Two-dimensional n-type pyrite with tuned hydrogen interstitials as a highly selective CO2 reduction catalyst

Density functional theory (DFT) calculations were employed to elucidate the impact of hydrogen interstitial (H-i) defects on the optical and efficacy of iron pyrite (FeS2) as a selective carbon dioxide reduction catalyst (CO2RR). Three different charge states were considered, namely H-i(1), H-i(0) or H-i(-1). Upon examining the formation energy of the various possible charge states that the H-i can accommodate, it was found that H-i will be incorporated in the structure as an n-type defect in the (+1) state across almost the entire bandgap. However, under heavy n-type growth conditions, it can act as an amphoteric dopant, and can accommodate the 3 states simultaneously. The performance of FeS2-H in CO2RR is compared to the pristine counterpart. The calculations show that the addition of H-i facilitates the methanol pathway by prioritizing the attachment of the COOH* intermediate. Consequently, H-i promotes the formation of C1 compounds with higher performance. This is achieved by inhibiting the competitor hydrogen evolution reaction (HER), leading to a significant improvement in the efficiency.