Structure-Activity-Stability Tradeoffs of Pt Cathodes in Alkaline Water Electrolysis: Article No. e78370

Due to its high activity for the hydrogen evolution reaction at low overpotential in alkaline conditions, platinum is a promising cathode catalyst material for next-generation, high current density alkaline water electrolysis (AWE). However, its implementation in industrially relevant zero-gap AWE remains poorly understood, particularly regarding catalyst utilization, durability, and impurity tolerance. Here we establish electrode structure-activity-stability relationships for a series of Pt cathodes prepared by galvanic displacement, sputtering, annealing, and dealloying, allowing systematic control over microstructure and adhesion. Annealed sputtered Pt presents moderate intrinsic activity but maintains stable operation over 1000 h at 2 A.cm-2. A leached nanoporous Pt cathode achieves a high electrochemically active surface area with sustained performance under industrially relevant conditions. Beyond intrinsic catalyst properties, we reveal that the presence of Fe impurities critically governs cathode behavior. Using a rotating disk electrode and single-cell studies, Fe is shown to deposit within the HER operating window, replacing Pt active sites and evolving into dendritic structures that dominate electrode performance. These findings demonstrate that the use of Pt cathodes in AWE is dictated not only by catalyst design but also by impurity management and establishing key design principles for next-generation high-current-density cathodes.