Self‐Limited Formation of Cobalt Nanoparticles for Spontaneous Hydrogen Production through Hydrazine Electrooxidation

Hydrogen (H 2 ) has emerged as a highly promising energy carrier owing to its remarkable energy density and carbon emission‐free properties. However, the widespread application of H 2 fuel has been limited by the difficulty of storage. In this work, spontaneous electrochemical hydrogen production is demonstrated using hydrazine (N 2 H 4 ) as a liquid hydrogen storage medium and enabled by a highly active Co catalyst for hydrazine electrooxidation reaction (HzOR). The HzOR electrocatalyst is developed by a self‐limited growth of Co nanoparticles from a Co‐based zeolitic imidazolate framework (ZIF), exhibiting abundant defective surface atoms as active sites for HzOR. Notably, these self‐limited Co nanoparticles exhibit remarkable HzOR activity with a negative working potential of −0.1 V (at 10 mA cm −2 ) in 0.1 m N 2 H 4 /1 m KOH electrolyte. Density functional theory (DFT) calculations are employed to validate the superior performance of low‐coordinated Co active sites in facilitating HzOR. By taking advantage of the potential difference between HzOR and the hydrogen evolution reaction (HER), a novel HzOR||HER electrochemical system is developed to spontaneously produce H 2 without external energy input. Overall, the work offers valuable guidance for developing active HzOR catalyst. The novel HzOR||HER electrochemical system represents a promising and innovative solution for energy‐efficient hydrogen production.