A floatable photocatalyst to synergistically promote CO2 reduction and water oxidation by creating oriented charge separation across a tri-phase interface†

Abstract

Artificial photosynthesis, which combines photocatalytic CO₂ reduction with water oxidation to produce carbon-based fuels and feedstocks, has gained extensive interest nowadays. To optimize this system, a synergistic promotion of CO₂ reduction and water oxidation is required. However, an obstacle to achieving this synergy is the contradiction in the preferred reaction environments between CO₂ reduction (preferring a gas–solid environment) and water oxidation (preferring a water–solid environment). To address this challenge, we have developed a floatable catalyst by sequentially layering Cu₂O, Ag and TiO₂ on a PTFE membrane support. When this catalyst floats on the gas–water boundary and is illuminated, oriented charge separation occurs across the membrane and the tri-phase (gas–water–solid) interface. Photogenerated electrons accumulate on the side of the membrane exposed to the gas phase, initiating gas–solid CO₂ reduction. Simultaneously, holes transfer to the side immersed in water, facilitating water–solid water oxidation. This design enhances the production rate by 120 fold and 10 fold for CO₂ reduction and water oxidation to H₂O₂ at most, and selectivity by up to 105 times and 2 times for these two half-reactions at most, when compared to a conventional gas–solid or water–solid system, or a tri-phase system on a catalyst without oriented charge separation. Distinctive to the generally considered catalyst-centered strategies, this study provides a new insight to optimize photocatalysis through the regulation of the reaction environment.