Efficient Photoelectrocatalytic\nReduction of CO<sub>2</sub> to Selectively Produce Ethanol Using FeS<sub>2</sub>/TiO<sub>2</sub> p–n Heterojunction Photoelectrodes

Herein, the FeS<sub>2</sub>/TiO<sub>2</sub> p–n\nheterojunction\nwas first utilized as a photoelectrode for the PEC reduction of CO<sub>2</sub> to selectively produce ethanol. The FeS<sub>2</sub>/TiO<sub>2</sub> photoelectrode was fabricated through electrochemical anodization,\nelectrodeposition, and vulcanization methods. The impact of the FeS<sub>2</sub> loading amount and applied bias on the PEC performance was\ninvestigated. The behavior of photocurrent polarity reverse is observed\ndepending on the FeS<sub>2</sub> loading amount, which is related\nto the energy band structure of the semiconductor/electrolyte interface.\nThe active sites for ethanol production were identified on TiO<sub>2</sub> nanotubes rather than on the FeS<sub>2</sub> surface. Incorporation\nof FeS<sub>2</sub> not only broadened the visible light absorption\nrange but also formed a p–n heterojunction with TiO<sub>2</sub>. FeS<sub>2</sub>/TiO<sub>2</sub> with an electrodeposition time\nof 15 min exhibits the highest ethanol yield of 1170 μmol L<sup>–1</sup> cm<sup>–2</sup> for 3.5 h of reaction under\nultraviolet–visible (UV–Vis) illumination at an applied\nbias of −0.7 V. Compared to TiO<sub>2</sub>, FeS<sub>2</sub>/TiO<sub>2</sub> showed significantly higher ethanol yield due to\nits appropriate loading amount of FeS<sub>2</sub> and the synergistic\neffect of strong UV–Vis light absorption and efficient separation\nand transfer of charge carriers at the p–n junction.