A hole inversion layer at the BiVO4/Bi4V2O11 interface produces a high tunable photovoltage for water splitting

Interface Engineering-Driven Room-Temperature Ultralow Gas Sensors with Elucidating Sensing Performance of Heterostructure Transition Metal Dichalcogenide Thin Films

In this report, we investigate the room-temperature gas sensing performance of heterostructure transition metal dichalcogenide (MoSe2/MoS2, WS2/MoS2, and WSe2/MoS2) thin films grown over a silicon substrate using a pulse laser deposition technique. The sensing response of the aforementioned sensors to a low concentration range of NO2, NH3, H2, CO, and H2S gases in air has been assessed at room temperature. The obtained results reveal that the heterojunctions of metal dichalcogenide show a drastic change in gas sensing performance compared to the monolayer thin films at room temperature. Nevertheless, the WSe2/MoS2-based sensor was found to have an excellent selectivity toward NO2 gas with a particularly high sensitivity of 10 ppb. The sensing behavior is explained on the basis of a change in electrical resistance as well as carrier localization prospects. Favorably, by developing a heterojunction of diselenide and disulfide nanomaterials, one may find a simple way of improving the sensing capabilities of gas sensors at room temperature.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Boosting photoelectrochemical efficiency by near-infrared-active lattice-matched morphological heterojunctions

Photoelectrochemical catalysis is an attractive way to provide direct hydrogen production from solar energy. However, solar conversion efficiencies are hindered by the fact that light harvesting has so far been of limited efficiency in the near-infrared region as compared to that in the visible and ultraviolet regions. Here we introduce near-infrared-active photoanodes that feature lattice-matched morphological hetero-nanostructures, a strategy that improves energy conversion efficiency by increasing light-harvesting spectral range and charge separation efficiency simultaneously. Specifically, we demonstrate a near-infrared-active morphological heterojunction comprised of BiSeTe ternary alloy nanotubes and ultrathin nanosheets. The heterojunction's hierarchical nanostructure separates charges at the lattice-matched interface of the two morphological components, preventing further carrier recombination. As a result, the photoanodes achieve an incident photon-to-current conversion efficiency of 36% at 800 nm in an electrolyte solution containing hole scavengers without a co-catalyst.

Anomalous Photoinduced Reconstructing and Dark Self-Healing Processes on Bi2O2S Nanoplates

We report an anomalous photoinduced reconstructing and dark self-healing process on Bi₂O₂S nanoplates by monitoring the time profile of open-circuit potential (OCP). When the light was switched on and off on the nanoplates, we observed pronounced and repeatable decrement-recovery cycles of the OCP signal, which are inexplicable by a rapid electron-hole separation-recombination process only as in a conventional semiconductor. It is proposed that upon irradiation, accumulation of photogenerated holes at the electrode surface caused oxidation of the S layers of Bi₂O₂S nanoplates into certain intermediates, which, when the light was turned off, were then reduced back to the original state by the electron back flow. Raman scattering spectroscopy provided te S-S vibrational signature of the intermediate, evidencing the hole oxidative dimerization of the S^2- species and the inverse reductive S-S dissociation process. The photophysics and photochemistry of semiconductor nanoplates reported here may inspire the development of energy devices, switches, and memristors.

Innovative multifunctional hybrid photoelectrode design based on a ternary heterojunction with super-enhanced efficiency for artificial photosynthesis

Electrochemical cells for direct conversion of solar energy to electricity (or hydrogen) are one of the most sustainable solutions to meet the increasing worldwide energy demands. In this report, a novel and highly-efficient ternary heterojunction-structured Bi₄O₇/Bi_3.33(VO₄)₂O₂/Bi₄₆V₈O₈₉ photoelectrode is presented. It is demonstrated that the combination of an inversion layer, induced by holes (or electrons) at the interface of the semiconducting Bi_3.33(VO₄)₂O₂ and Bi₄₆V₈O₈₉ components, and the rectifying contact between the Bi₄O₇ and Bi_3.33(VO₄)₂O₂ phases acting afterward as a conventional p-n junction, creates an adjustable virtual p-n-p or n-p-n junction due to self-polarization in the ion-conducting Bi₄₆V₈O₈₉ constituent. This design approach led to anodic and cathodic photocurrent densities of + 38.41 mA cm^-2 (+ 0.76 V_RHE) and- 2.48 mA cm^-2 (0 V_RHE), respectively. Accordingly, first, this heterojunction can be used either as photoanode or as photocathode with great performance for artificial photosynthesis, noting, second, that the anodic response reveals exceptionally high: more than 300% superior to excellent values previously reported in the literature.

Pulsed Laser Deposition of Bismuth Vanadate Thin Films-The Effect of Oxygen Pressure on the Morphology, Composition, and Photoelectrochemical Performance

Thin layers of bismuth vanadate were deposited using the pulsed laser deposition technique on commercially available FTO (fluorine-doped tin oxide) substrates. Films were sputtered from a sintered, monoclinic BiVO₄ pellet, acting as the target, under various oxygen pressures (from 0.1 to 2 mbar), while the laser beam was perpendicular to the target surface and parallel to the FTO substrate. The oxygen pressure strongly affects the morphology and the composition of films observed as a Bi:V ratio gradient along the layer deposited on the substrate. Despite BiVO₄, two other phases were detected using XRD (X-ray diffraction) and Raman spectroscopy—V₂O₅ and Bi₄V₂O₁₁. The V-rich region of the samples deposited under low and intermediate oxygen pressures was covered by V₂O₅ longitudinal structures protruding from BiVO₄ film. Higher oxygen pressure leads to the formation of Bi₄V₂O₁₁@BiVO₄ bulk heterojunction. The presented results suggest that the ablation of the target leads to the plasma formation, where Bi and V containing ions can be spatially separated due to the interactions with oxygen molecules. In order to study the phenomenon more thoroughly, laser-induced breakdown spectroscopy measurements were performed. Then, obtained electrodes were used as photoanodes for photoelectrochemical water splitting. The highest photocurrent was achieved for films deposited under 1 mbar O₂ pressure and reached 1 mA cm⁻² at about 0.8 V vs Ag/AgCl (3 M KCl). It was shown that V₂O₅ on the top of BiVO₄ decreases its photoactivity, while the presence of a bulk Bi₄V₂O₁₁@BiVO₄ heterojunction is beneficial in water photooxidation.

Photoelectrochemical OER activity by employing BiVO4 with manganese oxide co-catalysts

Inspired by natural photosynthesis, various manganese oxides have been studied as co-catalysts with BiVO₄ for photoelectrochemical water splitting.

Metal Chalcogenides on Silicon Photocathodes for Efficient Water Splitting: A Mini Overview

In the photoelectrochemical (PEC) water splitting (WS) reactions, a photon is absorbed by a semiconductor, generating electron-hole pairs which are transferred across the semiconductor/electrolyte interface to reduce or oxidize water into oxygen or hydrogen. Catalytic junctions are commonly combined with semiconductor absorbers, providing electrochemically active sites for charge transfer across the interface and increasing the surface band bending to improve the PEC performance. In this review, we focus on transition metal (di)chalcogenide [TM(D)C] catalysts in conjunction with silicon photoelectrode as Earth-abundant materials systems. Surprisingly, there is a limited number of reports in Si/TM(D)C for PEC WS in the literature. We provide almost a complete survey on both layered TMDC and non-layered transition metal dichalcogenides (TMC) co-catalysts on Si photoelectrodes, mainly photocathodes. The mechanisms of the photovoltaic power conversion of silicon devices are summarized with emphasis on the exact role of catalysts. Diverse approaches to the improved PEC performance and the proposed synergetic functions of catalysts on the underlying Si are reviewed. Atomic layer deposition of TM(D)C materials as a new methodology for directly growing them and its implication for low-temperature growth on defect chemistry are featured. The multi-phase TM(D)C overlayers on Si and the operation principles are highlighted. Finally, challenges and directions regarding future research for achieving the theoretical PEC performance of Si-based photoelectrodes are provided.

pH-Dependent photocatalytic performance of modified bismuth vanadate by bismuth ferrite

The photoelectrochemical performance of bismuth vanadate (BVO) improved by a thin layer of bismuth ferrite (BFO).

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Bismuth Vanadate Photoelectrodes with High Photovoltage as Photoanode and Photocathode in Photoelectrochemical Cells for Water Splitting

Using dual-photoelectrode photoelectrochemical (PEC) devices based on earth-abundant metal oxides for unbiased water splitting is an attractive means of producing green H₂ fuel, but is challenging, owing to low photovoltages generated by PEC cells. This problem can be solved by coupling n-type BiVO₄ with n-type Bi₄ V₂ O₁₁ to create a virtual p/n junction due to the formation of a hole-inversion layer at the semiconductor interface. Thus, photoelectrodes with high photovoltage outputs were synthesized. The photoelectrodes exhibited features of p- and n-type semiconductors when illuminated under an applied bias, suggesting their use as photoanode and photocathode in a dual-photoelectrode PEC cell. This concept was proved by connecting a 1 mol % W-doped BiVO₄ /Bi₄ V₂ O₁₁ photoanode with an undoped BiVO₄ /Bi₄ V₂ O₁₁ photocathode, which produced a high photovoltage of 1.54 V, sufficient to drive stand-alone water splitting with 0.95 % efficiency.

Pires M, Lacerda LCT, Ramalho TC, Dias A, Pereira MC. Electrocatalytic performance of different cobalt molybdate structures for water oxidation in alkaline media

Among the CoMoO₄ polymorphs, the α-phase exhibits the highest performance for the oxygen evolution reaction.

Synthesis of Bi2O3–Bi4V2O11 heterojunctions with high interface quality for enhanced visible light photocatalysis in degradation of high-concentration phenol and MO dyes

Bi₂O₃–Bi₄V₂O₁₁ heterostructures with high interface quality were synthesized by calcining Bi₂VO_5.5–Bi(OHC₂O₄)·2H₂O precursors. The Bi₂O₃–Bi₄V₂O₁₁ heterostructure exhibits outstanding photocatalytic activity for degrading phenol and MO dyes with high concentration under visible light irradiation.

Novel two-dimensional Bi4V2O11 nanosheets: controllable synthesis, characterization and insight into the band structure

Novel two-dimensional Bi₄V₂O₁₁ nanosheets were controllably prepared using a stable [Bi(EDTA)]⁻ complex, and their band structures were investigated as well.

Recent Advances in Bismuth-Based Nanomaterials for Photoelectrochemical Water Splitting

In recent years, bismuth-based nanomaterials have drawn considerable interest as potential candidates for photoelectrochemical (PEC) water splitting owing to their narrow band gaps, nontoxicity, and low costs. The unique electronic structure of bismuth-based materials with a well-dispersed valence band comprising Bi 6s and O 2p orbitals offers a suitable band gap to harvest visible light. This Review presents significant advancements in exploiting bismuth-based nanomaterials for solar water splitting. An overview of the different strategies employed and the new ideas adopted to improve the PEC performance of bismuth-based nanomaterials are discussed. Morphology control, the construction of heterojunctions, doping, and co-catalyst loading are several approaches that are implemented to improve the efficiency of solar water splitting. Key issues are identified and guidelines are suggested to rationalize the design of efficient bismuth-based materials for sunlight-driven water splitting.

Facile synthesis of CdS/Bi4V2O11 photocatalysts with enhanced visible-light photocatalytic activity for degradation of organic pollutants in water

The development of Z-scheme heterojunction photocatalytic systems is a promising strategy to produce hydrogen and for pollutant degradation.