Fast fabrication of Ta2O5 nanotube arrays and their conversion to Ta3N5 for efficient solar driven water splitting

This work shows that highly ordered and mechanically stable micrometer-long Ta₂O₅ nanotube arrays can be fabricated by galvanostatic anodization in a few seconds. Typically, ~ 7.7 μm long nanotubes can be grown at 1.2 A cm^− 2 in only 2 s. Such nanotubes can be converted to Ta₃N₅ nanotube arrays by nitridation. Photoelectrochemical (PEC) water splitting using AM 1.5G illumination yields for the Ta₃N₅ nanotube photoanode modified with cobalt phosphate (Co–Pi) remarkable photocurrents of 5.9 mA cm ⁻² at 1.23 V_RHE and 12.9 mA cm ⁻² at 1.59 V_RHE and after Ba-doping a value of 7.5 mA cm ⁻² at 1.23 V_RHE is obtained.     

Introducing Bidirectional Axial Coordination into BiVO4@Metal Phthalocyanine Core–Shell Photoanodes for Efficient Water Oxidation

Core-shell photoanodes have shown great potential for photoelectrochemical (PEC) water oxidation. However, the construction of a high-quality interface between the core and shell, as well as a highly catalytic surface, remains a challenge. Herein, guided by computation, we present a BiVO₄ photoanode coated with ZnCoFe polyphthalocyanine using pyrazine as a coordination agent. The bidirectional axial coordination of pyrazine plays a dual role by facilitating intimate interfacial contact between BiVO₄ and ZnCoFe polyphthalocyanine, as well as regulating the electron density and spin configuration of metal sites in ZnCoFe phthalocyanine, thereby promoting the potential-limiting step of *OOH desorption. The resulting photoanode displayed a high photocurrent density of 5.7±0.1 mA cm⁻² at 1.23 V_RHE. This study introduces a new approach for constructing core–shell photoanodes, and uncovers the key role of pyrazine axial coordination in modulating the catalytic activity of metal phthalocyanine.     

Enhanced Photoelectrochemical Water Oxidation from CdTe Photoanodes Annealed with CdCl2

Most CdTe photoanodes and photocathodes show positive and negative photocurrent onset potentials for water oxidation and reduction, respectively, and are thus unable to drive photoelectrochemical (PEC) water splitting without external applied biases. Herein, the activity of a CdTe photoanode having an internal p‐n junction during PEC water oxidation was enhanced by applying a CdCl₂ annealing treatment together with surface modifications. The resulting CdTe photoanode generated photocurrents of 1.8 and 5.4 mA cm^?2 at 0.6 and 1.2 V_RHE, respectively, with a photoanodic current onset potential of 0.22 V_RHE under simulated sunlight (AM 1.5G). The CdCl₂ annealing increased the grain sizes and lowered the density of grain boundaries, allowing more efficient charge separation. Consequently, a two‐electrode tandem PEC cell comprising a CdTe‐based photoanode and photocathode split water without any external bias at a solar‐to‐hydrogen conversion efficiency of 0.51 % at the beginning of the reaction.     

Highly Active GaN‐Stabilized Ta3N5 Thin‐Film Photoanode for Solar Water Oxidation

Ta₃N₅ is a very promising photocatalyst for solar water splitting because of its wide spectrum solar energy utilization up to 600 nm and suitable energy band position straddling the water splitting redox reactions. However, its development has long been impeded by poor compatibility with electrolytes. Herein, we demonstrate a simple sputtering‐nitridation process to fabricate high‐performance Ta₃N₅ film photoanodes owing to successful synthesis of the vital TaO_δ precursors. An effective GaN coating strategy is developed to remarkably stabilize Ta₃N₅ by forming a crystalline nitride‐on‐nitride structure with an improved nitride/electrolyte interface. A stable, high photocurrent density of 8 mA cm⁻² was obtained with a CoPi/GaN/Ta₃N₅ photoanode at 1.2 V_RHE under simulated sunlight, with O₂ and H₂ generated at a Faraday efficiency of unity over 12 h. Our vapor‐phase deposition method can be used to fabricate high‐performance (oxy)nitrides for practical photoelectrochemical applications.     

Unveiling the Activity and Stability Origin of BiVO4 Photoanodes with FeNi Oxyhydroxides for Oxygen Evolution

Understanding the origin of formation and active sites of oxygen evolution reaction (OER) cocatalysts is highly required for solar photoelectrochemical (PEC) devices that generate hydrogen efficiently from water. Herein, we employed a simple pH-modulated method for in situ growth of FeNi oxyhydroxide ultrathin layers on BiVO₄ photoanodes, resulting in one of the highest currently known PEC activities of 5.8 mA cm⁻² (1.23 V_RHE, AM 1.5 G) accompanied with an excellent stability. More importantly, both comparative experiments and density functional theory (DFT) studies clearly reveal that the selective formation of Bi−O−Fe interfacial bonds mainly contributes the enhanced OER activities, while the construction of V−O−Ni interfacial bonds effectively restrains the dissolution of V⁵⁺ ions and promotes the OER stability. Thereby, the synergy between iron and nickel of FeNi oxyhydroxides significantly improved the PEC water oxidation properties of BiVO₄ photoanodes.     

Stable Cocatalyst-Free BiVO4 Photoanodes with Passivated Surface States for Photocorrosion Inhibition

Improving charge transport and reducing bulk/surface recombination can increase the activity and stability of BiVO₄ for water oxidation. Herein we demonstrate that the photoelectrochemical (PEC) performance of BiVO₄ can be significantly improved by potentiostatic photopolarization. The resulting cocatalyst-free BiVO₄ photoanode exhibited a record-high photocurrent of 4.60 mA cm⁻² at 1.23 V_RHE with an outstanding onset potential of 0.23 V_RHE in borate buffer without a sacrificial agent under AM 1.5G illumination. The most striking characteristic was a strong “self-healing” property of the photoanode, with photostability observed over 100 h under intermittent testing. The synergistic effects of the generated oxygen vacancies and the passivated surface states at the semiconductor–electrolyte interface as a result of potentiostatic photopolarization reduced the substantial carrier recombination and enhanced the water oxidation kinetics, further inhibiting photocorrosion.     

In-situ Synthesis of the Thinnest In2Se3/In2S3/In2Se3 Sandwich-Like Heterojunction for Photoelectrocatalytic Water Splitting

The efficient utilization of solar energy for photoelectrocatalytic (PEC) water splitting is a feasible solution for developing clean energy and alleviating environmental issues. However, as the core of PEC technology, the existing photoanode catalysts have disadvantages such as poor photoelectrocatalytic conversion efficiency, low conductivity of photogenerated carriers, and instability. Here, we report the ultrathin two-dimensional sandwich-like (SW) heterojunction of In₂Se₃/In₂S₃/In₂Se₃ (SW In₂S₃@In₂Se₃) for the first time for PEC water splitting. Our findings identify the efficient separation of electrons and holes by constructing SW In₂S₃@In₂Se₃ heterojunction. The in situ synthesis of ultrathin nanosheet arrays by using surface substitution of Se atom to epitaxially grow cell In₂Se₃ maximizes the contact area of heterogeneous interface and accelerates the transmission of charge carrier. Benefitting from the unique structure and composition characteristic, SW In₂S₃@In₂Se₃ displays excellent performance in PEC water splitting. The photocurrent density of SW In₂S₃@In₂Se₃ reaches 8.43 mA cm⁻² at 1.23 V_RHE. Compared with In₂S₃, the SW In₂S₃@In₂Se₃ photoanode has nearly 12 times higher PEC performance, which represents the best performance among the In₂S₃-based photoanode heterojunction reported so far. The evolution rate of O₂ reaches 78.8 μmol cm⁻² h⁻¹, and the photocurrent has no apparent variety within 24 h.     

Ge‐Mediated Modification in Ta3N5 Photoelectrodes with Enhanced Charge Transport for Solar Water Splitting

Ta₃N₅ is a promising photoanode candidate for photoelectrochemical water splitting, with a band gap of about 2.1 eV and a theoretical solar‐to‐hydrogen efficiency as high as 15.9 % under AM 1.5 G 100 mW cm^?2 irradiation. However, the presently achieved highest photocurrent (ca. 7.5 mA cm^?2) on Ta₃N₅ photoelectrodes under AM 1.5 G 100 mW cm^?2 is far from the theoretical maximum (ca. 12.9 mA cm^?2), which is possibly due to serious bulk recombination (poor bulk charge transport and charge separation) in Ta₃N₅ photoelectrodes. In this study, we show that volatilization of intentionally added Ge (5 %) during the synthesis of Ta₃N₅ promotes the electron transport and thereby improves the charge‐separation efficiency in bulk Ta₃N₅ photoanode, which affords a 320 % increase of the highest photocurrent comparing with that of pure Ta₃N₅ photoanode under AM 1.5 G 100 mW cm^?2 simulated sunlight.     

Boosting the Photoactivity of BiVO4 Photoanodes by a ZnCoFe-LDH Thin Layer for Water Oxidation

Monoclinic bismuth vanadate (BiVO₄) has been used as an efficient photoanode material for photoelectrochemical water oxidation owing to its suitable band gap and nontoxicity. Nevertheless, the practical application of BiVO₄ photoanode has been severely limited by the surface charge recombination and sluggish kinetic, which leads to the obtained photoactivity of BiVO₄ is much lower than its theoretical value. In this case, ZnCoFe-LDH thin layer is conformally decorated on the porous BiVO₄ photoanode through a simple electrodeposition process. The results show that a boosted photoactivity and a remarkably enhanced photocurrent density (3.43 mA cm⁻² at 1.23 V_RHE) are attained for BiVO₄/ZnCoFe-LDH. In addition, the optimized BiVO₄/ZnCoFe-LDH photoanode exhibits significant negative shift in the onset potential (0.51 V_RHE to 0.21 V_RHE), promotes charge separation efficiency (49.3% to 60.4% in the bulk, 29.6% to 61.9% on the surface at 1.23 V_RHE) and enhanced IPCE efficiency (25.5% to 54.7% at 425 nm) compared with that of bare BiVO₄ photoanode. It is demonstrated that the boosted photoactivity of BiVO₄/ZnCoFe-LDH photoanode is mainly ascribed to the synergy effects of the formation of p-n heterojunction between ZnCoFe-LDH and BiVO₄ to accelerate the photogenerated charge transfer and separation, broaden light absorption, as well as promote the surface water oxidation kinetics.     

Interface Engineering of a CoOx/Ta3N5 Photocatalyst for Unprecedented Water Oxidation Performance under Visible‐Light‐Irradiation

Cocatalysts have been extensively used to promote water oxidation efficiency in solar‐to‐chemical energy conversion, but the influence of interface compatibility between semiconductor and cocatalyst has been rarely addressed. Here we demonstrate a feasible strategy of interface wettability modification to enhance water oxidation efficiency of the state‐of‐the‐art CoO_x/Ta₃N₅ system. When the hydrophobic feature of a Ta₃N₅ semiconductor was modulated to a hydrophilic one by in situ or ex situ surface coating with a magnesia nanolayer (2–5 nm), the interfacial contact between the hydrophilic CoO_x cocatalyst and the modified hydrophilic Ta₃N₅ semiconductor was greatly improved. Consequently, the visible‐light‐driven photocatalytic oxygen evolution rate of the resulting CoO_x/MgO(in)–Ta₃N₅ photocatalyst is ca. 23 times that of the pristine Ta₃N₅ sample, with a new record (11.3 %) of apparent quantum efficiency (AQE) under 500–600 nm illumination.     

Performance of dye-sensitized solar cells based on various sensitizers applied on TiO2-Nb2O5 core/shell photoanode structure

The present investigation described the performance of dye-sensitized solar cells (DSSCs) based on various sensitizers applied on TiO₂-Nb₂O₅ core/shell photoanode film. The novel photoanodes were prepared using composite of TiO₂ nanoparticles (TNPs) and TiO₂ nanorods (TNRs) as core (TNPRs) layer with Nb₂O₅ shell coating. As well, tantalum pentoxide (Ta₂O₅), a blocking layer applied over the core/shell film. The DSSCs were fabricated based on various sensitizers namely zinc phthalocyanine, indoline, indigo carmine, zinc porphyrin, N719, coumarin NKX-2700, polymer dye, quantum dots (QDs), perylene and squaraine. The I–V characteristics of the DSSCs, photocurrent density (Jsc), open-circuit voltage (Voc), fill factor (FF), and photoconversion efficiency (PCE) were determined under illumination of AM 1.5 G. Electrochemical impedance spectroscopy (EIS) analysis is carried out to study the charge transport and life-time of charge carriers at photoanode/dye/electrolyte interface of the DSSCs. The I–V and EIS results explicated that the core/shell with blocking layers were able to alleviate the electron transport and suppressed charge recombination at photoanode/dye/electrolyte interface of the DSSCs. Concerning the sensitizers, PCE of the DSSCs exemplify the order N719 > zinc porphyrin > coumarin NKX-2700 > indoline > squaraine > QDs > zinc phthalocyanine > perylene > polymer dye > indigo carmine dye. The results of the present work demonstrated that among the sensitizers studied, N719 showed the highest PCE and fill factor. Besides, the metal-free organic sensitizers (coumarin NKX-2700 and indoline) exhibited comparable PCE as compared to N719.     

Facile N≡N Bond Cleavage by Anionic Trimetallic Clusters V3−xTaxC4− (x=0–3): A DFT Study

Activation of N₂ on anionic trimetallic V_3−xTa_xC₄⁻ (x=0–3) clusters was theoretically studied employing density functional theory. For all studied clusters, initial adsorption of N₂ (end-on) on one of the metal atoms (denoted as Site 1) is transferred to an of end-on: side-on: side-on coordination on three metal atoms, prior to N₂ dissociation. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N₂ is facile under mild conditions. The reaction process can be divided into two processes: N₂ transfer (TRF) and N−N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has energy barriers similar to those of DIS. The overall energy barriers for heteronuclear V₂TaC₄⁻ and VTa₂C₄⁻ clusters are lower than those for homonuclear V₃C₄⁻ and Ta₃C₄⁻, showing that the doping effect is beneficial for the activation and dissociation of N₂. In particular, V−Ta₂C₄⁻ has low energy barriers in both TRF and DIS, and it has the highest N₂ adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V−Ta₂C₄⁻, is suggested to have high reactivity to N₂ activation, and may serve as a prototype for designing related catalysts at a molecular level.     

Efficient Hole Extraction from a Hole‐Storage‐Layer‐Stabilized Tantalum Nitride Photoanode for Solar Water Splitting

One of the major hurdles that impedes the practical application of photoelectrochemical (PEC) water splitting is the lack of stable photoanodes with low onset potentials. Here, we report that the Ni(OH)_x/MoO₃ bilayer, acting as a hole‐storage layer (HSL), efficiently harvests and stores holes from Ta₃N₅, resulting in at least 24 h of sustained water oxidation at the otherwise unstable Ta₃N₅ electrode and inducing a large cathodic shift of ≈600 mV in the onset potential of the Ta₃N₅ electrode.     

Tungsten doping of Ta3N5-nanotubes for band gap narrowing and enhanced photoelectrochemical water splitting efficiency

Ordered W-doped Ta₂O₅ nanotube arrays were grown by self-organizing electrochemical anodization of TaW alloys with different tungsten concentrations and by a suitable high temperature ammonia treatment, fully converted to W:Ta₃N₅ tubular structures. A main effect found is that W doping can decrease the band gap from 2 eV (bare Ta₃N₅) down to 1.75 eV. Ta₃N₅ nanotubes grown on 0.5 at.% W alloy and modified with Co(OH)_x as co-catalyst show ~ 33% higher photocurrents in photoelectrochemical (PEC) water splitting than pure Ta₃N₅.     

光电沉积Co-Pi对Ta3N5水分解性能的影响及机理

Co-Pi是一种低廉高效的氧化水产氧助催化剂,助催化剂担载方法及条件是光阳极太阳能水分解效率提升的关键因素之一。以光阳极材料Ta_3N_5为基底,针对光电沉积担载助催化剂Co-Pi开展了一系列研究,研究表明光电沉积Co-Pi过程中,照射光强的影响较小,而外加偏压和担载电量的影响很大,是Co-Pi担载的关键因素;通过阻抗谱测试定量分析了Co-Pi担载条件对Ta_3N_5/电解液界面载流子输运的影响,表明Co-Pi担载电压和电量直接影响界面光生载流子的传输,进而决定了Ta_3N_5水分解性能的高低;发现最优担载偏压对不同的Ta_3N_5均适用,而最优担载电量和光阳极的表面粗糙度存在正相关关系,要针对光阳极表面粗糙度调节助催化剂担载条件。     

Pristine Ta3N5 Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Ta₃N₅ is a promising photoelectrode for solar hydrogen production; however, to date pristine Ta₃N₅ electrodes without loading co‐catalysts have presented limited photoelectrochemical (PEC) performance. In particular, large external biasing has been required to run water oxidation, the origin of which is investigated herein. Ta₃N₅ nanotubes (NTs) prepared by nitridation were characterized by a wide range of techniques. The bandgap was confirmed by a novel PEC technique. Nondestructive synchrotron‐excited XPS has shown the presence of reduced Ta species deeper in the Ta₃N₅ surface. Lower photocurrent and transient spikes that were intense at lower applied biasing were observed under water oxidation; however, spikes were inhibited in the presence of a sacrificial agent and photocurrent was improved even at low biasing. It was observed for the first time that the lower PEC performance under water oxidation can be attributed to the presence of interband trapping states associated with pristine Ta₃N₅ NTs/electrolyte junction. These states correspond to the structural defects in Ta₃N₅, devastate PEC performance, and present the necessity to apply higher biasing. The key to circumvent them is to use a sacrificial agent in the electrolyte or to load a suitable co‐catalyst to avoid hole accumulation under water oxidation, thereby improving the phootocurrent. The findings on the interband states could also provide guidance for the investigation of PEC properties of new types of semiconducting devices.     

光电沉积Co-Pi对Ta3N5水分解性能的影响及机理

Co-Pi是一种低廉高效的氧化水产氧助催化剂,助催化剂担载方法及条件是光阳极太阳能水分解效率的提升的关键因素之一。以光阳极材料Ta₃N₅为基底,针对光电沉积担载助催化剂Co-Pi开展了一系列研究,研究表明光电沉积Co-Pi过程中,照射光强的影响较小,而外加偏压和担载电量的影响很大,是Co-Pi担载的关键因素;通过阻抗谱测试定量分析了Co-Pi担载条件对Ta₃N₅/电解液界面载流子输运的影响,表明Co-Pi担载电压和电量直接影响界面光生载流子的传输,进而决定了Ta₃N₅水分解性能的高低;发现最优担载偏压对不同的Ta₃N₅均适用,而最优担载电量和光阳极的表面粗糙度存在正相关关系,要针对光阳极表面粗糙度调节助催化剂担载条件。     

Enhancing Local CO2 Adsorption by L-histidine Incorporation for Selective Formate Production Over the Wide Potential Window

Electrochemical carbon dioxide reduction reaction (CO₂RR) to produce valuable chemicals is a promising pathway to alleviate the energy crisis and global warming issues. However, simultaneously achieving high Faradaic efficiency (FE) and current densities of CO₂RR in a wide potential range remains as a huge challenge for practical implements. Herein, we demonstrate that incorporating bismuth-based (BH) catalysts with L-histidine, a common amino acid molecule of proteins, is an effective strategy to overcome the inherent trade-off between the activity and selectivity. Benefiting from the significantly enhanced CO₂ adsorption capability and promoted electron-rich nature by L-histidine integrity, the BH catalyst exhibits excellent FE_formate in the unprecedented wide potential windows (>90 % within −0.1–−1.8 V and >95 % within −0.2–−1.6 V versus reversible hydrogen electrode, RHE). Excellent CO₂RR performance can still be achieved under the low-concentration CO₂ feeding (e.g., 20 vol.%). Besides, an extremely low onset potential of −0.05 V_RHE (close to the theoretical thermodynamic potential of −0.02 V_RHE) was detected by in situ ultraviolet-visible (UV-Vis) measurements, together with stable operation over 50 h with preserved FE_formate of ≈95 % and high partial current density of 326.2 mA cm⁻² at −1.0 V_RHE.     

Dual Plasmonic Au−Cu2−xS Nanocomposites: Design Strategies and Photothermal Properties

Coupling two different materials to create a hybrid nanostructured system is a powerful strategy for achieving synergistically enhanced properties and advanced functionalities. In the case of Au and Cu_2−xS, their combination on the nanoscale results in dual plasmonic Au−Cu_2−xS nanocomposites that exhibit intense photon absorption in both the visible and the near-infrared spectral ranges. Their strong light-absorbing properties translate to superior photothermal transduction efficiency, making them attractive in photothermal-based applications. There are several nanostructure configurations that are possible for the Au−Cu_2−xS system, and the successful fabrication of a particular architecture often requires a carefully planned synthetic strategy. In this Minireview, the different synthetic approaches that can be employed to produce rationally designed Au−Cu_2−xS nanocomposites are presented, with a focus on the experimental protocols that can lead to heterodimer, core–shell, reverse core–shell, and yolk–shell configurations. The photothermal behavior of these materials is also discussed, providing a glimpse of their potential use as photothermally active agents in therapeutic and theranostic applications.     

原位水解沉积制备高效氮化钽微球太阳能分解水光阳极

利用一种新的原位水解沉积方法,以在高湿度空气中老化的甲醇中作为溶剂,通过乙醇钽水解而成前驱体微球颗粒沉积,制备出了高效的Ta₃N₅微球光电极,其1.6 V（vs RHE）电极电位下的光电流值达到了6.6 mA·cm^-2。相反地,在新鲜的甲醇溶液中没有钽前驱体微球颗粒沉积。这表明甲醇中水的含量对Ta₃N₅微球光电极的形成十分重要。另外,本制备方法也能方便地在其他透明导电衬底上制备出Ta₃N₅。