CoOOH/CdIn2S4 film photoanodes driving unbiased tandem cells towards simultaneous efficient oxidation of benzyl alcohol and selective generation of ethanol from CO2 reduction

Abstract

In unbiased tandem cells, the production of C₂₊ products from CO₂ reduction on the cathode is dependent on the effective supply of charge from the photoanode. At present, the development and understanding of efficient photoanodes remain challenging. A CoOOH nanosheet coupled CdIn₂S₄ film (CoOOH/CdIn₂S₄) was investigated as a photoanode to drive solar benzyl alcohol oxidation. Relative to the CdIn₂S₄ photoanode, lower carrier recombination, better activity and faster kinetics were achieved on the CoOOH/CdIn₂S₄ photoanode for benzyl alcohol oxidation to benzaldehyde. Several investigations jointly revealed that the oxidation of benzyl alcohol to benzaldehyde on the CoOOH/CdIn₂S₄ photoanode is mediated through the formation of hydroxyl radicals and the slight change of β-CoOOH into γ-CoOOH. Additionally, CoOOH coupling with CdIn₂S₄ is more energetically favourable for benzyl alcohol oxidation to benzaldehyde. Consequently, the CoOOH/CdIn₂S₄ photoanode shows high Faraday efficiency and selectivity for benzyl alcohol oxidation. In the CoOOH/CdIn₂S₄ photoanode–Cu₂O cathode unbiased tandem cell, benzaldehyde and ethanol can be selectively produced from benzyl alcohol oxidation and CO₂ reduction, respectively. Additionally, the CoOOH/CdIn₂S₄ photoanode can work stably to drive the unbiased cell, and 88% of its initial activity can be maintained after 4 h of reaction.