Bismuth vanadate (BiVO4) thin film photoanodes for light‐induced water oxidation are deposited by a low‐cost and scalable spray pyrolysis method. The resulting films are of high quality, as indicated by an internal quantum efficiency close to 100 % between 360 and 450 nm. However, its performance under AM1.5 illumination is limited by slow water oxidation kinetics. This can be addressed by using cobalt phosphate (Co‐Pi) as a water oxidation co‐catalyst. Electrodeposition of 30 nm Co‐Pi catalyst on the surface of BiVO4 increases the water oxidation efficiency from ≈30 % to more than 90 % at potentials higher than 1.2 V vs. a reversible hydrogen electrode (RHE). Once the surface catalysis limitation is removed, the performance of the photoanode is limited by low charge separation efficiency; more than 60 % of the electron‐hole pairs recombine before reaching the respective interfaces. Slow electron transport is shown to be the main cause of this low efficiency. We show that this can be remedied by introducing W as a donor type dopant in BiVO4, resulting in an AM1.5 photocurrent of ≈2.3 mA cm−2 at 1.23 V vs. RHE for 1 % W‐doped Co‐Pi‐catalyzed BiVO4.

The electrocatalytic reduction of CO2 to chemical fuels has attracted significant attention in recent years. Among transition metals, silver shows one of the highest faradaic efficiencies for CO formation as the main reaction product; however, the exact mechanism for this conversion is not fully understood. In this work, we study the reaction mechanism of silver as a CO2 reduction catalyst using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) during electrochemical cycling. Using ATR-FTIR, it is possible to observe the reaction intermediates on the surface of Ag thin films formed during the CO2 electroreduction reaction. At a moderate overpotential, a proton coupled electron transfer reaction mechanism is confirmed to be the dominant CO2 reduction pathway. However, at a more negative applied potential, both the COO– and the COOH intermediates are detected using ATR-FTIR, which indicates that individual proton and electron transfer steps occur, offering a different pathway than at lower potentials. These results indicate that the CO2 reduction reaction mechanism can be potential dependent and not always involving a concerted proton coupled electron transfer, opening alternative pathways to optimize efficient and selective catalysts for desired product formation.

Grazing incidence operando EXAFS measurements allow observation of oxygen in oxide-derived silver catalysts, its effect on CO2 reduction is explained.

The field of electrochemical CO2 conversion is undergoing significant growth in terms of the number of publications and worldwide research groups involved. Despite improvements of the catalytic performance, the complex reaction mechanisms and solution chemistry of CO2 have resulted in a considerable amount of discrepancies between theoretical and experimental studies. A clear identification of the reaction mechanism and the catalytic sites are of key importance in order to allow for a qualitative breakthrough and, from an experimental perspective, calls for the use of in‐situ or operando spectroscopic techniques. In‐situ infrared spectroscopy can provide information on the nature of intermediate species and products in real time and, in some cases, with relatively high time resolution. In this contribution, we review key theoretical aspects of infrared reflection spectroscopy, followed by considerations of practical implementation. Finally, recent applications to the electrocatalytic reduction of CO2 are reviewed, including challenges associated with the detection of reaction intermediates.

Photocharging has recently been demonstrated as a powerful method to improve the photoelectrochemical water splitting performance of different metal oxide photoanodes, including BiVO4. In this work, we use ambient-pressure X-ray Raman scattering (XRS) spectroscopy to study the surface electronic structure of photocharged BiVO4. The O K edge spectrum was simulated using the finite difference method near-edge structure program package, which revealed a change in electron confinement and occupancy in the conduction band. These insights, combined with ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy analyses, reveal that a surface layer formed during photocharging creates a heterojunction with BiVO4, leading to favorable band bending and strongly reduced surface recombination. The XRS images presented in this work exhibit good agreement with soft X-ray absorption near-edge structure spectra from the literature, demonstrating that XRS is a powerful tool to study the electronic and structural properties of light elements in semiconductors. Our findings provide direct evidence of the electronic modification of a metal oxide photoanode surface as a result of the adsorption of electrolyte anionic species under operating conditions. This work highlights that the surface adsorption of these electrolyte anionic species is likely present in most studies on metal oxide photoanodes and has serious implications for the photoelectrochemical performance analysis and fundamental understanding of these materials.