PEC Properties Research Articles

Hierarchical structures of 2D g-C3N4 sheet supported 3D star-shaped flower CuO nanohybrids for improved photoelectrochemical water oxidation and visible light induced photodegradation of antibiotics

The interfacial interaction between different materials is favorable to the photoexcited charge separation, and it can also contribute complete performance to their individual benefits and create for the shortcomings to attain a complementary influence. But, it is still challenging to modify the preferred structure and heterojunction interface of catalyst materials using a facile and effective method. In this report, 2D g-C3N4 sheets supported 3D star-shaped flower like CuO nanohybrid p-n type heterojunction catalysts were prepared using simple facile synthesis technique and examined their catalytic activity and photoelectrochemical properties. The photocatalytic efficacies of TC using pure g-C3N4, CuO and CuO/g-C3N4 were 47.4%, 75.2% and 94.7% within the 30 min of visible light irradiation. The enhanced photodegradation performance of nanohybrids catalyst is due to the formation of heterojunction, subsequent in the photoexcited charge carrier’s active separation the improved ability of visible light absorption and development of p-n heterojunction. Moreover, PEC water oxidation properties were examined and CuO/g-C3N4 nanohybrid electrodes displays improved PEC properties than the pure CuO and g-C3N4. Furthermore, g-C3N4, CuO and CuO/g-C3N4 photoelectrode displays photocurrent density 0.85, 1.60 and 2.30 mA/cm−2, respectively. Therefore, 3D/2D nanohybrids with robust ability of visible light absorption could offer a novel method to create effective facilitating the growth of photoelectrodes for the PEC water oxidation and photodegradation for fast and effective antibiotic removal from the environment.

Boosting charge transport in the BiVO4 photoanode interface modified with an aluminum hydroxide layer for solar water oxidation

Modifying BiVO4 with Al(OH)3 layers improved its PEC properties due to an increase of surface wettability. The strong interfacial interaction with H2O played a vital role in efficient charge carrier transportation on the BiVO4 interface.

Boosting photoelectrochemical performance of CuFeO2/CuO photocathode by modulating heterojunction architecture and oxygen vacancies

This study aims to enhance the PEC properties of CuFeO2 nanosheets by constructing closely bonded CuFeO2/CuO heterostructures. CuO crystal-structured films were prepared using the sol-gel spin-coating method, wherein the annealing temperature was varied to modulate the content of oxygen vacancies. Compared to pristine CuFeO2 and two tandem architectures, the CuFeO2@VO-CuO core-shell architecture outperformed by yielding a photocurrent density of 68 μA/cm2, which marks an almost 8.5, 1.36 and 2.27 times enhancement. Experimental results verified solid atomic-level contact bonding at the CuFeO2@VO-CuO junction, thereby augmenting overall efficiency. Through the optimized fabrication process of the CuFeO2@VO-CuO core-shell heterostructure, carrier concentration and transport and electron-hole pair separation saw substantial improvement, further boosting its PEC performance. Critically, the presence of oxygen vacancies in the CuFeO2@VO-CuO heterostructure played a pivotal role. Oxygen vacancies eliminated potential traps for captured electrons at the interface and suppressed the formation of unoccupied interface states, reducing recombination of photogenerated electron-hole pairs. Moreover, oxygen vacancies facilitated conduction band alignment, promoting efficient separation and rapid transfer of photogenerated electron-hole pairs. In conclusion, the CuFeO2@VO-CuO core-shell heterostructure achieves efficient separation and transfer of photogenerated electron-hole pairs while effectively suppressing recombination, thanks to the synergy between the interfacial electric field and oxygen vacancies.

NiFe-LDH-Decorated Ti-Doped Hematite Photoanode for Enhancing Solar Water-Splitting Efficiency.

Ti-doped α-Fe2O3 nanorods were prepared by a facile hydrothermal method, followed by a NiFe-LDH catalyst that was electrodeposited on the doped α-Fe2O3 nanorods to structure an integrating photoanode Ti:Fe2O3/NiFe-LDH for improving solar PEC water-splitting efficiency. The structure and properties of electrode materials were characterized and the PEC properties of photoanodes were measured. The results show that the photocurrent density of the photoanode enhances 11.25 times at 1.23 V (vs RHE) and the IPCE value enhances 4.10 times at 420 nm compared with pristine α-Fe2O3. The enhancement is attributed to the separating of photogenerated electron-hole, the increase of carrier density, and the acceleration of the carrier transfer rate due to the dual action of doping and catalysis.

Mn-doped ZnS nanoparticle photoanodes: Synthesis, structural, optical, and photoelectrochemical characteristics

In this work, Mn-doped zinc sulfide (Mn:ZnS) nanoparticles (NPs) have been synthesized as a promising material for photoelectrochemical water splitting (PEC), using the co-precipitation method. PEC properties of Mn-doped zinc sulfide NPs were considered under the correlation between Mn-doping level and their particle size. The highest photocurrent density (8.03 mA cm−2) and largest photoconversion efficiency (0.63%) (at 0.4 V vs. RHE) were reached at 6 mol% Mn. Based on the results of used various materials characterization techniques, including transmission electron microscopy (TEM), X-ray diffraction, photoluminescence spectrum, and absorbance spectrum, it can be assessed that the outstanding PEC characteristics of Mn:ZnS photoanode are attributed to the narrow bandgap of Mn:ZnS nanoparticles and their notably small particle size, which is originated from the Mn-doping. For application, the stability and the effect of various electrolytes were also investigated.

More comprehensive heterojunction mechanism: Enhanced PEC properties originated from novel ZnIn2S4/Cu2S heterojunction assisted by changed surface states

The more comprehensive investigation of ZnIn2S4-based heterojunction mechanism is beneficial for rationalizing the PEC performances enhancement mechanism and optimizing the application of heterojunction. Herein, Cu2S is for the first time synthesized on ZnIn2S4 as a novel co-catalyst through in-situ ion exchange techniques. The holes are extracted and stored in ZnIn2S4/Cu2S through enhanced surface states (ss) due to the decreased holes transfer resistance to ss and improved ss capacitance, which improve the carrier separation efficiencies with the effect of built-in electric filed. With the sequential deposition of NiFe-LDH, despite the inevitable carrier recombination is caused by the conflicting chemical potentials between Cu and Ni ions at the Cu2S/NiFe-LDH interface, the carrier injection efficiency is increased to 71.60% due to the exposure of more intermediate surface states (iss). The highest photocurrent density of 1.56 mA/cm2 at 1.23 V (vs. RHE) is achieved by ZnIn2S4/Cu2S/NiFe-LDH when influence of the interface carrier recombination is counteracted by the synergistic effect containing extended light absorption, the construction of ZnIn2S4/Cu2S heterojunction and changed ss, which is 10.4 times higher than that of pristine ZnIn2S4. The work provides a more comprehensive approach to investigate the mechanism for enhanced PEC performances of ZnIn2S4-based heterojunction.

Incorporating Mesoporous Anatase TiO2 Spheres to Conductive Carbon Black Filled PVDF Membrane for Self-Cleaning Photo(electro)catalytic Filtration

Polyvinylidene fluoride (PVDF) membranes have been widely used for micro/ultrafiltration. However, their hydrophobicity leads to serious membrane fouling over time during the process of dye decolorization, which limits their practical application. Herein, PVDF, mesoporous TiO2 spheres (MTS, ∼460 nm), and carbon black (CB) are strategically hybridized via a polyvinylpyrrolidone (PVP)-assisted phase inversion method. The fabricated PVDF/CB/TiO2 conductive membrane prepared by optimal low-molecular-weight PVP (10 kDa) shows a highly porous structure with macro-voids, and MTS are firmly incorporated into the PVDF/CB membrane matrix with a morphologically intact structure, rendering the ternary and conductive membranes with excellent PEC properties. The decolorization rate of 0.50 mg/L methylene blue (MB) reaches 98.6% under the condition of 1.0 V bias potential and simulated solar light irradiation in a continuous cross-flow filtration process. The •O2– and •OH radicals and photogenerated holes (h+) are mainly responsible for MB decolorization in the PEC system. Our work provided a sustainable and efficient method for dye decolorization by combining the PEC system and membrane technology.

Surfactant assisted single step electrodeposition of CuInSe2 thin films with rich indium selenide surface over layer

Abstract In this work, we report on the electrodeposition of CuInSe2 (CIS) thin films with In2Se3 rich surface by a single step deposition technique. It was observed that the In-content deposited in CIS can be improved by the addition of sodium dodecyl sulfate as a surfactant. The presence of an In–Se rich layer was confirmed by electrochemical, compositional and Raman spectroscopy analysis. The photo-electrochemical properties of the as-deposited CuInSe2 thin films were found to be enhanced due to the presence of In–Se rich superficial layer. The presence of an In–Se layer over CIS may act as a p-n homo-junction which may be attributed as the primary reason for the improvement in the PEC properties.

Heterostructured 2D/2D ZnIn2S4/g-C3N4 nanohybrids for photocatalytic degradation of antibiotic sulfamethoxazole and photoelectrochemical properties

In recent years, antibiotic drugs have been extensively used owing to increased industrial growth, and this has created issues related to drinking water and a green environment. Different techniques have been used to resolve these issues, among which heterogeneous photocatalysis has been widely explored for the elimination of toxic compounds from wastewater resources. In this study, ZnIn2S4, g-C3N4, and ZnIn2S4/g-C3N4 hybrid heterostructured composites are synthesized via hydrothermal method and used these (i) for the removal of antibiotic sulfamethoxazole pollutant and (ii) photoelectrochemical water oxidation. The nanomaterials were characterized using X-ray diffraction, Scanning electron microscopy, transmission electron microscopy, and UV–vis spectroscopy. The developed hybrid heterostructured composites were able to degrade sulfamethoxazole pollutants as well as offer improved photoelectrochemical properties compared to pristine samples. The catalytic performance of the materials developed under visible light irradiation was greatly improved for the degradation of the antibiotic drug up to 89.4% in 2 h. Moreover, the hybrid heterostructured photoelectrode showed a better photocurrent density (8.68 mA/cm2) and exhibited ∼19.2 and 29.9 times greater photocurrent density than the pristine photoelectrodes. Such a considerably increased catalytic activity was attributed to the active separation of charge carriers and transmission. The study offers an innovative approach to develop effective catalysts, and for the degradation of sulfamethoxazole as well as the PEC properties for hydrogen production.

Investigate the suitability of g-C3N4 nanosheets ornamented with BiOI nanoflowers for photocatalytic dye degradation and PEC water splitting

The two-step thermal polymerization and solvothermal approach is used to construct nano heterostructures of FCN and BiOI (bismuth oxeye iodide), both of which are Nobel metal-free materials. This work reports the effect nano-heterostructure on the micro-structural, light absorption capability, PEC properties and pollutant degradation efficiency of the synthesised heterostructures. The addition to that formation of FCN/BiOI nano-heterostructure enhances the solar light absorption. The FCN/BiOI nano heterostructure shows 10 times higher photocurrent density than the BCN nanostructure and 3.8 time higher that FCN. The FCN/BiOI has a high induced photo-current density (20.17 mA/cm2) and H2 evolution rate (3762 μmol h−1 cm−2) under solar light illumination (λ ≥ 420 nm) in comparison with the other. Furthermore, the photocatalytic performance of this material for the breakdown of methyl red dyes was much greater. Under solar light irradiation, the azo dyes were degraded in 90 min. The FCN/BiOI nano-heterostructure has a higher dye degradation efficiency of 97.91%. The rapid transport of photo-induced electrons in the FCN/BiOI nanocomposite is responsible for the improvement in PEC and PC performances. These impressive findings suggest that this nanocomposite might be used to facilitate the PEC water splitting and the PC degradation of MR in the presence of light. The current research provides insight on how to best tailor composition and structure for efficient FCN photo-electrocatalysis water splitting and Methyl red dye degradation.

Comprehensive evaluation of photoelectrochemical performance dependence on geometric features of ZnO nanorod electrodes.

The impact of geometric features, light absorption spectra, and electrochemical active surface area on photoelectrochemical properties was investigated in this work. Nanoforests of ZnO nanorods with rationally controlled morphologies were grown on ITO substrates by the hydrothermal method and utilized as a model for this purpose. The size of the nanorods was systematically adjusted by varying the concentration of polyethyleneimine as a cation surfactant in the growth solution. It was found that the emergent geometric characteristics (i.e. the aspect ratio) increased almost at the same pace as the electrochemically active surface area, but the light scattering effect slightly increased as a result of the random spatial orientation of the nanorods. The large surface area and the void space between nanorods increased the photon-to-current conversion efficiency by promoting the hole transfer process at the electrode/electrolyte interface. A maximum photocurrent density of 0.06 mA cm-2 (0.5 V vs. NHE) for smaller diameter and length ZnO nanorods (ZnO-P1) was obtained under 365 nm UV light illumination. Additionally, we provide visual evidence that a shorter photogenerated hole diffusion distance results in improved charge separation efficiency using Mn2+ as the photogenerated hole imaging agent. Therefore, the present work demonstrates a facile strategy for nanoforest morphology improvement for generating strong contact at the ZnO NR electrode/electrolyte interface, which is favourable in energy conversion and storage technologies.

Direct growth of Bi2S3 nanorods onto the Bi2MoO6 nanoflakes: A promising heterostructure for efficient photoelectrochemical water-splitting application

Fabrication of heterostructure promises a potential approach to increase the hydrogen production performance of photoelectrodes under solar light irradiation. Herein, a two-step hydrothermal method was introduced to grow directly Bi2S3 nanorods onto the Bi2MoO6 nanoflakes to form Bi2MoO6/Bi2S3 heterostructure. This work is aimed to synthesize heterostructure photoelectrode for photoelectrochemical water splitting application. The as-prepared photoelectrodes were analyzed by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, and UV–vis spectroscopy. As a result, the heterostructure Bi2MoO6/Bi2S3 indicated a dramatic improvement in the PEC properties (1.41 mA/cm2). From the X-ray photoelectron spectroscopy valence band measurement, the suitable bandgap between Bi2MoO6 and Bi2S3 can promote charge transfer across the junction interface and suppress electron-hole recombination. Furthermore, coupling a narrow bandgap material Bi2S3 with Bi2MoO6 can form a type II- heterostructure, leading to enhancement of the light absorption under visible light irradiation. This work provides a promising and efficient photoanode for light harvesting and hydrogen production.

Construction of Z-scheme TiO2/Ag/ZIF-8 nanorod array film with boosting photocatalytic and photoelectrochemical properties

Improving photoanode charge separation ability is crucial to solar energy conversion efficiency. In this study, hydrothermal and in situ synthesis methods were used to fabricate novel Ag and ZIF-8 nanoparticles (NPs) to decorate plasmonic TiO2/Ag/ZIF-8 nanorod array films. The morphology, microstructure, chemical composition, optical properties, photocatalytic activity and photoelectrochemical performance of TiO2/Ag/ZIF-8 were systematically investigated. The results showed that TiO2/Ag/ZIF-8 exhibited robust photocatalytic and photoelectrochemical properties under visible light irradiation. The photocatalytic rate constant for tetracycline (0.01348 min−1) and photocurrent density (250.2 μA/cm2) of TiO2/Ag/ZIF-8 were 9.76 and 5.94 times that of TiO2, respectively. The optimal PC and PEC properties of TiO2/Ag/ZIF-8 were attributed to the synergistic effect of Ag and ZIF-8 NPs: i) the surface plasmon resonance effect of Ag NPs extends the absorption range of visible light; ii) the passivation effect of ZIF-8 suppresses photogenerated carrier recombination; iii) the N–Ti–O bonds between TiO2 and ZIF-8 elevate photogenerated carrier transfer.

Alternate-Target Layer-By-Layer Pulsed Laser Deposition of Epitaxial BiVO4 Thin Films

Bismuth vanadate (BiVO4) has emerged as one of the highest performing metal oxide photoelectrodes for solar energy-to-fuels applications [1, 2]. This achievement has been largely attributed to the development of high-quality synthesis techniques. Specifically, epitaxial synthetic routes to producing lattice-matched, near single-crystalline quality BiVO4 with minimal extrinsic defects have been essential to understand the fundamental and PEC properties of BiVO4 that are inaccessible by conventional bulk synthesis techniques. In addition, epitaxial synthesis may also be employed as a strategy to further improve the PEC properties of BiVO4 through, for instance, altering the band structure and enhancing the carrier dynamics by strain engineering. Hence, the ability to produce high-quality single-phase epitaxial BiVO4 films is desirable.To date, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) [3] have been used to fabricate epitaxial BiVO4 thin films, with PLD having the advantage of relatively simple experimental setup and material versatility. However, an oft-noted drawback in conventional PLD using single oxide targets is off-stoichiometry in the deposited films; this is especially so for BiVO4 which requires a Bi-rich compound target to achieve a stoichiometric BiVO4 film [4]. This problem is also expected in general for multinary oxides composed of elements with very different ablation properties. To alleviate the limitations of conventional PLD, we employ for the first time alternate-target layer-by-layer PLD as a more elegant approach to produce high quality epitaxial BiVO4 films. Briefly, constituent oxide targets are alternately ablated by an excimer laser (λ= 248 nm) to build the desired film one unit cell thick at a time. Stoichiometry is controlled by the number of shots corresponding to a specified laser fluence for the constituent oxide target.To demonstrate the method, we deposited epitaxial BiVO4 films onto (001)-oriented yttrium-stabilized zirconia (YSZ) using 4N-pure Bi2O3 and V2O5 targets. Films grown are single phase BiVO4 as shown by x-ray diffraction. Out-of-plane diffraction peaks indexed to BiVO4(00l) suggests epitaxy of the film onto the substrate; reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks further confirm the BiVO4(001) || YSZ(001) epitaxial relationship (top figure). Rocking curves of the BiVO4 (004) peak (FWHM ~ 0.015-0.041) indicate high crystalline perfection of the BiVO4 film, almost approaching that of the YSZ substrate (FWHM ~ 0.010). Thickness dependent-rocking curve studies reveal that BiVO4 films are strained to the substrate for film thicknesses under 22 nm; above this critical thickness, film relaxation ensues. In turn, the resulting optoelectronic properties of the BiVO4 film is dictated by its relaxation state. The optical band gap narrows with film relaxation as observed with spectroscopic ellipsometry. Moreover, steady-state photoluminescence emission spectroscopy reveals a sub-bandgap state (A 2, bottom figure) associated with strained BiVO4 films, on top of a state consistent with band-to-band recombination (B1 ). A higher energy sub-bandgap state (A 1, bottom figure) develops as the film relaxes. The implications of the relaxation state on the charge carrier dynamics and photoelectrochemical properties of BiVO4 will be discussed. Figure: (top) reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks; (bottom) photoluminescence emission spectra of strained and relaxed BiVO4 films.

Photoelectrochemical study of hydrothermally grown vertically aligned rutile TiO2 nanorods

Vertically oriented TiO2 nanorods (NRs) were grown on FTO coated glass substrate using a hydrothermal process without any seed layer. The morphology and crystallinity of the nanorods were analyzed using SEM, TEM, XRD and Raman spectroscopy. The growth mechanism of the TiO2 nanorods has been discussed. The chemical bonds were studied using XPS study. The PEC properties of the TiO2 NRs were investigated in detail. TiO2 NRs photoanode demonstrated photosensing behaviour with an ON/OFF ratio of ∼96.2 and photoconversion efficiency of ∼0.72%. The incident-photon-to-current conversion efficiency (IPCE) at an incident wavelength of 360 nm was ∼31.6%. The carrier decay life time was estimated from the photovoltage decay profile. The carrier concentration, flat band voltage, Debye length and depletion width at the TiO2 NRs/electrolyte interface were estimated from the Mott-Schottky (M−S) plot. The charge transport mechanism at the semiconductor/electrolyte interface was explored from the electrochemical impedance measurements.

Synergistic Effect of Ni2+ and Fe3+ of Bimetallic Oxyhydroxide NiFeOOH as OER Cocatalyst for Fe2O3 Photoanode with Enhanced Photoelectrochemical Water Splitting

Hydrogen production via photoelectrochemical water splitting represents one of the sustainable development approaches for future energy. Herein, we demonstrate the fabrication optimization of α-Fe2O3 nanoparticles modified by bimetallic oxyhydroxide NiFeOOH layers. The optimized α-Fe2O3/NiFeOOH photoanode is successfully applied for the photoelectrochemical hydrogen production process. The electrodeposition and annealing process of the α-Fe2O3 nanoparticles are optimized for better photoelectrochemical performance. NiFeOOH layers are subsequently deposited on the surface of the optimized α-Fe2O3 photoanode by the impregnation process. The physical and chemical characterization results show that bimetallic oxyhydroxide NiFeOOH layers are modified on the surface of the α-Fe2O3 nanoparticles with an amorphous form. After optimization, a highly enhanced photocurrent density is achieved in the optimized α-Fe2O3 photoanode with a value of 0.96 mA/cm2, which is 50-fold higher than that of the bare α-Fe2O3 photoanode (0.019 mA/cm2). After NiFeOOH layers were deposited, the photocurrent density of the α-Fe2O3/NiFeOOH photoanode is enhanced to 1.35 mA/cm2 (measured at 1.23 V versus RHE), 1.53-fold and 80-fold higher than those of the optimized α-Fe2O3 and bare α-Fe2O3 photoanodes, respectively. In addition, the α-Fe2O3/NiFeOOH photoanode yields an improved applied bias photon-to-current efficiency of 0.13% (measured at 1.05 V versus RHE), 1.65 times higher than that of the optimized α-Fe2O3 photoanode. Photoelectrochemical and electrochemical characterization confirms that the synergistic effect of Ni2+ and Fe3+ of the NiFeOOH cocatalyst on accelerating the consumption of holes and promoting the surface OER dynamics could improve the efficiency of electron/hole separation and injection in the α-Fe2O3/NiFeOOH photoanode. Therefore, the PEC properties of the α-Fe2O3 photoanode are significantly improved.

Cu doped NiO thin film photocathodes for enhanced PEC performance

The present report describes the fabrication of undoped NiO and Cu doped NiO based photocathodes synthesized by sol gel spin coating technique. Mott-Schottky, LSV and EIS measurements have been carried out to investigate the PEC properties of these photocathodes. 3% Cu doped NiO film exhibits the highest PEC performance among all photocathodes. The p-type semiconducting nature of all thin film samples has been confirmed from the M-S plots. Also, the values of carrier density have been tuned from 1.18 × 1020 to 1.36 × 1020 cm−3 for undoped NiO and 3% Cu doped NiO thin films. VB CB levels of the as-prepared photocathodes have been calculated from absorption spectra. 3Cu:NiO exhibits a significantly higher photocurrent density of −6.97 mA/cm2 at −1.5 V vs. Ag/AgCl in 0.1M NaOH solution under UV illumination. The superior PEC performance is due to efficient charge transport and reduced recombination rate of the photogenerated electron-hole pairs. These findings demonstrate the potential of Cu doped NiO photocathodes in water splitting applications.

Integrating heteromixtured Cu2O/CuO photocathode interface through a hydrogen treatment for photoelectrochemical hydrogen evolution reaction

Mono and divalent copper oxide (Cu2O and CuO) has been considered as a potential semiconductor photocathode with capability for hydrogen (H2) production. The use of one-dimensional (1D) nanostructures as photocathode is desirable for the photoelectrochemical water-splitting device due to the large surface areas, lateral carrier extraction property, and excellent light-harvesting potentiality. Accordingly, the numerous attempts to develop copper oxide heterojunctions via a bottom-up approach has been achieved, but, the resulting composites have suffered from the poor interfacial configuration. Here, we demonstrate the intimate modulation through the different ambient annealing of photocathodes could alter the nanostructure, light-harvesting, and optical bandgap. Accordingly, the Cu2O/CuO heterostructure was synthesized by in situ growth via simple electrochemical anodization of Cu foil followed by annealing in air, and then the surfaces of the heterostructure were sequentially modified by the formation of Cu(OH)2 via the post-annealing process under 4% hydrogen-argon mixed gas at 300 °C. As a result, a mild hydrogen treatment (H2@1min) was found to be effective in enhancing the PEC properties, due to the favorable formation of Cu2O/CuO/Cu(OH)2 layer, promoting the photogenerated charge collection yield; the generation of sufficient cation vacancies was closely related to the electronic conductivity and the charge-transfer yield. The TEM and XPS results confirmed that the hydrogen treatment found a slightly thin Cu(OH)2 layer was produced as an efficient co-catalyst from the inherent chemical reduction of prominent CuO phase to develop the junction of Cu2O/CuO/Cu(OH)2. Overall, the Cu2O/CuO/Cu(OH)2(H2@1min) film exhibited an obvious improvement in photocurrent density of −2.3 mA/cm2 at 0 V vs. reversible hydrogen electrode (RHE) (abbreviated as 0 VRHE) than those nanowires having −1.72 and −1.44 mA/cm2 of both Cu2O/CuO/Cu(H2@3min) and Cu2O/CuO(Air), respectively.

Charge carrier separation and enhanced PEC properties of BiVO4 based heterojunctions having ultrathin overlayers

The photoelectrochemical performance of a BiVO4 photoanode is limited by its poor charge transport properties, despite other useful optical absorption properties. Modifying the surface charge transport properties by forming heterojunction of BiVO4 with other metal oxides layers having ultralow thickness is a promising route, as it may facilitate charge separation/transport without affecting other properties of BiVO4. In this study, the structural, optical and PEC properties of heterojunction of BiVO4 having ultrathin overlayers of Fe2O3, MoO3 and ZnO has been investigated. The electrochemical impedance (via electrochemical impedance spectra in PEC cell) and surface photovoltage (using KPFM) measurements indicates improved charge transport owing to staggered band alignment and favourable band bending in case of BiVO4/MoO3 heterojunction as compared to pristine BiVO4, BiVO4/Fe2O3 and BiVO4/ZnO heterojunctions. Enhanced photocurrent density in BiVO4/MoO3 of ~0.22 mA/cm2 at 1.23 VRHE which is 6 times as compared to pristine BiVO4 layers has been observed. The results of the present study show that by forming heterojunction with a suitable semiconductor material can be used to enhance the PEC response by modifying the surface charge transfer characteristics and there is a large possibility of using other semiconductor materials for further investigations and improvement.

Understanding the role of uniformly coated carbon overlayers in hematite nanorod photoandes

As one of the most promising photoanode materials, the performance of hematite has been greatly hampered by poor conductivity and severe charge recombination. Here, we report a simple synthesis of N-doped carbon layer coated hematite via low temperature chemical vapor deposition method, where hydroxytyramine hydrochloride (abbreviated as DA) was used as the carbon precursor and hematite thin films as the substrate. The thickness of carbon layers can be adjusted by the amount of DA. The photocurrent densities of the carbon coated hematite nanorods reached up to 1.63 mA cm−2. Based on TEM, XPS, Mott-Schottky and EIS measurement, it was found that the carbon overlayers could simultaneously improve the conductivity in the bulk and passivate the surface state. The correlation between the thickness of carbon layers and the PEC properties were also discussed in detail.