In Situ Investigation of Interfacial Water in the Hydrogen Evolution Reaction: A Comparative Study Unraveling the Impact of Oxide Impurity

Understanding the sluggish kinetics of the hydrogen evolution reaction (HER) in neutral media is a grand challenge. The correlation between the interfacial water structure and HER activity has yet to be determined, particularly for catalysts with complex chemical compositions. Herein, we used in situ electrochemical and spectroscopic methods (e.g., surface-enhanced infrared absorption and shell-isolated nanoparticle-enhanced Raman spectroscopy) to investigate the evolution of the hydrogen bonding network of interfacial water molecules of typical HER catalysts (e.g., Pt/C and NiCo-phosphide, -sulfide, and -hybrid with/without oxide impurity) under potential bias in neutral media. The cathodic potentials always influenced the composition of interfacial water, rendering the records of distinct nominal tuning rates among different catalysts. Interestingly, we found that a suitable amount of surface oxide impurity, a HER inert phase, can drastically alter the dynamic behaviors of interfacial water, promoting the transition from ice-like and liquid-like water to free water while leading to an improved HER performance (j0 > 0.7 mA cm–2; η = 101.7 mV@10 mA cm–2). Such an effect was presumably correlated with the hydrophilic moieties, as evidenced by the in situ studies of pure oxide and hydroxide controls. This work provides insights of understanding the activity of the HER in neutral media, paving the way to the rational design of electrocatalysts.