Transition metal doped into defective boron nitride nanotubes for CO2RR: Regulation of catalytic activity and mechanism by curvature effect

Utilizing electrochemical CO2 reduction reaction (CO2RR) to synthesize chemical fuels is an effective strategy to alleviate environmental pollution and energy crisis. In this work, a series of single transition metal atoms (TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd) are doped into boron nitride nanotubes (BNNTs) of BN divacancy defect with different curvature parameters, which are named as TM-DVBNNT(n, n), and their CO2RR catalytic performance is systematically studied by density functional theory (DFT) methods. To begin with, the calculation results of formation energy and dissolution potential show that all TM-DVBNNT(n, n) have good thermodynamic and electrochemical stability. Secondly, after calculation of Gibbs free energy, Mn-, Fe-, Ru-, and Rh-DVBNNT(5, 5) have good catalytic performance with the corresponding limiting potential (UL) values of -0.43, -0.40, -0.27, and -0.50 V, respectively. Based on this, we further investigate the influence of curvature on the stability, activity, and mechanism of Ru-DVBNNT(n, n) with the highest activity. It is worth noting that as the diameter of Ru-DVBNNT(n, n) continues to increase, their stability and activity also continue to enhance, and Ru-DVBNNT(8, 8) with the largest diameter is expected to become the best performing CO2RR electrocatalyst with the UL value of -0.16 V. Besides, for Ru-DVBNNT(3, 3) and Ru-DVBNNT(4, 4), their final product is HCOOH. In contrast, the CH4 product is more inclined to form on Ru-DVBNNTs with chiral indexes of (5, 5), (6, 6), (7, 7), and (8, 8). In summary, this work has laid a solid theoretical foundation for future experimental design of nanotube structures.