Improved Photoelectrochemical Performance of WO/BiVO Heterojunction Photoanodes via WO Nanostructuring.

WO/BiVO heterojunction photoanodes can be efficiently employed in photoelectrochemical (PEC) cells for the conversion of water into molecular oxygen, the kinetic bottleneck of water splitting. Composite WO/BiVO photoelectrodes possessing a nanoflake-like morphology have been synthesized through a multistep process and their PEC performance was investigated in comparison to that of WO/BiVO photoelectrodes displaying a planar surface morphology and similar absorption properties and thickness. PEC tests, also in the presence of a sacrificial hole scavenger, electrochemical impedance analysis under simulated solar irradiation, and incident photon to current efficiency measurements highlighted that charge transport and charge recombination issues affecting the performance of the planar composite can be successfully overcome by nanostructuring the WO underlayer in nanoflake-like WO/BiVO heterojunction electrodes.

Ni(II)-doped CuWO photoanodes with enhanced photoelectrocatalytic activity.

CuWO has emerged in the last years as a ternary metal oxide material for photoanodes application in photoelectrochemical cells, thanks to its relatively narrow band gap, high stability and selectivity toward the oxygen evolution reaction, though largely limited by its poor charge separation efficiency. Aiming at overcoming this limitation, we investigate here the effects that Cu(II) ion substitution has on the photoelectrocatalytic (PEC) performance of copper tungstate. Optically transparent CuWO thin-film photoanodes, prepared via spin coating and containing different amounts of Ni(II) ions, were fully characterized via UV-Vis spectroscopy, XRD and SEM analyses, and their PEC performance was tested via linear sweep voltammetry, incident photon to current efficiency and internal quantum efficiency analyses.

Nature of Charge Carrier Recombination in CuWO Photoanodes for Photoelectrochemical Water Splitting.

CuWO is a ternary semiconductor oxide with excellent visible light harvesting properties up to 550 nm and stability at high pH values, which make it a suitable material to build photoanodes for solar light conversion to hydrogen via water splitting. In this work, we studied the photoelectrochemical (PEC) performance of transparent CuWO electrodes with tunable light absorption and thickness, aiming at identifying the intrinsic bottlenecks of photogenerated charge carriers in this semiconductor. We found that electrodes with optimal CuWO thickness exhibit visible light activity due to the absorption of long-wavelength photons and a balanced electron and hole extraction from the oxide.

Strong-Proton-Adsorption Co-Based Electrocatalysts Achieve Active and Stable Neutral Seawater Splitting.

Direct electrolysis of pH-neutral seawater to generate hydrogen is an attractive approach for storing renewable energy. However, due to the anodic competition between the chlorine evolution and the oxygen evolution reaction (OER), direct seawater splitting suffers from a low current density and limited operating stability. Exploration of catalysts enabling an OER overpotential below the hypochlorite formation overpotential (≈490 mV) is critical to suppress the chloride evolution and facilitate seawater splitting.

Enhanced Charge Carrier Separation in WO/BiVO Photoanodes Achieved via Light Absorption in the BiVO Layer.

Photoelectrochemical (PEC) water splitting converts solar light and water into oxygen and energy-rich hydrogen. WO/BiVO heterojunction photoanodes perform much better than the separate oxide components, though internal charge recombination undermines their PEC performance when both oxides absorb light. Here we exploit the BiVO layer to sensitize WO to visible light and shield it from direct photoexcitation to overcome this efficiency loss.

Ultrafast Charge Carrier Dynamics in CuWO Photoanodes.

CuWO is a ternary metal oxide semiconductor with promising properties for photoelectrochemical (PEC) water splitting and solar light conversion, due to its quite low band gap (2.3 eV) and high stability in an alkaline environment. Aiming at understanding the origin of the relatively low PEC efficiency attained with CuWO photoanodes, we here investigate transparent CuWO electrodes prepared by a simple solution-based method through the combination of femtosecond transient absorption spectroscopy with electrochemical, PEC, and photochromic characterizations.

WO/BiVO Photoanodes: Facets Matching at the Heterojunction and BiVO Layer Thickness Effects.

Photoelectrochemical solar energy conversion offers a way to directly store light into energy-rich chemicals. Photoanodes based on the WO/BiVO heterojunction are most effective mainly thanks to the efficient separation of photogenerated charges. The WO/BiVO interfacial space region in the heterojunction is investigated here with the increasing thickness of the BiVO layer over a WO scaffold.

Effective Visible Light Exploitation by Copper Molybdo-tungstate Photoanodes.

The need for stable oxide-based semiconductors with a narrow band gap, able to maximize the exploitation of the visible light portion of the solar spectrum, is a challenging issue for photoelectrocatalytic (PEC) applications. In the present work, CuW Mo O ( = 2.0 eV for = 0.

Photoinduced electron transfer in WO/BiVO heterojunction photoanodes: effects of the WO layer thickness.

The PEC performance of WO/BiVO heterojunction photoanodes with a fixed BiVO thick top layer and different WO layer thicknesses was investigated under backside irradiation, in comparison with the performance of the same electrodes without a top BiVO layer. While the performance of these latter increase with increasing WO thickness, the presence of a BiVO layer, besides leading to an effective sensitization up to 520 nm, leads to a decrease of incident photon to current efficiency in the short wavelength's range. After having excluded major WO filter effects, this has been attributed to charge carrier recombination effects occurring when both oxides get excited and becoming more relevant with increasing WO thickness and decreasing excitation wavelength.

Photoinduced Charge-Transfer Dynamics in WO/BiVO Photoanodes Probed through Midinfrared Transient Absorption Spectroscopy.

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