Interfacial engineering to create ionically bonded heterostructures for ampere-level chlorine-free anodic reactions in seawater
Suraj Loomba, Muhammad Waqas Khan, Muhammad Haris, Sharafadeen Gbadamasi, Vasundhara Nettem, Kevin Tran, Patrick D. Taylor, Lars Thomsen, Anton Tadich, Michelle J. S. Spencer, Nasir Mahmood
Abstract
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.