How can phosphides catalyze CO2 reduction reaction?

The electrochemical method for converting CO₂ into valuable products is one of the promising and novel methods to fight against the massive emission of CO₂ from industries and transportation sectors. In this study, we performed density functional theory calculations to investigate the activity and selectivity of transition metal phosphide (TMP) catalysts for the conversion of CO₂ into formic acid, methanediol, and methanol. We studied 29 TMPs and only 6 were found promising for the CO₂RR application. Free energy diagrams were drawn to obtain onset potentials required for product formation on different catalyst surfaces. The comparison of HER and CO₂RR indicated that the formation of the OCHO intermediate was more dominant and suitable for further protonation until the product was formed. Our studies revealed CrP and VP as excellent candidates to produce only formic acid in aqueous form with the onset potential values of -0.25 V and -0.20 V vs RHE, respectively. In addition, TiP was found to be an effective material for forming formic acid, methanediol, and methanol with the onset potential values of -0.43 V, -0.62 V, and -0.62 V, respectively. This study provides fundamental aids for the conversion of CO₂ into useful green energy fuels.