Monodisperse Os‐O‐Co Modules Enable Ampere‐Level Hydrazine‐Assisted Seawater Splitting in Membraneless Electrolyzers

Abstract Hydrazine oxidation‐assisted seawater electrolysis (HzOR‐SWE) is critical for addressing freshwater scarcity and energy crises. However, the development of this technology has been significantly impeded by the absence of efficient catalysts capable of cleaving N─H bonds during the hydrazine oxidation reaction (HzOR). Herein, Monodispersed Os‐O‐Co modules are constructed within a cobalt hydroxide structure via an in situ osmium (Os) single‐atom modification strategy to serve as a bifunctional catalyst. The d‐p orbital hybridization in the structure shifts the d‐band center of Os sites away from the Fermi level, weakening the adsorption energy of reaction intermediates and exhibiting the lowest N─H dehydrogenation energy barrier for HzOR and moderate active hydrogen adsorption energy for hydrogen evolution reaction (HER). When integrated into a membraneless flow cell (MFC), the catalyst demonstrates exceptional performance in HzOR‐SWE, requiring only 0.768 V to deliver 1.0 A cm −2 with a remarkable rate of 31.9 moles of hydrogen per kilowatt‐hour (kWh). This represents a 70.7% energy saving compared to conventional seawater splitting systems (2.62 V, 7.6 kWh mol −1 ). This work holds significant importance for advancing the economic viability of low‐energy seawater electrolysis for hydrogen production.