Tuning the interfacial electric field via potential-zero-charge engineering for boosted alkaline hydrogen evolution

Water dissociation is the kinetic bottleneck of the alkaline hydrogen evolution reaction (HER) and is strongly governed by the interfacial electric field. However, its precise and quantitative modulation remains challenging. Here, we report a molecular modification strategy to tune the interfacial electric field using the potential of zero charge (PZC) as a key descriptor. Pyridine sulfonic acid anchors onto CoS₂ via pyridinic nitrogen, inducing interfacial charge redistribution, while the hydrophilic sulfonate group modulates the local electrostatic environment through interactions with interfacial water. Potential-dependent surface charge analysis reveals a positive PZC shift of 40 mV, indicating an enhanced interfacial electric field under working potentials. In situ Raman spectroscopy shows pronounced changes in water vibrational modes, suggesting a reorganized hydrogen-bond network that facilitates water transport and dissociation. Density functional theory calculations correlate the PZC shift with a reduced water dissociation barrier (from 0.73 to 0.51 eV). As a result, the modified CoS₂ exhibits an ultralow overpotential of 23.3 mV at 10 mA cm^-2 and a Tafel slope reduced from 151.3 to 54.6 mV dec^-1. This work establishes PZC as an effective descriptor for regulating interfacial electric fields and enhancing alkaline HER.