Single-Site, Heterogeneous Electrocatalytic Reduction of CO2 in Water as the Solvent

Creating stable surface-bound molecular catalysts for CO2 reduction in aqueous solutions for either electrochemical or photoelectrochemical reduction is a continuing challenge. We report here the preparation and characterization of thin oxide/carbon nanotube electrodes on fluorine-doped tin oxide (FTO) electrodes. The electrodes were prepared by atomic layer deposition (ALD) of similar to 15 nm of TiO2 followed by a layer of carbon nanotubes and a thin (2 nm) overlayer of TiO2 for surface stabilization and binding. The phosphonate-derivatized version of the known aqueous solution catalyst for H-2/CO reduction, [Ru-II(tpy-Ph CH2 PO3H2)(Mebim-py)(H2O)](PF6)(2) (tpy-Ph-CH2-PO3H2 = (4-([2, 2':6',2"-terpyridin]-4'-yObenzyl)phosphonic acid; Mebim-py = 3-methyl-lpyridyl-benzimidazol-2-ylidene), was added to the surface and stabilized by addition of a thin overlayer of TiO2 by ALD. In the derivatized electrodes, the catalyst maintains its reactivity toward CO2 reduction in the short-term, giving mixtures of H-2/CO that vary from 1.5 at -0.96 V to 5.6 at -1.16 V vs NHE in 0.5 M NaHCO3 with a turnover number of 308 after 15 min of electrolysis.