Ultralow‐Loading Platinum Catalysts Anchored by Lacunary POMs Proton Pumps for Proton Exchange Membrane Water Electrolysis

Abstract Developing highly active and stable electrocatalysts for practical proton exchange membrane water electrolyzers (PEMWEs) operating at industry‐relevant current densities remains a significant challenge. In particular, the hydrogen evolution reaction (HER) at ampere‐level current densities leads to the rapid consumption of interfacial protons, resulting in sluggish kinetics. Herein, a strategy is proposed to reduce the proton transfer energy barriers and improve the HER kinetics at high current densities by anchoring tri‐lacunary Keggin‐type polyoxometalates (POMs) on Pt. The lacunary POMs clusters function as proton pumps, increasing the connectivity of hydrogen bond networks and enabling proton transfer via a proton‐coupled electron transfer mechanism. In addition, an unconventional Tafel step mediated by short‐pathway hydrogen spillover from POMs clusters to Pt active sites is also created. As a result, an ultra‐high mass activity of 782.94 A·mg _Pt ⁻¹ and remarkable durability over 6000 h at a current density of 2000 mA·cm ⁻² can be simultaneously achieved in a practical PEMWE with an ultralow Pt loading mass of 4.2 µg _Pt ·cm ⁻² . The strategy provides new opportunities in developing next‐generation low‐Pt electrocatalysts for PEMWE applications.