Electrocatalysis of carbon compounds on rutile transition metal oxide catalysts : an ab initio study

Rutile transition metals have lately been reported to exhibit outstanding catalytic activity. Whereas the Oxygen Evolution Reaction (OER) has been intensively studied on these catalysts, only very few mentions exist of these materials catalyzing the CO2 Reduction Reaction. It is in the scope of this work to investigate both electrocatalytic reactions at low potential on IrO2 and RuO2 slabs. Ab initio computations implementing Density Functional Theory (DFT) are used to calculate the total energy of structures with adsorbates. Stability analyses are performed using relative stability diagrams to screen for interesting reaction intermediates in a wide potential range. Free energy diagrams are constructed to identify potential limiting steps in the studied reaction mechanisms. To the extent possible, results are systematically confronted to reference work. The critical influence of Zero Point Energy (ZPE) and van der Waals (vdW) corrections on the simulations are exposed. RuO2 is found to display increased affinity with OER intermediates as compared to IrO2. A hydrogen-covered surface reconstruction (Ir2O) on a IrO2 slab is shown to exhibit competing stability with conventional IrO2 surface intermediates at potentials below −0.52 V . Within the thermodynamic limits of this work, IrO2 displays better affinity with carbon adsor- bates and better performances in the CO2 Reduction Reaction to methane than RuO2. The CO2 Reduction Reaction is shown to become favorable as from potentials as low as −0.22V on an IrO2 catalyst, in contrast to −0.47V on RuO2. At last, CO2 reduction through a COH∗ intermediate on an IrO2 catalyst appears to be an interesting lead.