Unveiling Electrode–Electrolyte Interfacial Synergy in CTAB‐Modulated Pd Single‐Atom Catalysts for Efficient H 2 O 2 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/CeO 2 ‐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 (H 2 O→*OOH→H 2 O 2 ). 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 H 2 O 2 decomposition. As a result, the Pd/CeO 2 ‐MXene+CTAB system achieves a low electron transfer number of 2.02 and a high H 2 O 2 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.