Bismuth vanadate (BiVO4) with a band gap of ∼2.4 eV has emerged as one of the visible photocatalysts that can absorb light below 520 nm. The electron/hole pairs that are generated following BiVO4 band gap excitation are effective for water splitting, especially when BiVO4 is combined with other metal oxides such as WO3. We report a solution processed method for designing transparent WO3/BiVO4 heterojunction electrodes and observe a synergistic effect on the photoelectrochemical activity of WO3/BiVO4, with the combined system performing dramatically better than either individual component. Using ultrafast transient absorption spectroscopy, we elucidated the electronic interaction between WO3 and excited BiVO4. Moreover, the photocatalytic reduction of thionine by WO3/BiVO4 as well as by each individual oxide component is used to track electron injection processes and determine the energetics of the studied systems. In the composite WO3/BiVO4 film a shifted quasi-Fermi level results, due to electronic equilibration between the two materials. The better performance of WO3/BiVO4 heterojunction electrodes is thus a consequence of the electron injection from BiVO4 into WO3, followed by back electron transfer from WO3 to the holes in BiVO4.

We report formate production via CO2 electroreduction at a Faradaic efficiency (FE) of 93% and a partial current density of 930 mA cm -2 , an activity level of potential industrial interest based on prior techno-economic analyses. We devise a novel catalyst synthesized using InP colloidal quantum dots (CQDs): the capping ligand exchange introduces surface sulfur, and XPS reveals the generation, operando, of an active catalyst exhibiting sulfur-protected oxidized indium and indium metal. Surface indium metal sites adsorb and reduce CO2 molecules, while

Due to its ∼2.4 eV band gap, BiVO 4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO 3 /BiVO 4 heterojunction films, the electrons photoexcited in BiVO 4 are injected into WO 3 , overcoming the lower charge carriers' diffusion properties limiting the PEC performance of BiVO 4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO 4 excitation, a favorable electron transfer from photoexcited BiVO 4 to WO 3 occurs immediately after excitation and leads to an increase of the trapped holes' lifetime in BiVO 4 . However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO 4 . PEC measurements reveal the implication of these wavelengthdependent ultrafast interactions on the performances of the WO 3 /BiVO 4 heterojunction.

The dynamics of photopromoted electrons in BiVO 4 , WO 3 and WO 3 /BiVO 4 heterojunction electrodes has been directly probed by transient absorption (TA) mid-infrared (mid-IR) spectroscopy in the picosecond to microsecond time range. By comparing the dynamics recorded with the two individual oxides at 2050 cm-1 with that of the heterojunction system after excitation at different wavelengths, electron transfer processes between selectively excited BiVO 4 and WO 3 have been directly tracked for the first time. These results support the charge carrier interactions which were previously hypothesized by probing the BiVO 4 hole dynamics through TA spectroscopy in the visible range. Nanosecond mid-IR TA experiments confirmed that charge carrier separation occurs in WO 3 /BiVO 4 electrodes under visible light excitation, persisting up to the microsecond timescale.