further demonstrate preferential excess-proton accommodation and dynamic redistribution within the PA network. VT-DRIFTS measurements reveal PA-induced changes in the temperature-dependent hydroxyl response of HY, while calculated harmonic infrared spectra of representative proton configurations provide molecular-level insight into interfacial proton interactions and hydrogen bond reorganization. Electrochemical measurements further show that HY incorporation reduces proton transport and ORR charge transfer resistances while increasing Pt electrochemical accessibility. These findings identify BAS-mediated proton injection and redistribution as a promising molecular strategy for regulating PA-based electrochemical interfaces.