A study published in the Journal of the American Chemical Society reveals that the orientation of water molecules on a platinum (Pt) surface significantly influences the kinetics of the hydrogen evolution reaction (HER) in alkaline media. The research, led by Aamir Hassan Shah and colleagues at the University of California, Los Angeles, combines experimental and theoretical approaches to investigate how pH affects HER on Pt surfaces. The study shows that the HER Tafel slope changes from approximately 110 mV/decade at pH 7–10 to about 53 mV/decade at pH 11–13, indicating a shift in the rate-determining step of the reaction. This change is attributed to a reorganization of interfacial water molecules from an O-down to H-down configuration when the pH exceeds 10. This structural change weakens the O–H bond in the water molecules, enhancing HER kinetics in alkaline conditions. The researchers used cyclic voltammetry (CV) and electrical transport spectroscopy (ETS) to probe the Pt surface at different pH levels. CV studies revealed that the hydrogen underpotential deposition (Hupd) peak potential is pH-dependent above pH 10, while ETS measurements showed a significant increase in conductance above pH 10, suggesting a change in surface adsorbates. Theoretical calculations, including fixed-potential density functional theory (FP-DFT) and ab initio molecular dynamics (AIMD), confirmed that the interfacial water molecules adopt an O-down configuration below pH 11 and flip to a H-down configuration above pH 11. This structural change leads to a weakened O–H bond and improved HER kinetics. The study provides the first direct evidence of the reorganization of interfacial water molecule configuration at pH ~10 and offers a molecular-level understanding of the non-trivial pH-dependent HER kinetics in alkaline media. The findings highlight the importance of interfacial water orientation in determining HER activity and could guide the rational design of optimized electrode-electrolyte conditions for alkaline electrolysis.A study published in the Journal of the American Chemical Society reveals that the orientation of water molecules on a platinum (Pt) surface significantly influences the kinetics of the hydrogen evolution reaction (HER) in alkaline media. The research, led by Aamir Hassan Shah and colleagues at the University of California, Los Angeles, combines experimental and theoretical approaches to investigate how pH affects HER on Pt surfaces. The study shows that the HER Tafel slope changes from approximately 110 mV/decade at pH 7–10 to about 53 mV/decade at pH 11–13, indicating a shift in the rate-determining step of the reaction. This change is attributed to a reorganization of interfacial water molecules from an O-down to H-down configuration when the pH exceeds 10. This structural change weakens the O–H bond in the water molecules, enhancing HER kinetics in alkaline conditions. The researchers used cyclic voltammetry (CV) and electrical transport spectroscopy (ETS) to probe the Pt surface at different pH levels. CV studies revealed that the hydrogen underpotential deposition (Hupd) peak potential is pH-dependent above pH 10, while ETS measurements showed a significant increase in conductance above pH 10, suggesting a change in surface adsorbates. Theoretical calculations, including fixed-potential density functional theory (FP-DFT) and ab initio molecular dynamics (AIMD), confirmed that the interfacial water molecules adopt an O-down configuration below pH 11 and flip to a H-down configuration above pH 11. This structural change leads to a weakened O–H bond and improved HER kinetics. The study provides the first direct evidence of the reorganization of interfacial water molecule configuration at pH ~10 and offers a molecular-level understanding of the non-trivial pH-dependent HER kinetics in alkaline media. The findings highlight the importance of interfacial water orientation in determining HER activity and could guide the rational design of optimized electrode-electrolyte conditions for alkaline electrolysis.