Mixed-Functionalized Sc2 CTx (T=O, OH, F) MXene for Electrocatalytic CO2 Reduction: Insight from First-Principles Calculations

A microscopic understanding of the mixed-functionalized MXenes (M2X-Tx; Tx=O, OH, and F) are extremely important to the design of efficient CO2 catalytic activity. Here, we report a first-principles study of the CO2 activation on pure O, OH, and F and mixed-functionalized Sc2C MXene surfaces. We find that CO2 adsorption energy can be tuned by changing the coverage of O, OH, and F functional groups on the surface. Fully terminated O and F Sc2C forms weak interactions with CO2 molecules (binding energy -0.136 and -0.168eV) whereas mixed-functionalized Sc2C surface exhibits higher binding energy(-0.364eV). In the mixed-functionalized Sc2C case, only O sites allow CO2 reduction (F and OH are inactive) and finally converts into methane (CH4). Ab-initio-based Bader charge analysis and projected density of state calculations reveal strong bonding between the C atom of CO2 and O functional group. The Gibbs free-energy calculation confirms the conversion of HCO into H2CO to be a rate-limiting step with the limiting potential 1.387 eV. In the mixed-functionalized surface, as we increase the number of OH groups in the vicinity of O sites, the binding energy increases (transiting from a physisorption to a chemisorption regime). However, increasing the amount of O coverage turns out to be detrimental to the catalytic activity. Our study highlights the role of different functional groups in achieving efficient CO2 catalytic activity on Sc2C MXene, which can further help us to design experiments accordingly.