Allotropes selection apropos of photocatalytic CO2 reduction from first principles studies

Materials engineering of allotropism provides a possible strategy for controling CO 2 photoreduction into various C1 products. However, the understanding of the mechanism for tuning products selectivity through allotropism is still lacking. Herein, three structures of known phosphorus allotrope, i.e. black phosphorus (BP), fibrous red phosphorus (RP), and helical coil phosphorus (CP), were modelled as a CO 2 reduction photocatalyst and studied by first principles density functional theory calculations. Three adsorption sites (P 6C , P 2B , and P T ) of CO 2 on the phosphorus allotropes were investigated. The most stable adsorption configuration for each allotrope was then selected for further study. The quantum topological analysis revealed that CO 2 adsorption interaction on BP and RP exhibits physical binding of van der Waals interaction while CP shows physical binding of Keesom interaction. The CO 2 adsorption interaction is shown to be crucial in determining the activation barrier for the initial proton-coupled electron transfer of CO 2 → COOH. The pathways for different C1 products, including CO, HCOOH, C, CH 2 O, CH 3 OH, and CH 4 , were examined by comparing the rate determining step (RDS) obtained via Gibbs free energy analysis. RP and CP show higher selectivity towards the two- and four-electron C1 products. CP evidences a lower activation barrier for the two- and four-electron products RDS while BP exhibits higher selectivity towards the six- and eight-electron reduction products. The difference in selectivity of each of the allotropes was attributed to its distinct p-band center. This study divulges an important understanding on the possible product selectivity modulation for CO 2 photoreduction based on allotropism. • The effects of allotropism on CO 2 photoreduction were investigated by DFT. • ELF and QTAIM revealed the nature of CO 2 adsorption interaction with the allotropes. • The desired CO 2 reduction pathways were determined from Gibbs free energy change. • The p -band center was found to play a crucial role in the products selectivity.