Nitrogen defect and 2D interface effect of MXene/h-BN heterostructures for CO₂ reduction: a DFT study

Electrochemical reduction of CO₂ to value-added chemicals offers a promising strategy to mitigate major greenhouse gases while enabling sustainable fuel production. Recently, two-dimensional materials have attracted significant attention as electrocatalysts for various electrocatalytic reactions due to their unique structural and electronic properties. In this work, we explore the electrocatalytic potential of hetero-structures, comprising -OH-terminated Ti₃C₂ MXene combined with hexagonal boron nitride (MX/h-BN), and nitrogen-defective h-BN (MX/h-BN-Nvac), towards the CO₂ reduction reaction (CO₂RR) using first-principles-based DFT-D methods. The presence of MXene layers modifies the electronic structure of h-BN by transferring charge density toward the h-BN layer, leading to a notable reduction in both work function and band gap. In MX/h-BN-Nvac, this charge density transfer is localized near the N-vacant site, whereas in MX/h-BN it is delocalized throughout the whole 2D sheet of h-BN. In MX/h-BN-Nvac, the extent of electronic structure modulation is less prominent than in MX/h-BN. Both the heterostructures promote CO₂ adsorption and activation; however, their subsequent reduction pathways differ significantly. Following the adsorption and activation, subsequent CO₂RR proceeds via multiple proton-coupled electron transfer steps along both the COOH and OCHO pathways, leading to CH₄ and CH₃OH as the final products. On MX/h-BN, the OCHO pathway is identified as energetically favoured, enabling selective conversion to CH₄ and CH₃OH as the final products. Similarly, MX/h-BN-Nvac also follows the OCHO pathway, while the COOH route is hindered by strong CO binding, leading to catalyst surface poisoning and reduced catalytic performance. Overall, the MX/h-BN hetero-structure demonstrates superior electrocatalytic performance, highlighting that defect-free interfacial electronic modulation can be a cost-effective and efficient electrocatalyst for the electrochemical conversion of CO₂ to CH₄ or CH₃OH. However, inclusion of implicit solvation reverses the relative activity, making MX/h-BN-Nvac more favourable under aqueous conditions.