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Nanohybrid photoanodes made of mixed phase TiO2 nanorods (NRs) decorated with reduced graphene oxide (rGO) is fabricated by one step hydrothermal technique. Addition of rGO influences the phase formation of the TiO2 and optimum mixed phase formation of rutile (16%) and anatase (84%) TiO2 polymorphs is achieved at 1.0 wt% rGO decoration. Using rGO decorated TiO2 hybrid photoanodes, bacteriorhodopsin sensitized solar cells is fabricated with liquid and quasi-state electrolyte. Decoration of 1.0 wt% rGO upon TiO2 NRs boosted the photocurrent (Jsc = 2.2 mA/cm2) generation and photoconversion (η = 1.3%) efficiency which is 94% enhanced than pristine TiO2 NRs photoanodes. Experimental observation showcase higher rGO decoration (>1.0 wt% rGO) suppress the charge transport due to the formation of self-induced trapping sites within the transfer network. Minimum charge transfer resistance and maximum charge collection efficiency of ∼98% is achieved at 1.0 wt% rGO decorated TiO2 nanorods photoanodes. The ideal decoration of rGO (1.0 wt%) in photoanodes significantly improves the bio-sensitizer loading, charge transfer, electron lifetime and reduces the recombination of the BSSCs. Thus nanohybrid (rGO-TiO2 NR) photoanode assembled BSSC exhibit higher photoconversion efficiency than earlier BSSCs fabricated with nanoparticle (P25 mixed-phase TiO2) and nanorod (rutile and anatase pristine TiO2) based photoanodes.

Herein, we report the surface treatment on Zr4+/Al3+ codoped α-Fe2O3 photoanode for high-performance photoelectrochemical water splitting. A high-temperature quenching exhibits the Zr4+/Al3+ codoping in α-Fe2O3 photoanode without damaging morphology. The presence of Zr4+/Al3+ codoping shows a cathodic shift in onset potential, but lack of increment in photocurrent reveals the major role of passivation and the minimum doping effect of aluminum. Additionally, CoOx cocatalyst exhibits increment in photocurrent with the greater cathodic shift in onset potential than the pristine α-Fe2O3 nanorods. The CoOx surface-reworked Zr4+/Al3+ codoped α-Fe2O3 photoanode displays the highest photocurrent of 1.5 mA/cm2 at 1.23 V vs. RHE (76% increment over the pristine α-Fe2O3) and 0.7 mA/cm2 at 1.0 V vs. RHE (102% increment over the pristine α-Fe2O3). The systematic characterization carried out using x-ray diffraction and scanning electron microscopy confirms that after Zr4+/Al3+ codoping, and surface treatment, the crystalline structure, and morphology of the photoanodes remains unchanged. X-ray photoelectron spectroscopy confirmed the existence of Zr4+/Al3+ codopants in the hematite nanostructure. The electrochemical properties of the photoanode suggest that Al3+ and Zr4+ codoping, as well as surface treatment with CoOx, cocatalyst lowers charge transfer resistance across the FTO/hematite interface, and hematite/electrolyte interface. This designs not only lowers onset potential but also offers the blueprint for the development of an efficient catalyst for solar water oxidation.

CuO is a narrow band gap p-type semiconducting material having a wide range of applications. However, it is quite challenging to obtain phase pure CuO nanostructures grown directly on Cu substrate as most of the synthesis techniques like thermal oxidation results in the formation of additional Cu2O phase. In this work, we report the growth of CuO nanoflakes without the formation of Cu2O by a facile two-step synthesis process which consist of electrochemical anodization of Cu foil followed by low-temperature hydrothermal treatment at 100 °C. The phase purity of the sample is confirmed through XRD, XPS, and HRTEM. Further, photocurrent response of the sample is evaluated, and a rapid thermal treatment was used to improve the photo-response without altering the phase and morphology of the CuO nanoflakes. Such a process at 400 °C for 10 s resulted in a high photocurrent density of −4.6 mAcm−2 (at 0.05 V vs. RHE under AM 1.5G conditions). Electrochemical impedance spectroscopy and Mott Schottky analysis shows the direct role of rapid thermal treatment in increasing the charge carrier density of the sample.

A facile strategy of electrophoretic deposition has been employed to fabricate a thin film photoelectrochemical (PEC) sensor of functionalized N–doped graphene quantum dots (F–NGQDs) embedded in BiOBr nanosheets, which were prepared by a two–step hydrothermal method, loaded onto indium–tin–oxide coated glass substrate (F–NGQDs/BiOBr/ITO). Electrophoretic deposition provides a mild and environmentally friendly method for PEC film formation. Multiple techniques were applied to investigate the electronic, optical properties and structure of F–NGQDs/BiOBr thin films photoelectrodes. It was found that F–NGQDs/BiOBr thin films with NGQDs/BiOBr heterojunction possess an enhanced charge transfer and absorption wavelengths under visible light, particularly when compared to pristine F–BiOBr films, thus producing an increase in the observed photocurrent. Sensing performance measurements showed the F–NGQDs/BiOBr/ITO photoelectrode has a higher photoelectric response current to paracetamol, it was used to detect trace paracetamol under visible light irradiation. The sensor exhibited a wide linear range, low detection limit and good sensitivity, given the photoactivity of NGQDs/BiOBr heterojunction. The developed PEC sensor displayed an acute response to paracetamol in a linear range of 0.01 μM–20.0 μM with a detection limit of 3.33 nM, under optimal conditions. Here we present evidence that F–NGQDs/BiOBr/ITO photoelectrode is a promising candidate for PEC analysis.

A photoelectrochemical (PEC) sensor based on hierarchically porous Cu-BTC/g-C3N4 nanosheet (Cu-BTC/CN-NS, BTC = benzene-1,3,5-tricarboxylic acid) material was constructed for the first time. As a composite material, the hierarchically porous Cu-BTC can help to efficiently capture suitable pesticide molecules and accelerate signal transmission, while CN-NS possesses good optical performance. Under the irradiation of visible light, the Cu metal center can coordinate with the added glyphosate to form Cu-glyphosate complexes, leading to the increased steric hindrance of electron transfer and consequently resulted in an obvious decrease in photocurrent. Through this strategy, the constructed sensor can realize the detection of glyphosate from non-electroactive to electroactive. The results indicate that this photoelectrochemical sensor has a low detection limit of 1.3 × 10−13 mol L−1 and a wide detection range (1.0 × 10−12–1.0 × 10−8 mol L−1 and 1.0 × 10−8 ∼ 1.0 × 10−3 mol L−1). Furthermore, this Cu-BTC/CN-NS based sensor has the characteristics of short detection time and easy operation. It has great potential applications in photoelectrochemical analysis.

A promising electrode with three-dimensional (3D) AuNPs/ZnO/Cu2O heterojunction nanowires (NWs) was developed and applied as photocathode for sensitive photoelectrochemical (PEC) immunoassay toward carcinoembryonic antigen (CEA, Ag). Firstly, Cu2O NWs were grown in situ on a Cu foil substrate to provide large specific surface area. After the modification of ZnO layer on the Cu2O NWs, the ZnO/Cu2O heterojunction structure was formed, which can increase the harvest of light energy and play a role in charge separation and transport. With further modification of gold nanoparticles (AuNPs), the good electric conductivity of the AuNPs would induce enhanced charge separation between Cu2O and ZnO. Thus, the photocurrent response of the prepared 3D AuNPs/ZnO/Cu2O NWs photocathode was significantly improved by synergistic effects of each element in the 3D structure. As a result, the fabricated cathodic PEC immunosensor exhibited high sensitivity with a low detection limit of 0.36 pg/mL (S/N = 3) for CEA detection. Furthermore, good specificity and well anti-interference capability toward real sample detection was achieved.

Vertically aligned one-dimensional (1D) materials offer numerous advantages for photoelectrochemical (PEC) energy conversion due to highly accessible surface area, direct charge transport pathway along the aligned direction, and suppressed electron-hole recombination. Hierarchical 1D-2D materials generate heterogeneous interfaces that can modify intrinsic chemical and physical material properties. Here, we report an ultra-high-aspect-ratio perfectly aligned 2D MoS2-1D TiO2 nanobelts (NBs) heterostructured nanoforest electrode and demonstrate enhanced PEC performance. The vertically aligned nanoforest electrode with an ultra-high aspect ratio of approximately 3000 was achieved using high-voltage electrophoretic deposition (EPD). The thickness of the vertical nanoforest correlated well with the length of the NBs and there was no evidence of vertical stacking. In addition, both semi-conductive 2H phase and metallic 1T phase MoS2 were discovered to form on TiO2 (011) and (001) surfaces, respectively. The nanoforest drastically enhanced light penetration into the interstice of the electrode and increased the probability of photon–semiconductor interaction due to reduced band gap as well as local surface plasmonic resonance (LSPR) evidenced by numerical studies. A remarkable 98% enhancement of the PEC photocurrent was achieved for the MoS2–TiO2 NB forest electrode compared with its un-aligned counterpart.

A novel 3D leaf-like Fe2O3-Bi2O3-Bi2S3 photoelectrocatalyst was constructed through electrodeposition and hydrothermal reaction and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and UV–Vis absorbance spectra. Results indicated the successful construction of 3D leaf-like Bi2O3-Bi2S3 nanosheets covered Fe2O3 nanoparticles, which could favor light refraction, improve light absorption, reduce charge transfer resistance, and facilitate the separation of photogenerated electron-hole pairs. The photocurrent density of Fe2O3-Bi2O3-Bi2S3 was ca. 8 and 7 times higher than that of bare Fe2O3 at 0.45 V vs Ag/AgCl under visible and UV–vis light irradiation, respectively. The Fe2O3-Bi2O3-Bi2S3 film exhibited higher photoelectrocatalytic (PEC) performance on the degradation of refractory pollutants than Fe2O3 and Fe2O3-Bi2O3 films under visible irradiation. Effects of applied potential and trapping agents were studied. The main active species in PEC process was the h+, HO• and O2•-. A proposed mechanism of charge transfer in Fe2O3-Bi2O3-Bi2S3 was discussed. This work provided a potential candidate material for PEC application in environmental remediation.

The development of photoanodes capable of photoelectrochemical water splitting is a sustainable approach for the storage of solar power to conveniently useable chemical energy. In this study, we report that amorphous CoP film can be grown on α-Fe2O3 nanorods to fabricate a core-shell structure via a simple reductive electrodeposition strategy. Under the irradiation of simulated sunlight (100 mW cm−2), the composite electrode shows that the onset potential demonstrates a 200 mV cathodic shift and the photocurrent density is enhanced from 0.45 to 0.90 mA cm−2 at 1.23 V vs reversible hydrogen electrode (RHE) when compare with the bare α-Fe2O3 electrode in 1 M KOH electrolyte. Long-term photoelectrolysis reveals that this electrode has excellent stability and possesses a near-unity Faradaic efficiency toward oxygen evolution. Mechanistic studies support the role of CoP film in enhancing photoelectrochemical performance and indicate that the remarkable photoelectrochemical performance of this composite electrode is mainly due to the retardation of surface photogenerated h+/e− recombination.

Contamination of water bodies by harmful and recalcitrant organic substances is a global challenge. A promising technique for removing these organics from water/wastewater is photoelectrocatalytic oxidation which combines electrolytic and photocatalytic processes. Herein, we report the degradation of emerging pharmaceutical pollutants – acetaminophen and ciprofloxacin – at a BiVO4/BiOI photoanode under visible irradiation via photoelectrocatalytic process. The BiVO4/BiOI was electrodeposited on a FTO glass and characterised with XRD, SEM, EDS and diffusive reflectance UV–Vis. The results confirmed the successful electrodeposition of BiVO4/BiOI on the glass substrate. Mott-Schotty plots confirmed the formation of p-n heterojunction between the two electrodeposited semiconductors. The calculated charge carrier density of BiVO4/BiOI was higher than those of pristine BiVO4 and BiOI. The binary electrode also gave improved photocurrent response compared with unitary electrodes. Degradation efficiencies of 68% and 62% were achieved upon the application of the prepared photoanode (FTO/BiVO4/BiOI) in PEC degradation of acetaminophen and ciprofloxacin respectively using a bias potential of 1.5 V within 2 h. A synthetic pharmaceutical wastewater containing a mixture acetaminophen and ciprofloxacin was also treated with the photoanode. The photoanode was also effective in the degradation of dye. The findings of this study suggest the suitability of the prepared photoanode for the photoelectrocatalytic degradation of organic pharmaceutical pollutants in wastewater.

We developed a two-step method to prepare Mo-doped CuWO4 NF array films, which involved a hydrothermal process to grow Mo-doped WO3 NF arrays and a follow-up thermal solid-state reaction to convert WO3 to CuWO4. The obtained Mo-doped CuWO4 NF array films retained the network structure of crosslinked CuWO4 NFs when the Mo-to-W atomic ratio in precursor solution is lower than 2 : 3. Mo doping not only narrowed the bandgap of CuWO4 but also significantly improved its electron density, both benefiting the photoelectrochemial (PEC) performance for oxygen evolution reaction (OER). The Mo-doped CuWO4 NF array films exhibited a high catalytic activity toward PEC OER, and the activity varied as a function of the Mo doping concentration. The highest activity was obtained on 32 at.% Mo-doped samples, with photocurrent densities of 0.62 mA cm−2 and 1.23 mA cm−2 at 1.23 V and 1.60 V vs RHE, respectively, which are the highest values among those reported in literature. Moreover, even at high OER overpotentials, the Mo-doped CuWO4 NF array films showed an excellent stability in weak alkaline solution. This work indicates that cation doping is an effective strategy to prepare highly efficient CuWO4-based photoanodes for PEC OER.

Hematite (α-Fe2O3) is one of the most promising photoanode materials to realize solar-to-hydrogen energy conversion via photoelectrochemical water splitting. However, α-Fe2O3 still suffers from serious charge recombination rate and its practical application in solar water splitting is severely hindered by its low carrier mobility. Hence, Ti-doped α-Fe2O3 (Ti-Fe2O3) nanoarrays with surface phosphate ions (Pi) functionalization are successfully synthesized and demonstrate synergistic enhanced photoelectrochemical water oxidation performance. The resulting Ti-Fe2O3/Pi photoanode nanoarrays exhibit an onset potential as low as 0.88 V vs. RHE and a significantly promoted photocurrent density of 1.56 mA/cm2 at 1.23 V vs. RHE under AM 1.5G illumination in 0.1 M KOH solution, which is much higher than those of Ti-Fe2O3 (0.92 mA/cm2) and pristine α-Fe2O3 (0.5 mA/cm2). Comprehensive structural and photoelectrochemical analysis reveal that the enhanced photoelectrochemical water oxidation performance can be ascribed to the synergistic effect of surface Pi functionalization. The phosphates could not only act passivation effect to enhance the photogenerated voltage and lower the onset potential by suppress the charge recombination, but also improve the surface PEC water oxidation kinetics to increase the photocurrent by accelerating the surface charge separation and utilization. This work along with in-depth understanding the role of Pi functionalization is expected to provide new vision for improving the PEC performance of metal oxide photoanodes.

A core-shell structure of Mg@CdS quantum dots (QDs) with ZnS passivation layer deposited on TiO₂ mesoporous film, denoted as TiO₂/Mg@CdS/ZnS, is fabricated as photoanode for enhancement of quantum dot sensitized solar cells efficiency. High resolution transmission electron microscope images and X-Ray photoelectron spectroscopy analysis confirm the core sell structure of Mg@CdS. Introduction of Mg nanoparticles in the photoanode indicates a rise in photovoltage and photocurrent density by decreasing the charge recombination and increasing the photon capturing ability indicated by photoluminescence and diffuse reflectance spectroscopy, respectively. TiO2/Mg@CdS signifies excellent charge injection and transfer efficiency in photoanode. Moreover, Zinc sulfide is utilized as the passivation layer to inhibit electron recombination between photoanode and electrolyte interface. The achieved power conversation efficiency of the TiO₂/Mg@CdS/3ZnS is 7.47% which is significantly higher than TiO₂/CdS (2.87%) and TiO₂/Mg@CdS (5.37%) photoanodes. Electrochemical impedance spectroscopy implies the higher charge recombination resistance between photoanode and electrolyte interface in solar cell fabricated using TiO₂/Mg@CdS/3ZnS photoanode. Refereed/Peer-reviewed

The combination of transition metal-based cocatalysts with semiconductors is a promising route to improve the photoelectrochemical performance in solar water splitting. However, it is difficult to evaluate the catalytic ability for cocatalysts quantitatively. Herein, we use kelvin probe force microscopy technique, combining with Mott-Schottky method, to investigate the cocatalysts from the point of surface potential and Femi level. Through synthesis the nickel/cobalt oxide nanoparticles and nanoporous bismuth vanadate (BiVO4), the result indicates the surface potential of NiCoO2 coated BiVO4 is lower than pristine BiVO4 and BiVO4 coated by NiO and CoO cocatalysts respectively. The lower surface potential means a more upward band bending structure at the interface of electrode and electrolyte, which can promote the separation of electron-hole pairs and enhance the charge transfer kinetics. Thus, the NiCoO2/BiVO4 photoanode achieve a remarkable photocurrent density of 2.34 mA/cm2 for water oxidation, and the charge separation and oxidation kinetics efficiencies are 61.9% and 72.7% respectively. In all, our studies provide a new mechanistic insight into cocatalysts for solar energy conversion.

An impedance assisted novel electrochemical technique has been employed to develop copper oxide (Cu2O) thin films on F-doped tin oxide (FTO)-coated glass substrate. Application of various potentials (−0.60 to −0.40 vs (Ag/AgCl)/V) in the presence of different ranges of frequency can lead to the attainment of high-quality Cu2O crystallites. The dependency of the frequency boundary (i.e. in terms of deposition time) with structural, morphological, optical and photoelectrochemical (PEC) behavior of the Cu2O thin films have been studied. The PEC performance of the optimized Cu2O electrode significantly enhances the water reduction photocurrent to −2.9 mA cm−2. The Cu2O thin film developed in this study exhibits superior photoelectrochemical performance in comparison with the conventionally electrodeposited materials.

Anodic TiO2 nanotubes are potential candidates for industrial scale and stable photoelectrochemical water oxidation. Major roadblocks for the realization of this technology however are the limited light absorption, as this material usually absorbs only in the UV, and the sluggish water oxidation kinetics at the electrode/electrolyte interface. Various efforts have nonetheless demonstrated absorption and photocurrent generation with visible light while a typical solution for the slow water oxidation is electrode modification via oxygen evolution catalysts; Ni Fe (oxy) hydroxides in particular are among the highest turn-over efficiency and low-cost catalysts. Studies about loading Ni Fe (oxy) hydroxides onto anodic TiO2 nanotubes by electrodeposition methods are rarely reported and the influence of the loaded catalysts on the photoanode performance is not fully understood. In this work, Ni Fe (oxy) hydroxides are first electrodeposited on Au substrates; the as-deposited catalysts indicate enhanced oxygen evolution catalytic activity. The same deposition method is then applied at various TiO2 nanotube systems. Specifically, mouths, walls and whole bodies of anodic TiO2 nanotubes are electrodeposited with Ni Fe (oxy) hydroxides and the corresponding photo response to water oxidation are investigated. We show that at relatively low applied potential (≤1.5 V vs. RHE) the Ni Fe (oxy) hydroxides layer significantly reduces photon absorption and facilitates interfacial recombination, leading to a decreased photocurrent density. In contrast, at relatively high bias (>1.5 V vs. RHE), the oxygen evolution is enhanced due to the intrinsic electro-catalytic properties of the loaded catalysts. Synergistic effect are not found in the three Ni Fe (oxy) hydroxide films deposited at TiO2 nanotube systems.

Small perturbation techniques such as intensity-modulated photocurrent spectroscopy (IMPS) have become an essential tool to unravel the complex, interrelated processes that govern the charge carrier dynamics in photoelectrochemically active materials for solar water splitting. We have fabricated CuWO4-based photoelectrodes by chemical modification of a WO3 nanorod array as a partially sacrificial template. The electrodes have been characterized by photoelectrochemical techniques including IMPS as a function of the annealing temperature, transforming WO3 either partially or completely to CuWO4. The optical properties illustrate the transformation with the absorbance onset moving from the typical onset for WO3 (about 2.5 eV) to that of CuWO4 (about 2.1 eV). In pure CuWO4 photoelectrodes bulk recombination dominates the photoelectrochemical performance, while for FTO|WO3@CuWO4 heterojunction photoelectrodes much larger charge separation and external quantum efficiencies are obtained. In addition, CuWO4 serves as a protective layer for the WO3 material that is not generally stable in neutral aqueous solutions. The FTO|WO3@CuWO4 heterojunction material was further explored as an underlayer substrate, using a thin BiVO4 film as overlayer. The advantages of this configuration include improved light harvesting as BiVO4 is a direct semiconductor with a much larger absorption coefficient than CuWO4, which is characterized by an indirect gap. It is found that the FTO|WO3@CuWO4 underlayer efficiently extracts the photogenerated electrons from the BiVO4 overlayer, hence, the inclusion of a second heterojunction plays an essential role in improving the charge separation and internal quantum efficiency, minimizing both bulk and surface recombination.

The charge separation and transfer are critical steps during the photoelectrochemical processes. In this paper, we focus on the interfacial properties within the heteropolyacid (denoted as PW12) modified WO3 heterojunction film synthesized by an epitaxial growth method. The characterizations show that heteropolyacid is formed on the surface of WO3 plates with less interfacial defects between PW12 and WO3. The PW12/WO3 photoanodes synthesized via the in-situ method display a photocurrent density of 0.65 mA/cm2 at 1.23 V vs. RHE, which exhibits 1.6 times as much as the bare WO3. And the composite achieves the maximum value of 1.52 mA/cm2 at 1.8 V vs. RHE, while those of PW12/WO3 films prepared by a dip-coating method and pristine WO3 films are just 1.10 and 0.85 mA/cm2. The improvements in PEC performances of PW12/WO3 photoanodes (in-situ) were attributed to the higher electron transmission rate and longer electron lifetime resulted from the less interfacial defects. Moreover, the PW12/WO3 film was treated with TiCl4 solution to form a TiO2/PW12/WO3 ternary heterojunction, which exhibits a higher photocurrent density of 1.89 mA/cm2. The current research has proposed a new perspective and method for the design of highly efficient heterojunction photoelectrodes and inorganic synthesis.

A novel CdS/ZnO/TiO2 hierarchical heterostructure for photoelectrochemical (PEC) application was fabricated by growing ZnO nanorods (NRs) onto TiO2 nanosheets (NSs) with dominant high-energy {001} facets via hydrothermal method, subsequently coated CdS quantum-dots (QDs) sensitized layer via successive ionic layer adsorption and reaction (SILAR) technique. The as-prepared TiO2, ZnO/TiO2 and CdS/ZnO/TiO2 films were characterized by XRD, SEM, TEM, UV–vis absorption spectrum and EIS techniques to investigate the effects of ZnO NRs and CdS QDs on the structure, morphology, optical property and charge carrier transmission characteristics. The results demonstrated that the growth of ZnO NRs obviously enlarges the specific surface area, while the deposition of CdS QDs significantly enhances the light harvesting ability. And the heterojunctions formed among TiO2 NSs, ZnO NRs and CdS QDs effectively promote the photogenerated charge carrier transport and separation, simultaneously inhibit the photogenerated electron-hole recombination. Moreover, it is notable that ZnO NRs trend to grow on the low-energy {101} facets of TiO2 NSs due to the impact of crystal facet controlling agent, which can effectively shorten the electron conduction path-ways and facilitate the photogenerated electron-hole separation due to the lower band edge position of {101} facets than that of {001} facets. As a result, the photocurrent density of the optimized CdS/ZnO/TiO2 composite film enhances to an excellent value of 12.1 mA/cm2 at a potential of 0 V vs SCE, which is more than 27 times higher than that of bare TiO2 NSs films. In addition, the corresponding optimal condition and physical mechanism were also discussed in the paper.

Photoelectrochemical water splitting can be regarded as a promising technology for renewable hydrogen production. In the current work, a facile hydrothermal synthesis method was used to directly grow TiO2 flower-like structures/TiO2 nanorods on a conductive glass substrate. Moreover, three different gold deposition methods, namely, a photoreduction method (PR), the Turkevich method (TK) and a combination of both methods (CM), were applied to decorate the formed flower-like structures with gold nanoparticles (GNPs). The type of deposition technique affected the size, size distribution, loading, surface coverage and shape of the obtained GNPs. With the PR technique, the photocurrent increased 3.5-fold compared to that of the bare flower-like structures. With the TK method, a narrow GNP distribution was obtained, yielding a 6.15-fold increase in photocurrent. Using the CM approach, a 1.21-, 26.86- and 12.79-fold increase was observed for current density compared to that of the corresponding bare samples. All samples showed stable chronoamperometric performance under illumination without any signs of photocorrosion or performance deterioration. Electrochemical impedance spectroscopy showed that the CM approach decreased the semiconductor/electrolyte interfacial resistance to 37, 2.5 and 3.1% of the values for the bare samples. Bode phase plots showed that the stacked flower-like structures can be considered electron-hole recombination centres, leading to an observable broadening of the maximum-frequency peak.

Four isomeric organic dyes featuring D-A′-π-A configuration with 5-methylbenzothiadiazole as auxiliary acceptor have been synthesized and characterized as sensitizer for dye-sensitized solar cell. The dyes with methyl unit attached near donor exhibited high molar extinction coefficients when compared to the isomeric dyes possessing methyl unit near acceptor segment. Due to this, the former dyes exhibited two fold high power conversion efficiencies when compared to the later dyes. The high efficiency of the dyes containing methyl near donor arises from the enhanced photocurrent density and open-circuit voltage values. The electrochemical impedance spectra demonstrated favourable electron injection, longer electron lifetime and effective charge recombination resistance for dye-sensitized solar cells based on these dyes. The attenuation in the coplanarity between the donor and acceptor with benzothiadiazole due to the presence of methyl group significantly affected the donor-acceptor interactions and charge migration kinetics.

The poor surface charge separation and transfer properties as well as sluggish water oxidation kinetics jointly limit the performance of BiVO4 photoanode for water oxidation. In this work, p-type CuCoO2 with high-spin Co3+(Oh) was investigated as co-catalyst to synergistically improve the surface charge separation and transfer efficiencies as well as reaction kinetics of BiVO4 film for photoelectrochemical water oxidation. In comparison with the photocurrent on BiVO4 photoanode for water oxidation (1.21 mA/cm2 at 1.23 V vs. RHE), the CuCoO2-coupled BiVO4 (CuCoO2/BiVO4) photoanode exhibits a higher photocurrent density of 3.32 mA/cm2 at 1.23 V vs. RHE under AM 1.5G illumination. In addition, a significant improvement on the reaction stability is achieved on the CuCoO2/BiVO4 photoanode, about ∼79% water oxidation activity is retained on the CuCoO2/BiVO4 photoanode after operating at 0.8 V vs. RHE for 5 h, while only ∼9% activity is retained on the BiVO4 photoanode. The boosted water oxidation activity and stability on CuCoO2/BiVO4 photoanode could be attributed the synergistic effect that originated from CuCoO2-electrocatalysis and BiVO4-photocatalysis in thermodynamics and kinetics. Specifically, p-n heterojunctions are formed in the coupling interface between CuCoO2 (p-type) and BiVO4 (n-type), which thermodynamically improve the surface charge separation and transfer efficiencies of BiVO4 photoanode during water oxidation. Simultaneously, the high-spin Co3+(Oh) of CuCoO2 could act as active sites to accelerate the water oxidation of CuCoO2/BiVO4 photoanode in kinetics. In addition, Cu2+ active sites are formed for water oxidation through the oxidation reaction of photogenerated holes with the Cu+ of CuCoO2.

A microbial biosensor based on the cyanobacteria Anabaena variabilis was developed for online herbicide detection through inhibition of generated photocurrent. Specifically, atrazine and diuron were employed as model photosynthesis-inhibiting herbicides. To fabricate the biosensor, bacterial cells were immobilized on a carbon felt electrode using alginate as an entrapping polymer and p-benzoquinone (BQ) as the redox mediator to sustain the electron transfer. The current generated by the photo-bioelectrocatalytic oxidation of water was evaluated. During the calibration, an immediate concentration-dependent decrease of the photocurrent was observed after the injection of the tested herbicides. The biosensor showed a sensitivity of −24.6 μA μM−1 cm−2 towards atrazine up to 0.56 μM. As diuron is a much stronger photosynthesis inhibitor, the biosensor allows only turn on/turn off detection for this compound. In order to avoid the release of the mediator in solution, the encapsulation of BQ in the polymer was tested. Addition of activated carbon was necessary to create a conductive network inside the alginate matrix, enabling to achieve a sensitivity of −7.7 μA μM−1 cm−2 towards atrazine up to 131 μM (lower limit of detection 64 nM). Therefore, not only the entrapment prevented the release of BQ in solution, but improved the operating range of the sensor, with a limited decrease of sensitivity that does not hinder its application. These characteristics make the biosensor suitable for environmental analysis, opening for the on-line monitoring of herbicides.

In this paper, a facile one-step vacuum annealing process has been developed to fabricate the coaxial carbon-TiO2 nanotube arrays (CC-TNAs) film. The obtained composite film is composed of TiO2 nanotubes self-doped by oxygen vacancies (V.os), and an ultrathin carbon layer covering on the outer wall of TiO2 nanotubes. This composite film exhibited high absorbency from UV to NIR wavelength region, high electric conductivity, and photothermal effect. As a photoanode for hydrogen generation, the film showed promising light response in Na2S/Na2SO3 aqueous solution under a broad wavelength range from UV to NIR wavelength region. The study of the working mechanism revealed that a unique non-stepped photocurrent was resulted from the photothermal effect of CC-TNAs film in the electrolyte environment. The performance of this photothermo-electrochemical (PTEC) process is determined by the co-existence of the V.os and the coaxial carbons of TNAs. This study provides new insight into the design, preparation, and correlation between the structure and performance for new semiconductor-carbon nanocomposites.

Increasing the photocurrent is one of the main objectives of the current research on aqueous photovoltaic cells, the emerging green, alternative technology in solar energy conversion devices. In such a scenario, this work deals with the thorough understanding of the electrochemical and photoelectrochemical effects of the TiCl4 treatment onto TiO2 electrodes, a well-known process for traditional dye-sensitized solar cells, and here, to our knowledge, investigated for the first time in water-based systems. From the quantitative evaluation of the photoelectrochemical parameters, it emerges that the TiCl4 treatment beneficially affects the photovoltaic parameters: it doubles the sunlight conversion efficiency values, inhibits the recombination of photogenerated electrons with oxidized redox mediator ions, and ensures stable and reproducible cell performance at the laboratory scale. (C) 2019 Elsevier Ltd. All rights reserved.

The effect of incorporating silver nanowires (Ag NWs) and TiO2 nanofibers (NFs) into a tri-layer photoanode of dye sensitized solar cells (DSSCs) have been investigated. Ag NWs with diameter 60–90 nm and length of 1–2 μm were synthesized via polyol reduction method. TiO2 nanofibers (NFs) with diameter 80–120 nm were prepared by electrospinning. The DSSC with tri-layer photoanode made with a composite of TiO2 P25, Ag NWs and TiO2 NFs sandwiched between two TiO2 P25 layers exhibited power conversion efficiency of 9.74% and open circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) of 727.4 mV, 19.8 mA cm−2 and 67.6% respectively under the irradiance of 100 mW cm−2. The efficiency of the reference DSSC with TiO2 P25/P25/P25 tri-layer photoanode of the same thickness was found to be 6.69%. The efficiency enhancement of the DSSC with Ag NWs and TiO2 NF incorporated composite, tri-layer photoanode compared to the reference DSSC is 45.6%. This is evidently due to the enhancement in short-circuit photocurrent density (Jsc) by (a) localized surface plasmon resonance effect by Ag NWs and (b) increased light harvesting by multiple scattering events by the presence of TiO2 NFs.

The anatase titania with large fraction of {001} facet on the mesoscopic anatase titania scaffold in the hybrid perovskite solar cells exhibited higher photocurrent and open-circuit voltage. The higher performance with {001}-dominant anatase titania with the fraction of 74% were discussed with the characteristic electron transport properties in addition to the energy levels of trap states and conduction band as compared with those properties of conventional anatase titania scaffold. The resulted higher photocurrent and open-circuit voltage were attributed to the enhancement of the electron injection and suppression of the carrier recombination, respectively, at the titania/perovskite semiconductor interface. Accepted version

Heterojunction electrode requires thermodynamically favored band edge energetics to boost charge separation for efficient photoelectrochemical (PEC) water splitting. In this study, we report that TiO2 nanorods (NRs) doped with W, formed by solid state diffusion, can tune the band structure to construct a Type II staggered heterojunction with BiVO4. The W-TiO2/BiVO4 heterojunction overcomes the intrinsic energy barrier between BiVO4 and TiO2 NRs by downward shifting of conduction band position, exhibiting 4-times higher PEC performance (2.5 mA/cm2) than TiO2/BiVO4. Moreover, the photocurrent characteristics and photon-to-current conversion efficiency (IPCE) indicate that the W-TiO2/BiVO4 heterojunction retains the small onset potential of TiO2 and light harvesting capability of BiVO4. Especially, compared to popular WO3/BiVO4 heterojunction, the W-TiO2/BiVO4 heterojunction can present better stability towards long-term solar water splitting due to the compatibility of pH sensitivity. This study can shed a new insight on design of heterojunction by regulating band edge energetics for PEC water splitting.

Porphyrin based nanomaterials have attracted widespread attention due to their similarity of the key dyes of natural photosynthesis. To develop new chromophores for photoelectrochemical (PEC) devices, in this work, we synthesized 3 different aggregated nanostructures of meso-tetra(4-carboxyphenyl)porphine (TCPP) via self-assembly technique. The micro-environments of porphyrin self-assembly were modulated by using sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) as “soft template” respectively, aqueous solution without surfactant as control. Due to the different driving forces of self-assembly, the as-prepared TCPP nanostructures exhibited remarkably different morphologies, electrochemical and PEC properties. Among them, the self-assembled TCPP using SDS (SA-TCPP/SDS) possessed enhanced PEC performance. In presence of dopamine, a significant photocurrent response can be feasibly obtained in aqueous media at −0.4 V (vs. Ag/AgCl). Moreover, the self-assembly process was also investigated using in situ UV–visible spectroscopy and the corresponding structure formation mechanisms were proposed.

For successful production of photobioelectrodes two major aspects have to be addressed: The proper orientation of the photo-active biomolecules on the electrode surface and a good electrical connection with the electrode. In this work a step-by-step procedure for the successful construction of a photosystem I (PSI)-based photobioelectrode is shown. First, the orientation of PSI on a ruthenium hexamine-thiol-modified gold surface is improved: Here, positively charged ruthenium hexamine complexes allow for a better and a more directed assembly of PSI with the luminal side to the electrode. In a second step, an improved electrical communication of the PSI reaction center with the electrode is achieved by employing carboxy-modified C70-fullerenes. Due to the outstanding electrical properties of the small fullerene nanoparticles and their accessibility towards the PSI's reaction center and the electrode, the system shows an enhanced magnitude of the cathodic photocurrent (15 μA cm−2 at U = - 0.300 V vs. Ag/AgCl) and a positive onset potential of the cathodic photocurrent generation (Uonset = + 0.157 V vs. Ag/AgCl). In conclusion, it can be stated that this study demonstrates alternative approaches in meeting key demands for the construction of PSI-based photobioelectrodes resulting in relatively high IQE values (ca. 10%) and turnover frequencies (ca. 228 e− s−1).

New approaches for coupling Au NPs to the photoanode of dye sensitized solar cells (DSSCs) were proposed herein, aiming to improve the typical energy conversion efficiency of these cells. For this purpose, colloidal Au NPs with different particles sizes, ∼5 nm and ∼22 nm, were chemically synthesized and attached (i) directly to titanium dioxide (TiO2) or (ii) to TiO2 surface modified with siliceous shells enriched in dithiocarbamate moieties (SiO2/SiDTC). Photoanodes composed by films of TiO2 anatase, TiO2@Au NPs (∼5 nm and ∼22 nm), or TiO2 functionalized with SiO2/SiDTC, loaded with colloidal Au NPs, were made. DSSCs were set-up in a typical sandwich configuration, using the photoanode, a Pt counter electrode, and an iodide electrolyte solution (I−/I3−). In general, a relevant contribution in the plasmonic DSSC performance was evidenced by using Au NPs of ∼22 nm loaded in different amounts 23.9 wt%, 31.0 wt% and 44.0 wt%. Photoanodes composed by 23.9% of Au yielded an increment of 14.40% in photocurrent and of 11.21% in the overall power conversion efficiency (PCE), when compared to the conventional one. In turn, the new strategy used in the chemical modification of the conventional photoanodes with dithiocarbamate groups showed also a significant improvement of the DSSC parameters.

Pd@CdS@ZnO core-shell nanorods (NRs) have been prepared by using novel an easy chemical synthesis process. The superior catalytic activity of Pd@CdS@ZnO nanorods is attributable to the effective separation of electrons-hole pairs. The excitation-wavelength-dependent catalytic performance of Pd@CdS@ZnO NRs showed significant enhancement at the wavelengths analogous to the CdS layer. The recyclability results revealed a strong ability for the degradation of toxic organic pollutants with favorable reusable photocatalytic efficiency. Electrochemical impedance and photocurrent detection analysis further confirmed a reduced in the charge transfer resistance of Pd@CdS@ZnO NRs owing to embedded Pd NPs and coating of a CdS layer on ZnO NRs.

Regioisomeric quinoxaline-based dyes (NQXs) were synthesized to study the effect of substitution patterns on the performance of quinoxaline-based dye sensitized solar cells (DSSCs). The 1H NMR results indicated that the substitution patterns of ethylene groups on the quinoxaline unit greatly affect the molecular architecture through C H⋯N hydrogen bonding, which also influenced the absorption and efficiency of the DSSCs. The highest occupied molecular orbital (HOMO) levels of the NQXs were estimated to range from 0.94 to 0.99 V by cyclic voltammetry and visible absorption studies, which is suitable for DSSCs. The photocurrent density-voltage curves and incident photon-to-electron conversion efficiency spectra of NQXs indicated that the introduction of phenothiazine groups at the 2- and 3-positions of quinoxaline is the most effective pattern for quinoxaline-based organic sensitizers in DSSCs.

The present paper reports the effect of nitrogen modification on photoelectrochemical (PEC) water oxidation behavior of Bi2O3 semiconductor thin film. The semiconductor particles were synthesized via hydrothermal route using Bi(NO3)3 as a Bi3+ ion precursor and urea as the nitrogen source followed by drop-cast the particles and annealing the film at 600 °C. The synthesized Bi2O3 exhibited band gap energy of 3.01 eV, calculated from the UV–visibleabsorption spectrum which decreases to 2.75 eV through N-modification. Water oxidation behavior of the material has been tested through linear sweep voltammetry under periodic illumination. Highest photo-current of 180 μAcm−2 has been measured for water oxidation reaction at 0.95 V vs. Ag/AgCl, under illumination of 35 mWcm−2. N-incorporation can enhance the photocurrent up to 50% whereas the visible responsiveness of the material improves significantly as confirmed from electrochemical action spectra and UV–visible absorption spectra. The photocatalytic activity of the semiconductor particles was confirmed through decoloration of Rhodamine-B dye, by spectrophotometric measurements.

Two nitrogen-rich heterocycle donor dyes, NP-2 and NP-3, have been strategically designed and synthesized to construct functionalized self-assembly layers. Through the formation of N⋯H hydrogen bonds between these nitrogen-rich heterocycle donors and 4-tert-butylbenzoic acid (PTBBA), the electron leak points (imine group ( N )) may be plugged, thus blocking excited-state electron lateral transferring between the adsorbed dyes and electron leaking from electron-transporting channel into the electrolyte. Furthermore, the huge 3-dimensional sizes of such supramolecule sensitizers can not only suppress dye aggregation, but enhance the photoresponse capacity in visible region. Therefore, the devices based on NP-2@PTBBA and NP-3@PTBBA, which obtained by the cocktail sensitization procedures, can be improved by increasing the open-circuit photovoltage (Voc) without any loss of the short-circuit photocurrent density (Jsc) owing to the synergy effect between self-assembly and co-sensitization. Although the device based on NP-3/PTBBA via the stepwise sensitization procedure delivers lower efficiency, it can remain at 103.14% of the initial efficiency as a result of parallel increase in Jsc and Voc values. Overall, the design principles provide a clear road map of supramolecular dye-sensitized solar cells (SDSSCs) and demonstrate the potential of 1,3,5-triazine-based dyes in solar cells research.

The photocurrent of BiVO4 is limited by surface recombination not surface catalysis, which is currently reported as the main restrict factor for high efficiency photo-electrochemical (PEC) water splitting. To solve this problem, an ultrathin Ni:FeOOH (∼8 nm) modified nanoporous BiVO4 photoanode (BiVO4@Ni:FeOOH) was constructed with core-shell structure for PEC water oxidation. Attributed to the p-n hetero-junction formed between BiVO4 and Ni:FeOOH, the photocurrent density of BiVO4@Ni:FeOOH increased by a factor of 11 (2.86 mA cm−2 at 1.23 V vs. RHE), together with ∼180 mV negative shift of onset potential under AM 1.5 G irradiation (100 mW cm−2) in comparison to the pristine BiVO4. More importantly, detailed insight into the fate of the photo-generated charge carriers at the surface is investigated. Intensity modulated photocurrent spectroscopy (IMPS) is used to investigate the surface carrier dynamics of BiVO4 and BiVO4@Ni:FeOOH. IMPS results and hole scavenger measurement (HSM) certify the main role of Ni:FeOOH is to improve surface recombination by largely decreasing the surface recombination rate constant (krec), not surface catalysis. This work demonstrates Ni:FeOOH can facilitate local surface kinetics and reduce recombination rates as well and be used in other photoelectrodes especially the photoanodes with surface defects for PEC water splitting.