A MXene-supported single atom catalyst selectively converts CO2 into methanol and methane†

Abstract

Single atom catalysts (SACs) have emerged as new-generation catalysts that exhibit unique properties and catalytic activity due to their tunable coordination environment and uniform catalytic active sites. MXenes are two-dimensional inorganic materials composed of thin layers of nitrides, carbides or carbonitrides of transition metals, which have been recently used as supports for single metal atoms (SMAs) due to their superior electronic, thermal, and mechanical properties. The catalytic active sites in SACs are too far from each other to enable H–H and C–C coupling through the Tafel process, suggesting that both H₂ production—via the hydrogen evolution reaction—and multi-carbon product (C₂₊) formation—via the CO₂ reduction reaction—are significantly suppressed on these catalysts. Therefore, these catalysts are expected to be selective towards single carbon (C₁) products in electrochemical CO₂RR. However, there are few computational studies that have investigated MXene-supported SACs towards the CO₂RR, especially for C₁ products such as methane and methanol. In the present study, density functional theory (DFT) is used to systematically evaluate the stability of the MXene support and SAC, and to screen different MXene structures for selective CO₂RR to C₁ products. Among a combination of ten metals and four supports screened, five catalysts exhibit low limiting potentials for C₁ products, especially methanol: Ni/Pd@Ti₃C₂O₂ and Ru/Fe/Co@Mo₂CO₂. Ni exhibits an exceptionally low reaction energy of 0.27 eV towards methane, while all others exhibit low reaction energy toward methanol ranging from 0.3 to 0.60 eV. The novel and in-depth understanding attained in this systematic high throughput DFT study guides the experimentalist to synthesize SACs based on MXene materials, with exceptional activity and selectivity for highly reduced C₁ products.