A team led by researchers form Temple University has developed earth-abundant electrocatalysts—Mo₂C and Ti₃C₂ MXenes—for the electroreduction of CO₂ to CO. In an open-access paper in the RSC journal ChemComm, the researchers report that Mo2C and Ti3C2 exhibited Faradaic efficiencies of 90% (250 mV overpotential) and 65% (650 mV overpotential), respectively, for the reduction of CO₂ to CO in acetonitrile using an ionic liquid electrolyte.

The researchers found that the use of ionic liquid 1-ethyl-2-methylimidazolium tetrafluoroborate as an electrolyte in organic solvent suppressed the competing hydrogen evolution reaction. Density functional theory (DFT) calculations suggested that the catalytic active sites are oxygen vacancy sites on both MXene surfaces. Also, a spontaneous dissociation of absorbed COOH species to a water molecule and absorbed CO on Mo₂C promote the CO₂RR.

The development of the electrochemical CO₂ reduction reaction (CO₂RR) would help to create a closed carbon cycle around the burning of fossil fuels and potentially mitigate environmental problems resulting from the release of CO₂ to the atmosphere. The utility of an efficient CO₂RR would not only include the suppression of greenhouse gas emission, but it could potentially extend to the generation of industrially valuable chemicals that are now obtained through the petroleum industry. Development of earth-abundant and relatively inexpensive catalysts, however, that efficiently drive the electrochemical CO₂RR to produce fuels and commodity chemicals still remains a challenge.

… In the current study we investigated the ability of Mo₂CT_x and Ti₃C₂T_x (MXenes), comprised of earth abundant elements, to catalyze the electrochemical CO₂RR. MXenes are a class of 2D materials comprised of transition metal carbides, nitrides, and carbonitrides derived from ternary carbides and nitrides, mostly MAX phases.

The name MAX is derived from the composition of the material where “M” denotes an early transition metal, “A” an A-group metal such as aluminium or gallium and “X” denotes carbon and/or nitrogen. MXenes have the general formula M_n+1X_nT_x (n=1-4) where Tx represents the surface functional groups, mostly –OH, –F, and =O. The Tx notation, however, is dropped hereafter from the general formula for brevity. Relevant to the current study, a prior density functional theory (DFT) computational study suggested that M₃C₂ MXenes are promising materials for the CO₂RR. The experimental studies discussed in this contribution evaluate the Mo₂C and Ti₃C₂ MXenes for the CO₂RR.

—Attanayake et al.

Resources

• Nuwan H. Attanayake, Huta Raj Banjade, Akila Thenuwara, Babak Anasori, Qimin Yan and Daniel Strongin (2020) “Electrocatalytic CO₂ reduction on earth abundant 2D Mo₂C and Ti₃C₂MXenes” Chemical Communications doi: 10.1039/D0CC05822J