Dual-strategy of hetero-engineering and cation doping to boost energy-saving hydrogen production via hydrazine-assisted seawater electrolysis

Abstract

When compared with pure water, hydrogen produced by seawater electrolysis has a better practical application potential. By replacing the oxygen evolution reaction (OER) and competitive chlorine evolution reaction (ClER) with the thermodynamically favorable anodic hydrazine oxidation reaction (HzOR) in alkaline seawater, energy-saving hydrogen production can be achieved. In this study, Fe/Co dual-doped Ni2P and MIL-FeCoNi heterostructures (FeCo-Ni2P@MIL-FeCoNi) arrays with simultaneous cation doping and hetero-engineering provide excellent bifunctional electrocatalytic performance for HzOR and hydrogen evolution reaction (HER) in alkaline seawater electrolyte. Overall hydrazine splitting (OHzS) in seawater is impressive, with a low cell voltage of only 400 mV required to reach 1000 mA cm−2 and stable operation for 1000 h to maintain above 500 mA cm−2. As a proof-of-concept, the OHzS system can save 3.03 kW h when producing 1.0 L of H2 when compared with the N2H4-free seawater system, resulting in energy-saving H2 production. Density functional theory calculations show that the combination of Co-doping and the fabrication of FeCo-Ni2P and MIL-FeCoNi heterointerfaces can result in a low water dissociation barrier, optimized hydrogen adsorption free energy toward HER, and favorable adsorbed dehydrogenation kinetics for HzOR. This processing route paves the way for a practical approach to the efficient utilization of hydrogen, which is abundant in the ocean energy field, to achieve a carbon-neutral hydrogen economy.