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. 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 products (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 little computational studies that investigate MXene-supported SACs towards the CO2RR, especially for C1 products such as methane and methanol. In the present study, the 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 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 0.3 eV towards methane, while all others exhibit low reaction energy toward methanol ranging from 0.37 to 0.60 eV. The novel and in-depth understanding attained in this systematic high throughput DFT study guide the experimentalist to synthesize SACs based on MXene materials, with exceptional activity and selectivity for highly reduced C1 products.