Energy-Efficient and Selective Hydrogen Extraction from Hydrazine.
The utilization of hydrazine (N2H4) as a liquid-phase carrier offers a promising approach for on-demand H2 production. However, its splitting is challenged by parasitic cleavage of the N-N bond, which generates ammonia byproducts and wastes energy. Here, we designed a single-atomic catalyst comprising Ru(IV) coordinated by four oxygen atoms on a Ti felt, achieving near-quantitative selectivity (99.9%) for N2 and H2 at an ultralow cell voltage of 35 mV with a current density of 100 mA cm-2, significantly outperforming conventional Ru-based catalysts with N2 selectivity below 66%. Mechanistic investigations reveal that O-coordination stabilizes the high-valent Ru(IV) in a low-spin d4 electronic state. This electronic state promotes a monodentate end-on adsorption configuration of N2H4, enhancing electron donation from the terminal adsorbed N2H4 while minimizing the Ru→N back-donation into the N-N σ* orbital. Consequently, N-N cleavage is effectively suppressed, promoting successive N-H bond cleavage for clean H2 release. Impressively, this catalyst enabled direct conversion of aerospace wastewater containing 1,780 ppm of N2H4 to pure H2 (99.99%) with a net-negative carbon footprint of -2.25 kg CO2/t, offering an innovative and sustainable approach for waste-to-energy in the environmental and energy fields.