Engineering the Interfacial Proton Microenvironment via Amorphous‐Crystalline Heterostructures for pH‐Universal Hydrogen Electrocatalysis

The pH‐universality of hydrogen evolution reaction (HER) electrocatalysts enables their cost‐effective and scalable application. Proton behavior regulation enhances HER activity under specific pH conditions, yet achieving pH‐universal performance remains a significant challenge. Here, we propose interfacial proton engineering to achieve pH‐universal HER within the built‐in electric field (BIEF) of a crystalline/amorphous Re‐based heterostructure (Re (c) /ReO x (a) ). Specifically, the catalyst exhibits a hydrophilic and aerophobic surface that facilitates mass transport, and its doubled free water content enhances proton source accessibility, promoting water dissociation at amorphous ReO x sites. Simultaneously, BIEF‐induced strong electronic interaction generates low‐valence Re sites with a downshifted d ‐band center, enabling efficient proton retention and conversion, thereby creating an “acid‐like” microenvironment in alkaline media. In situ Raman and ΔpH analyses confirm the constructed interfacial proton microenvironment, demonstrating a triple synergy of free water enrichment, water dissociation, and proton retention. As a result, the Re (c) /ReO x (a) shows a minimal overpotential gap of only 11 mV at 1 A cm −2 across the pH range. Its cost‐normalized activity is 20.6 and 106.8 times higher than that of Pt/C in acidic and alkaline media, with excellent alkaline stability for 1000 h at 1 A cm −2 . This work provides an interfacial proton perspective for designing pH‐universal HER electrocatalysts.