Photoelectrochemical Activity Research Articles

BiVO4 Photoanode with NiV2O6 Back Contact Interfacial Layer for Improved Hole-Diffusion Length and Photoelectrochemical Water Oxidation Activity.

The short hole diffusion length (HDL) and high interfacial recombination are among the main drawbacks of semiconductor-based solar energy systems. Surface passivation and introducing an interfacial layer are recognized for enhancing HDL and charge carrier separation. Herein, we introduced a facile recipe to design a pinholes-free BiVO4 photoanode with a NiV2O6 back contact interfacial (BCI) layer, marking a significant advancement in the HDL and photoelectrochemical activity. The fabricated BiVO4 photoanode with NiV2O6 BCI layer exhibits a 2-fold increase in the HDL compared to pristine BiVO4. Despite this improvement, we found that the front surface recombination still hinders the water oxidation process, as revealed by photoelectrochemical (PEC) studies employing Na2SO3 electron donors and by intensity-modulated photocurrent spectroscopy measurements. To address this limitation, the surface of the NiV2O6/BiVO4 photoanode was passivated with a cobalt phosphate electrocatalyst, resulting in a dramatic enhancement in the PEC performance. The optimized photoanode achieved a stable photocurrent density of 4.8 mA cm-2 at 1.23 VRHE, which is 12-fold higher than that of the pristine BiVO4 photoanode. Density Functional Theory (DFT) simulations revealed an abrupt electrostatic potential transition at the NiV2O6/BiVO4 interface with BiVO4 being more negative than NiV2O6. A strong built-in electric field is thus generated at the interface and drifts photogenerated electrons toward the NiV2O6 BCI layer and photogenerated holes toward the BiVO4 top layer. As a result, the back-surface recombination is minimized, and ultimately, the HDL is extended in agreement with the experimental findings.

Light‐Induced Dynamic Activation of Copper/Silicon Interface for Highly Selective Carbon Dioxide Reduction

Numerous studies have shown a fact that phase transformation and/or reconstruction are likely to occur and play crucial roles in electrochemical scenarios. Nevertheless, a decisive factor (such as facet, phase etc.) behind the diverse photoelectrochemical activity and selectivity of various copper/silicon photoelectrodes is still largely debated and missing in the community, especially for possibly dynamic behaviors of metal catalyst/semiconductor interface. Herein, through in situ X‐ray absorption spectroscopy and transmission electron microscope, a model system of Cu nanocrystals with well‐defined facets on black p‐type silicon (BSi) is demonstrated to unprecedentedly reveal the dynamic phase transformation of forming irreversible silicide at Cu nanocrystal‐BSi interface, which is validated to originate from the atomic interdiffusion between Cu and Si driven by light‐induced dynamic activation process. The presence of in situ formed silicide can significantly enhance photovoltage and deliver a record‐high onset potential above ‐0.4 V versus reversible reference electrode (RHE) for photoelectrochemical CH4 production. Significantly, the adaptive junction at Cu/Si interface is activated by an expansion of interatomic Cu‐Cu distance, which efficiently restricts the C‐C coupling pathway but strengthens the bonding with key intermediate of *CHO for CH4 yield, resulting in a remarkable 16‐fold improvement in the product ratio of CH4/C2 products.

Light-Induced Dynamic Activation of Copper/Silicon Interface for Highly Selective Carbon Dioxide Reduction.

Numerous studies have shown a fact that phase transformation and/or reconstruction are likely to occur and play crucial roles in electrochemical scenarios. Nevertheless, a decisive factor (such as facet, phase etc.) behind the diverse photoelectrochemical activity and selectivity of various copper/silicon photoelectrodes is still largely debated and missing in the community, especially for possibly dynamic behaviors of metal catalyst/semiconductor interface. Herein, through in situ X-ray absorption spectroscopy and transmission electron microscope, a model system of Cu nanocrystals with well-defined facets on black p-type silicon (BSi) is demonstrated to unprecedentedly reveal the dynamic phase transformation of forming irreversible silicide at Cu nanocrystal-BSi interface, which is validated to originate from the atomic interdiffusion between Cu and Si driven by light-induced dynamic activation process. The presence of in situ formed silicide can significantly enhance photovoltage and deliver a record-high onset potential above -0.4 V versus reversible reference electrode (RHE) for photoelectrochemical CH4 production. Significantly, the adaptive junction at Cu/Si interface is activated by an expansion of interatomic Cu-Cu distance, which efficiently restricts the C-C coupling pathway but strengthens the bonding with key intermediate of *CHO for CH4 yield, resulting in a remarkable 16-fold improvement in the product ratio of CH4/C2 products.

Graphene Quantum Dots as Hole Extraction and Transfer Layer Empowering Solar Water Splitting of Catalyst-Coupled Zinc Ferrite Nanorods.

Despite the narrow band gap energy, the performance of zinc ferrite (ZnFe2O4) as a photoharvester for solar-driven water splitting is significantly hindered due to its sluggish charge transfer and severe charge recombination. This work reports the fabrication of a hybrid nanostructured hydrogenated ZnFe2O4 (ZFO) photoanode with enhanced photoelectrochemical water-oxidation activity through coupling N-doped graphene quantum dots (GQDs) as a hole transfer layer and Co-Pi as a catalyst. The GQDs not only reduce the surface-mediated nonradiative electron-hole pair recombination but also induce a built-in interfacial electric field leading to a favorable band alignment at the ZFO/GQDs interface, helping rapid photogenerated hole separation and serving as a conducting hole transfer highway, improve the hole transportation into the Co-Pi catalyst for enhanced water oxidation reaction kinetics. The optimized ZFO/GQD/Co-Pi hybrid photoanode delivers a 23-fold photocurrent enhancement at 1.23 V versus the reversible hydrogen electrode (RHE) and a significant 360 mV reduction in the onset potential, reaching 0.65 VRHE compared with the ZFO photoanode under 1 sun illumination in a neutral electrolytic environment. This investigation underscores the mechanism of synergistic interplay between the hole transport layer and cocatalyst in boosting the solar-illuminated water-splitting activity of the ZFO photoanode.

Work function-tunable graphene/WO3 heterojunctions for high-performance photoelectrochemical cell: UV-treatment effect and defective graphene

Designing hybrid photoelectrodes with graphene capable of efficient charge-carrier transfer and excellent chemical stability is an effective strategy for developing high-performance photoelectrochemical (PEC) cells. However, it remains unclear how the PEC properties are enhanced and how to control the junction properties in graphene/metal oxide heterojunction-based photoelectrodes. Here, we develop a deterministic junction to enhance PEC performance in graphene/tungsten trioxide (WO3)-based photoelectrodes by tuning the work function of graphene. It reveals that the band structure of graphene/WO3 heterojunctions can be modified by ultraviolet (UV) treatment on WO3 thin films. This modification is supported by the observation that a single-layer graphene/UV-treated WO3 photoelectrode exhibits significantly enhanced PEC activities toward the oxygen evolution reaction (OER) (evidenced by features like a threefold increase in photocurrent, an onset potential shift, and improved stability), whereas the single-layer graphene/untreated WO3 electrode demonstrates improved properties for the hydrogen evolution reaction (HER). Additionally, defects in the graphene layer formed during PEC water splitting contribute to high catalytic activities of the graphene/WO3 photoelectrode due to a decrease in the Gibbs free energy for OER and HER. These results emphasize that band structure engineering via work function tuning in graphene/WO3 heterostructures can provide multiple benefits for high PEC performance and long-term stability.

Nonconjugated Polymers Enabled Solar Water Oxidation.

Wholly distinct from conjugated polymers which are featured by generic charge transfer capability stemming from a conjugated molecular structure, solid nonconjugated polymers mediated charge transport has long been deemed as theoretically impossible because of the deficiency of π electrons along the molecular skeleton, thereby retarding their widespread applications in solar energy conversion. Herein, we first conceptually unveil that intact encapsulation of metal oxides (e.g., TiO2, WO3, Fe2O3, and ZnO) with an ultrathin nonconjugated polyelectrolyte of branched polyethylenimine (BPEI) can unexpectedly accelerate the unidirectional charge transfer to the active sites and foster the defect generation, which contributes to the boosted charge separation and prolonged charge lifetime, ultimately resulting in considerably improved photoelectrochemical (PEC) water oxidation activities. The interfacial charge transport origins endowed by BPEI adornment are elucidated, which include acting as a hole-withdrawing mediator, promoting vacancy generation, and stimulating the directional charge flow route. We additionally ascertain that such charge transport characteristics of BPEI are universal. This work would unlock the charge transfer capability of nonconjugated polymers for solar water oxidation. The nonconjugated insulating polymer was utilized as a charge transport mediator for boosting charge migration and separation over metal oxides toward solar water oxidation.

Stacked High‐Entropy Hydroxides Promote Charge Transfer Kinetics for Photoelectrochemical Water Splitting

AbstractAlthough various kinds of cocatalyst are developed and decorated on the bismuth vanadate (BiVO4) photoanode, its photoelectrochemical (PEC) water splitting performance is limited owing to severe charge recombination and sluggish oxygen evolution reaction (OER). Herein, a high‐entropy hydroxide electrocatalyst (FeCoNiMoCrOOH) is constructed as a co‐catalyst deposited on BiVO4 with a good PEC activity and stability in potassium borate buffer, addressing substantial charge recombination and poor surface oxygen evolution reaction of the material. FeCoNiMoCrOOH synthesized by a simple electrodeposition stacking strategy, delivers an overpotential of 172 mV at 10 mA cm−2 with a stability of 600 h under alkaline conditions, representing one of the best performances on high‐entropy‐based catalysts. The FeCoNiMoCrOOH/BiVO4 photoanode shows a photocurrent density of 5.23 mA cm−2 at 1.23 VRHE with 100 h durability in potassium borate buffer. Experimental investigations and theoretical calculations demonstrate that the synergistic effect of Mo and Cr in FeCoNi catalyst effectively decreases the dissolution Fe, Co, and Ni after long‐term operation, increases the charge transfer kinetics, and promotes OER and PEC performances, therefore enhancing the photocorrosion resistance of BiVO4. This work provides a new avenue to design high entropy‐based electrocatalysts boosting solar water splitting activity and stability.

Sonication supported green modulation of Fe:MoO3/g-C3N4 heterojunction as solar light sensitive photocatalyst for dye degradation and photoelectrochemical water splitting

The concerns of dye in an aquatic system associated with acute toxicity and carcinogenicity, and the increase in demand for hydrogen production has led to a keen interest in advancing solar driven methodologies utilizing potent photocatalysts to address environmental concerns through sustainable remediation practices. In this pursuit, we synthesized a heterostructure comprised of Fe doped MoO3 (Fe:MoO3), anchored on g-C3N4 sheet as a photocatalyst denoted as Fe:MoO3/g-C3N4, employing a sonication supported green synthesis method with the aid of Murraya paniculata leaf extract. We explored structural, morphological, and surface characteristics using various analytical techniques, including X-Ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, Field emission scanning electron microscopy (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM), X-Ray photoelectron spectroscopy, and BET for a comprehensive surface analysis. The outcomes highlighted the exquisitely oriented and interconnected arrangement of MoO3 nano rods ensconced within a piled layer of g-C3N4. The XRD patterns unveiled the coexistence of g-C3N4 and Fe:MoO3 within the heterojunction structure. FESEM and HRTEM image analysis of Fe:MoO3/g-C3N4 heterojunction reveals a g-C3N4 nanosheet wrapping the Fe:MoO3 nanoparticles with the formation of nanorods of MoO3 with an average thickness of 9.46 nm containing circular Fe nanoparticles with a mean diameter of 8.97 nm. This intricate configuration resulting in a decrease of the size of the nanoparticle caused by effective sonication-supported green modulation configuration facilitated an optimized charge flow, contributing to the elevated photo assisted catalytic performance of the heterojunction. The Fe:MoO3/g-C3N4 semiconductor heterojunction exhibited a considerable surface area and pore volume, inherently amplifying the sites of the activity on the surface and thereby enhancing photoactivity. As opposed to both g-C3N4 and the Fe:MoO3 nanoparticles, the Fe:MoO3/g-C3N4 semiconductor heterojunction showcased enhanced photocatalytic effectiveness in the degradation of dye Crystal violet (CV). Under optimized circumstances, the photo assisted degradation of dye CV by the semiconductor heterojunction adhered to pseudo-first-order kinetics. The active species responsible for the photo assisted degradation process is identified as •O2−. These findings not only emphasize the enhanced efficacy of the developed semiconductor heterojunction but also reveal its potential for addressing the environmental challenges posed by dye CV contamination through prolonged and efficient photocatalytic remediation practices. A marked improvement in both photo assisted catalytic and photoelectrochemical (PEC) water splitting activities under visible light exposure was showcased. The augmented performance of the Fe:MoO3/g-C3N4 semiconductor heterojunction in photodegradation and PEC water splitting activities can be attributed to the extended absorption of visible light. Additionally, the synergistic influence of g-C3N4, contributes positively to the separation of charges and expedites the transfer efficiency of photogenerated charge carriers. This synergy enhances the overall effectiveness of the nanoparticles in harnessing visible light for efficient water-related processes.

Fabrication of piezotronic ZnO p-n homojunction via metal/oxygen defects modulation for efficient photoelectrocatalysis

Homojunction is a viable alternative strategy to realize excellent charge separation for enhancing photoelectrocatalytic performance. However, the feasible regulation of the homojunction interface remains challenging. Herein, a ZnO n-p homojunction with the piezotronic effect is constructed via an in-situ solvothermal method for enhancing photoelectrocatalytic activity. ZnO nanorods are transformed from n-type to p-type ZnO nanoparticles with zinc vacancies, leading to the n-p homojunction. The optimal NPZ-36 exhibits a superior photocurrent density of 1.56 mA/cm2 at 1.23 V vs. RHE and a high incident photon to current conversion efficiency of 75 % at 360 nm. Impressively, with the merits of inherent piezoelectric and photocatalytic properties of wurtzite ZnO, the piezoelectric-enhanced photoelectrochemical activity originates from the simultaneous promotion of bulk charge transfer and interfacial charge separation in ZnO n-p homojunction. The photocurrent density of NPZ-36–900 can reach to 2.02 mA/cm2 under the stirring rate of 900 rpm, which is 2.1 times higher than that of pure ZnO photoanode.

Superhydrophilicity of photocatalytic branched TiO2 nanorods/In2S3 heterostructure for water purification

In2S3 / branched TiO2 nanorods (br-TiO2) heterostructure was prepared by a simple route using three-step methods as a visible and solar light photocatalyst for water treatment applications. Structural properties have been carried out by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and atomic force microscopy has been used to determine the morphology and the surface roughness of samples. The In2S3/ br-TiO2 heterojunction confirm the presence of both structures of Rutile TiO2 and cubic β-In2S3. Optical results showed that the heterojunction exhibited increased absorption ability in the visible light, indicating an increased photoactivity for In2S3/ br-TiO2 in the visible light. Wettability studies reveal that In2S3/ br-TiO2 film is superhydrophilic with water contact angle of 0°. Photocatalytic activity of heterojunction In2S3/ br-TiO2 was assessed with remarkable degradability performance of 85% after 80 min under solar irradiation. The reusability test highlighted that the In2S3/ br-TiO2 still maintained high photocatalytic activity over five cycles. The photoelectrochemical activity was evaluated. The results showed the successful development of In2S3/ br-TiO2 heterostructure with better photoactivity properties. The In2S3/ br-TiO2 electrode achieved remarkably improved current density (0.59 mA.cm2 at 0.6 V vs Ag/AgCl) compared to br-TiO2 and In2S3.These results reveal that In2S3/ br-TiO2 thin films being excellent photoactivity along with its superhydrophilic nature which it is possesses great potential toward the development of newly synthesizable catalysts in the field of water purification.

Killing two birds with one stone: Enhancing the photoelectrochemical water splitting activity and stability of BiVO4 by Fe ions association

Killing two birds with one stone: Enhancing the photoelectrochemical water splitting activity and stability of BiVO4 by Fe ions association

Impact of Co-Doping on the Visible Light-Driven Photocatalytic and Photoelectrochemical Activities of Eu(OH)3.

The microwave-assisted synthesis approach was used to synthesize Eu(OH)3 and Co-Eu(OH)3 nanorods. Various techniques were used to investigate the structural, optical, and morphological features of the Eu(OH)3 and Co-Eu(OH)3 NRs. Both Eu(OH)3 and Co-Eu(OH)3 NRs were found to be hexagonal with crystallite sizes ranging from 21 to 35 nm. FT-IR and Raman spectra confirmed the formation of Eu(OH)3 and Co-Eu(OH)3. Rod-shaped Eu(OH)3 and Co-Eu(OH)3 with average lengths and diameters ranging from 27 to 50 nm and 8 to 12 nm, respectively, were confirmed by TEM. The addition of Co was found to increase the particle size. Furthermore, with increased Co doping, the band gap energies of Co-Eu(OH)3 NRs were lowered (3.80-2.49 eV) in comparison to Eu(OH)3, and the PL intensities with Co doping were quenched, suggesting the lessening of electron/hole recombination. The effect of these altered properties of Eu(OH)3 and Co-Eu(OH)3 was observed through the photocatalytic degradation of brilliant green dye (BG) and photoelectrochemical activity. In the photocatalytic degradation of BG, 5% Co-Eu(OH)3 had the highest response. However, photoelectrochemical experiments suggested that 10% Co-Eu(OH)3 NRs showed improved activity when exposed to visible light. As a result, Co-Eu(OH)3 NRs have the potential to be a promising visible-light active material for photocatalysis.

Melamine Cyanaurate Microrods Decorated with SnO2 Quantum Dots for Photoelectrochemical Applications

This study employs a simple and cost-effective technique to enhance the photoelectrochemical (PEC) water-splitting performance of melamine cyanaurate microrods (M), SnO2 nanostructures (S), and melamine cyanaurate microrods decorated with SnO2 quantum dots (MS) by optimizing NaOH and Na2SO3 electrolytes. Notably, the MS electrode demonstrates a remarkable improvement in PEC efficiency in Na2SO3 solution associated with NaOH solution. Specifically, the induced currents of the MS anode in the Na2SO3 electrolyte are approximately 6.28 mAcm−2 more than those observed in the NaOH electrolyte solution. It is revealed that SO32− anions effectively consume the holes, leading to improved separation of the generated charge pairs. This effective charge separation mechanism significantly contributes to the enhanced PEC performance observed in Na2SO3 electrolytes. The findings of this study suggest a capable approach for improving the PEC activity of the materials through the careful optimization of the supported electrolytes.

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.

Collaborative role of co-doping and surface modifying for adjusting surface state of hematite to release the photoelectrochemical activity

Inhibition of bulk and interfacial charge carrier recombination is an urgent solution to release furthest the photoelectrochemical potential abilities of hematite photoelectrode. Herein, the Zr-Y dual metal co-doping engineering and Co/Fe dual metal-organic frameworks cocatalyst layer were employed for modifying hematite photoanode. The novel CoFe-MOF/Zr-Y:Fe2O3 nanoarray composite photoanode exhibits higher PEC activity, the photocurrent density at 1.23 V vs.RHE is increased by 4.7 times than that of the pristine α-Fe2O3. The gain in bulk charge separation efficiency was mainly attributed to the synergistic effect between the two doping ions to improve the electrical conductivity. Wherein, Zr4+ doping endows more free electrons in the bulk α-Fe2O3 and Y3+ introduction causes polaron mobility enhancement. For another, co-doping could reduce the recombination surface state, but form the intermediate surface state to promote hole transfer, thus effectively inhibiting the severe recombination of photogenerated electrons and holes. Furthermore, the CoFe-MOF cocatalyst coating with abundant active sites not only expedites the oxygen evolution reaction kinetics process, but also passivates the surface hole trapping state more thoroughly, resulting in efficient interfacial hole transfer and utilization. This work affords a new collaborative role of co-doping and surface modifying effective avenue for adjusting surface state of hematite to release the photoelectrochemical activity.

Innovative syntheses of immobilized CuxO semiconductors grown on 3D prints and their photoelectrochemical activity for sulfamethoxazole degradation

Traditional copper oxide manufacturing processes require high energy consumption, high synthesis temperatures, and long process times. This study proposes an innovative additive manufacturing process to support immobilized copper oxide, offering greater design flexibility and customization. CuxO semiconductors were synthesized on 3D-printed substrates via the anodization process and evaluated for their effectiveness in degrading sulfamethoxazole (SMX). XRD analysis of the samples revealed the presence of both CuO and Cu2O crystalline phases, this mixture of oxides helps to expand the absorption range of visible light. The immobilized CuxO semiconductors exhibited band gaps ranging between 1.6 and 1.8 eV. Negative current densities and Mott-Schottky analysis confirmed the nature of the p-type semiconductor. Semiconductors grown by 3D printing demonstrated remarkable degradation capacity for the antibiotic sulfamethoxazole (SMX), achieving 60% degradation after 360 minutes under visible light. Kinetic degradation tends to be a first-order and zero-order model. TOC analysis further revealed the formation of reaction intermediates during SMX degradation, ultimately leading to the mineralization of the contaminant. Based on these results, we report, for the first time CuxO semiconductors grown on large 3D-printed substrates as promising photocatalysts for the degradation of emerging water pollutants. Based on these results, we report, for the first time, that CuxO semiconductors grown on large 3D-printed substrates are promising photocatalysts for the degradation of emerging water contaminants. Furthermore, it should be emphasized that the proposed method is faster and does not require subsequent thermal treatments for its functionalization, making it attractive for various industrial applications.

In situ polymerised polyaniline films over multi-walled carbon nanotubes coatings for enhanced photoelectrochemical performance

Polyaniline (PANI), which is a π-conjugated polymer, has stood out as a promising candidate for dihydrogen generation in photoelectrochemical (PEC) cells owing to its suitable optoelectronic properties and excellent stability. Nevertheless, the PEC performance of this material is still far from adequate for technological applications. Herein, we have focused on improving the PEC performance of PANI films by combining this polymer with multi-walled carbon nanotubes (MWCNTs) layers. Specifically, we have assessed the PEC activity of the in situ polymerised PANI films onto FTO substrates coated with different amounts of MWCTNs for the hydrogen evolution reaction (HER). The FTO/MWCNTs/PANI films with the optimum deposited amount of MWCNTs (i.e., 30 μL) featured a 2.4-fold increase of the cathodic photocurrent density response for the HER compared to that of FTO/PANI film. Moreover, the FTO/(30 μL)-MWCNTs/PANI films exhibited good PEC stability, as observed by the relatively low cathodic photocurrent density decay of up to 7% during 3720 s of stability test. Based on joint analyses of physical and PEC characterisation, the improved PEC performance for the FTO/(30 μL)-MWCNTs/PANI films were assigned to the combined contribution of the following factors: (i) enhancement of light absorption; (ii) possible improvement of excitons dissociation; (iii) minimisation of the electron-hole recombination process; and (iv) facilitation of electrons transfer at the PANI|electrolyte interface for the HER. The enhancement of PEC performance achieved in this work for the fully organic photocathode composed of MWCNTs/PANI paves the way to invest in additional modifications seeking to further improve the dissociation of excitons and the interfacial transfer of charge carriers for the light-driven HER.

Effect of tantalum doping on the Fe2O3 toward photoelectrochemical water oxidation

Metal doping is an effective method to increase the photogenerated carrier concentration and improve the carrier transport performance of Fe2O3 for photoelectrochemical water oxidation. This work synthesized a series of Ta-doped Fe2O3 nanoparticles on FTO glasses using a hydrothermal-pyrolysis method. The XPS, XRD, and Raman spectra demonstrated that the Ta5+ dopants occupy the Fe3+ sites. The Ta-doped Fe2O3 photoanodes show noticeable improvement in photoelectrochemical water oxidation via enhanced electron separation and transfer competence. Doping Ta into Fe2O3 forces the Fermi level of Fe2O3 to move to the conduction band, leading to the decrease of charge transfer resistance in Fe2O3 and water oxidation on the surface. Moreover, the carrier concentration was increased. Whereas, to maintain the charge neutrality of the system, the Ta doping inhibits the formation of oxygen vacancies, which act as the effective defects. Consequently, 2%Ta-Fe2O3 performed the optimum enhanced photoelectrochemical water oxidation activity.

A Photoelectrochemical Sensor for the Sensitive Detection of Cysteine Based on Cadmium Sulfide/Tungsten Disulfide Nanocomposites.

In this work, a CdS-nanoparticle-decorated WS2 nanosheet heterojunction was successfully prepared and first used to modify ITO electrodes for the construction of a novel photoelectrochemical sensor (CdS/WS2/ITO). The thin-film electrode was fabricated by combining electrophoretic deposition with successive ion layer adsorption and reaction techniques. The results indicated that the synthesized heterojunction nanomaterials displayed excellent photoelectrochemical performance which was much better than that of pristine CdS nanoparticles and 2D WS2 nanosheets. Owing to the formation of the surface heterojunction and the effective interfacial electric field, the enhanced separation of photogenerated electron-hole pairs led to a remarkable improvement in the photoelectrochemical activity of CdS/WS2/ITO. This heterojunction architecture can protect CdS against photocorrosion, resulting in a stable photocurrent. Based on the specific recognition between cysteine and CdS/WS2/ITO, through the specificity of Cd-S bonds, a visible-light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine, with an extremely low detection limit of 5.29 nM and excellent selectivity. Hence, CdS-WS2 heterostructure nanocomposites are promising candidates as novel advanced photosensitive materials in the field of photoelectrochemical biosensing.

Enhanced Photoelectrochemical Activity Realized from WS2 Thin Films Prepared by RF‐Magnetron Sputtering for Water Splitting

AbstractWe report the synthesis of tungsten sulfide (WS2) films using RF‐magnetron sputtering at different RF powers. X‐ray diffraction (XRD) data confirm the hexagonal crystal structure of WS2 with an average crystallite size of ∼44.54 Å. With increased RF power, the preferred orientation of WS2 crystallites shifts from (002) to (100). Linear sweep voltammetry (LSV) was used to assess the Photoelectrochemical (PEC) activity of WS2 films. The film deposited at 150 W demonstrated the highest photocurrent density of 5.44 mA/cm2. The 150 W film also showed a lower Tafel slope of ∼0.374 V/decade, indicating superior PEC activity. Mott Schottky's (MS) analysis revealed a notable shift in the flat band potential towards the negative side, suggesting a shifting of the Fermi level towards the conduction band. WS2 film grown at 150 W demonstrated a majority charge carrier density of 6.2×1021 cm−3 and a depletion layer width of 1.54 nm. The observed low charge transfer resistance of 155 Ω contributed to the enhanced PEC activity with a relaxation time constant of 37 ms. These properties suggest that WS2 can be suitable for PEC water splitting.