Unveiling Electrode-Electrolyte Interfacial Synergy in CTAB-Modulated Pd Single-Atom Catalysts for Efficient H2O2 Electrosynthesis.

The design of high-activity single-atom catalysts (SACs) toward two-electron oxygen reduction is dominated by regulating the adsorption energy of *OOH intermediates at active sites, whereas the critical factor of proton activity at the catalyst-electrolyte interface has received insufficient attention. Herein, an electrode-electrolyte synergistic strategy was employed to modulate the electronic structure of Pd single-atom sites via the construction of a Pd/CeO2-MXene heterostructure and hydrogen bond strength using cetyltrimethylammonium bromide (CTAB) additive. X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations revealed that the real active sites are Pd single-atom sites anchored via Pd-O-Ce bonding, which significantly reduces the free energies of the key reaction steps (H2O→*OOH→H2O2). In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) further verified that CTAB adsorbed at the reaction interface can enhance the hydrogen bond strength of interfacial water molecules, reduce the supply of interfacial *H species, and thereby effectively suppress H2O2 decomposition. As a result, the Pd/CeO2-MXene+CTAB system achieves a low electron transfer number of 2.02 and a high H2O2 selectivity of 98.8% at 0.5 V. This study provides a novel insight into the rational design of proton-coupled electrocatalysts through the integration of interfacial hydrogen bond engineering and single-atom catalysts.