Electrochemical reduction of CO₂ on graphene supported transition metals - towards single atom catalysts

In this study, we have investigated the use of single metal atoms supported on defective graphene as catalysts for the electrochemical reduction of CO₂ using the first-principles approach and the computational hydrogen electrode model. Reaction pathways to produce a variety of C₁ products CO, HCOOH, HCHO, CH₃OH and CH₄ have been studied in detail for five representative transition metals Ag, Cu, Pd, Pt, and Co. Different pathways were revealed in contrast to those found for metallic crystalline surfaces and nanoparticles. These single atom catalysts have demonstrated a general improvement in rate limiting potentials to generate C₁ hydrocarbons. They also show distinct differences in terms of their efficiency and selectivity in CO₂ reduction, which can be correlated with their elemental properties as a function of their group number in the periodic table. Six best candidates for CH₄ production are identified by conducting computational screening of 28 d-block transition metals. Ag has the lowest overpotential (0.73 V), and is followed by Zn, Ni, Pd, Pt and Ru with overpotentials all below 1 V. Cu in the supported single atom form shows a strong preference towards producing CH₃OH with an overpotential of 0.68 V well below the value of 1.04 V for producing CH₄.