Energy-Efficient and Selective Hydrogen Extraction from Hydrazine

Abstract

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.