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

Abstract

Density functional theory (DFT) calculations were employed to elucidate the impact of hydrogen interstitial (Hi) 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 Hi1, Hi0 or Hi−1. Upon examining the formation energy of the various possible charge states that the Hi can accommodate, it was found that Hi 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 Hi facilitates the methanol pathway by prioritizing the attachment of the COOH* intermediate. Consequently, Hi 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.