High Photoelectrochemical Activity Research Articles

Homo-Nuclear Hetero-Atomic Conjugated Reticular Oligomers for Heterojunction: A Novel "Electron Medium" for Panel Photoelectrocatalysis.

A substantial challenge in employing covalent organic frameworks (COFs) for photoelectrochemical (PEC) water splitting lies in improving their solution-processability while concurrently facilitating the transfer of charges and mass to the catalytic sites. Herein, we synthesize a solution-processable conjugated reticular oligomers (CROs), and further embed ruthenium (Ru) into the CRO, forming a CRO-Ru with homo-nuclear hetero-atomic. Thereafter, CRO and CRO-Ru construct an organic-organic heterojunction membrane at the nanoscale. Thisdesign achieves perfect lattice matching, significantly reducing the energy barrier of mass transfer, and effectively lowering the recombination rate of charge carriers. The optimized photocathode, CuI/CRO-Bpy:CRO-Bpy-Ru-1:1+P3HT/SnO2/Pt, exhibits an efficiency of 111.0µAcm-2 at 0.4V versus a reversible hydrogen electrode (RHE). Compared with the original bulk COFs and CROs, the efficiency is significantly improved. The apparent improvements in charge carrier separation and transfer are responsible for the high PEC activity. In the heterojunction, the incorporation of CRO-Bpy-Ru with a longer excited-state lifetime and a substantial built-in electric field has effectively accelerated the photo-induced electron transfer from the conduction band (CB) of CRO-Bpy to the valence band (VB) of CRO-Bpy-Ru, effectively suppressing the recombination of charges. These findings offer significant guidance for the design and optimization of high-performance photoelectrochemical catalysts.

Peculiar photoelectrochemical activity of zinc oxide and tin dioxide

Zinc oxide thin films made by pulsed reactive magnetron sputtering combined with RF ECWR plasma on FTO or ITO substrates exhibit high photoelectrochemical activity for water splitting under UV light, but are unstable against photocorrosion. It can be suppressed by a protective layer of SnO2 made by atomic layer deposition. The SnO2 layer is quasi-amorphous in the as-received state, but the thermal treatment causes partial crystallization to cassiterite, without significant change of the optical band gap. Ferrocene in acetonitrile electrolyte solution is a useful redox probe for the blocking-quality tests of thin films of n-semiconductors. Both ZnO and SnO2 are sensitive to irreversible electrochemical doping at potentials negative to the flatband potential. The flipping of electrochemical work functions of the Zn-terminated (0001) and O-terminated (000–1) faces of ZnO (wurtzite) takes place in acetonitrile vs. aqueous electrolyte solutions. The potentials for photocurrent onset are near the flatband potentials in an aqueous electrolyte solution for both ZnO and SnO2.

Oxygen-doped ZnIn2S4 as a highly active and etchable photoactive material for chlorpyrifos detection

The development of a high-performance photoactive material and an effective and efficient analysis strategy are important for photoelectrochemical (PEC) analysis. We report here the enhanced PEC activity and etchable property of oxygen-doped ZnIn2S4 (O-ZnIn2S4) and its application for PEC detection of organophosphorus pesticides (OPs). O-ZnIn2S4 prepared by thermally treating ZnIn2S4 in air atmosphere can show much higher PEC activity than pristine ZnIn2S4, because oxygen doping can decrease the band gap and thereby increase the visible-light absorption. It is found that O-ZnIn2S4 can be etched by hydrogen peroxide, so O-ZnIn2S4 can be used for PEC analysis based on the etching strategy. Enzymatic reactions catalyzed by acetylcholinesterase and choline oxidase can produce hydrogen peroxide to etch the O-ZnIn2S4 modified on photoelectrode, so a “signal-off” state is achieved. OPs can inhibit the activity of acetylcholinesterase, and the etching of O-ZnIn2S4 is weakened, enabling “signal-on” PEC detection of OPs. Chlorpyrifos is selected as a model for PEC detection of OPs. The detection limit for chlorpyrifos detection is 2 × 10−4 mg L−1 with a linear range from 0.001 to 50 mg L−1. The present study not only develops a high-performance photoactive material for PEC analysis but also provides an efficient PEC sensing strategy based on ZnIn2S4 etching.

Fabrication of TiO2 nanorods/γ-graphyne boosting junction-driven charge transfer for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is a viable method for converting renewable solar energy into storable chemical energy. Herein, the newly emerged two-dimensional sp- and sp2-carbon hybridized graphyne sheets were successfully coupled with thin film-like arrays of titanium dioxide nanorods, forming an efficient 2D-1D heterojunction. The microstructure and composition of obtained γ-graphyne/TiO2 films were well characterized. And enhanced photoelectrochemical properties were demonstrated. The γ-graphyne/TiO2 photoelectrode achieves a photocurrent density of 1.31 mA/cm2 at 1.23 V (vs. RHE), which is 1.7 times over that of pristine titanium dioxide. An improvement of photoconversion efficiency by 2.2 folds was observed. The high PEC activity of γ-graphyne/TiO2 originates from band alignment and interfacial junction between π-conjugated graphyne sheets and TiO2 nanostructure, greatly promoting charge transfer and diminishing defective excitation and recombination. By virtue of the γ-graphyne nanosheets, largely increased number of useful photons and catalytic active sites are triggered. This work provides a reference for the photoelectrochemical application of semiconductive γ-graphyne and a specific and proven method for the utilization of solar energy.

Surface Engineering of GaN Photoelectrode by NH3 Treatment for Solar Water Oxidation

<p>Photoelectrochemical (PEC) water splitting is a vital source of clean and sustainable hydrogen energy. Moreover, the largescale H<sub>2</sub> production is currently necessary, while long-term stability and high PEC activity still remain important issues. In this study, a GaN-based photoelectrode was modified by an additional NH<sub>3</sub> treatment (900°C for 10 min) and its PEC behavior was monitored. The bare GaN exhibited a highly crystalline wurtzite structure with the (002) plane and the optical bandgap was approximately 3.2 eV. In comparison, the NH<sub>3</sub>-treated GaN film exhibited slightly reduced crystallinity and a small improvement in light absorption, resulting from the lattice stress or cracks induced by the excessive N supply. The minor surface nanotexturing created more surface area, providing electroactive reacting sites. From the surface XPS analysis, the formation of an N-Ga-O phase on the surface region of the GaN film was confirmed, which suppressed the charge recombination process and the positive shift of E<sub>FB</sub>. Therefore, these effects boosted the PEC activity of the NH<sub>3</sub>-treated GaN film, with <italic>J</italic> values of approximately 0.35 and 0.78 mA·cm<sup>−2</sup> at 0.0 and 1.23 V<sub>RHE</sub>, respectively, and an onset potential (V<sub>on</sub>) of −0.24 V<sub>RHE</sub>. In addition, there was an approximate 50% improvement in the <italic>J</italic> value within the highly applied potential region with a positive shift of V<sub>on</sub>. This result could be explained by the increased nanotexturing on the surface structure, the newly formed defect/trap states correlated to the positive V<sub>on</sub> shift, and the formation of a GaO<sub>x</sub>N<sub>1-x</sub> phase, which partially blocked the charge recombination reaction.</p>

Two-dimensional perovskite SrNbO2N with Zr doping for accelerating photoelectrochemical water splitting

• Two-dimensional SrNbO 2 N:Zr plates were nitrided from layered perovskite Sr 5 Nb 4 O 15 . • Zr 4+ was doped in Sr 5 Nb 4 O 15 during flux-assisted calcination. • The 2D SrNbO 2 N:Zr photoanode (λ<680 nm) exhibited high PEC activity. • The photoactivity mainly originated from the 2D surface morphology of SrNbO 2 N:Zr. • Controlling the surface morphology of SrNbO 2 N accelerates separation and transfer of charges. The superior ability of perovskite-type SrNbO 2 N to absorb intensive visible light makes it a potential semiconductor to produce hydrogen and oxygen by photoelectrochemical (PEC) water splitting under sunlight. The surface morphologies, such as shape and structure, of the oxynitride strongly affect its photoactivity, although the mechanism has been hardly studied. Herein, we report a two-dimensional (2D) porous SrNbO 2 N plate with Zr doping, nitrided from layered perovskite Sr 5 Nb 4 O 15 and also its largely enhanced PEC water splitting activity. Zr 4+ was doped in Sr 5 Nb 4 O 15 during flux-assisted calcination using KCl, producing 2D-type truncated-octahedral Sr 5 Nb 4 O 15 :Zr plates approximately 50 nm in thickness. The nitridation completely transformed Sr 5 Nb 4 O 15 :Zr to 2D single-crystalline SrNbO 2 N:Zr with a large surface area, which was subsequently used to fabricate a thin and uniform photoanode by the spin coating method. As a result, the Co(OH) x /SrNbO 2 N:Zr/FTO photoanode capable of absorbing visible light of up to 680 nm exhibited an activity of 2.0 mA cm −2 at 1.23 V vs the reversible hydrogen electrode for water splitting under AM 1.5G simulated sunlight. This improvement in photoactivity mainly originated from the 2D surface morphology of SrNbO 2 N:Zr, which is clearly distinguishable from 3D-type oxynitrides. According to electrochemical analyses, the 2D structure of SrNbO 2 N:Zr boosted the separation and accelerated the transfer of charges photogenerated during the water splitting, thus driving the reaction further. Therefore, the result empirically demonstrates that controlling the surface morphology of SrNbO 2 N is an effective strategy to suppress the recombination of charges and minimize their diffusion pathway, eventually enhancing the PEC activity.

Ultra-thin carbon doped TiO2 nanotube arrays for enhanced visible-light photoelectrochemical water splitting

TiO2 has been widely employed as a photocatalyst for water splitting owing to its high activity, low cost, abundance, safety, and stability. However, the further utilization of TiO2 is still confined to the wide band gap and the rapid recombination speed. Carbon has metallic conductivity and a large electron storage capacity, which can help to absorb photoexcited electrons and enhance charge separation and transfer. Herein, we fabricated the ultra-thin carbon-doped TiO2 nanotube arrays (TNTAs). The as-prepared UTC-doped TiO2@TNT exhibited high photoelectrochemical (PEC) activity, realizing a high H2 evolution rate up to 41.3 μmol cm-2 h−1 (AM 1.5G) and 1.3 μmol cm-2 h−1 (visible light), which exhibit significantly narrowed band gaps and decreased charge resistance. Using ultra-thin carbon doping in TiO2 nanotube arrays opens up a new avenue for optimizing photocatalysts for PEC water splitting.

Polymeric carbon nitride as a platform for photoelectrochemical water-splitting cells.

Polymeric carbon nitride (CN) materials are promising low-cost photocatalysts that exhibit a combination of chemical and physical properties suitable for converting light into redox activity on their surface. In this perspective, we describe our experience with this family of materials as light absorbers that serve as an anode in photoelectrochemical cells toward water-splitting. We describe some of the CN deposition techniques and procedures established in our lab. The knowledge gained from powder-based photocatalysis is implemented in photoelectrochemical scenarios and is used to determine the merits and shortcomings of resulting layers. We show how the preparation methods are oriented based on these factors and how high photoelectrochemical water-splitting activity develops in photoanodes we developed where CN(s) act as photoabsorbers. Lastly, we present our view on the future prospects of this field.

Dissolution of WO3 modified with IrOx overlayers during photoelectrochemical water splitting

AbstractWO3, an abundant transition metal semiconductor, is one of the most discussed materials to be used as a photoanode in photoelectrochemical water‐splitting devices. The photoelectrochemical properties, such as photoactivity and selectivity of WO3 in different electrolytes, are already well understood. However, the understanding of stability, one of the most important properties for utilization in a commercial device, is still in the early stages. In this work, a photoelectrochemical scanning flow cell coupled to an inductively coupled plasma mass spectrometer is applied to determine the influence of co‐catalyst overlayers on photoanode stability. Spray‐coated WO3 photoanodes are used as a model system. Iridium is applied to the electrodes by atomic layer deposition in controlled layer thickness, as determined by ellipsometry and x‐ray photoelectron spectroscopy. Photoactivity of the iridium‐modified WO3 photoanodes decreases with increasing iridium layer thickness. Partial blocking of the WO3 surface by iridium is proposed as the main cause of the decreased photoelectrochemical performance. On the other hand, the stability of WO3 is notably increased even in the presence of the thinnest investigated iridium overlayer. Based on our findings, we provide a set of strategies to synthesize nanocomposite photoelectrodes simultaneously possessing high photoelectrochemical activity and photostability.

Codoping g-C3N4 with boron and graphene quantum dots: Enhancement of charge transfer for ultrasensitive and selective photoelectrochemical detection of dopamine

The development of superior photoelectrochemical (PEC) sensors for biosensing has become a major objective of PEC research. However, conventional PEC-active materials are typically constrained by a weak photocurrent response owing to their limited surface-active sites and high electron-hole recombination rate. Here, a boron and graphene quantum dots codoped g-C3N4 (named GBCN) as PEC sensor for highly sensitive dopamine (DA) detection was fabricated. GBCN exhibited the greatest photocurrent response and PEC activity compared to free g-C3N4 and g-C3N4 doped with boron. The proposed PEC sensor for DA determination exhibited a broad linear range (0.001–800 μM) and a low detection limit (0.96 nM). In particular, a sensitivity up to 10.3771 μA/μM/cm2 was seen in the case of GBCN. The high PEC activity can be attributed to the following factors: (1) the boron and graphene quantum dots co-doping significantly increased the specific surface area of g-C3N4, providing more adsorption sites for DA; (2) the dopants extended the absorption intensity of g-C3N4, red-shifting the absorption from 470 to 540 nm; and (3) the synergism of boron and graphene quantum dots efficiently boosted the photogenerated electrons migration from the conduction band of g-C3N4 to graphene quantum dots, facilitating charge separation. In addition, GBCN also exhibited good anti-interference ability and stability. This research may shed light on the creation of a highly sensitive and selective PEC platform for detecting biomolecules.

Degradation of contaminants of emerging concern in a secondary effluent using synthesized MOF-derived photoanodes: A comparative study between photo-, electro- and photoelectrocatalysis

Three metal-organic framework (MOF)-based photoanodes were prepared by deposition on TiO2 nanotubes using Ti as substrate (Ti/TiO2NT): i) Ti/TiO2NT-Au@ZIF-8, ii) Ti/TiO2NT-Ru3(BTC)2, iii) Ti/TiO2NT-UiO-66(Zr)NH2. These photoanodes were characterized by FEG-SEM, EDX and DRX. The analyses showed a successful modification and a high homogeneity of the different MOFs on the Ti/TiO2NT surface. The photoanodes were studied in the degradation of Contaminants of Emerging Concern (CECs) in a spiked secondary effluent from a Municipal Wastewater Treatment Plant (MWWTP). Sodium diclofenac (DCF), sulfamethazine (SMT) and carbamazepine (CBZ) were used as CECs at low concentration (200 μg/L each CEC). The samples were preconcentrated using Solid Phase Extraction (SPE) and analyzed by a HPLC-DAD system. The MOF-based photoanodes exhibited a high photoelectrochemical (PEC) activity towards the oxidation of CECs, achieving up to 50%, 70% and 80% of removal using Ti/TiO2NT-Au@ZIF-8, Ti/TiO2NT-UiO-66(Zr)NH2, Ti/TiO2NT-Ru3(BTC), respectively. The influence of the generation of hydroxyl radical was then studied. The results indicate that PEC degradation using Ti/TiO2NT-Ru3(BTC)2 and Ti/TiO2NT-UiO-66(Zr)NH2 is more affected by the concentration of the radical.

Surface modification of CuInS2 photocathodes with ruthenium co-catalysts for efficient solar water splitting

In this work, the photoelectrochemical H2 production activity of CuInS2 photocathodes is investigated after sequential surface modification with a-MoSx, Pt, or Ru. Although Ru has much inferior electrocatalytic activity to Pt for hydrogen evolution reaction (HER), a Ru-modified CuInS2/a-MoSx photocathode shows higher photoelectrochemical (PEC) activities than a Pt-modified one. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and other (photo)electrochemical characterizations were carried out for the surface-modified CuInS2 photocathode to reveal the origin of the high PEC activity. The energy level of Ru on CuInS2/a-MoSx photocathodes is more suitable for the electron transfer between semiconductor–metal-electrolytes, and it leads to a fast electron transient time during PEC reaction by the improved carrier lifetime. This result implies that the Ru modification of photocathodes can be one of potential strategies for tuning band alignment and improving PEC activities.

3D Core-Shell Heterostructures of WO3/Bi2MoO6 and MoS2/BiVO4 for Efficient Photoelectrochemical Water Splitting

Hydrogen has attracted increasing attention as clean energy for fuel cells over the past decade. Photoelectrochemical (PEC) water splitting is considered the most feasible production method. However, its practical efficiency depends significantly on the photogeneration rate of electron (e−) and hole (h+) on a semiconductor photoanode and the rapid separation of these charge carriers. Also, a proper match of small and large bandgap positions is necessary. 3D core-shell heterostructures of WO3/Bi2MoO6/Co‐Pi and BiVO4/MoS2 were synthesized using hydrothermal/electrodeposition and electrodeposition/plasma-enhanced atomic layer deposition (PECALD), respectively. The as-prepared WO3/Bi2MoO6/Co‐Pi hetero-photocatalyst exhibited significantly high photoelectrochemical activity, where its photocurrent efficiency was 4.6 times greater than that of the constituent WO3. For the BiVO4/MoS2 photoelectrode, an optimal thickness of the MoS2 layer was controlled by the number of PEALD cycles. The highest photocurrent (2.1 mA cm-2) was produced from the electrode with a 6 nm layer-thickness, 2.4 times higher than the pristine BiVO4 at an external bias of 1 V vs. Ag/AgCl. The appropriate bandgap alignment between layers can corroborate such drastic improvement in the PEC properties. A detailed investigation into the photoelectrochemical reaction mechanism showed that enhancement of the PEC performance was attributed to the finely deposited MoS2 layer, which expands the spectral absorption edge of solar light and enhances the suppression of electron-hole pair recombination because of the proper alignment match between the two semiconductors with a small and large bandgap. Furthermore, a heterojunction charge-transfer mechanism was proposed to verify the role of the co-catalyst, Co‐Pi, in enhancing the photocurrent at the WO3/Bi2MoO6 photoanode under the same applied bias.

Microwave-assisted metal-ion attachment for ex-situ zirconium doping into hematite for enhanced photoelectrochemical water splitting

Ex-situ doping into hematite films is carried out via a short-duration (∼60 s) microwave-assisted metal-ions attachment (MWMA) of tetravalent Zr4+ ion on the surface of FeOOH/FTO, followed by high temperature annealing (HTA) to fabricate Zr4+:Fe2O3/FTO photoanode for photoelectrochemical (PEC) water splitting. Compared to a simple dipping attachment without microwave irradiation, this MWMA allows a much larger amount of attached Zr4+-ions on the FeOOH precursor, leading to a properly doped photoanode of much higher PEC activity. The primary effect of Zr4+ doping is to improve the charge transport characteristics in the bulk of hematite. In addition, it also boosts charge injection efficiency at the semiconductor and electrolyte interface by forming an inadvertent passivation layer and promoting hole transfer via surface states. As a result, the Zr4+:Fe2O3/FTO photoanode shows a higher photocurrent density of 1.54 mA cm−2 at 1.23 VRHE under 1 Sun irradiation relative to undoped Fe2O3/FTO (1.02 mA cm−2) or Zr4+:Fe2O3/FTO (1.19 mA cm−2) prepared without MWMA.

Oxygen vacancy-regulated TiO2 nanotube photoelectrochemical sensor for highly sensitive and selective detection of tetracycline hydrochloride

Investigation of the mechanism of oxygen vacancy-regulated photoelectrochemical sensors for highly sensitive and selective determination of biomolecules containing electron-donating groups is an innovative research field. In this study, oxygen vacancy-regulated TiO2 nanotube arrays (Ov-TNTs) with high photoelectrochemical activity were synthesized and applied to defect tetracycline hydrochloride (TC). The synergistic effect of oxygen vacancies and Ti3+ droves Ov-TNTs with a narrow energy band to generate more photogenerated carriers under irradiation. The photocurrent response of the oxygen vacancy-regulated photoelectrochemical sensor decreased with increasing TC concentration, which could be mainly attributed to adsorption of TC, which consumed part of the oxygen vacancies on the surface of Ov-TNTs. This system had excellent linearity in the range of 0.1–1000 nM with a detection limit of 0.33 nM (S/N = 3). In addition, the sensor was highly selective for TC determination due to the mutual electrostatic interaction between negatively charged TC-containing electron-donating groups (-NH2 and -OH) and positively charged Ov-TNTs. This study provided a foundation for developing an oxygen vacancy-regulated adsorptive photoelectrochemical sensor.

W:BiVO4-WO3-V2O5 heterostructures increase light absorption and charge transport in photoanodes for water splitting

Efficient light absorption and charge separation and transfer are the main obstacles that still need to be addressed to increase the performance of photoanodes for the water oxidation reaction. Here, we show that the combination of W:BiVO4, WO3, and V2O5 can simultaneously improve light absorption and the separation and transport of electrons and holes in the photoanode and consequently its photoelectrochemical performance for the water oxidation reaction. The high photoelectrochemical activity of the photoanode is due to the different bandgap energies of W:BiVO4 (2.44 eV), WO3 (2.90 eV), and V2O5 (2.27 eV), which provide higher absorption of visible light and improved charge transport in the heterojunction: V2O5 facilitates the transport of holes while WO3 increases electron mobility. As a result, the W:BiVO4-WO3-V2O5 photoanode produces a photocurrent density as high as 8.2 mA cm−2 at 1.23 V vs. RHE in sodium sulfate electrolyte (pH 6.96). By modifying the surface of the W:BiVO4-WO3-V2O5 photoanode with an electrocatalyst for water oxidation, the photocurrent can reach 12.1 mA cm−2. Thus, the multiple ternary heterojunctions of W:BiVO4-WO3-V2O5 proved an efficient strategy for producing high-performance photoanodes for photoelectrochemical applications.

Phase evolution in annealed Ni-doped WO3 nanorod films prepared via a glancing angle deposition technique for enhanced photoelectrochemical performance

Ni-doped WO3 nanorod films were fabricated via a reactive magnetron cosputtering with a glancing angle deposition technique. The crystal structure and surface morphology were observed using grazing incident X-ray diffraction and field emission Scanning Electron Microscopy, respectively. The chemical compositions and oxidation state of each element were investigated by X-ray photoemission spectroscopy. The local structure and phase evolution were investigated via X-ray absorption spectroscopy. The local structure of Ni atoms in WO3 nanorod films is characterized as a NiWO4 nanocluster in the WO3 matrix, which is supported by calculated spectra. The phase information obtained after annealing demonstrates that short-length order in amorphous transitions to crystallinity. The phase information of the local structures were acquired and discussed as well as the effect on the annealing process. The coupling of amorphous WO3, crystalline WO3, and amorphous NiWO4 exhibits high photoelectrochemical activity of the sample annealed at 400 °C, which was observed with a large current density (2.35 μA/cm2) at 1.20 V vs. Ag/AgCl under visible light irradiation, which is greater than that of the unmodified WO3 photoelectrode (1.38 μA/cm2).

Molybdenum doped bilayer photoanode nanotubes for enhanced photoelectrochemical water splitting

Conversion of solar energy into hydrogen energy via photoelectrochemical (PEC) water splitting is one of the most promising approaches for generation of clean and sustainable hydrogen energy in order to address the alarming global energy crisis and environmental problems. To achieve superior PEC performance and solar to hydrogen efficiency (STH), identification, synthesis, and development of efficient photoelectrocatalysts with suitable band gap and optoelectronic properties along with high PEC activity and durability is highly imperative. With the aim of improving the performance of our previously reported bilayer photoanode of WO3 and Nb and N co-doped SnO2 nanotubes i.e. WO3-(Sn0.95Nb0.05)O2:N NTs, herein, we report a simple and efficient strategy of molybdenum (Mo) doping into the WO3 lattice to tailor the optoelectronic properties such as band gap, charge transfer resistance, and carrier density, etc. The Mo doped bilayer i.e. (W0.98Mo0.02)O3-(Sn0.95Nb0.05)O2:N revealed a higher light absorption ability with reduced band gap (1.88 eV) in comparison to that of the undoped bilayer (1.94 eV). In addition, Mo incorporation offered improvements in charge carrier density, photocurrent density, with reduction in charge transfer resistance, contributing to a STH (∼3.12%), an applied bias photon-to-current efficiency (ABPE ∼ 8% at 0.4 V), including a carrier density (Nd ∼ 7.26 × 1022 cm−3) superior to that of the undoped bilayer photoanode (STH ∼2%, ABPE ∼ 5.76%, and Nd ∼5.11 × 1022 cm−3, respectively). The substitution of Mo6+ for W6+ in the monoclinic lattice, forming the W–O–Mo bonds altered the band structure, realizing further enchantments in the PEC reaction and charge transfer kinetics. Additionally, doped bilayer photoanode revealed excellent long term PEC stability under illumination, suggesting its robustness for PEC water splitting. The present work herein provides a simple and effective Mo doping approach for generation of high performance photoanodes for PEC water splitting.

Photoelectrochemical performance of tubewall‐separated titanium dioxide nanotube array photoelectrode

AbstractTitanium dioxide nanotube array (TiO2 NTA) grown on titanium substrate has been fabricated as active photoelectrode for organic compound degradation. TiO2 NTA shows the tubewall‐separated nanotube arrangement and anatase crystal structure. Transient photocurrent of 1.86 mA and open‐circuit photovoltage of 0.26 V are determined to keep stable level under ultraviolet (UV) light irradiation, indicating its high photoelectrochemical activity. The cathodic polarization process causes more feasible electron transfer than the equilibrium process and anodic polarization process, which is consistent with the declining current response at an increasing positive potential. The photocatalytic activity of TiO2 NTA is fully evaluated through UV light‐induced photocatalysis and photoelectrocatalysis degradation of organic dye X‐3B as a reactant pollutant. The pseudo‐first‐order reaction rate constant is enhanced from 0.00346 min−1 for photocatalysis to 0.00521 min−1 for photoelectrocatalysis using Langmuir–Hinshelwood kinetic model of heterogeneous catalysis. The tubewall‐separated nanotube structure could induce photoelectron directional transport and provide extra interspace for reactant organic molecule diffusion at accessible surface area. The positive potential applied on TiO2 NTA could further promote photoelectron–hole pair separation. Two strategies of photoelectron generation and photoelectron–hole separation are accordingly adopted to improve its electro‐assisted photocatalytic activity. Therefore, the tubewall‐separated TiO2 NTA could present the promising photoelectrocatalysis application.

Non-enzymatic photoelectrochemical sensors based on Schiff base and chitosan co-decorated TiO2 nanosheets for dopamine detection

TiO2 nanosheets (TiO2 NSs) with a high percentage of {001} facets show high photoelectrochemical activity, but they only can utilize ultraviolet light due to the wide band gap. Thus, a new Schiff base monocrystal were synthesized and used to sensitize TiO2 NSs. And then we constructed photoelectrochemical (PEC) sensors based on Schiff base sensitized TiO2 NSs for dopamine (DA) detection. The sensitized TiO2 NSs can extend the absorption spectrum range to the visible light region, and the photocurrent of the PEC sensors was increased byone order of magnitude. Chitosan further decorated the sensors to enhance the selectivity. DA was oxidized by hole and covalently linked with chitosan. Subsequently, the DA oxide acted as electron acceptor to cause photocurrent quenching, enabling quantitative and selective detection of DA. The PEC sensors have wide detection range from 0.0005 to 5.0 mM with the detection limit (LOD) of 0.206 μM (S/N = 3). The non-enzymatic PEC sensors have a good selectivity which can distinguish DA from ascorbic acid (AA) and uric acid (UA), and also have reliable stability and recovery, thus, it has a good application prospect in biomedicine.