MOF-derived 1D/3D N-doped porous carbon for spatially confined electrochemical CO2 reduction to adjustable syngas

Electrochemical reduction of CO2 to syngas (CO and H-2) offers an efficient way to mitigate carbon emissions and store intermittent renewable energy in chemicals. Herein, the hierarchical one-dimensional/three-dimensional nitrogen-doped porous carbon (1D/3D NPC) is prepared by carbonizing the composite of Zn-MOF-74 crystals in situ grown on a commercial melamine sponge (MS), for electrochemical CO2 reduction reaction (CO2RR). The 1D/3D NPC exhibits a high CO/H-2 ratio (5.06) and CO yield (31 mmol g(-1) h(-1)) at -0.55 V, which are 13.7 times and 21.4 times those of 1D porous carbon (derived from Zn-MOF-74) and N-doped carbon (carbonized by MS), respectively. This is attributed to the unique spatial environment of 1D/3D NPC, which increases the adsorption capacity of CO2 and promotes electron transfer from the 3D N-doped carbon framework to 1D carbon, improving the reaction kinetics of CO2RR. Experimental results and charge density difference plots indicate that the active site of CO2RR is the positively charged carbon atom adjacent to graphitic N on 1D carbon and the active site of HER is the pyridinic N on 1D carbon. The presence of pyridinic N and pyrrolic N reduces the number of electron transfer, decreasing the reaction kinetics and the activity of CO2RR. The CO/H-2 ratio is related to the distribution of N species and the specific surface area, which are determined by the degree of spatial confinement effect. The CO/H2 ratios can be regulated by adjusting the carbonization temperature to adjust the degree of spatial confinement effect. Given the low cost of feedstock and easy strategy, 1D/3D NPC catalysts have great potential for industrial application.