Water structure and local potential distribution at Pt surface in alkaline cation mediated hydrogen evolution regulable by electric field

The impact of alkaline media on hydrogen evolution reaction (HER) rate and selectivity is crucial for advancement of water electrolysis technology. Herein, we revealed the mechanism through which alkali metal cations (AM ⁺ ) influence HER performance of Pt electrodes. We quantified the interfacial potential drops, which are regulatable by E-field and found that the local surface concentration of AM ⁺ is 5.0 ~ 8.6 times higher than in the bulk solution. Decreasing AM ⁺ concentration through reverse E-field disrupts adsorbate-surface interactions and boosts HER activity without affecting hydrogen binding energetics and kinetics. Complexes of OH ^δ− -(H ₂ O) _x -AM ⁺ are formed near the interface, impacting intermediate product detachment. The presence of AM ⁺ also plays a role in restructuring interfacial water and improving proton transfer efficiency. For Li ⁺ , the reorientation of O-H bonds towards Pt surface facilitates the HER process. These findings shed light on potential avenues for enhancing the efficiency of HER processes.