Unravelling the adsorption and electroreduction performance of CO₂ and N₂ over defective and B, P, Si-doped C₃Ns: a DFT study

Two-dimensional carbon-based materials have great potential for electrocatalysis. Herein, we screen 12 defective and doped C3N nanosheets by evaluating their CO2RR and NRR activity and selectivity vs. the HER based on density functional theory calculations. The calculation results suggest that all 12 C(3)Ns can enhance CO2 adsorption and activation. And P-N-V-C-C3N is the best electrocatalyst for the CO2RR towards HCOOH with U-L = -0.17 V, which is much more positive than most of the reported values. B-N-C3N and P-N-C3N are also good electrocatalysts that promote the CO2RR towards HCOOH (U-L = -0.38 V and -0.46 V). Moreover, we find that Si-C-C3N can reduce CO2 to CH3OH, adding an alternative option to the limited catalysts available for the CO2RR to CH3OH. Furthermore, B-C-V-C-C3N, B-C-V-N-C3N, and Si-C-V-N-C3N are promising electrocatalysts for the HER with |Delta G(H*)| <= 0.30 eV. However, only three C(3)Ns of B-C-V-C-C3N, Si-C-V-N-C3N, and Si-C-V-C-C3N can slightly improve N-2 adsorption. And none of the 12 C(3)Ns are found to be suitable for the electrocatalytic NRR because all the Delta e(NNH*) values are larger than the corresponding Delta G(H*) values. The high performance of C(3)Ns in the CO2RR stems from the altered structure and electronic properties, which result from the introduction of vacancies and doping elements into C3N. This work identifies suitable defective and doped C(3)Ns for excellent performance in the electrocatalytic CO2RR, which will inspire relevant experimental studies to further explore C(3)Ns for electrocatalysis.