Dipole-Induced Water Orientation at PtO_x/NiO Heterostructures for Efficient Alkaline Hydrogen Evolution

The sluggish hydrogen evolution reaction (HER) in alkaline media is fundamentally limited by the high energy barrier of H₂O dissociation, which is strongly governed by the orientation and hydrogen-bond environment of interfacial H₂O molecules. Here, we reported a heterostructured electrocatalyst comprising PtO_x nanoclusters anchored on NiO (PtO_x/NiO) that overcomes this limitation by regulating the interfacial H₂O configuration. Combined in-situ experimental and theoretical investigations revealed that PtO_x/NiO established a strengthened dipole field, which induced a preferential H-down orientation of interfacial H₂O, thereby lowering the H₂O dissociation barrier. Meanwhile, partially oxidized Pt sites optimize hydrogen intermediate binding, increasing surface proton availability and facilitating subsequent HER. As a result, the PtO_x/NiO delivered outstanding HER performance in alkaline electrolyte, requiring only 27 mV overpotential at 10 mA cm^-2. This work establishes interfacial dipole engineering as an effective strategy for accelerating H₂O activation, offering new mechanistic insight and a generalizable framework for designing high-efficiency alkaline HER electrocatalysts.