Aspects of Photoelectrocatalytic Reduction of CO2 on Titanium Oxide Catalysts Modified with Ag, Au, and Pt

The work investigated the influence of the nature and amount of the applied noble metal, as well as the physicochemical properties of the initial TiO2 on the process of photoelectrocatalytic reduction of CO2. Catalysts of the compositions x% Me/TiO2 (where Me = Ag, Au, Pt; and x = 0.1–2 wt %) were synthesized on the basis of titanium dioxide of the brands Evonik P25 (anatase : rutile ratio = 75 : 25) and EuroSupport (anatase >99%) by chemical reduction from metal salts using NaBH4. The samples were characterized by X‑ray powder diffraction analysis, X-ray photoelectron spectroscopy, and UV–Vis diffuse reflectance spectroscopy. The catalytic properties of the obtained samples were studied in the photoelectrocatalytic reduction of carbon dioxide in 0.1 M KHCO3 electrolyte at a potential of –700 mV versus Ag/AgCl/KCl(sat) under irradiation at a wavelength of 371 nm. Data on the accumulation of total organic carbon in the solution showed that, for each supported metal, the activity of the samples based on EuroSupport anatase-rich TiO2 is 20% higher than the activity of the samples based on Evonik P25 rutile-containing TiO2 at identical values of current efficiency. A conclusion was made about the observed decrease in electron energy and the reducing capacity of the catalyst by the rutile phase in Evonik P25 TiO2. Based on the relationship between the activity and utilization efficiency of metals in the CO2 reduction process, Au was selected as the preferred metal for photoelectrocatalytic CO2 reduction.