A Heterogenised Molecular Electrocatalyst for Round-the-Clock Green Hydrogen Production by Solar-Electrolyser and Zinc-Air Batteries.

Solar energy-driven seawater electrolysis presents a sustainable method for producing high-purity green hydrogen to address the energy crisis. Developing a robust electrocatalyst for seawater splitting is crucial for green fuel production with solar integration. This study introduces a silica-anchored cobaloxime system as a multifunctional electrocatalyst for overall seawater splitting in conjunction with photovoltaic cells. The system achieves a solar-to-hydrogen generation efficiency of 14%, a power conversion efficiency of 17.4%, and a round-trip energy efficiency of 80%. A single-stack electrolyser using this catalyst produces an average of 0.82 mmol h-1 of green hydrogen and 0.44 mmol h-1 of oxygen, with a hydrogen conversion efficiency of approximately 80 kWh kg-1 under natural sunlight. The same catalyst also shows bidirectional O2 reduction and evolution activity, enabling solar energy storage through a rechargeable zinc-air battery (RZAB). A photovoltaic-RZAB-electrolyser triad was established for indirect green hydrogen production using stored renewable energy. The catalyst-containing RZAB system is effectively charged by a photovoltaic (PV) cell, achieving 25% energy efficiency, and facilitates seawater splitting without sunlight at an energy conversion efficiency of 84%. The strategic application of the catalyst as a multifunctional electrocatalyst enables sustainable green hydrogen production both during the day and night under practical conditions.