PEC System Research Articles

Signal-off photoelectrochemical aptasensor for kanamycin: Strand displacement reaction combines p-n competition

A“signal-off” photoelectrochemical aptasensor based on p-n type semiconductor competitive quenching effect and strand displacement reaction was constructed for the determination of kanamycin. Au NPs@MgIn2S4-graphene composite was used as n-type photoactive semiconductor material. In the presence of the kanamycin, strand displacement reaction was triggered and the p-type CuInS2 quantum dots labeled aptamer was introduced on the Au NPs@MgIn2S4-graphene surface. The CuInS2 quantum dots can competitive consume the electron donors (AA) and light energy of the PEC system, thus quenched the anodic photocurrent of Au NPs@MgIn2S4-graphene. The photocurrent decreased with the increase of kanamycin concentration. The linear range of kanamycin was 1.0 pM–10 μM, and the detection limit was 1.7 pM. In addition, the method can be used for the determination of kanamycin in milk and honey.

Hydrogen production of ZnO and ZnO/Ag films by photocatalysis and photoelectrocatalysis

This paper reports the hydrogen production of ZnO and ZnO/Ag films prepared by sol-gel method. All films were evaluated under solar light simulated using photocatalytic and photoelectrocatalytic systems. XRD results revealed that hexagonal crystal structure of ZnO is presented in all films and SEM micrographs indicate a well-defined sphere-shaped morphology. By increasing the amount of Ag, band-gap value is slightly shift in the absorbance spectra towards the visible light region. Besides the increase of Ag dopant, roughness is modified improving the light absorption due to the scattering on the surface of the films. ZnO and ZnO/Ag films were used as active materials in photocatalytic and photoelectrocatalytic system for H2 production. The presence of Ag favoured the existence of active sites (estimated by Turnover Frequency, TOF) and enhances the charge transfer avoiding the electron-hole pair recombination in ZnO films for H2 production as it was determined by photoluminescence and electrochemical measurements. In the photocatalytic system, the film containing 5% of Ag as dopant produces an amount of H2 of about 3.5-times higher than ZnO undoped film. While in the photoelectrochemical system, the density of donors increases in ZnO due to the presence of Ag, but also the charge transfer resistance decreases, which improves the electrical and charge transport properties of ZnO, making the PEC system more efficient.

Visible-light-driven peroxymonosulfate activation in photo-electrocatalytic system using hollow-structured Pt@CeO2@MoS2 photoanode for the degradation of pharmaceuticals and personal care products

In this study, we constructed an innovative photo-electrocatalysis-assisted peroxymonosulfate (PEC/PMS) system to degrade pharmaceuticals and personal care products (PPCPs). A hollow-structured photoanode (i.e., Pt@CeO2@MoS2) was specifically synthesized as a photoanode to activate PMS in the PEC system. As proof of concept, the Pt@CeO2@MoS2 photoanode exhibited superior degradation performance toward carbamazepine (CBZ) with PMS assistance. Specifically, the kinetic constant of PEC/PMS (k = 0.13202 min−1) could be enhanced about 87.4 times compared to that of the PEC system (0.00151 min−1) alone. The PMS activation mechanism revealed that the synergistic effect between the hollow material and the change of surface valence states (Ce3+ to Ce4+) and (Mo4+ to Mo6+) contribute to enhancing the degradation efficiency of the visible-light-driven PEC/PMS process. The scavenger testing and EPR showed that 1O2, O2•−, SO4•− and •OH play dominant roles in the SR-AOPs. Furthermore, the applicability of Pt@CeO2@MoS2 used in SR-AOPs was systematically investigated regarding of the reaction parameters and identification of intermediates and dominant radicals as well as the mineralization rate and stability. The outcomes of this study can provide a new platform for environmental remediation.

Polyoxometalate@g-C3N4 nanocomposite for enhancing visible light photoelectrocatalytic performance

The prepared g-C3N4 under morphology controlling shows better physic and chemical performance. The synergistic effect of POM and g-C3N4 in the hybrid improves its high photocatalytic capability. The research indicates that g–C3N4–based material is a potential photoelectrode for PEC degradation. Besides, the PMoV nanocomposite shows better activities in the PEC and removal efficiency of RhB. Compared with the same PEC system, the degradation time of RhB is shorter and the degradation efficiency is higher for the MCN/PMoV catalysts.

Visible‐Light‐Responsive TiO2/NiFe Mixed Metal Oxide‐Carbon Photocatalytic Fuel Cell with Synchronous Hydrogen Peroxide Production

AbstractThe photocatalytic fuel cell (PFC) synergistically utilizes the photocatalytic oxidation of biomass and the electrochemical reaction of the fuel cell to selectively reduce oxygen to produce hydrogen peroxide (H2O2) at room temperature. Herein, we report a PEC system that NiFe‐layered double oxide (LDO)/TiO2 as photoanode, carbon black as cathode for utilizing biomass and oxygen to simultaneously convert solar energy into electricity and produce hydrogen peroxide without applied electric bias. The photoanode catalyst was fabricated with TiO2‐supported NiFe mixed metal oxides (MMO) which obtained by layered double hydroxides (LDHs) pyrolysis. The research results indicate that under solar irradiation, the photocurrent density and faraday efficiency have a significantly improved compared with pure NiO/TiO2. With methanol as the feeding fuel at the photoanode, the optimal device yields an excellent open circuit voltage (Voc), short circuit current (Jsc) and a maximum power density (Pmax) of 0.78 V, 1093 μA/cm2 and 169 μW/cm2, respectively. This performance improvement is attributed to the Fe3+ doped in NiFe‐MMO and use TiO2 as an electron transport layer. Simultaneously, the hydrogen peroxide concentration reached 0.443 mM after 180 min illumination at the cathode, the generation rate was optimized to 0.126 μmol/min/cm2 at neutral aqueous solution. The PEC system exhibited an excellent higher rate of production for H2O2, and faraday efficiency (FE) reached 31.7 %. This PFC is a green technology for photocatalytically oxidize biomass at the photoanode and convert solar energy into electricity as well as supply it to the cathode to reduce O2 to produce H2O2 efficiently.

Efficient degradation of trimethylamine in gas phase by petal-shaped Co-MoS2 catalyst in the photo-electrochemical system

It is necessary to explore the best treatment to eradicate trimethylamine [TMA] in air, since it is toxic and hazardous to the living organism. Photocatalysis, a low-cost and environmentally friendly technology, has been studied in comparison with photo-electrochemical catalysis in the removal of TMA gas. In this study, it is most quickly and efficiently degraded using Co-MoS2 composite catalyst in an integrated system of (PEC) photo-electrochemical catalysis. The performance of the catalyst and system was evaluated by TMA removal ratio. As a result, the catalyst has good degradation performance for TMA in the PEC system, which indicates that it has high photocatalytic activity and high apparent quantum efficiency. In addition, the stability of the Co-MoS2 catalyst in the PEC is better than in PC due to the presence of the external bias generated by the assisted electrochemistry in the PEC system.

Efficient urine removal, simultaneous elimination of emerging contaminants, and control of toxic chlorate in a photoelectrocatalytic-chlorine system

Urine, which is an important waste biomass resource, is the main source of nitrogen in sewage and contains large quantities of emerging contaminants (ECs). In this study, we propose a new method to efficiently remove urine, simultaneously eliminate ECs, and control the generation of toxic chlorate during urine treatment using a photoelectrocatalytic-chlorine (PEC-Cl) system. A type-II heterojunction of WO3/BiVO4 was used as a photoanode to generate chlorine radicals (Cl•) by decreasing the oxidation potential of WO3 valence band for the highly selective conversion of urine to N2 and the simultaneous degradation of ECs in an efficient manner. The method presented surprising results. It was observed that the amount of toxic chlorate was significantly inhibited by circumventing the over-oxidation of Cl− by holes or hydroxyl radicals (•OH). Moreover, the removal of urea nitrogen reached 97% within 90 min, while the degradation rate of trimethoprim in urine was above 98.6% within 60 min, which was eight times more than that in the PEC system (12.1%). Compared to the bare WO3 photoanode, the toxic chlorate and nitrate generated by the WO3/BiVO4 heterojunction photoanode decreased by 61% and 44%, respectively. Thus, this study provides a safe, efficient, and environmentally-friendly approach for the disposal of urine.

Photocatalytic and photoelectrochemical performances of Mo, Ni and Cu decorated metal chalcogenides

In this study, the syntheses of RGO-Cd(1-x)ZnxS photocatalysts has been accomplished by the solvothermal and thermal sulphurization methods in one spot in order to achieve well and homogeneous distribution of Cd(1-x)ZnxS particles on RGO sheets. Moreover, RGO-Cd(1-x)ZnxS photocatalysts were modified with doping and loading of Mo, Ni, and Cu to tailor the band structure of the composites. The hydrogen production performances of these photocatalysts were compared for the first time under solar light irradiation in a PC and PEC systems. The PC activity tests showed that the photocatalysts prepared with solvothermal method exhibited higher activity than those synthesized with thermal sulphurization. In addition, PC performances of the photocatalysts loaded by photodeposition technique were found to be higher than the ones prepared with doping approach. On the other hand, the photocatalysts synthesized with the sulphurization method displayed higher PEC performance than those prepared solvothermally. This study explains the fundamental effects of the photocatalyst preparation approaches on PC and PEC hydrogen productions. The results offered a new perspective for the effect of loading and doping of RGO-Cd(1-x)ZnxS photocatalysts on the hydrogen production efficiency.

Ultrasensitive photoelectrochemical immunosensor for procalcitonin detection with porous nanoarray BiVO4/CuxS platform as advanced signal amplification under anodic bias

A new, porous nanoarray BiVO4/CuxS (PN-BiVO4/CuxS) platform as an advanced signal amplification strategy under anodic bias on the process of electrochemical catalysis assisted self-enhancing based photoelectrochemical (ECASE-based PEC) without electron donors was established for ultrasensitive procalcitonin (PCT) detection. The system operated upon that the PN-BiVO4/CuxS electrode could enhance separation of e−/h+ pairs under illumination of visible-light because the energy levels between BiVO4 and CuxS matched well. Afterwards, the photoexcited electrons could shift to working electrode as output signal, while the photoexcited holes could oxidize water under anodic bias to produce hydrogen peroxide (H2O2) that was subsequently reduced by CuxS, which resulted in significantly enhanced photocurrent intensity by electrochemical process. To further enhance the sensitivity of PEC immunosensor, amino-modified polystyrene (PS) nanoparticles act as labels for immobilizing secondary antibodies (Ab2) to form PS@Ab2 conjugates for construction of sandwich-type immunosensor on the basis of ECASE-based PEC strategy. The designed PEC immunosensor exhibited a linear concentration range from 50 fg mL-1 to 100 ng mL-1, with a low detection limit of 17.3 fg/mL (S/N = 3) for PCT, and achieved good selectivity, acceptable stability, and high sensitivity. This work first conducted the ECASE-based PEC system, and we believed it will provide a new perspective for developing innovative signal amplification toward detection of other biomarker in the future.

Enhancement of Photoelectrochemical Reduction by LaFeO3 Photocathodes Coated with Electroless Deposited Nickel Boride Catalyst

Great efforts have been paid to enhance the photoelectrochemical performances of LaFeO3. However, there have rarely been reported about modifying of LaFeO3 with transitional metal borides for enhanced photoelectrochemical activities. Herein, we prepared LFO/Ni–B composite electrodes by immersing LFO into the prepared electroless plating solution. The optimized LFO/Ni–B composite exhibits a 373% improvement of the photocurrent density and exhibits an anodic shift of onset potential. Systematic studies reveal that the improvement of PEC activity should be attributed to enhanced electrochemically active surface area and electrocatalytic properties, reduced resistance of the PEC system, and a more pronounced downward band bending at the photoelectrode/electrolyte interface.

(Invited) Solar Energy Conversion Enhanced By the Structure and Surface Improvements of Quaternary Semiconductors

Solar energy conversion with high yield and cost-effective ratio requires use of materials which are easily available, stable within the time and flexible in structure in order to allow improvements in their intrinsic and surface properties. A class of such materials are perovskites with ABO3 structure or kesterites. The basic structure of ABO3, has a high structural tolerance factor and can be maintained with a wide variety of constituent elements. As a result, the composition-property relationship can be systematically investigated while keeping the same crystal structure. Also, due to the exceptional stability of the structure, the valency, stoichiometry, and vacancy of perovskite compounds can be varied widely in order to tune optical, electrical and catalytic properties. Therefore, the challenge is to couple the synthetic approach with an expected outcome resulting from the theoretical calculations. In this presentation we will show the study on quaternary Ln1-xNixTiO3 that revealed the optical and electronic properties might be affected by varying La content in the matrix under employment of a reductive atmosphere of H2. This constitutes a unique and advantageous feature for its use in solar energy conversion. Understanding the effect of La doping and Ni segregation occurring under the reductive atmosphere on the photoelectrochemical properties of the La1-xNixTiO3 will generate new set of knowledge while providing a facile route to tune photon absorption and charge transport properties. A similar study will be presented for kesterite Cu2ZnSnS4. The questions which will be undertaken are: does La doping favourably affect the electron-hole separation in addition to the enhancement of photon absorption?; how do oxygen vacancies created by ion doping and reduction in hydrogen affect the charge transport properties?; can Ni segregation affect the catalytic property of the Ln1-xNixTiO3 surface?. The same questions will be applied to kesterite based PEC system upon ion doping and applied atmosphere. We will try to answer these questions through use transient absorption spectroscopy approach allowing to follow changes in charge carrier dynamics from the sub nanoseconds up to seconds timescales upon introduction of any variable to the system.

A novel electrochemical method for simultaneous measurement of real-time potentials and photocurrent of various photoelectrochemical systems

Two-electrode configuration is preferably used in practical application of various photoelectrochemical systems, such as green fuel production and cathodic protection. Photo electrodes are extendedly studied but the effects of the dark electrodes on overall performance of PEC systems are not experimentally figured out. To address this issue, herein, a novel electrochemical method achieving simultaneous measurement of photocurrent and real-time potential of the photo electrode and the dark electrode is proposed. With this method, the actual band positions and band bending of the photo electrode under photocurrent going through can be determined correctly. By investigating photoelectrochemical hydrogen production and cathodic protection with ZnO photo anodes, it is revealed that the amplitude of photocurrent is not solely determined by the number of light generated electrons on the photo electrode but also strongly affected by their consuming rate for electrochemical reactions on the dark electrode. These applications demonstrate the practicality, reliability and universality of the proposed method for comprehensive understanding the reactions of various photoelectrochemical systems and eventually for their better development.

Fabricating MoS2 nanoflakes photoanode with unprecedented high photoelectrochemical performance and multi-pollutants degradation test for water treatment

In this work, vertically aligned MoS2 nanoflakes on Ti foil have been successfully prepared by different hydrothermal methods (using water or ammonia solvent) towards fabricating photoanodes with high visible light photoelectrochemical performance. The few-layered MoS2 (4–10 nm) nanoflakes electrode grown in water exhibits unprecedented higher photocurrents under visible light irradiation, and the stability of the few-layered MoS2 electrode was markedly enhanced by annealing the sample at 300 °C. The underlying mechanisms accounting for the superior photoelectrochemical performance of the few-layered MoS2 nanoflakes are found to be correlated with their phase, crystallinity, length, number of layers and photon absorption efficiency etc. Furthermore, the photoelectrochemical degradation of organic chemicals including rhodamine B dye, 4-chlorophenol, chlorpyrifos and ciprofloxacin selected as different types of pollutants in wastewater was evaluated and compared utilizing the few-layered MoS2 nanoflakes photoanode. The photoelectrochemical degradation efficiency is strongly influenced by the molecular structures and properties of pollutants and experimental condition parameters such as solution pH, oxygen concentration and applied bias potential. The available high electron cloud density sites induced by the electron-withdrawing functional groups in different substrates might determine the substrate-specific PEC degradation efficiency. The present MoS2-based PEC system could be further optimized for efficient degradation of recalcitrant pollutant like ciprofloxacin.

Graphdiyne Nanowall for Enhanced Photoelectrochemical Performance of Si Heterojunction Photoanode.

Graphdiyne (GDY), a new member of 2D carbon material family, was introduced into a Si heterojunction (SiHJ)-based photoelectrochemical water splitting cell. With assistance of magnetron-sputtered NiOx, the plateau photocurrent density of SiHJ/GDY/NiO x-10 nm with optimized NiO x film thickness was twice higher than that of SiHJ/NiO x-10 nm, demonstrating the catalytic function of GDY itself as well as the synergistic effect between GDY and NiO x. The results verified that GDY is a promising photoelectrode material candidate to realize highly efficient PEC performance, and pave a novel pathway to further improve Si-based PEC system.

Coating Polymeric Carbon Nitride Photoanodes on Conductive Y:ZnO Nanorod Arrays for Overall Water Splitting

AbstractPolymeric carbon nitride (PCN) photosensitizers are proposed replacements for their inorganic counterparts in solar‐to‐fuel conversion via photoelectrochemical water splitting. However, intense charge recombination, primarily because of surface defects, limits the use of PCN in PEC systems. Now, photoanodes are designed by coating PCN films onto highly conductive yttrium‐doped zinc oxide (Y:ZnO) nanorods (NRs) serving as charge collectors. The generation of charge carriers can therefore be promoted by this type II alignment. The charge collectors would be kept nearby for charge separation and transport to be used in the interfacial redox reactions. The photocurrent density of the polymer electrode is improved to 0.4 mA cm−2 at 1.23 V vs. the reversible hydrogen electrode in a Na2SO4 electrolyte solution under AM 1.5 illumination. The result reveals a more than 50‐fold enhancement over the PCN films achieved by powder; the efficiency can be preserved at 95 % for 160 minutes.

Coating Polymeric Carbon Nitride Photoanodes on Conductive Y:ZnO Nanorod Arrays for Overall Water Splitting.

Polymeric carbon nitride (PCN) photosensitizers are proposed replacements for their inorganic counterparts in solar-to-fuel conversion via photoelectrochemical water splitting. However, intense charge recombination, primarily because of surface defects, limits the use of PCN in PEC systems. Now, photoanodes are designed by coating PCN films onto highly conductive yttrium-doped zinc oxide (Y:ZnO) nanorods (NRs) serving as charge collectors. The generation of charge carriers can therefore be promoted by this type II alignment. The charge collectors would be kept nearby for charge separation and transport to be used in the interfacial redox reactions. The photocurrent density of the polymer electrode is improved to 0.4 mA cm-2 at 1.23 V vs. the reversible hydrogen electrode in a Na2 SO4 electrolyte solution under AM 1.5 illumination. The result reveals a more than 50-fold enhancement over the PCN films achieved by powder; the efficiency can be preserved at 95 % for 160 minutes.

Light‐Driven BiVO4–C Fuel Cell with Simultaneous Production of H2O2

AbstractPhotoelectrochemical (PEC) systems have been researched for decades due to their great promise to convert sunlight to fuels. The majority of the research on PEC has been using light to split water to hydrogen and oxygen, and its performance is limited by the need of additional bias. Another research direction on PEC using light, is to decompose organic materials while producing electricity. In this work, the authors report a new type of unassisted PEC system that uses light, water and oxygen to simultaneously produce electricity and hydrogen peroxide (H2O2) on both the photoanode and cathode, which is essentially a light‐driven fuel cell with H2O2 as the main product at the two electrodes, meanwhile achieving a maximum power density of 0.194 mW cm‐2, an open circuit voltage of 0.61 V, and a short circuit current density of 1.09 mA cm‐2. The electricity output can be further used as a sign for cell function when accompanied by a detector such as a light‐emitting diode (LED) light or a multimeter. This is the first work that shows H2O2 two‐side generation with a strict key factors study of the system, with a clear demonstration of electricity output ability using low‐cost earth abundant materials on both sides, which represents an exciting new direction for PEC systems.

Decoration of wide bandgap semiconducting materials for enhancing photoelectrochemical efficiency of PEC systems.

The production of photoanodes based on wide-band gap materials such as TiO2 is economically viable because of the low cost of synthesis methods. Contrary to economic aspects, wide-band gap semiconductor materials have a significant disadvantage due to low sensitivity to photons of visible light. To increase the photoactive parameters of the material of the electrodes in the visible range, the methods for decorating nanomasses of titanium dioxide by narrow-gap semiconductors are used. One of the most suitable narrow-gap semiconductor materials are CdS and Fe2O3. Controlled deposition of such materials on wide-gap semiconductors allows to regulate both the diffusion time of charge carriers and the band structure of TiO2/Fe2O3 and TiO2/CdS composites. The dimensions of the structure of the photoelectrode material of the cell have a large influence on the characteristics of the photocatalyst created. Thus, in the hematite structures of nanometre dimension, the rate of recombination of charge carriers fades away in comparison with bulk structures. Reducing the size of CdS structures also positively affects the nature of the photocatalytic reaction.

Highly efficient degradation of berberine chloride form wastewater by a novel three-dimensional electrode photoelectrocatalytic system.

Fe2O3/graphite (Fe2O3/C) and nano-TiO2-coated glass bead were prepared by impregnation and sol-gel method respectively and employed as the catalyst of a novel three-dimensional electrode photoelectrocatalytic (3-D PEC) system. The photoexcited electrons can transfer from TiO2, Fe2O3 to counter electrode. It improves the migration of photoexcited charges, retards the fast recombination of electron-hole, and increases the lifetime of photogenerated holes (h+). In addition, the cycle reaction of Fe3+/Fe2+ on Fe2O3/C surface enhanced the Fenton reaction which can produce more hydroxyl radicals (·OH) and promote the capacity of mineralization of the pollutants. This novel 3-D PEC system showed excellent performance for the degradation of berberine chloride form (BCF). At the pH value of 3, 93% BCF was removed within 60min; besides, 98.64% COD removal rate, 78.96% mineralization, 21.47% mineralization current efficiency, and just 3.16kWhg-1TOC energy cost were obtained in 120min. In this study, we proposed the 3-D PEC mechanism. Electron spin resonance (ESR) and scavenging experiments suggest that the major reactive oxygen species (ROS) are superoxide radicals (O2·-), ·OH, and h+, while the role of sulfate radical (SO4·-) is insignificant. This work provides a new dimension for the design of reactors for wastewater treatment and the construction of the 3-D PEC system can potentially be utilized in water purification.

Strategies for Plasmonic Hot‐Electron‐Driven Photoelectrochemical Water Splitting

AbstractPhotoelectrochemical water splitting (PEC‐WS) was inspired by the natural photosynthesis process that utilizes sunlight energy to produce chemical energy through splitting water to form hydrogen and oxygen. One recent promising and innovative approach in this field is to implement the concept of plasmonic to PEC‐WS devices. This Review provides a systematic overview of the plasmonic and hot‐electron‐driven PEC‐WS and elucidates their possible mechanisms for plasmon‐mediated energy transfer. In the first section, we provide a brief summary of the basics of PEC‐WS and the strategies employed to maximize its conversion efficiency. Highlighting the advantages of the plasmonic‐based PEC system, in the next part we cluster our discussion based on the basics of plasmonics and the involved energy transfer mechanisms, which are classified as radiative (scattering, optical near field coupling) and nonradiative energy transfer (hot electron injection, plasmon resonant energy transfer) processes for plasmonic metal–semiconductor junctions as a photoactive material. Then, the recent research efforts in this field are categorized and discussed in three main sections: 1) nanoplasmonic units, 2) nanostructured support scaffolds, and 3) interface engineering with state‐of‐the‐art demonstrations. Finally, we conclude our Review with pointing out the challenges and perspectives of the plasmonic‐based architectures for future water‐splitting devices.