Photoelectrocatalytic Cell Research Articles

Static Organic p‐n Junctions in Photoelectrodes for Solar Ammonia Production with 86 % Internal Quantum Efficiency

AbstractFor photoelectrocatalytic cells, a limitation exists in finding appropriate photoelectrode configurations that couple efficient extraction of high‐energy electrons from absorbed photons and selective catalysis. Here we report an organic p‐n junction approach to fabricate molecular photoelectrodes for conversion of solar energy and nitrate into valuable ammonia product. Solar irradiation of the photoelectrode generates charge‐separated states with electrons and holes spatially separated at the n‐type and p‐type components, as revealed by surface photovoltage mapping, at a quantum yield of 90 %. The high‐flux photogenerated electrons are rapidly transferred to the catalyst for solar ammonia production from nitrate reduction at an external quantum efficiency (EQE) and an internal quantum efficiency (IQE) of 57 % and 86 %, respectively. Time‐resolved spectroscopic studies reveal that the large IQE originates from the combined high efficiencies for photoelectron generation, catalyst activation and dark catalysis. In a flow‐cell setup coupled with a silicon solar cell, the photoelectrode without bias generates photocurrent of 57 mA cm−2 and ammonia at an EQE of 52 %.

Charge Photoaccumulation in Covalent Polymer Networks for Boosting Photocatalytic Nitrate Reduction to Ammonia.

In the design of photoelectrocatalytic cells, a key element is effective photogeneration of electron-hole pairs to drive redox activation of catalysts. Despite recent progress in photoelectrocatalysis, experimental realization of a high-performance photocathode for multi-electron reduction of chemicals, such as nitrate reduction to ammonia, has remained a challenge due to difficulty in obtaining efficient electrode configurations for extraction of high-throughput electrons from absorbed photons. This work describes a new design for catalytic photoelectrodes using chromophore assembly-functionalized covalent networks for boosting eight-electron reduction of nitrate to ammonia. Upon sunlight irradiation, the photoelectrode stores a mass of reducing equivalents at the photoexcited chromophore assembly for multielectron reduction of a copper catalyst, enabling efficient nitrate reduction to ammonia. By introducing the new photoelectrode structure, it is demonstrated that the electronic interplay between charge photo-accumulating assembly and multi-electron redox catalysts can be optimized to achieve proper balance between electron transfer dynamics and thermodynamic output of photoelectrocatalytic systems.

WO3/Bi2WO6 photoanode enhancement for photoelectrocatalytic water oxidation; scan rate effect optimization in the cyclic voltammetry deposition method

The photoelectrocatalytic approach is a very efficient technology for eliminating microorganisms and organic contaminants. The development of photoanode is widely recognized as a crucial approach to enhancing the efficiency of photoelectrocatalytic cells. The key goal of this methodology is to enhance the efficacy of photoelectrocatalytic oxidation by optimizing composited photoanode fabrication. This research development focuses mainly on fabricating composite WO3/Bi2WO6 semiconductor thin films with high water oxidation efficiency and favorable photoelectrocatalytic E. coli degradation applications. Cyclic voltammetry was utilized to create WO3/Bi2WO6 thin coatings on conducting glass while optimizing the photoelectrocatalytic activity via the scan rate parameter. The characteristics of the developed electrode, including charge transfer resistance, optical properties, morphology, crystal structure, chemical composition, and oxidation numbers, were investigated to improve photoelectrocatalytic activity. It was observed that the scanning rate significantly influenced the characteristics of the WO3/Bi2WO6 electrode and the photoelectrocatalytic activity on water oxidation. It was discovered that the WO3/Bi2WO6 electrode prepared with a scan rate of 25 mV/s exhibited the greatest photoelectrocatalytic water oxidation as well as distinguishing characteristics from other conditions. The decision to utilize decreased scanning rates has been determined to optimize the reaction kinetics and improve the film-forming properties of WO3/Bi2WO6. Significantly, the developed electrode can also be used to eliminate 87.5% of E.coli in 15 minutes via a photoelectrocatalytic catalytic mechanism. The photoanode composed of WO3/Bi2WO6 has promising capabilities in removing microorganisms and organic pollutants, making it a viable candidate for future advancements in wastewater management applications.

Development of a photoelectrocatalytic method to improve the efficiency of E. coli removal

The photoelectrocatalytic technology has attracted significant attention for effectively eliminating organic matter and microbiological pollutants in the environment, owing to its remarkable efficiency and low power consumption. The major goal of this research is to develop and determine the optimal conditions that will facilitate the photoelectrocatalytic technique's enhancement of E. coli eradication. The WO3/BiVO4 photoanode was fabricated on a conductive glass substrate using the automatic dip coating process, employing a layer-by-layer deposition method. Subsequently, the WO3/BiVO4 photoanode was calcinated at 550 °C for 60 minutes. The produced WO3/BiVO4 electrodes were employed as working electrodes to investigate and determine the optimal parameters for enhancing the eradication of E. coli process. The primary factors investigated in this study were the concentration of KCl electrolyte solution and the applied potential. These parameters were examined to identify the best circumstances that would result in the highest efficiency for the degradation of E. coli in a photoelectrochemical system. The study also aimed to comprehend the catalytic mechanism implicated in eliminating E. coli by implementing three different processes: photocatalysis, electrocatalysis, and photoelectrocatalysis. We discovered that the key factors directly influencing E. coli eradication effectiveness under the photoelectrocatalytic process were applied potential and electrolyte solution concentration. The optimum conditions eliminated 99.99% of E. coli in 150 minutes with an initial concentration of 106 CFU/ml, an electrolyte concentration of 0.01 M KCl, and an applied potential of 2.0 V. The study confirmed photoelectrocatalytic cells' efficacy in removing microorganisms and recommended their application in a wider range of wastewater treatment systems.

Surface Modification of TiO2/g-C3N4 Electrode with N, P Codoped CQDs for Photoelectrocatalytic Degradation of 1,4-Dioxane

The aim of this study was to synthesize N, P codoped CQDs modifying TiO2/g-C3N4 nanorod array (i.e., N, P-CQD/TCN NA) photoanodes for the degradation of 1,4-dioxane (1,4-D) and to explore the possibility of the photoelectrocatalytic (PEC) process in wastewater treatment. With the characterization of N, P-CQD/TCN NA anodes, 1,4-D degradation and pesticide wastewater was tested in the PEC cell, respectively. Under a bias voltage of 1.2 V and visible light, the current density of the N, P-CQD/TCN NAs was much higher than that of the CQD/TCN NAs (0.15 vs. 0.11 mA/cm2). The removal of 1,4-D reached 97% in the PEC cell within 6 h. The high performance of the N, P-CQD/TCN NA anodes could be attributed to the efficient charge separation, narrowed energy gap, and high upconverted PL properties. The C4 and C6 positions of 1,4-D were the preferential sites for the nucleophilic attack to form intermediates. The COD removal in the pesticide wastewater was kept stable at ~80% in a five-cycle operation using the PEC cell with the N, P-CQD/TCN NA photoelectric anodes. The results from this study should provide a promising way to develop novel photoelectric catalysts and to expand PEC application in wastewater treatment.

Recent progress of bismuth vanadate-based photoelectrocatalytic water splitting

<p indent=0mm>With increasing energy demands and ever-growing environmental concerns, solar energy and hydrogen energy have attracted worldwide attention. In particular, hydrogen energy not only has a high energy density, but also is clean, renewable, and carbon-free, when compared with primary energy sources such as coal, oil, and natural gas and secondary energy sources such as coal gas, petrol, and diesel. Photoelectrocatalytic (PEC) water splitting for hydrogen generation is a process in which a PEC cell containing photoelectrodes and electrolyte is used to split water into hydrogen and oxygen by solar energy. Therefore, PEC water splitting is one of the ideal ways to covert and store solar energy to hydrogen energy in terms of chemical bond energy. In a PEC cell, the photoanode is commonly based on n-type semiconductors and the photocathode based on p-type semiconductors. The efficiency of a PEC cell is determined by performance of these photoelectrodes interfaced with the electrolyte. However, because the oxygen evolution reaction on the photoanode is kinetically sluggish involving four electrons and the valance band maximum of photoanodes must be more positive than <sc>1.23 V</sc> versus reversible hydrogen electrode, suitable n-type semiconductors are quite few for this purpose, limiting the common photoanodes to low efficiencies for PEC water splitting. In recent years, the bismuth vanadate photoanode has attracted great attention due to its relatively high theoretical maximum photocurrent density <sc>(~7 mA cm^–2)</sc> and suitable band structure for water splitting, compared with other traditional photoanodes such as titanium dioxide, tungsten oxide, and zinc oxide. Extensive efforts have been made to unleash the full potential of the bismuth vanadate photoanode for PEC water splitting. In this mini review, we survey and analyze the design ideas and synthesis methods of high-performance bismuth vanadate photoanodes by looking back at the research progress made over the past few years on improving the light harvesting efficiency, photo-generated carrier separation efficiency and surface oxygen evolution efficiency of bismuth vanadate photoanodes. The strategies for improving the efficiencies of the bismuth vanadate photoanodes include defect state introduction, crystal facet and morphology control, and heterojunction engineering. Among the strategies, a single one, such as the defect state introduction, may enhance efficiencies of several processes (e.g., photo-generated carrier separation efficiency and surface oxygen evolution efficiency) of bismuth vanadate at the same time, but sometimes, it may enhance the efficiency of one process but degrade the efficiencies of others for the bismuth vanadate photoanode. Thus, how to comprehensively consider the cooperative mechanism to enhance the efficiencies of all the processes involved in PEC water splitting is the key to obtaining high performance bismuth vanadate photoanodes. At present, bismuth vanadate-based photoanodes have exhibited an extremely high photocurrent density and photo-generated carrier separation efficiency at higher bias voltage (over <sc>5 mA cm^–2</sc> at <sc>1.23 V</sc> versus reversible hydrogen electrode with over 90% photo-generated carrier separation efficiency), but the light reflection of bismuth vanadate-based photoanodes makes it unable to reach the theoretical maximum photocurrent density <sc>(~7 mA cm^–2).</sc> Moreover, the efficiencies of bismuth vanadate-based photoanodes at low bias voltages are still too low. Therefore, the future development direction should be to obtain higher photocurrent density at a lower voltage, and increase the absorption efficiency and wavelength range of bismuth vanadate to reach the theoretical photocurrent density and beyond. Although bismuth vanadate photoanodes are not necessarily the final large-scale application scheme of PEC water splitting in the future, their studies will help to provide guidelines for searching new high-performance photoanode materials.

Role of nanostructure in the behaviour of BiVO4–TiO2 nanotube photoanodes for solar water splitting in relation to operational conditions

BiVO4 nanoparticles deposited onto TiO2 nanotube arrays (TNT) are used as heterostructured photoanodes in a compact-design photo-electrocatalytic (PEC) cell for solar-driven water splitting. No dopants, photosensitizers or other cocatalysts are added to enhance the catalytic activity but attention is focused on the relationship between TNT nanostructure (necessary for the novel compact-design PEC cell) and method of BiVO4 deposition. Three indicators are used to evaluate the catalytic performances: i) photocurrent density, ii) H2 production rate, and iii) solar-to-hydrogen efficiency (STH). Their dependence on photoanode characteristics (i.e. grade of TNT crystallinity) and operational parameters, such as anolyte concentration (NaOH in the range 0.1–1.0 M) and type of solar illumination (open spectrum or AM 1.5G filtered light), is analysed. While a linear relationship is observed between H2 production rate and photocurrent density, the behaviour of STH efficiency is more complex. An ordered and crystalline TNT film is necessary to maximize photocurrent density and H2 production rate, which can be further enhanced by depositing BiVO4. However, the methodology of BiVO4 deposition and the specific TNT nanoarchitecture have a marked influence in terms of light absorption, electronic conductivity and rate of reaction between photogenerated holes and OH−. This leads to an improvement or a depression of the photocatalytic behaviour as BiVO4 may in some cases favour charge recombination. Thus, understanding the role of the photoelectrodes in relation to the operational conditions may favour the preparation of scalable electrodes for improving performances of PEC cells in the generation of solar fuels.

Synergic effect of ZnO nanostructures and cobalt phosphate co-catalyst on photoelectrochemical properties of GaN

Novel PEC cell design based on GaN/ZnO/CoPi heterojunction cascade was synthesized using united metal organic chemical vapor deposition (MOCVD), hydrothermal, and photo-electrodeposition strategy. Two different type of ZnO architectures viz., honeycomb (HON) and nanorods (NRs) were grown on the GaN layer by executing structure directing agents of multiwall carbon nanotubes, and ZnO buffer layer, enhancing photoelectrocatalytic (PEC) activity toward oxygen evolution reaction (OER). In an expansion of such approach, the PEC activity was further improved by incorporating photo-electrodeposited cobalt phosphate (CoPi) in synthesis system accompanying negative shift of the photocurrent onset potential. A steady-state and highest photocurrent density (Jph), of 4.81 ± 0.02 mA/cm2 was obtained with GaN/ZnO NRs/CoPi heterojunction cascade electrode at 1.23 V verses reversible hydrogen electrode (VRHE) under simulated sunlight illumination. PL result shows quenching of photoluminescence with CoPi modification acts as co-catalyst and preferably captures hole from ZnO NRs which likely to facilitate the electron-hole (e−/h+) pair separation and OER reaction kinetics. However, CoPi modified GaN/ZnO HON and pristine GaN photoelectrodes exhibited relatively lesser photocurrent densities. Experimental evidences by electrochemical impedance (EIS) and incident photon to current conversion efficiency (IPCE) confirmed superior electrical conductivity, light absorption capability and charge transfer across GaN/ZnO NRs/CoPi heterojunction interfaces attributable to type II band alignment together with dominant synergistic effect of ZnO NRs nanostructures and CoPi oxidation co-catalyst which could augment PEC water splitting. This work encourages futuristic insights into integrated synthesis methods toward development of high performance photoelectrodes based on underexplored GaN and other heterostructures.

Solar/photoelectrocatalytic cell development for H2 production and simultaneous organic dye degradation

The situation of alternative energy and environmental management is an urgent problem that must be solved. This research aims to improve photoelectrocatalytic (PEC) cells for hydrogen (H2) production and simultaneous organic degradation as an alternative way to solve this problems. We developed Cu2O film fabrication using a cyclic voltammetry deposition (CVD) method for optimal H2 production efficiency. We designed the PEC cell using a Cu2O photocathode developed in conjunction with a WO3/BiVO4 photoanode for simultaneous H2 production and organic dye degradation. The PEC cell was then designed to separate H2 gas from the system, including the solar cells as bias potential units to save energy in the operation process. The Cu2O photocathode shows high efficiency of H2 production related to its absorption properties and morphology, as well as a charge transfer rate improvement. The optimum conditions for FTO/Cu2O electrode fabrication was the precursor solution's original pH value and a scan rate of 50 mV/s for 20 cycles with hydrogen generation of 5.9 mL/h. The developed solar/PEC cell presents high efficiency for methylene blue (MB) degradation up to 97% for 3 h under an applied potential of 0.4 V and visible light irradiation. The highlight of this developed cell is a high-efficiency Cu2O cathode for H2 production, and the designed PEC cell can simultaneously eliminate organic waste. Notably, the design of the solar cell panel as an applied potential unit can reduce the energy consumption of the system. This developed solar/PEC cell suitable for the alternative energy and waste water treatment applications.

Photoelectrocatalytic H2 evolution enhancement over CuO-decorated TiO2 nanocatalysts and promoting E. coli degradation

The objective of this research is to improve cathode electrode fabrication for high-efficiency hydrogen (H2) evolution and to promote Escherichia coli (E. coli) degradation at the anode electrode. The heterojunction of the TiO2/CuO photocathode was synthesized via sputtering of the TiO2 nanocatalyst on the CuO electrode for enhancing the H2 evolution efficiency. The effect of calcination temperatures for Cu2O conversion to high-catalytic CuO and priority deposition of the TiO2 layer were optimized to improve the photoelectrocatalytic (PEC) activity and charge transfer process. The optical properties, morphology, crystalline structure, and chemical composition were characterized to clarify the PEC activity improvement. The developed TiO2/CuO photocathode combined with the BiVO4/WO3 photoanode was designed in the PEC cell for H2 production and simultaneous E. coli degradation. Cu2O was changed to a narrower bandgap energy of CuO at the calcination temperature over 400 °C and presented high crystallinity and proper morphology when the temperature was increased to 550 °C. The CuO-decorated TiO2 nanocatalyst can improve the morphology and charge transfer process at the heterojunction of the TiO2/CuO electrode. The small particle size of TiO2 at the outer side can improve the surface roughness and serve as electron separation to reduce the recombination effect of CuO, resulting in high-efficiency H2 evolution. The developed PEC cell can produce H2 up to 5800 μL for 150 min and E. coli degradation up to 100% for 22 min under the PEC process. We can confirm that the developed TiO2/CuO cathode electrode is highly effective in H2 production and is sufficient in promoting the E. coli degradation process at the BiVO4/WO3 anode electrode. The findings of this research are beneficial in high-efficiency heterojunction semiconductor electrodes development and PEC cell designs for energy and environmental applications.

P-doped WO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; semiconductor with enhanced conduction band on highly efficient photoelectrocatalytic reduction of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Global warming is considered a serious climate problem caused by excessive emissions of carbon dioxide. Studies on catalytic conversion of CO2 are significant in terms of reducing CO2 concentration in the atmosphere, thus remain popular in the field. The photoelectrocatalytic (PEC) reduction of CO2 is an environment-friendly and efficient method to convert excessive CO2 into chemicals. With such conversion, the greenhouse effect can be alleviated through the storage and transformation of solar energy into chemical energy. WO3 is an n-type semiconductor with wide band gap and low conduction band position. Therefore, the use of WO3 is rare for photocatalytic water splitting and CO2 reduction. Although some techniques are used to improve the ability of WO3 in photocatalytic water splitting, the light quantum efficiency (AQE) is still less than TiO2. In current study, a facile method is explored to enhance the conduction band position of semiconductors, thereby improving the photoelectrocatalytic reduction of CO2. To the best of our knowledge, this is the first paper includes novel P-doped WO3 catalysts being designed, prepared, and used in the reduction of CO2 to carbon-based chemicals in water. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and electron paramagnetic resonance (EPR) experiments were applied to confirm the formation of new catalysts. The photoelectric properties of new catalysts were characterized by UV-vis, linear sweep voltammetry (LSV), Mott-Schottky, and electrochemical impedance spectroscopy (EIS) experiments. We have developed a new type of hybrid semiconductor (P-doped WO3 vertical bar) as catalytic materials by introducing the vaporized phosphide (NaH2PO2) onto the surface of WO3 substrate under the flow of argon gas in a tube furnace. The PEC cell of P-doped WO3 vertical bar SCE vertical bar BiVO4 was equipped with a trielectrode system and powered by a chemical workstation, in which, p-doped WO3 vertical bar was used as photocathodes in photoelectrocatalytic reduction of CO2. The PEC cell was fulfilled with an electrolyte containing 1 mmol/L photosensitizer Eosin Y and 0.1 mol/L KHCO3, and bubbled with pure CO2 in 30 min to saturation, the experiment of CO2 reduction in water was carried out with a proper voltage under irradiation of simulated sun light (300W Xe lamp) to generate methanol, ethanol, acetone, etc. Our results indicates that the conduction band position of p-doped WO3 increases from -0.13 to -0.54 V along with the increase of P-doped quantity, augmenting its ability to reduce CO2. It can be seen that p-doped WO3 with oxygen vacancies has higher activity than pure WO3, in which, the highest activity is the catalyst 15-P, approaching to 0.4% AQE equal to natural plant, yielding methanol in a rate of 20.8 mu mol/(L h cm(2)) and acidic acid at a rate of 4.7 mu mol/(L h cm(2)). The influence of oxygen vacancies on the reaction is positive and verified by the quenching experiments of H2O2. The more oxidation time, the less oxygen vacancies. The EPR signal of 15-P catalyst treated by 2 h oxidation was reduced to 10%. The catalytic activity of CO2 reduction was decreased to 50%. In summary, we designed and prepared a new type of p-doped WO3 hybrid semiconductor material as efficient catalysts for photoelectrocatalytic reduction of CO2, resulting carbon-based chemicals. P-doped WO3 improves the conduction band position of the semiconductors, increases oxygen vacancies and defect sites. Therfore, the activity and efficiency of catalytic reduction of CO2 can be improved. The low voltage is favoured to ethanol production, and high voltage is favoured to acid production. The experimental results have guiding significance for the development of new hybrid semiconductor materials and their photoelectrocatalytic reduction of CO2.

Photoelectrocatalytic reactor improvement towards oil-in-water emulsion degradation

Oil-in-water (O/W) emulsion is critical wastewater that is challenging to eliminate and requires a long treatment process, and it is necessary to develop highly effective removal methods before releasing it into natural water sources. This research has selected the photoelectrocatalytic (PEC) technique to solve this problem by developing a PEC reactor for high efficiency in O/W degradation and understanding the essential factors related to the PEC reactor's efficiency improvement. The PEC reactor has been designed on a large scale with suitable positioning of an electrode that is, designing a light source near the anode electrode to enhance light irradiation efficiency and including a circulating pump to provide continuous flow to the solution through the electrode surface. We studied the main factors of supporting the electrolyte, electrode characteristics, and catalytic process. We investigated the O/W-degradation efficiency using a UV/Vis spectrophotometer, chemical oxygen demand (COD) measurement, and GC-MS analysis. We optimized the PEC reactor using the developed BiVO4 photoanodes and placed them parallel with the zinc plates. Then, we controlled the applied potential at 1.0 V in 0.1 M Na2SO4 supporting an electrolyte under visible light irradiation. The developed PEC reactor can be degraded in the O/W emulsion up to 76% and decreased the COD value up to 78% for 7h. This PEC cell can be completely decomposed of many functional groups, such as carbonyl, ester, nitrile, amine, phosphate, chloro group, and nitro group, that were contained in the O/W substance. The highlight of this research is the designed light source and circulating pump inside of the PEC reactor to enhance the light irradiation, refresh the anode electrode, and understand the critical factor for the improvement of O/W-degradation efficiency. This PEC reactor presents a high-efficiency O/W degradation with practical use and a fast process suitable for further application in high turbidity of wastewater treatment from the oil industry.

Analysis of the factors controlling the performance of a photoelectrocatalytic cell separated by UF membrane in degrading methylene blue

Methylene blue (MB) is a toxic and colorful organic matter that exists in the wastewater of textile industries. Difficult biodegradability of MB causes biological treatment methods that cannot sufficiently biodegrade it. In photoelectrocatalytic (PEC) methods, by converting the radiation energy to the electricity, MB is degraded efficiently in the anolyte chamber. Using the ultrafiltration (UF) membrane rather than a high-priced cation exchange membrane (CEM) decreases the cost of the PEC pilot. Therefore, in this study, different dependent and independent variables that affect the performance of the PEC are investigated to evaluate the technical feasibility of using ultra-filtration membrane as a separator of anode and cathode chambers. The results demonstrate an increase in the anolyte MB concentration up to 15 mg/l augments the PEC performance. In the best condition, the MB, turbidity, and color removal percent are 51.56%, 65.62%, and 64.19%, respectively, and produced power is 1.075 μW when the anolyte MB concentration, the pH, and the illumination density are 15 mg/l, 3, and 12 W, respectively. Also, the results indicate the removal percentage of the MB, turbidity, and color in either anolyte or catholyte rises in the anolyte acidic conditions and higher illumination densities. Besides, the changes in the EC and pH of anode and cathode chambers during the experiment are investigated, and finally, the relations between MB, color, and turbidity removal percentage are evaluated. As a result, it is found that the UF membrane is a suitable candidate to be used in PEC pilots.

Synthesis of indium sulfide photoanode, its characterization and application for degradation of methylene blue and methyl orange

The researches on methylene blue (MB) and methyl orange (MO) destructions were carried out using indium sulfide (In2S3) photoanode in photoelectrocatalytic system. It consisted of In2S3 thin film as an anode synthesized by chemical bath deposition (CBD) on FTO and platinum as a cathode. Characterization with EDX showed the presence of In2S3 with a composition close to In2S3 for 10 min deposition. The In2S3 band gap measurement was obtained 2.49 eV. Photocurrent measurement revealed that In2S3 had n-type semiconductor property. The application of In2S3 thin film as photoanode in a photoelectrocatalytic cell for MB and MO treatments gave degradation’s yields ca. 71 and 55 %, respectively, under illumination with a 20 watt UV lamp, a bias voltage of 0.5 V for 150 min and with sample concentration of 25 mg/L.

Photoelectrocatalytic improvement of copper oxide thin film fabricated using anodization strategy application in nitrite degradation and promoting oxygen evolution

This research is to develop Cu oxide thin film preparation using the anodization technique for the highest efficiency nitrite degradation and promoting oxygen evolution improvement. The electrochemical cell is developed by designing the electrode position to enhance the efficiency of Cu oxide thin film deposition on the anode electrode. The effects of precursor solution temperature, deposition time, and calcination temperature were studied to enhance the photoelectrocatalytic water reduction properties. The characteristics of the fabricated Cu oxide thin film were studied using scanning electron microscope, X-ray diffraction, and electrochemical impedance spectroscopy methods related to the photoelectrocatalytic activity improvement. The calcination temperature is a significant factor affecting physical properties, crystalline structure, morphology, and charge transfer rate, which relate to the photoelectrocatalytic activities. We have succeeded in developing the photoelectrocatalytic cell using the developed Cu oxide photocathode in cooperation with the FTO/WO3/BiVO4 photoanode for nitrite degradation and simultaneous oxygen production up to 98% and 6.0 mgO2/L for 120 min, respectively. This research is especially suitable for further development leading to a water treatment application that eliminates inorganic ions and increases the dissolved oxygen value in an aquarium system.

The effect of inner-sphere reorganization on charge separated state lifetimes at sensitized TiO2 interfaces.

Improving the efficiency of photo-electrocatalytic cells depends on controlling the rates of interfacial electron transfer to promote the formation of long-lived charge separated states. Ultimately, for efficient catalytic assemblies to see widespread implementation, repeated electron transfer in the absence of charge recombination needs to be realized. In this study, a series of manganese-based transition metal complexes known to undergo charge transfer-induced spin crossover are employed to study how significant increases in inner-sphere reorganization energy affect the rates of interfacial electron transfer. Each complex is characterized by transient spectroscopic and electrochemical methods to calculate the rate of electron transfer to a model chromophore anchored to the surface of a TiO2 film. Likewise, open-circuit voltage decay measurements were used to determine the voltage-dependent lifetime of injected electrons in TiO2 in the presence of each complex. To further characterize the rates of electronic recombination, density functional theory was used to calculate the inner-sphere and outer-sphere reorganization energy for each complex. These calculations were then combined with classical Marcus theory to determine the theoretical rate of back-electron transfer from the TiO2 conduction band. These results show that, in model complexes, a significant reduction in the recombination rate constant is achieved for complexes possessing a significant inner-sphere reorganization energy.

Anode Photovoltage Compensation‐Enabled Synergistic CO2 Photoelectrocatalytic Reduction on a Flower‐Like Graphene‐Decorated Cu Foam Cathode

AbstractAn interconnected and hierarchically structured electrode composed of a Cu nanoparticle‐modified flower‐like reduced graphene oxide‐decorated copper foam (Cu NP/f‐RGO/CF) is crafted and exploited for photoelectrocatalytic (PEC) reduction of CO2 in a TiO2 nanotube photoanode‐driven PEC cell. Anode photovoltage compensation confers a more negative cathode potential for CO2 reduction, thus leading to a synergistic effect between photocatalysis (PC) and electrocatalysis (EC). CO2 reduction rate under PEC condition is 5.4× higher than that of the simple sum under PC and EC processes. The well‐defined flower structure of RGO in the CF scaffold effectively prevents its self‐agglomeration, which increases its adsorption towards CO2 with improved electron‐transfer kinetics due to the 3D interconnected structure with abundant electron transfer pathways. DFT calculations further reveal the absorption and activation of CO2 on Cu NP/f‐RGO capitalize on the CC bond with RGO and OCu bond with Cu NPs, thereby leading to a bended and stretched structure. The enhanced CO2 adsorptivity and activation on the hierarchical Cu NP/f‐RGO/CF electrode significantly improve CO2 reduction and facilitate the conversion of C1 products to high‐order products. This research highlights the great prospect of anode photovoltage compensation enables synergistic photoelectrocatalysis and 3D hierarchical electrode for CO2 drastic reduction into high‐order products.

Photoelectrodeposition of BiVO4 layer on FTO/WO3 photoanodes for highly efficient photoelectrocatalytic chemical oxygen demand sensor applications

The research focus is on developing the photoelectrocatalytic (PEC) technique to obtain the simple, rapid, and nontoxic method for chemical oxygen demand (COD) sensor application. We have developed the heterojunction of a WO3/BiVO4 layer deposition on a fluorine-doped tin oxide (FTO) substrate using an electrodeposition method. The highlight of this development is the capability to immobilize a BiVO4 layer on the FTO/WO3 semiconductor electrode through our novel photoelectrodeposition method. A FTO/WO3/BiVO4 characteristics were studied to confirm the chemical composition, crystalline structure, morphology, optical properties, and charge transfer resistance. The results showed that the high efficiency of the BiVO4 layer deposited on the FTO/WO3 electrode improved the visible light absorption, surface morphology, and charge transfer rate and enhanced the PEC activities over the FTO/WO3 electrode by up to 2.5 times. The FTO/WO3/BiVO4 electrode was applied as a photoanode for COD determination using the designed PEC cell. The developed PEC cell exhibits relative standard deviation of 2.03% and percentage recovery of 98%, which indicate the method’s high precision and accuracy for COD determination. The proposed PEC cell for the COD sensor represents a simple, rapid, low-cost, environmentally friendly, and highly efficient method for COD monitoring in a wastewater treatment system.

Using ultra filtration membrane in photo electrocatalytic desalination cell (UF-PEDC)

Several methods have been invented to desalinate saltwater for industrial or domestic uses, but still, they need to be improved to reduce the cost and environmental impacts. In this study, a desalination cell is inserted in the middle of photoelectrocatalytic cells to separate ions, and drag them into the electrolytes. The driving force, in this method, is ultraviolet illumination, exciting coated titanium nanotubes on the anode electrode, and then produces electron/hole pairs. Holes degrade organic matters, and electrons are transferred by an external circuit to the cathode chamber. Ultrafiltration membrane (UF) is used for the first time as a separator barrier between chambers in this photo redox desalination method. The performance of photo electro desalination cell (UF-PEDC) in different independent parameters like salt content, pH, resistivity, and illumination density is investigated. The UF-PEDC desalinates 42.54% of saltwater with the total dissolved solids (TDS) of 78.57 g/l and also degrades 96.46% of methylene blue as an organic matter after 70 h. This experiment shows that UF-PEDC can operate longer, more efficient, and with a higher TDS removal rate than microbial desalination cells and is a suitable choice to desalinate hypersaline streams produced in reverse osmosis methods.

Novel photoelectrocatalytic/solar cell improvement for organic dye degradation based on simple dip coating WO3/BiVO4 photoanode electrode

This work focuses on developing a novel photoelectrocatalytic (PEC) cell combined with a solar cell for the highest efficiency, simplest process, and most energy savings to degrade organic dyes in wastewater. FTO/WO3/BiVO4 photoanode electrode fabrication was developed with the simple layer-by-layer dip coating method, which allows production to be scaled up in the future. The fabricated WO3/BiVO4 shows thin film properties of high porosity, good visible light absorption, and ability to cover the entire FTO substrate area. The developed FTO/WO3/BiVO4 electrode exhibits high oxidation activity and high durability, and it can be applied to the PEC cell prototype by working under the catalytic mechanism of light irradiation and bias potential for organic dye degradation. The novel PEC cell was especially designed to include a solar cell to convert light into electrical energy that is stored in batteries for potential bias at the anode electrode and to supply electricity to the light-irradiated electrode and solar cell panel under the electrical circuit's controller. The result shows that the developed PEC cell prototype can operate on its own without using external power and is able to degrade methylene blue and rhodamine B dyes up to 94% and 93% in 3 h, respectively. This research provides a novel, innovative PEC cell prototype that is highly effective at removing various organic dye substances, uses a simple method, offers an energy saving process, and is a very interesting way to further a large industrial dye wastewater treatment system.