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, SO₄^2– 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.