Curing BiVO4 Photoanodes with Ultraviolet Light Enhances Photoelectrocatalysis

Cl- modification for effective promotion of photoelectrochemical water oxidation over BiVO4

Postsynthetic treatment is an attractive method to enhance photoelectrochemical water splitting. The facile Cl^- modification approach developed in this work remarkably promotes the photocurrent density of BiVO₄ up to 2.7 mA cm^-2 by facilitating carrier transfer in addition to a charge carrier separation efficiency enhancement.

Photoelectrochemical Decomposition of Lignin Model Compound on a BiVO4 Photoanode

The photoelectrochemical decomposition of lignin model compounds at a BiVO₄ photoanode is demonstrated with simulated sunlight and an applied bias of 2.0 V. These prototypical lignin model compounds are photoelectrochemically converted into the corresponding aryl aldehyde and phenol derivatives in a single step with conversion of up to ≈64 % over 20 h. Control experiments suggest that vanadium sites are electrocatalytically active, which precludes the need for a redox mediator in solution. This feature of the system is corroborated by a layer of V₂ O₅ deposited on BiVO₄ serving to boost the conversion by 10 %. Our methodology capitalizes on the reactive power of sunlight to drive reactions that have only been studied previously by electrochemical or catalytic methods. The use of a BiVO₄ photoanode to drive lignin model decomposition therefore provides a new platform to extract valuable aromatic chemical feedstocks using solar energy, electricity and biomass as the only inputs.

Strong Light-Matter Interactions in Au Plasmonic Nanoantennas Coupled with Prussian Blue Catalyst on BiVO4 for Photoelectrochemical Water Splitting

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO₄ ) nanostructures, yielding Au-capped BiVO₄ (Au-BiVO₄ ). The formation of multiple size/dimension Au capping islands provides strong light-matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO₄ (through the excitation of Fabry-Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub-band-gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au-BiVO₄ /PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO₄ photoanode was obtained as 190 μA cm^-2 , whereas it was boosted to 295 μA cm^-2 and 1800 μA cm^-2 for Au-BiVO₄ and Au-BiVO₄ /PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic-based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs.

Efficient BiVO4 Photoanodes by Postsynthetic Treatment: Remarkable Improvements in Photoelectrochemical Performance from Facile Borate Modification

Water-splitting photoanodes based on semiconductor materials typically require a dopant in the structure and co-catalysts on the surface to overcome the problems of charge recombination and high catalytic barrier. Unlike these conventional strategies, a simple treatment is reported that involves soaking a sample of pristine BiVO4 in a borate buffer solution. This modifies the catalytic local environment of BiVO4 by the introduction of a borate moiety at the molecular level. The self-anchored borate plays the role of a passivator in reducing the surface charge recombination as well as that of a ligand in modifying the catalytic site to facilitate faster water oxidation. The modified BiVO4 photoanode, without typical doping or catalyst modification, achieved a photocurrent density of 3.5 mA cm-2 at 1.23 V and a cathodically shifted onset potential of 250 mV. This work provides an extremely simple method to improve the intrinsic photoelectrochemical performance of BiVO4 photoanodes.

Black phosphorene as a hole extraction layer boosting solar water splitting of oxygen evolution catalysts

As the development of oxygen evolution co-catalysts (OECs) is being actively undertaken, the tailored integration of those OECs with photoanodes is expected to be a plausible avenue for achieving highly efficient solar-assisted water splitting. Here, we demonstrate that a black phosphorene (BP) layer, inserted between the OEC and BiVO₄ can improve the photoelectrochemical performance of pre-optimized OEC/BiVO₄ (OEC: NiOOH, MnO_x, and CoOOH) systems by 1.2∼1.6-fold, while the OEC overlayer, in turn, can suppress BP self-oxidation to achieve a high durability. A photocurrent density of 4.48 mA·cm⁻² at 1.23 V vs reversible hydrogen electrode (RHE) is achieved by the NiOOH/BP/BiVO₄ photoanode. It is found that the intrinsic p-type BP can boost hole extraction from BiVO₄ and prolong holes trapping lifetime on BiVO₄ surface. This work sheds light on the design of BP-based devices for application in solar to fuel conversion, and also suggests a promising nexus between semiconductor and electrocatalyst.

Photoelectrochemical water splitting affords an integrated approach for converting light to fuel, but devices typically suffer poor activities and stabilities. Here, authors incorporate black phosphorene into bismuth vanadate photoanodes to boost hole extraction and device lifetimes.

Rapid Formation of a Disordered Layer on Monoclinic BiVO4 : Co-Catalyst-Free Photoelectrochemical Solar Water Splitting

A surface disordered layer is a plausible approach to improve the photoelectrochemical performance of TiO₂ . However, the formation of a crystalline disordered layer in BiVO₄ and its effectiveness towards photoelectrochemical water splitting has remained a big challenge. Here, we report a rapid solution process (within 5 s) that is able to form a disordered layer of a few nanometers thick on the surface of BiVO₄ nanoparticles using a specific solution with a controllable reducing power. The disordered layer on BiVO₄ alleviates charge recombination at the electrode-electrolyte interface and reduces the onset potential greatly, which in turn results in a photocurrent density of approximately 2.3 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode (RHE). This value is 2.1 times higher than that of bare BiVO₄ . The enhanced photoactivity is attributed to the increased charge separation and transfer efficiencies, which resolve the intrinsic drawbacks of bare BiVO₄ such as the short hole diffusion length of around 100 nm and poor surface oxygen evolution reactivity.

Water Splitting via Decoupled Photocatalytic Water Oxidation and Electrochemical Proton Reduction Mediated by Electron-Coupled-Proton Buffer

Water splitting mediated by electron-coupled-proton buffer (ECPB) provides an efficient way to avoid gas mixing by separating oxygen evolution from hydrogen evolution in space and time. Though electrochemical and photoelectrochemcial water oxidation have been incorporated in such a two-step water splitting system, alternative ways to reduce the cost and energy input for decoupling two half-reactions are desired. Herein, we show the feasibility of photocatalytic oxygen evolution in a powder system with BiVO₄ as a photocatalyst and polyoxometalate H₃ PMo₁₂ O₄₀ as an electron and proton acceptor. The resulting reaction mixture was allowed to be directly used for the subsequent hydrogen evolution with the reduced H₃ PMo₁₂ O₄₀ as electron and proton donors. Our system exhibits excellent stability in repeated oxygen and hydrogen evolution, which brings considerable convenience to decoupled water splitting.