Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

Abstract

Screen-printing is a commonly used method for the preparation of photoelectrodes. Although previous studies have explored the effect of the number of printed layers on the efficiency of dye-sensitized solar cells, its interplay with the photoelectrocatalytic properties of the electrodes has rarely been examined. This study focuses on this issue by studying the photoelectrocatalytic oxidation of methanol over TiO 2 electrodes. Incident photon-to-current efficiencies reached 87 % at the optimal conditions of monochromatic (338 nm) irradiation of one-layer films at 0.2 V vs NHE. However, the irradiation wavelength and applied bias strongly influenced the relative behavior of the films. For instance, at 0.5 V and 327 nm irradiation, the one-layer electrode was 6 times more efficient than the four-layer one, while at 385 nm the four-layer electrode was 3.5 times more efficient. The results were explained on the basis of differing light absorption properties and charge carrier lifetimes. Modelling and quantification of the electron diffusion length (5.7 μm) helped to explain why the two-layer electrode (4.89 μm thick) showed the most consistent efficiencies across all conditions. Complementarily, transient absorption spectroscopy was used to correlate the thicknesses with charge carrier lifetimes. Electron transfer to FTO was apparent only for the thinner electrode. Our work shows that the optimization of photoelectrocatalytic processes should include the number of layers as a key variable.[a] C.The concentration of the transients follows a linear relation with the change in reflectance as long as the latter is lower than 10 %. [33] The measurements were performed in the wavelength range from 400 to 630 nm in 10 nm steps, 50 shots were averaged, and the data points were reduced to 200. 4 5 6 7 8

Mechanistic Insights into Selective Acetaldehyde Formation from Ethanol Oxidation on Hematite Photoanodes by Operando Spectroelectrochemistry

“…Such highly oxidative power results in the faradaic efficiency around 30 % for methanol oxidation to form formaldehyde [10] . Further formaldehyde oxidation to formic acid on TiO 2 over reaction time was observed in both PEC [5b] and transient absorption [5d] measurements, which is not observed in our study herein using α‐Fe 2 O 3 , indicative of the difference in thermodynamic activation barrier causing different reaction pathway. Our results indicating the thermodynamic and kinetic challenge for the oxidation of organic molecules is further supported by a recent study of oxidation reactions using TiO 2 for complete removal of persistent organic pollutants [3a] .…”

“…However, such impressive PEC results were only reported with a few metal oxide materials. For example, hematite (α‐Fe 2 O 3 ) and bismuth vanadate (BiVO 4 ) have been reported as suitable candidates for alcohol oxidation to form aldehyde with >90 % faradaic efficiency, [1a,9] whereas merely 30–60 % of faradaic efficiency of methanol oxidation to formaldehyde using titanium dioxide (TiO 2 ) were reported, [5b,10] clearly indicating that the reaction mechanism differs from materials and this particular challenge has not been significantly considered to date.…”

Charge Carriers in Commercial Photocatalysts: Fractal Kinetics and Effect of “Inert” Additives

“…These examples have shown the suitability of the model for the fit of transient signals for powdered photocatalysts, but the model can be applied for fitting the signals of photocatalyst films, as well. A recent work showed that the lifetime and the decay constant of screen-printed TiO 2 electrodes depend on the number of printed layers, and thus on the thickness of the films [14]. In Fig.…”

“…Thus, the transient signal decays faster for the one-layer electrode compared to the multilayer electrodes. These TiO 2 electrodes are one example where both, the second order model and the fractal kinetics model, are suitable for fitting the transient decays, and they also lead to similar results [14]. However, by fitting with the fractal kinetics model the fractal parameter h is obtained in addition, which is directly related to the surface roughness of the electrodes.…”

“…Adapted with permission from Ref. [14] Fig. 10 Average particle sizes of the commercial photocatalysts PC500, KronoClean 7050, PC105, and of the white pigment Kronos 1001.…”