Electrocatalytic CO₂ Reduction over Cu₃P Nanoparticles Generated via a Molecular Precursor Route

The design of nanoparticles (NPs) with tailored morphologies and finely tuned electronic and physical properties has become a key strategy for controlling selectivity and improving conversion efficiency in a variety of important electrocatalytic transformations. Transition metal phosphide NPs, in particular, have emerged as a versatile class of catalytic materials due to their multifunctional active sites and composition- and phase-dependent properties. Access to targeted transition metal phosphide NPs with controlled features is necessary to tune the catalytic activity. To this end, we have established a solution-synthesis route utilizing a molecular precursor containing M-P bonds to generate solid metal phosphide NPs with controlled stoichiometry and morphology. We expand here the application of molecular precursors in metal phosphide NP synthesis to include the preparation of phase-pure Cu₃P NPs from the thermal decomposition of [Cu(H)(PPh₃)]₆. The mechanism of [Cu(H)(PPh₃)]₆ decomposition and subsequent formation of Cu₃P was investigated through modification of the reaction parameters. Identification and optimization of the critical reaction parameters (i.e., time, temperature, and oleylamine concentration) enabled the synthesis of phase-pure 9-11 nm Cu₃P NPs. To probe the multifunctionality of this materials system, Cu₃P NPs were investigated as an electrocatalyst for CO₂ reduction. At low overpotential (-0.30 V versus RHE) in 0.1 M KHCO₃ electrolyte, Cu₃P-modified carbon paper electrodes produced formate (HCOO-) at a maximum Faradaic efficiency of 8%.