Selective reduction of CO2 to alcohol products on octahedral catalyst of carbonized Cu(BTC) doped with Pd nanoparticles in a photoelectrochemical cell

Abstract In order to directionally convert CO2 into liquid fuels, Cu(BTC) doped with Pd nanoparticles was carbonized to obtain a novel octahedral catalyst C-Pd/Cu for selective reduction of CO2 to alcohol products. XRD patterns showed that Cu characteristic peak in C-8 wt% Pd/Cu catalyst shifted to the lowest angle at 2θ=43.22°among all the prepared catalysts (2θC-1.6 wt% Pd/Cu = 43.3°, 2θC-4.8 wt% Pd/Cu = 43.29°, 2θC-11.2 wt% Pd/Cu = 43.26°, 2θC-14.4 wt% Pd/Cu = 43.28°). The inter planar distance of Cu nanoparticles in C-8 wt% Pd/Cu catalyst was 2.0915 nm, which was larger than those in other catalysts. XPS spectra showed main peak shift to lower binding energy, representing the influence of Pd doping to Cu. SEM and TEM indicated that many ∼70 nm Cu particles and ∼10 nm Pd nanoparticles uniformly distributed in ∼250 nm porous carbon-based octahedral particles. Raman spectrum implied that C-Pd/Cu catalyst with many defects (band ratio ID/IG = 0.84) provided more active sites for intermediates adsorption and facilitated electron transfer. BET result showed C-Pd/Cu catalyst had many mesporous. It was found by density functional theory (DFT) calculations that C-Pd/Cu catalyst had good selectivity towards alcohol products such as methanol, the reaction energy towards producing CH3OH was 19.5 eV lower than that of producing HCOOH. The pathway CO2 → COOH∗ → CO∗ + H2O → COH∗ → HCOH∗ → CH2OH∗ → CH3OH was the most favored to produce CH3OH. CO2 photoelectrochemical reduction reaction was then conducted in a photoelectrochemical reduction cell (PEC) to verify the calculation result. The total carbon atom conversion rate over C-8 wt% Pd/Cu catalyst reached 2380 nmol·h−1 cm−2 with a high liquid products selectivity towards alcohol products, which was in good agreement with DFT calculation results. And the PEC system was proved to have more energy input under the same applied voltage compared with the electrochemical system.