On factors of ions in seawater for CO2 reduction

Performing solar-driven CO2 reduction reaction (CO2RR) on the sea is desirable for future renewable energy landscape. However, CO2RR cannot be directly operated in natural seawater due to the unsuitable ionic environment. Herein, we studied CO2RR from the perspective of ions in seawater electrolyte on Copper. We find that multi-ions mixture in seawater could accelerate CO2RR by tuning electrode, local pH, and bulk electrolyte simultaneously. Specially, Na+_K+ mixture has a workable buffer capacity for regulating local pH and activating CO2 within electric-double-layer. Cl–_Br– mixture induces microstructural and actively changes on Cu electrode. While, in anions-mixture, SO42– would lower overpotential by reducing polarization loss in bulk electrolyte. Under this hierarchical structure of multi-ions in local environment, a well-performed CO2RR is achieved after optimizing ions-concentration and anode catalysts. Finally, by coupling a gas diffusion electrode with optimized seawater, the photovoltaic-driven electrolyzer obtained a 9.88 % solar-to-fuel efficiency (6.15 % solar-to- carbon-based fuels) under direct sunlight.