Porous Tantalum Nitride Single Crystal at Two‐Centimeter Scale with Enhanced Photoelectrochemical Performance

Pore walls as high-way for efficient bulk charge transfer in porous SrTiO3 single crystals boosting photocatalytic overall water splitting

Suppressing carrier recombination in bulk and facilitating carrier transfer to surface via rational structure design is of great significance to improve solar-to-H2 conversion efficiency. We demonstrate a facile hydrothermal method to synthesize porous SrTiO3 single crystals (SrTiO3-P) with exposed (001) facets by introducing carbon spheres as templates. The obviously increased surface photovoltage and photocurrent response indicate that the interconnected pore walls act as enormous charge transfer "highways", accelerating carrier transport from bulk to surface. Furthermore, the absence of grain boundaries and high crystallinity could also lower the carrier recombination rate. Thus, the SrTiO3-P photocatalyst loaded with Rh/Cr2O3 as cocatalyst exhibits 1.5 times higher overall water splitting activity than that of solid SrTiO3, with gas evolution rate of 19.99 μmol h-1 50 mg-1 for H2 and 11.37 μmol h-1 50 mg-1 for O2. Additionally, SrTiO3-P also shows superior stability without any decay during cycling testing. This work provides a new insight into designing efficient multicomponent photocatalysts with a single-crystal porous structure.

Fast annealing fabrication of porous CuWO4photoanode for charge transport in photoelectrochemical water oxidation

Ternary-phase CuWO4oxide with an electronic band gap of 2.2-2.4 eV is a potential candidate photoanode material for photoelectrochemical (PEC) water splitting. Herein, we present an efficient method to prepare CuWO4film photoanode by combining hydrothermal method and hybrid microwave annealing (HMA) process. In comparison with conventional thermal annealing (CTA), HMA can achieve CuWO4thin film within minutes by using SiC susceptor. When the CuWO4photoanode is prepared by HMA, its PEC water oxidation performance improves from 0.21 to 0.29 mA cm-2at 1.23 VRHEcomparing with the one prepared by CTA. The origin of the enhanced photocurrent was investigated by means of complementary physical characterizations and PEC methods. The results demonstrated that the obtained HMA processed CuWO4photoanode not only exhibited intrinsic porous nanostructures but also abundant surface hydroxyl groups, which facilitated sufficient mass transport and the charge transfer. Our results highlight the application of HMA for the fast fabrication of porous film photo-electrodes without using sacrificial template.

Confined liquid crystallization governed by electric field for API crystal polymorphism screening and massive preparation

Active pharmaceutical ingredients (APIs) crystal preparation is a significant issue for the pharmaceutical development attributed to the effect on anti-inflammatory, anti-bacteria, and anti-viral, etc. While, the massive preparation of API crystal with high polymorphism selectivity is still a pendent challenge. Here, we firstly proposed a criterion according to the molecular aggregation, molecular orientation, and hydrogen bond energy between INA molecules from molecular dynamics (MD) simulations, which predicted the hydrogen bond architecture in crystal under different electric fields, hinting the recognition of crystal polymorphism. Then, an electric field governing confined liquid crystallization was constructed to achieve the INA crystal polymorphism screening relying on the criterion. Further, magnifying confined liquid volume by 5000 times from 1.0 μL to 5.0 mL realized the massive preparation of INA crystal with high polymorphic purity (>98.4%), giving a unique pathway for crystal engineering and pharmaceutical industry on the development of innovative and generic API based drugs.

Multifunctional Supramolecular Hydrogel Modulated Heterojunction Interface Carrier Transport Engineering Facilitates Sensitive Photoelectrochemical Immunosensing

Highly responsive interface of semiconductor nanophotoelectrochemical materials provides a broad development prospect for the identification of low-abundance cancer marker molecules. This work innovatively proposes an efficient blank WO3/SnIn4S8 heterojunction interface formed by self-assembly on the working electrode for interface regulation and photoregulation. Different from the traditional biomolecular layered interface, a hydrogel layer containing manganese dioxide with a wide light absorption range is formed at the interface after an accurate response to external immune recognition. The formation of the hydrogel layer hinders the effective contact between the heterojunction interface and the electrolyte solution, and manganese dioxide in the hydrogel layer forms a strong competition between the light source and the substrate photoelectric material. The process effectively improves the carrier recombination efficiency at the interface, reduces the interface reaction kinetics and photoelectric conversion efficiency, and thus provides strong support for target identification. Taking advantage of the process, the resulting biosensors are being explored for sensitive detection of human epidermal growth factor receptor 2, with a limit of detection as low as 0.037 pg/mL. Also, this study contributes to the advancement of photoelectrochemical biosensing technology and opens up new avenues for the development of sensitive and accurate analytical tools in the field of bioanalysis.

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Engineering band structuring via dual atom modification for an efficient photoanode

Efficient carrier separation is important for improving photoelectrochemical water splitting. Here, the morphology modification and band structure engineering of Ta3N5 are accomplished by doping it with Cu and Zr using a two-step method for the first time. The initially interstitially-doped Cu atoms act as anchors to interact with subsequently doped Zr atoms under the influence of differences in electronegativity. This interaction results in Cu,Zrg-Ta3N5 having a dense morphology and higher crystallinity, which helps to reduce carrier recombination at grain boundaries. Furthermore, the gradient doping of Zr generates a band edge energy gradient, which significantly enhances bulk charge separation efficiency. Therefore, a photoanode based on Cu,Zrg-Ta3N5 delivers an onset potential of 0.38 VRHE and a photocurrent density of 8.9 mA cm-2 at 1.23 VRHE. Among all the Ta3N5-based photoanodes deposited on FTO, a Cu,Zrg-Ta3N5-based photoanode has the lowest onset potential and highest photocurrent. The novel material morphology regulation and band edge position engineering strategies described herein provide new ideas for the preparation of other semiconductor nanoparticles to improve the photoelectrochemical water splitting performance.

Enhanced Spatial Charge Separation in a Niobium and Tantalum Nitride Core-Shell Photoanode: In Situ Interface Bonding for Efficient Solar Water Splitting

Tantalum nitride (Ta3 N5 ) has emerged as a promising photoanode material for photoelectrochemical (PEC) water splitting. However, the inefficient electron-hole separation remains a bottleneck that impedes its solar-to-hydrogen conversion efficiency. Herein, we demonstrate that a core-shell nanoarray photoanode of NbNx -nanorod@Ta3 N5 ultrathin layer enhances light harvesting and forms a spatial charge-transfer channel, which leads to the efficient generation and extraction of charge carriers. Consequently, an impressive photocurrent density of 7 mA cm-2 at 1.23 VRHE is obtained with an ultrathin Ta3 N5 shell thickness of less than 30 nm, accompanied by excellent stability and a low onset potential (0.46 VRHE ). Mechanistic studies reveal the enhanced performance is attributed to the high-conductivity NbNx core, high-crystalline Ta3 N5 mono-grain shell, and the intimate Ta-N-Nb interface bonds, which accelerate the charge-separation capability of the core-shell photoanode. This study demonstrates the key roles of nanostructure design in improving the efficiency of PEC devices.

Near-infrared responsive sulfur vacancy-rich CuS nanosheets for efficient antibacterial activity via synergistic photothermal and photodynamic pathways

Defect engineering has been proven to be an effective approach for electronic structure modulation and plays an important role in the photocatalytic performance of nanomaterials. In this study, a series of CuS nanosheet sulfur vacancies (V_S) are constructed by a simple hydrothermal synthesis method. The CuS with the highest V_S concentration exhibits strong antibacterial performance, achieving bactericidal rates of 99.9% against the Gram-positive Bacillus subtilis and Gram-negative Escherichia coli bacteria under 808 nm laser irradiation. Under illumination, the temperature of the catalyst increases from 23.5 °C to 53.3 °C, and with a high photothermal conversion efficiency of 41.8%. For E. coli and B. subtilis, the reactive oxygen species (ROS) production that is induced by the CuS group is 8.6 and 9.6 times greater, respectively, than that of the control group. The presence of V_S facilitates the enhancement of the light absorption capacity and the separation efficiency of electron-hole pairs, thereby resulting in improved photocatalytic performance. The synergistic effect of photothermal therapy (PTT) and photodynamic therapy (PDT) is aimed at causing oxidative damage and leading to bacterial death. Our findings provide an effective antibacterial strategy and offer new horizons for the application of CuS catalysts with V_S in the NIR region.

Porous single-crystalline vanadium nitride octahedra with a unique electrocatalytic performance

Here we grow porous single-crystalline vanadium nitride that has a good performance in the HER, showing high activity and stability.

LaTaON2 Mesoporous Single Crystals for Efficient Photocatalytic Water Oxidation and Z-Scheme Overall Water Splitting

LaTaON₂ porous single crystals (PSCs), integrating structural coherence and porous microstructures, will warrant promising photocatalytic performance. The absence of grain boundaries in PSCs ensures rapid photocarrier transportation from bulk to the surface, thereby mitigating photocarriers' recombination. Porous microstructures not only provide ample reachable surface to host photochemical reactions but also reinforce photon-matter interactions by additional photon reflection/scattering. Here, we have synthesized LaTaON₂ PSCs via a topotactic route and show significantly improved photocatalytic performance. Efficient water oxidation into O₂ has been realized by LaTaON₂ PSCs with an apparent quantum efficiency as high as 5.7% at 420 ± 20 nm. Stable overall water splitting into stoichiometric H₂ and O₂ has also been achieved in a Z-scheme setup using LaTaON₂ PSCs as the O₂ evolution photocatalyst. These results not only prove that PSCs facilitate photocarrier migrations, which in turn deliver exceptional photocatalytic performance, but also imply that PSCs are useful to reinvigorate conventional semiconductor photocatalysts toward efficient solar energy conversions.

Maximizing Oxygen Evolution Performance on a Transparent NiFeOx/Ta3N5 Photoelectrode Fabricated on an Insulator

A transparent Ta₃N₅ photoanode is a promising candidate for the front-side photoelectrode in a photoelectrochemical (PEC) cell with tandem configuration (tandem cell), which can potentially provide high solar-to-hydrogen (STH) energy conversion efficiency. This study focuses in particular on the semiconductor properties and interfacial design of transparent Ta₃N₅ photoanodes fabricated on insulating quartz substrates (Ta₃N₅/SiO₂), typically the geometric area of 1 × 1 cm² in contact with indium on its edge. This material utilizes the self-conductivity of Ta₃N₅ to make the PEC system operational, and the electrode would strongly reflect the intrinsic nature of Ta₃N₅ without a back contact that is commonly introduced. First, PEC measurements using acetonitrile (ACN)/H₂O mixed solution were made to elucidate the intrinsic photoresponse in the presence of tris(2,2'-bipyridine)ruthenium(II) bis(hexafluorophosphate) (Ru(bpy)₃(PF₆)₂) without water contact which avoids a multielectron-transfer oxygen evolution reaction (OER) and photoinduced self-oxidation. The potential difference between the onset potential of Ru²⁺ PEC oxidation by Ta₃N₅/SiO₂ and the redox potential of Ru^2+/3+ in the nonaqueous environment was about 0.7 V. While a stable photoanodic response was observed for Ta₃N₅/SiO₂ in the nonaqueous phase, the addition of a small quantity of water into this nonaqueous system led to the immediate deactivation of Ta₃N₅/SiO₂ photoanode under illumination by self-photooxidation to form TaO_x at the solid/water interface. In aqueous phase, flatband potentials estimated from Mott-Schottky analysis varied with solution pH (constant potential against reversible hydrogen electrode (RHE)). Photoelectrode modification by a transparent NiFeO_x layer was attempted. The complete coverage of the Ta₃N₅ surface with transparent NiFeO_x electrocatalysts, achieved by an optimized spin-coating protocol with controlled Ni-Fe precursors, allowed for the successful protection of Ta₃N₅ and demonstrated an extremely stable photocurrent for hours without any additional protective layers. The stability of the resultant NiFeO_x/Ta₃N₅/SiO₂ was limited not by Ta₃N₅ but mainly by a NiFeO_x electrocatalyst due to Fe dissolution with time.

Boosted dehydrogenation of ethane over porous vanadium-based single crystals

Schematic illustration of the dehydrogenation of ethane over porous single crystals.