Interfacial engineering to create ionically bonded heterostructures for ampere-level chlorine-free anodic reactions in seawater

Production of hydrogen directly from seawater can be a sustainable method; however, corrosive and competitive chlorine chemistry at the anode interfere with the oxygen evolution reaction (OER). Special materials need to be designed to avoid chlorine chemistry; hence, a two-dimensional metal-organic framework@WO 3 .B 2 O 3 (MOF@WB) heterostructure with ionic bonds was engineered, which can deliver ~10x better performance and is ~65% more economical than commercial IrO 2 for OER. Our system is stable in alkaline seawater for over 1000 h without chlorine evolution and remains functional even after sitting idle for 5 days, making it integrable with renewable power sources. The catalyst also operated stably at the industrial-scale current density of 1.58 A cm -2 for over 100 h with 99% performance retention in alkaline seawater. Theoretical calculations reveal that B assists in the adsorption of the MOF on the WO 3 substrate via the creation of ionic bonds, resulting in optimized surface geometries for selective reactions, which safeguard against chlorine chemistry. B 2 O 3 helps modulate the B-OH sites at the interface via B-O-B bond hydrolysis, activating the OER kinetics, hence providing an ideal platform for effective direct seawater catalysis to produce low-cost hydrogen. A 2D Co-MOF@WO 3 .B 2 O 3 heterostructure was synthesized via a solid-liquid interfacial growth with an ionic Co-O-W bond at the heterointerface where B helps in better adsorption of Co-MOF over the surface of WO 3 while B 2 O 3 hydrolyze to modulate the B-OH sites at the interface. The ionic bond between the two components is crucial in achieving improved performance, stability, and protection against corrosive chlorine chemistry. • WB/MOF was constructed via solid-liquid interfacial growth process at room-temperature. • B just underneath the surface of WO 3 creates ideal platform for MOF growth. • B 2 O 3 at interface acts as “hydroxyl ions hungry” Lewis acid and improves OH-accepting ability. • MOF and WB are connected via ionic bond at the interface, helps in selective OER. • Catalyst delivers ampere-level current density and remains stable over 1000 h in seawater.