Photoelectrochemical Studies Research Articles

Rationally constructing intercrossed CuInS2 nanosheets on TiO2 nanorods for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting serves as an intriguing strategy for solar energy storage and conversion, but still suffers from the poor efficiency. In this work, a Z-scheme heterostructure comprised of CuInS2 nanosheets and TiO2 nanorods with an intercrossed structure was fabricated. Boosted by the well-matched structure, the as-prepared CuInS2/TiO2 hybrid achieved a high photo-electrocatalytic hydrogen evolution rate of 12.4 µmol/h, which was16 times greater than pure TiO2, owing to more effective solar energy utilization and interfacial photocarrier separation. Furthermore, PEC studies demonstrated that the novel hybrid offered a much higher photocurrent density than the nanoparticle counterpart, which could be ascribed to the elevated separation efficiencies of the photogenerated electron-hole pairs, and accompanied by efficient charge carrier transport. Based on the obtained results, this work provided a potential and promising approach for the fabrication of photo-electrocatalyst, which may inspire additional mechanism research of PEC and photo-electrocatalytic systems with hierarchical architecture.

Nanocrystalline TiO2 sensitized with CdS quantum dots for photoelectrochemical study

Nanocrystalline TiO2 sensitized with CdS quantum dots for photoelectrochemical study

Boosting the photoexcited charge collection and transportation via BiVO4/Fe-TiO2 NRs in Type-II heterojunction for efficient photoelectrochemical water splitting

Photoexcited charge separation and their efficient transportation in bulk as well as in heterojunction based photocatalysts is a challenging issue. Therefore, seeding free BiVO4@Fe-TiO2 NRs heterojunction is developed to have molecular extrinsic defects via Fe doping in TiO2 nanorods (NRs) as a strategy in type-II heterojunctions for photoelectrochemical water splitting. Structural characterizations of BiVO4@Fe-TiO2 NRs confirm the introduction of extrinsic defects in doped Fe-TiO2 NRs. Morphological studies evaluate the homogeneous deposition of BiVO4@Fe-TiO2 NRs to form core–shell heterostructure. In photoelectrochemical studies, BiVO4@0.2 %Fe-TiO2 shows highest photocurrent density of 1.52 mA/cm2 in comparison to BiVO4@undoped TiO2 NRs with 0.52 mA/cm2 and pristine TiO2 NRs with 45μA/cm2 at 1.23 vs. RHE under 100 mW/cm2 light intensity. These findings elucidate the importance of modified host substrates of Fe-TiO2 NRs to extract photoexcited electrons from guest BiVO4 that has enhanced PEC performance with maximum electron mobility, efficient interfacial charge transfer and enhanced electron quenching window in type-II heterojunctions.

Revealing electronic structure of nanostructured cobalt titanate via a combination of optical and electrochemical approaches toward water splitting and CO2 reduction

AbstractBackgroundThe shortage of clean energy has become a serious problem due to the rapid development of societies and the increasing consumption of fossil fuels. Metal oxide semiconductor nanomaterials have been studied as photo‐/electrocatalysts for water splitting in terms of clean energy generation. Applications of semiconductors depend on their electronic structures. Therefore, elucidating the electronic diagram is essential for determining the specific applications of novel semiconductors.ResultsHerein, we demonstrate using a combination of UV–visible diffuse reflectance spectroscopy (DRS) and Mott–Schottky analysis via electrochemical impedance spectroscopy for sketching the electronic diagram of nanostructured cobalt titanate (CoTiO3) prepared by the sol–gel method. UV–visible DRS studies reveal a band gap of 2.5 and 2.1 eV for direct and indirect transitions of prepared nanostructured materials, respectively. Mott–Schottky analysis shows a 0.8 V versus Ag/AgCl value for the flat band potential for CoTiO3. We further show the application of this diagram toward the interpretation of the electrochemical behavior of nanostructured CoTiO3 for electrochemical water splitting reactions and the electrochemical CO2 reduction reaction (eCO2RR).ConclusionThe presented electrochemical and photoelectrochemical studies demonstrate nanostructured CoTiO3 as an effective catalyst for electrochemical water oxidation and the eCO2RR. Moreover, our results provide valuable information for further investigation of water splitting and photovoltaic energy conversion. © 2023 Society of Chemical Industry (SCI).

Solvent and surfactant modulated diversification of Gd2MoO6 nanostructure for optimizing photodegradation of amphetamine under visible light and photoelectrochemical study

The effectiveness of nanomaterials has opened up new horizon towards their application as heterogeneous photocatalysts. A novel nanocatalyst Gd2MoO6 is developed by employing different solvents and capping agent to observe its catalytic activity towards pharmaceutical waste degradation under visible light irradiation. Two organic solvents, dimethyl formamide (DMF) and ethylene glycol (EG) were used in four different synthesis routes to demonstrate the morphological diversification and nucleation mechanism of the said nanocatalyst. The effect of surfactant assisted synthesis on morphology, texture and opto-electronic properties of as-prepared nanocatalyst was studied. Rigorous characterization techniques were carried out to establish the robust charge transfer mechanism as well as degradation kinetics. The addition of CTAB helped to evolve ultrathin nanoflakes like morphology while using DMF, whereas broken agglomerated diffused morphology was found in EG-based route. The role of oxygen vacancy based surface defect towards trapping of more charge carriers are also established in this work. The optical characteristics were identified by UV–VIS spectrum of as-prepared samples which revealed the more optimized band gap of samples towards visible light. The computational study via Density Functional Theory calculation verified its optoelectronic properties with the experimentally obtained one. Along with high crystallinity and better electrochemical property, Gd2MoO6 nanoflakes were able to show outstanding photodegradation ability by degrading amphetamine, a complex hazardous drug to more than 97%. The possible degradation pathway was also defined by the LC-MS/MS analysis. The developed catalysts also showed excellent results in photoelectrochemical water splitting generating a current density of 5.87 mA/cm2.

Defective TiO2 Nanotube Arrays for Efficient Photoelectrochemical Degradation of Organic Pollutants.

Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photoelectrodes. In this work, a simple procedure was applied to prepare reduced TiO2 nanotube arrays (NTAs) (TiO2-x) via a one-step reduction method using NaBH4. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO2-x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO2-x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO2-x NTAs was nearly 3 times higher than that of pristine TiO2. It was found that increasing OVs in TiO2 affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO2-x photoanode was used in the photoelectrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products.

Times effect on morphological, structural and optical behaviors of cds thin films for photoelectrochemical cells application

Cadmium Sulphide thin films have been successfully electrodeposited on a conducting Indium-Tin-Oxide (ITO) glass substrate, with different deposition time (10 min, 20 min, and 30 min). The Scanning electron microscopy (SEM), UV-Vis spectrophotometry, X-ray diffraction (XRD), and Atomic force microscopy (AFM) were used to characterize the morphological of films obtained. Moreover, Mott–Schottky (MS) measurements and Photoelectrochemical (PEC) measurements were carried out to study their structural, optical and electrical properties respectively. XRD result points to high crystallinity oriented along (002) planes. The studies reveal that the optical transmission increases with decreasing time of deposition. Mott-Schottky and Photoelectrochemical studies indicates that the CdS thin films display n-type semiconductor, which allows used as layer in photovoltaic cell applications.

Photoelectrocatalytic N2 fixation and C-H oxyfunctionalization driven by H2O oxidation

Solar-driven N2 fixation offers a green alternative to the highly energy-intensive Haber-Bosch process that releases more than 300 million metric tons of CO2 annually to form NH3. However, N2-reducing photoelectrochemical (PEC) studies have not elucidated how an oxidation reaction affects the N2 reduction reaction (NRR). Here, we report a bias-free PEC platform for N2 reduction to NH3 and H2O oxidation to O2 and H2O2. Under solar light, the molybdenum-doped bismuth vanadate-based photoanodes extract electrons from H2O and transfer them to the silicon photovoltaic-wired hematite photocathode. The light-absorbing cathode receives the electrons to drive the NRR, which is influenced by the H2O oxidation reaction’s conditions. Furthermore, the integration of PEC NRR with H2O2-dependent biocatalytic oxyfunctionalization achieves simultaneous synthesis of valuable chemicals on both electrodes. This work presents the first example of a PEC NRR platform coupled with H2O oxidation and H2O2-dependent oxygenation for unbiased chemical synthesis using N2, H2O, and sunlight.

A Hybrid S‐Scheme WS2/BiOI Heterojunction Photocatalyst for Wastewater Treatment

AbstractThere is a growing demand for efficient methods to decrease hazardous organic contaminants in wastewater. Herein, a novel S‐scheme WS2/BiOI heterojunction photocatalyst was prepared by a one‐pot solvothermal process. The structural morphology, crystal structure and optical absorption studies were studied. The sugar‐like nanocrystals of WS2 are deposited on 3D‐BiOI marigold flowers, providing high surface area with increased visible light absorption. The photocatalytic activity of the synthesized materials was studied by visible light degradation of Rhodamine‐B (RhB). The optimized 20 wt.% WS2 in the composite photocatalyst (band gap 2.25 eV) exhibited a 98.9 % photocatalytic degradation activity with a rate constant of 0.0940 min−1 with performance retained after 3 consecutive recycling runs. Photoelectrochemical studies revealed excellent stability, increased separation and migration ability of charge carriers with lower charge resistance in the optimized WS2/BiOI photocatalyst.

Development of a sensitive ZnO/CuO/Au electrochemical sensor for measuring Glyphosate

In addition to its low cost and stability, the sensor has numerous environmental sensing application possibilities. In this research, we use a ZnO/CuO structure that is structurally analogous to the PN junction, which speeds up electron flow and increases electrode sensitivity. We next modified the composite's surface with Gold Nanoparticles, so increasing the electrode's active area. We next examined the surface topography and microstructure of our manufactured electrodes using a variety of characterisation analytical methods. Finally, a series of electrochemical and photoelectrochemical studies were conducted to evaluate the Glyphosate sensing characteristics of the electrodes we had created.Testing revealed that the resulting electrodes had high electrical conductivity and, thus, enhanced sensitivity to Glyphosate. When compared to other herbicide sensors, the resulting electrode has a low detection limit and a decent detection range (6.9 μmol L−1 to 230 μmol L−1). Our manufactured sensor electrode has the potential to be a very sensitive composite electrode for use in modern herbicide detection sensors.

Enhanced charge carrier transfer process in nickel titanate nanostructures for environmental remediation of industrial dye.

The effective charge carrier transfer process in one-dimensional (1D) NiTiO3 nanofibers and NiTiO3 nanoparticles was demonstrated experimentally, showcasing an effective photocatalytic enhancement under visible light ambience. The rhombohedral crystal structure of NiTiO3 nanostructures was confirmed using X-ray diffractometer (XRD). The morphology and optical characteristics of the synthesized nanostructures were characterized using scanning electron microscopy (SEM) and UV-visible spectroscopy (UV-Vis). Nitrogen adsorption-desorption analysis corresponding to NiTiO3 nanofibers showcased porous structures with an average pore size of ~3.9 nm. The photoelectrochemical (PEC) measurement studies revealed an enhanced photocurrent for the NiTiO3 nanostructures, confirming enhanced charge carriers transportation in fibers than in particles due to the delocalized electrons in the conduction band, thereby hindering the photoexcited charge carrier's recombination. The photodegradation efficiency of methylene blue (MB) dye under the visible light irradiation revealed an enhancement in the rate of degradation for NiTiO3 nanofibers when compared to NiTiO3 nanoparticles.

2D Ti3C2 MXene interfaced ZnO/WO3 thin film nanostructures towards improved photoelectrochemical water splitting

We explored the morphology evolution approach for sustained photoelectrochemical (PEC) water splitting by developing dual heterojunction. Herein, novel ZnO/WO3/Ti3C2 photoelectrode has been developed for the first time by the integration of flake-like ZnO, nanocrystal featured WO3, and layer-structured two-dimensional (2D) Ti3C2 MXene morphologies towards PEC activity under simulated solar light. By adjusting the radio frequency (RF) magnetron sputtering and post-annealing, flake-like/nanocrystals featured ZnO/WO3 heterostructure observed with uniform growth of WO3 nanocrystals over the flake-like ZnO. Further, efficient integration of layer-structured 2D Ti3C2 MXene on ZnO/WO3 was provided through spin-coating. Utilizing robust surface interface between ZnO, WO3, and Ti3C2, optical transmittance and band gap have been modified. Accordingly, ZnO/WO3/Ti3C2 improved the photocurrent generation about 1.4 × 10−3 A/cm2 compared to pure ZnO (7.8 × 10−4 A/cm2) and ZnO/WO3 (1.1 × 10−3 A/cm2) at +0.4 V. These findings further provided a photoconversion efficiency of 1.16 % by the ZnO/WO3/Ti3C2 at +0.4 V. The PEC studies proved that electrically conductive Ti3C2 MXene can significantly separate the charge carriers from ZnO/WO3. On the other hand, this morphology-induced architecture proved sustainable surface interaction with KOH electrolyte than Na2SO3 and Na2SO4 media. Overall, the above developments suggest a robust interface in ZnO/WO3/Ti3C2 under controlled surface morphology and PEC water splitting activity.

Direct Growth of Polymeric Carbon Nitride Nanosheet Photoanode for Greatly Efficient Photoelectrochemical Water-Splitting.

A general method for the direct synthesis of highly homogeneous and dense polymerized carbon nitride (PCN) nanosheet films on F: SnO2 (FTO) is developed. Detailed photoelectrochemical (PEC) water-splitting studies reveal that the as-synthesized PCN films exhibit outstanding performance as photoanode for PEC water-splitting. The optimal PCN photoanode exhibits excellent photocurrent density of 650µA cm-2 , and monochromatic incident photon-to-electron conversion efficiency (IPCE) value up to 30.55% (λ= 400nm) and 25.97% (λ= 420nm) at 1.23 VRHE in 0.1m KOH electrolyte. More importantly, the PCN photoanode has an excellent hole extraction efficiency of up to 70 ± 3% due to the abundance of active sites provided by the PCN photoanode nanosheet, which promotes the transport rates of OER-relevant species. These PCN films provide a new benchmark for PCN photoanode materials.

Surface-Related Factors Affecting the Photocatalytic Process of Semiconductor Oxides: Ceria and Titania

Nanoparticles of CeO2, with rod-, and cubic-morphology, were synthesized by hydrothermal method and compared with commercial polyhedral ceria particles. Comparison of the synthesized CeO2 with the commercial powder revealed the influence of its defectivity with the absorption edge energy. The defectivity of CeO2 has also been determined in correlation with the photocatalytic performance of CeO2 per unit particles area, under narrow band UV-light (LED) condition. Analysis of the photocatalytic performance of the synthesized and commercial CeO2, as well as the reference TiO2 powder, revealed an enhancement in the decolorization of methylene blue dye (MB) with pH. The improvement in photocatalysis was associated with the surface charge condition of CeO2 particles, which controls the adsorption of molecules during the process. Furthermore, it was observed that the highly negative surface charge of cubic-morphology CeO2 favored the decolorization of MB, despite the low BET surface area. The photoelectrochemical study of ceria electrodes revealed a low photopotential compared to that of TiO2, the impact of which leads to a worse photocatalytic performance of CeO2 compared to TiO2.

Rapid Synthesis of Ultrathin Ni:FeOOH with In Situ-Induced Oxygen Vacancies for Enhanced Water Oxidation Activity and Stability of BiVO4 Photoanodes

The coupling of oxygen evolution reaction (OER) catalysts with photoanodes is a promising strategy for enhancing the photoelectrochemical (PEC) performance by passivating photoanode's surface defect states and facilitating charge transfer at the photoanode/electrolyte interface. However, a serious interface recombination issue caused by poor interface and OER catalysts coating quality often limits further performance improvement of photoanodes. Herein, a rapid Fenton-like reaction method is demonstrated to produce ultrathin amorphous Ni:FeOOH catalysts with in situ-induced oxygen vacancies (Vo) to improve the water oxidation activity and stability of BiVO4 photoanodes. The combined physical characterizations, PEC studies, and density functional theory calculations revealed that the reductive environment in a Fenton-like reaction in situ produces abundant Vo in Ni:FeOOH catalysts, which significantly improves charge separation and charge transfer efficiency of BiVO4 while also offering abundant active sites and a reduced energy barrier for OER. As a result, Ni:FeOOH-Vo catalysts yielded a more than 2-fold increased photocurrent density in the BiVO4 photoanode (from 1.54 to 4.15 mA cm-2 at 1.23 VRHE), accompanied by high stability for 5 h. This work not only highlights the significance of abundant Vo in catalysts but also provides new insights into the rational design and fabrication of efficient and stable solar water-splitting systems.

Structural Regulation of Thiophene-Based Two-Dimensional Covalent Organic Frameworks toward Highly Efficient Photocatalytic Hydrogen Generation

Two imine-based 2D covalent organic frameworks (COFs) with slight differences in their core structures are presented. The COF containing benzotrithiophene moieties with better planarity and π-conjugation (BTTh-TZ-COF) shows much better photocatalytic activity than the COF with trithienylbenzene cores (TThB-TZ-COF). Further photoelectrochemical study reveals the catalytic mechanism in more detail. Since other factors such as crystallinity, porosity, and optical bandgaps are equal, the different structures of the cores in the two similar COFs are the major contributors to the significantly different photocatalytic performance. The better electron delocalization of the planar trithiophene-based core and the enhanced D-A interactions between the triazine and trithiophene units in BTTh-TZ-COF create efficient charge separation and transfer, thus leading to superior photocatalytic hydrogen evolution activity. A new strategy for preparing high-performance organic photocatalysts for solar-energy conversion is revealed by this study.

Electrochemical studies of halide perovskite and its correlation for photocatalytic applications

Lead based hybrid organic-inorganic halide perovskite (LHP) possess extraordinary optical, electronic and structural properties. A simple perovskite formed by the cation (MA+) with anion (I− and Br−) enhance efficacy of catalytic reaction towards organic pollutant or more specifically dye degradation. This study focuses on a comparative photo-electrochemical study of MAPbX3 (; X = I, Br) whose physical and chemical properties are examined by XRD, FTIR, FESEM, EDX, UV–Vis and Raman spectroscopy. The results obtained from the photocatalytic studies depicted that the I and Br based MAPbX3 perovskite which are synthesised in monitored ambient conditions, evinced appreciable photocatalytic performance for methylene blue degradation. The experiments performed in visible light resulted in a removal percentage of 77% for MAPbBr3 and 88% for MAPbI3 in 140 mins under Xenon lamp based solar stimulator. The cyclic voltammetry plots revealed the quasi-reversible nature of both the samples as well as the qualitative information about the oxidation and reduction processes giving us estimates of mechanism corresponding to calculated HOMO and LUMO positions.

Crystal strain engineering of AgBr/TiO2 for visible-light photocatalysis: Balancing light absorption and charge carrier kinetics

Addition of noble metals and/or their halides certainly improves the visible-light photocatalytic activity of TiO2, but whether this improvement is due to better photoabsorption capacity of the noble metal or enhanced photoelectrical properties of TiO2 itself, is still a subject of debate. Furthermore, the optimized load of noble metal halides at which best photocatalytic activity in TiO2 occurs hasn’t been explained in the literature consistently. Herein, we investigate the change in intrinsic lattice strain of TiO2 at different AgBr loadings which imparts selective optoelectronic properties turning AgBr/TiO2 system into a visible-light photocatalyst. XRD analysis reveals that beyond a maximum strain developed at an optimum AgBr loading level, the grain boundary interface can no longer withstand the increased strain at Ti—Ti, and Ti—O bonds and a chain of thermodynamically governed crystalline phase transformation within TiO2 begins. Faster dye degradation kinetics corroborate the hypothesis that the catalyst possessing maximum lattice strain shows superior photocatalytic properties. Photoelectrochemical studies was used to quantify the rate of charge transfer (kct) and rate of recombination (kr) of photogenerated electrons and holes. These studies revealed that although higher AgBr concentration may increase charge transfer through plasmon resonance but ultimately kr controls the total charge carrier flux that determines the photocatalytic efficicency of TiO2. Our work highlights methods in which the optimum loading of AgBr can be determined and presents fundamental insight into the role of lattice strain in balancing optical and electrical properties of TiO2 for constructing high-performance photocatalysts suitable for visible light application.

Synthesis and photoelectrochemical catalytic properties of polyoxometalate supported on zeolitic imidazolate Framework, ZIF-9–PMo12

Development of photocatalysts for hydrogen generation is highly imperative in the current scenario for resolving the worldwide energy crisis. Continuous efforts are being made to find low-cost and durable photocatalysts with better light absorption capacity to mitigate energy issues. Herein, a new p-n heterojunction photocatalyst has been synthesized successfully using a polyoxometalate (POM), phosphomolybdic acid (PMo12), and zeolitic imidazolate framework (ZIF-9). Photoelectrochemical studies under visible-light irradiation revealed that ZIF-9–PMo12 exhibits a higher photocurrent density than pure ZIF-9. The support of ZIF-9 prevented the instability of PMo12 in aqueous solutions and improved the photoresponse ability of ZIF-9. The p-n junction formation impedes the recombination of electrons and holes, resulting in the improved photocatalytic property. Photoelectrochemical experiments confirmed the photocatalytic features, and thus this work paves the way for the development of an efficient, stable, and low-cost photocatalyst for green H2 generation.

Preparation of direct Z-scheme Bi2WO6/TiO2 heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H2 production

Direct Z-scheme Bi2WO6/TiO2 heterojunction photocatalyst was prepared by one-step solvothermal method. The catalyst was characterized by XRD, TEM, XPS, UV–Vis DRS, photoluminescence spectroscopy and photoelectrochemical studies. The photocatalytic hydrogen production experiments show that Bi2WO6 did not generate H2 and the H2-production rate of TiO2 is only 0.1 mmol⋅g−1h−1. The hydrogen production rate of the Bi2WO6/TiO2 heterojunction photocatalyst reaches 12.9 mmol⋅g−1h−1, which is 129 times that of TiO2. Compared with TiO2, the enhanced H2-production activity of the heterojunction catalyst can be attributed to the wider light absorption range and the efficient separation and migration of carriers at the close contact interface between Bi2WO6 and TiO2. Based on the work functions of Bi2WO6, TiO2 and their heterojunctions, combined with the results of electron paramagnetic resonance spectroscopy and Mott-Schottky measurements, the photocatalytic H2 production mechanism of Z-scheme heterojunction Bi2WO6/TiO2 was proposed. This work provides an easy and simple way to design a binary Z-scheme photocatalyst with efficient catalytic H2-production activity without electron mediators.