Efficient Photoelectrocatalytic Reduction of CO₂ to Selectively Produce Ethanol Using FeS₂/TiO₂ p–n Heterojunction Photoelectrodes

Herein, the FeS₂/TiO₂ p-n heterojunction was first utilized as a photoelectrode for the PEC reduction of CO₂ to selectively produce ethanol. The FeS₂/TiO₂ photoelectrode was fabricated through electrochemical anodization, electrodeposition, and vulcanization methods. The impact of the FeS₂ loading amount and applied bias on the PEC performance was investigated. The behavior of photocurrent polarity reverse is observed depending on the FeS₂ loading amount, which is related to the energy band structure of the semiconductor/electrolyte interface. The active sites for ethanol production were identified on TiO₂ nanotubes rather than on the FeS₂ surface. Incorporation of FeS₂ not only broadened the visible light absorption range but also formed a p-n heterojunction with TiO₂. FeS₂/TiO₂ with an electrodeposition time of 15 min exhibits the highest ethanol yield of 1170 μmol L^-1 cm^-2 for 3.5 h of reaction under ultraviolet-visible (UV-Vis) illumination at an applied bias of -0.7 V. Compared to TiO₂, FeS₂/TiO₂ showed significantly higher ethanol yield due to its appropriate loading amount of FeS₂ and the synergistic effect of strong UV-Vis light absorption and efficient separation and transfer of charge carriers at the p-n junction.