Advances in photo-assisted seawater splitting promoted by green iron oxide-carbon nitride photoelectrocatalysts

Abstract

Solar-driven seawater electrolysis for hydrogen fuel production holds an outstanding potential towards the development of a carbon-neutral and sustainable energy infrastructure, but the development of green, efficient and stable photoelectrocatalysts selectively promoting oxygen evolution remains a formidable challenge. Motivated by this issue, in this work we propose a tailored combination of two economically viable materials, α-Fe₂O₃ and graphitic carbon nitride (gCN), to fabricate promising anodes – eventually decorated with cobalt phosphate (CoPi) particles – for alkaline seawater photosplitting. The target systems were fabricated via an original multi-step route, involving the plasma-enhanced chemical vapor deposition of iron(III) oxide on conducting glasses, the introduction of gCN in very small amounts by a rapid and facile electrophoretic process, and final annealing in air. A comprehensive characterization revealed the successful fabrication of composites featuring a tailored surface defectivity, a controlled nano-organization, and a close Fe₂O₃/gCN interfacial contact. After decoration with CoPi, the best performances corresponded to a Tafel slope of ≈100 mV dec⁻¹ and overpotential values enabling us to rule out the competitive hypochlorite formation. In addition, photocurrent densities at 1.23 V vs. RHE showed a nearly 7-fold increase upon Fe₂O₃ functionalization with both gCN and CoPi. These amenable results, directly dependent on the electronic interplay at Fe₂O₃/gCN heterojunctions and on CoPi beneficial effects, are accompanied by a remarkable long-term stability, and may open up attractive avenues for clean energy production using natural resources.