Harnessing the Potential of MXenes for Electrochemical Nitrogen and Carbon Dioxide Reduction Reactions: Recent Advances Based on First-Principles Simulations

Energy conversion processes involving the electrochemical reduction of small molecules such as N2 and CO2 using renewable energy sources hold great promise for the sustainable development of mankind. N2 reduction leads to NH3, a key chemical used in fertilizers, and the CO2 reduction results in the production of industrially relevant value-added chemicals with a decrease in the carbon footprint. However, the lack of suitable electrocatalysts with low overpotentials and high selectivity due to the inert nature of N2 and CO2 molecules is central to the development of next-generation technologies for these complicated and kinetically slow energy conversion processes. Recently, layered two-dimensional metal carbides and nitrides, collectively called MXenes, have shown considerable ability for driving a wide spectrum of chemical transformations owing to their excellent properties such as high surface area, tunable surface chemistry, and excellent electrical conductivity. Moreover, the interfacial chemistry of these layered materials can be easily engineered to tune their activity for driving complex electrocatalytic processes. Accordingly, this review provides a comprehensive overview of the latest advances made in understanding the nitrogen reduction reaction (NRR) and CO2 reduction reaction (CO2RR) activity of MXenes from an electronic-structure-driven and mechanistic perspective, with a primary emphasis on insights derived from density functional theory. We primarily highlight the intricate role of surface functionalization, mixed termination, defect chemistry, and single atom engineering in modulating reaction pathways, selectivity, and kinetic barriers for NRR and CO2RR. In addition to thermodynamic screening based on limiting potentials, recent progress in microkinetic modeling and experimentally benchmarked performance metrics is critically discussed to bridge the gap between theoretical predictions and experimental observations. Furthermore, a comprehensive analysis of the reaction mechanism of NRR and CO2RR to identify the key scaling relationships between the limiting potential, electronic properties, and adsorption energy of intermediates is discussed in detail to facilitate the catalyst design for these energy conversion processes. Finally, the challenges and opportunities associated with MXene-based electrocatalysts─including stability, surface reconstruction, suppression of competing hydrogen evolution reaction, and scalable synthesis─are discussed, along with a forward-looking outlook on emerging strategies such as operando spectroscopy, data-driven catalyst discovery, multiscale modeling, and alternative 2D materials for advancing NRR and CO2RR technologies.