Angelw: palladium catalyst supported by transition metal carbides for carbon dioxide electroreduction

The large-scale application of fossil fuels results in excessive carbon dioxide emissions, which may accelerate ocean acidification and greenhouse effect Electrochemical conversion of carbon dioxide into fuel and other chemicals (such as carbon monoxide, hydrocarbon, formic acid, alcohol, etc.) is an effective way to alleviate the increase of CO2 concentration in the atmosphere The synthesis gas with controllable H 2 / CO ratio is an important chemical raw material, which is mainly produced by carbon dioxide electroreduction (CO 2rr) and hydrogen evolution reaction (her) In order to realize the effective conversion of CO 2, Co 2rr catalyst is essential However, many co 2rr catalysts are precious metal catalysts, whose Limited reserves and high prices limit the development of CO 2rr Transition metal carbide (TMC) is widely used in the field of electrochemistry It is necessary to develop a TMC for CO2 RR Recently, Professor Liu Changjun from Tianjin University and Professor Jingguang g Chen (Chen Jingguang) from Columbia University prepared a variety of palladium supported transition metal carbides, and studied their co 2rr catalytic activity Relevant research results were published in angelw Chem Int ed (DOI: 10.1002 / anie 201900781) Firstly, several TMC (Mo 2C, WC, NBC and TAC) films were prepared, and PD was supported on TMC films by PVD, thus Pd / TMC film catalyst was obtained In addition, the CO 2rr activity of Pd / TMC film catalyst was evaluated At - 0.9 V vs rhe, TMC and Pd / TMC catalyze the reaction of CO2 RR, and the rate of H 2 and CO formation is inversely proportional Compared with TMC, PD modified TMC (Pd / TMC) significantly increased the production rate of H 2 and Co Among all TMC and Pd / TMC, TAC has the best catalytic activity, Pd / NBC has good catalytic activity, and Mo 2C and WC do not show significant catalytic activity (Figure 1) The stability of Pd / TAC and Pd / NBC films was studied by chronoamperometry (CA) The results show that the two catalysts have stable current density in the process of CO2 RR (source: angelw Chem Int ed.) then, the author further evaluated the catalytic activity of Powder Catalyst Co 2rr with CO current density (JCO) as the evaluation index For the catalyst with the same Pd loading (10 wt%), the current density of CO increases with the increase of negative potential, which indicates that the increase of negative potential will promote the CO 2rr reaction At the initial potential of - 0.5V, the JCO of Pd / C and Pd / NBC are almost the same, but the JCO of Pd / TAC is higher than that of the two In the whole potential range, J Co value shows the trend of Pd / TAC > Pd / NBC > Pd / C (Figure 2a) Interestingly, it is found that Pd / TAC with 10 wt% loading has higher JCO value (Figure 2b) by the normalization analysis of electrochemical active surface area At the same Pd loading (10 wt%), Pd / TAC showed the highest co selectivity (Figure 2C) Based on the experimental results of thin film and powder catalyst, it is considered that TMC carrier has synergistic effect on the regulation of CO 2rr catalytic activity and product selectivity (source: angelw Chem Int ed.) next, the author explored the actual crystal phase of PD on TMC during CO2 RR process The peak A and B of Pd / TAC were transferred to lower energy when the voltage of 0.3V to - 0.5V was applied At the same time, it is further confirmed by in-situ X-ray diffraction that in the process of CO2 RR, hydrogen is inserted into PD lattice and PDH is formed (source: angel Chem Int ed.) finally, in order to further explore the CO 2rr activity of PDH / NBC and PDH / TAC, the DFT calculation was carried out and the geometry of the combination of * CO and * HOCO intermediates and catalysts on PDH / TAC was optimized (Figure 4A and 4B) It is found that the intermediates of * CO and * HOCO are easy to be adsorbed when they are at the top The free energy diagram of CO2 RR shows that the formation of * HOCO is thermodynamically advantageous DFT results also predicted that the activity of CO2 RR should follow the order of PDH / TAC > PDH / NBC > PDH *The formation of HOCO is the key step to control the activity of CO 2rr on the metal surface TAC substrate changes the activity of CO 2rr by adjusting the adsorption of * HOCO (source: angelw Chem Int ed.) conclusion: Professor Liu Changjun from Tianjin University and Professor Jingguang g Chen from Columbia University studied the CO 2rr catalytic activity of Pd catalyst supported by TMC, and finally selected Pd / TAC catalyst with excellent Co 2rr activity and stability This study provides a new idea for the development of other TMC supported noble metal catalysts in electrochemical reactions.