Drop In Photocurrent Research Articles

A split-type photoelectrochemical immunosensing platform based on atom-efficient cation exchange for physiological monitoring

Ultrasensitive and accurate physiological monitoring is of great significance for disease diagnosis and treatment. In this project, an efficient photoelectrochemical (PEC) split-type sensor on the basis of controlled release strategy was established with great success. Heterojunction formation between g-C3N4 and Zn-doped CdS improved the visible light absorption efficiency, reduced carrier complexation, improved the PEC signal, and increased the stability of the PEC platform. Compared to the traditional model of immunosensors, the process of antigen-antibody specific binding was done in a 96 microplate, and the sensor separated the immune reaction from the photoelectrochemical conversion process, eliminating mutual interference. Cu2O nanocubes were used to label the second antibody (Ab2), and acid etching using HNO3 released a large amount of divalent copper ions, which exchanged cations with Cd2+ in the substrate material, causing a sharp drop in photocurrent and improving the sensitivity of the sensor. Under the optimized experimental conditions, the PEC sensor based on the controlled release strategy for CYFRA21-1 target detection had a wide concentration linear range of 5 × 10−5 to 100 ng/mL with a low detection limit of 0.0167 pg/mL (S/N = 3). This intelligent response variation pattern could also offer the possibility of additional clinical applications for other target detection.

Enhanced Phase Stability of Compressive Strain-Induced Perovskite Crystals.

Control of strain in perovskite crystals has been considered as an effective strategy to ensure the phase stability of perovskite films where a compressive strain is particularly preferred over a tensile strain due to a lowered Gibbs free energy by the unit cell contraction effect. Here we adapt the strategy of strain control into perovskite solar cells in which the compressive strain is applied by utilizing a thermal expansion difference between the perovskite film and an adjacent layer. Poly(4-butylphenyldiphenylamine), with a higher thermal expansion coefficient compared to that of perovskite, is employed as a substrate for perovskite crystal growth at 100 °C, followed by cooling to room temperature. The applied compressive strain at the interface, as a result of a greater contraction of the polymer compared to the perovskite film, is confirmed by grazing incidence X-ray diffraction showing a red peak shift with increasing secondary angle. The compressive strain-induced perovskite film shows relatively constant absorbance spectra as a function of time. In the meantime, the absorbance spectra of a film without strain control exhibit a gradual decay with developing an Urbach tail. Importantly, the effect of strain engineering is remarkably prominent in the long-term photovoltaic performance. The photocurrent drops by 41% over 911 h without controlling strain, which is significantly improved by employing compressive strain, showing only a 6% drop in photocurrent from a shelf-stability test without encapsulation. It is also noted that an S-shaped kink appears in the current-voltage curves since 579-h-long storage for the device without strain control, leading to unreliable and overestimated fill factor and conversion efficiency. On the other hand, a 16% increase in fill factor with a stable performance is derived over 911 h from the compressive strain-induced device.

Accessing in Situ Photocorrosion Under Realistic Light Conditions

High-impact photoelectrode materials for photoelectrochemical (PEC) water splitting are distinguished by synergistically attaining high photoactivity and stability at the same time. With numerous efforts toward optimizing the activity, the bigger challenge of tailoring the durability of photoelectrodes to meet industrially relevant levels remains. In situ photostability measurements using flow cells hold great promise in understanding stability-related properties1-3 compared to traditional procedures, such as measuring the drop in photocurrent over time at 1.23 VRHE.In this work, a photoelectrochemical scanning flow cell connected to an inductively coupled plasma mass spectrometer (PEC-ICP-MS) and equipped with a solar simulator, Air Mass 1.5 G filter, and monochromator was developed (Figure 1A). The established system is capable of independently assessing basic PEC metrics, such as photopotential, photocurrent, incident photon to current efficiency (IPCE), and band gap in a high-throughput manner, as well as the in situ photocorrosion behavior of photoelectrodes under standardized and realistic light conditions by coupling it to an ICP-MS.4 In situ photocorrosion measurements conducted on spray-coated WO3 revealed that dissolution starts at 0.8 VRHE with the dissolution rate rapidly increasing past 1.2 VRHE, coinciding with the onset of the saturation photocurrent (Figure 1B). Wavelength-dependent photodegradation measurements show that WO3 only dissolved when irradiated with wavelengths lower than its band gap (Figure 1C). By using standardized illumination conditions such as AM 1.5 G under 1 Sun, the obtained dissolution characteristics are translatable to actual devices under realistic light conditions. The gained insights can then be utilized to advance synthesis and design approaches of novel PEC materials with improved photostability.Another aspect of flow cell systems is that they are well suited for operation in a high-throughput manner. In fact, scanning droplet cells have been successfully employed for rapid (photo)electrochemical screening of (photo)electrocatalyst libraries.5, 6 In here, we demonstrate proof-of-concept approaches for a full automation of the presented system to establish a platform that is capable of not only performing complete sets of PEC measurements but at the same time assess the in situ photostability of a photoelectrode material library. Such a platform would enable material discovery, which is tailored to search not only for the most active but also for the most stable PEC material. References Knöppel, J.; Zhang, S.; Speck, F. D.; Mayrhofer, K. J. J.; Scheu, C.; Cherevko, S., Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion. Electrochem. Commun. 2018, 96, 53-56.Dworschak, D.; Brunnhofer, C.; Valtiner, M., Photocorrosion of ZnO Single Crystals during Electrochemical Water Splitting. ACS Appl Mater Interfaces 2020, 12 (46), 51530-51536.Zhang, S.; Rohloff, M.; Kasian, O.; Mingers, A. M.; Mayrhofer, K. J. J.; Fischer, A.; Scheu, C.; Cherevko, S., Dissolution of BiVO4 Photoanodes Revealed by Time-Resolved Measurements under Photoelectrochemical Conditions. The Journal of Physical Chemistry C 2019, 123 (38), 23410-23418.Jenewein, K. J.; Kormányos, A.; Knöppel, J.; Mayrhofer, K. J. J.; Cherevko, S., Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS Measurement Science Au 2021, 1 (2), 74-81.Gregoire, J. M.; Xiang, C.; Liu, X.; Marcin, M.; Jin, J., Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements. Rev. Sci. Instrum. 2013, 84 (2), 024102.Sliozberg, K.; Schafer, D.; Erichsen, T.; Meyer, R.; Khare, C.; Ludwig, A.; Schuhmann, W., High-throughput screening of thin-film semiconductor material libraries I: system development and case study for Ti-W-O. ChemSusChem 2015, 8 (7), 1270-8. Figure 1

Solar Energy Conversion through Thylakoid Membranes Wired by Osmium Redox Polymer and Indium Tin Oxide Nanoparticles.

For several decades, much attention has been paid to thylakoid membranes (TMs) as photocatalysts for converting solar light to electricity. Despite extensive research, current technology provides only limited photocurrents. Here, a novel method based on TM-composite material was developed for achieving high photocurrent. When a thin film composed of TMs, osmium redox polymer (Os-RP), and indium tin oxide nanoparticles (ITOnp) was formed on a porous graphite surface, appreciable photocurrent as high as 0.5 mA cm-2 was achieved at 0.4 V vs. Ag/AgCl. Each component plays its own role in transferring electrons from TMs to the anode, resulting in sharp drop in photocurrent with missing any component. Optimization between these three components showed 1 : 0.5 : 30 (TM/Os-RP/ITOnp) was the best ratio. Action spectra confirmed that TMs was the origin of photocurrent. It was inferred from blocking experiments using 3-(3,4-dichlorophenyl)-1,1-dimethylurea as an inhibitor that about 41 % of photocurrent was transferred from QA in photosystem II to the electrode via Os-RP and ITOnp. Quantum efficiencies at 430 and 660 nm were 12.2 and 18.5 %, respectively. Turnover frequency for water oxidation depended upon the amount of the composite. A complete cell with Pt/C cathode produced Pmax of 122 μW cm-2 at 758 μA cm-2 under one sun illumination, which is the highest power density to our knowledge. This study opened a possibility of using TMs as photocatalysts for solar energy conversion.

Amorphous Co–Pi anchored on CdSe/TiO2 nanowire arrays for efficient photoelectrochemical hydrogen production

Photoelectrochemical (PEC) water splitting into hydrogen and oxygen using hybridized semiconductor photoelectrodes has become a promising strategy for converting solar energy into clean and sustainable H2 fuel. Here, we report a promising hybrid photoanode constructed by electrodepositing an amorphous Co–Pi film onto semiconducting CdSe/TiO2 nanowire arrays for photoelectrochemical hydrogen production. This photoanode exhibits a high water-splitting photocurrent density, which is attributed to the broad visible light absorption and efficient charge carrier separation by the virtue of the type-II heterojunction formed between TiO2 and CdSe. Photoconversion efficiency of Co–Pi/CdSe/TiO2 and CdSe/TiO2 photoanodes increase by 3.3 and 2.1 times, compared with the pristine TiO2 photoanode. Moreover, Co–Pi/CdSe/TiO2 photoelectrode shows greatly improved PEC stability, the drop in photocurrent of Co–Pi/CdSe/TiO2 nanowire arrays photoelectrode is about 10% after 1 h illumination, because of the addition of the Co–Pi film protecting the light absorber CdSe/TiO2 from photocorrosion. The enhanced PEC performance mechanism of triple hybrid photoanode is also discussed in this paper.

Ni Mg Mixed Metal Oxides for p-Type Dye-Sensitized Solar Cells.

Mg Ni mixed metal oxide photocathodes have been prepared by a mixed NiCl2/MgCl2 sol-gel process. The MgO/NiO electrodes have been extensively characterized using physical and electrochemical methods. Dye-sensitized solar cells have been prepared from these films, and the higher concentrations of MgO improved the photovoltage of these devices; however, there was a notable drop in photocurrent with increasing Mg(2+). Charge extraction and XPS experiments revealed that the cause of this was a positive shift in the energy of the valence band, which decreased the driving force for electron transfer from the NiO film to the dye and, therefore, the photocurrent. In addition, increasing concentrations of MgO increases the volume of pores between 0.500 and 0.050 μm, while reducing pore volumes in the mesopore range (less than 0.050 μm) and lowering BET surface area from approximately 41 down to 30 m(2) g(-1). A MgO concentration of 5% was found to strike a balance between the increased photovoltage and decreased photocurrent, possessing a BET surface area of 35 m(2) g(-1) and a large pore volume in both the meso- and macropore range, which lead to a higher overall power conversion efficiency than NiO alone.

Inkjet Printing of Functionalized TiO2Catalytic Layer for Water Oxidation Reaction

ABSTRACTOur investigations with silane-modified TiO2have revealed a beneficial effect of functionalization on the photoelectrochemical performance on spin-coated electrodes. However, in order to produce large area photoelectrodes, a more scalable manufacturing technology is required. Inkjet printing can fulfil this role and furthermore allow a finer control over coating morphologies. In this work, inkjet-printed photoelectrodes were prepared with silane-functionalized TiO2nanoparticles, and investigated as electrodes for photoactivated water splitting. The catalyst layers, having thickness around 700 nm, were printed on FTO-coated glass supports, from cellulose stabilized dispersions. For comparison, electrodes of similar thicknesses were also prepared by spin-coating. After removing the stabilizer at 300 °C under air atmosphere, the electrodes were characterized in photoelectrochemical cells containing 0.5 M H2SO4as electrolyte and a platinum ring as counter electrode. Under simulated sunlight, the best photocurrent densities for the oxygen evolution reaction were obtained for the inkjet-printed electrodes prepared with functionalized particles (up to 0.26 mA cm-2at 1.2 V against the standard hydrogen electrode (SHE), compared to 0.18 mA cm-2for spin coated). Microscopy of the printed electrodes shows structurally homogenous coatings with evenly distributed roughness. Under continuous illumination at 0.7 V (SHE), the electrodes showed no significant drop in photocurrent within five hours.

Influence of the hole-transport layer on the initial behavior and lifetime of inverted organic photovoltaics

The inverted organic photovoltaic (OPV) device architecture represents an important advancement due to the relative environmental stability of the electron transport layer (ETL) and hole-collecting contact. We investigated the initial and long-term behavior of inverted devices to identify changes taking place at the Ag hole-collecting contact. We show that efficient hole collection can be obtained after modifying the Ag contact by thermal annealing, long-term exposure to ambient atmosphere, or employing a high work function organic hole-transport layer (HTL). We find that whether or not the device employs an organic HTL, degradation of the photocurrent initially follows a simple exponential decay. After prolonged illumination (>500 h), devices with an organic HTL fail catastrophically due to a precipitous drop in photocurrent. Based on evidence for pinhole-induced degradation observed in photocurrent maps, we propose a nucleation and island growth mechanism and a model for the photocurrent behavior employing a modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Devices that do not contain an HTL appear to degrade by a mechanism other than pinhole ingress resulting in a more uniform degradation of the photocurrent across the active area.

Photoelectrochemical Sensor for the Rapid Detection of in Situ DNA Damage Induced by Enzyme-Catalyzed Fenton Reaction

Photoelectrochemical sensors were developed for the rapid detection of oxidative DNA damage induced by Fe2+ and H2O2 generated in situ by the enzyme glucose oxidase. The sensor is a multilayer film prepared on a tin oxide nanoparticle electrode by layer-by-layer self-assembly and is composed of separate layers of a photoelectrochemical indicator, DNA, and glucose oxidase. The enzyme catalyzes the formation of H2O2 in the presence of glucose, which then reacts with Fe2+ and generates hydroxyl radicals by the Fenton reaction. The radicals attack DNA in the sensor film, mimicking metal toxicity pathways in vivo. The DNA damage is detected by monitoring the change of photocurrent of the indicator. In one sensor configuration, a DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine), was employed as the photoelectrochemical indicator. The damaged DNA on the sensor bound less Ru(bpy)2(dppz)2+ than the intact DNA, resulting in a drop in photocurrent. In another configuration, ruthenium tris(bipyridine) was used as the indicator and was immobilized on the electrode underneath the DNA layer. After oxidative damage, the DNA bases became more accessible to photoelectrochemical oxidation than the intact DNA, producing a rise in photocurrent. Both sensors displayed substantial photocurrent change after incubation in Fe2+/glucose in a time-dependent manner. And the detection limit of the first sensor was less than 50 microM. The results were verified independently by fluorescence and gel electrophoresis experiments. When fully integrated with cell-mimicking components, the photoelectrochemical DNA sensor has the potential to become a rapid, high-throughput, and inexpensive screening tool for chemical genotoxicity.

Photoelectrochemical DNA Sensor for the Rapid Detection of DNA Damage Induced by Styrene Oxide and the Fenton Reaction

Rapid and sensitive detection methods are in urgent demand for the screening of an overwhelming number of existing and new chemicals as potential DNA-damaging agents. In this study, two photoelectrochemistry-based DNA sensor configurations were employed in the detection of DNA damage caused by styrene oxide and Fe2+/H2O2. The organic compound and heavy metal represent genotoxic chemicals possessing two major damaging mechanisms, DNA adduct formation and DNA oxidation. In the first sensor configuration, a ruthenium tris(bipyridine)-labeled avidin film and a double-stranded calf thymus DNA (ds-DNA) film were assembled successively on tin oxide nanoparticle film electrodes. Photogenerated Ru(III) oxidized guanidine and adenosine bases in DNA and gave rise to photocurrent. DNA damage was detected after the reaction of the DNA film with either styrene oxide or Fe2+/H2O2, which exposed more DNA bases for photooxidation and resulted in increased photocurrent. In the second configuration, an unlabeled avidin film and a ds-DNA film were assembled on the semiconductor electrode. A DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a: 2',3'-c]phenazine), was employed as the photoelectrochemical signal reporter. After the chemical reaction with the damaging agents, the DNA film bound less Ru(bpy)2(dppz)2+, accompanied by a drop in photocurrent. Both sensors were used to follow the reaction course in styrene oxide and Fenton reagents and produced similar results. According to the data, damage of the DNA film was complete in 1 h in Fenton reagents and in 3 h in styrene oxide. In addition, the Fenton reaction induced much more severe damage than styrene oxide. The results demonstrate for the first time that the photoelectrochemical DNA sensor can detect both DNA adduct formation and DNA oxidation. It has the potential of becoming a screening tool for the rapid assessment of the genotoxicity of existing and new chemicals.

Insight Into Electric Potential Distribution Within Mesoporous Titanium Dioxide Films

Charge transport and potential distribution in mesoporous semiconductor films operating in an electrolyte, especially those composed of TiO2 nanoparticles, are still the subject of wide debate. Herein we describe a series of experiments, performed under band-gap energy illumination of nanostructured TiO2 films, intended to shed new light on the actual electric potential profile across such three-dimensional electrode. Our approach stems from quite a general observation that addition of various electron acceptors to a solution containing an efficient hole scavenger (e.g., methanol, formic acid) results in a marked drop of the maximum photocurrent at the mesoporous TiO2 film electrodes whatever the applied anodic bias might be. We have chosen an electron acceptor, MV2+ dication, which-due to its negative redox potential, more negative than that of the bottom of conduction band of TiO2 in acidic media - causes a drop of the photooxidation current only in alkaline but not in acidic solutions of hole scavengers. Measurements of the incident photon-to-current efficiencies as a function of wavelength show that the drop of the photocurrent after the MV2+ addition, observed in alkaline formate solution extends practically over the whole range of wavelengths. As the optical penetration depth in TiO2 for the wavelengths close to its band edge is expected to match approximately the chosen film thickness, we can conclude that major part of the electric potential drop in the TiO2 electrode occurs actually close to the back contact.

Photoelectrochemical Studies on Nanocrystalline Hematite Films

Nanocrystalline hematite films supported on conducting glass have been prepared from colloidal Fe{sub 2}O{sub 3} particles, giving a roughness factor of about 30. The current-potential characteristic showed an abnormal drop in photocurrent under reverse polarization. Photocurrent yields are low over the entire potential range. In the presence of iodide the abnormal drop was removed and the photocurrent yield increased. Action spectra were determined by illumination from the electrolyte side and the conducting glass support, respectively. The incident photon-to-current conversion efficiencies (IPCE) is a factor of 100 higher in the former compared to the latter case if water is used as a hole scavenger. In the presence of iodide this ratio is diminished 4-fold due to an increase in the IPCE value measured by illumination from the electrolyte side. The poor photocurrent yields observed are due to charge carrier recombination. Recombination at surface sites can be partially intercepted by adsorbed iodide. 9 refs., 9 figs.

Effect of electron quenchers on the thermalization range parameter and ionization quantum yield of photoelectrons produced by vacuum-UV irradiation of 2,2-dimethylbutane and 2,2,4-trimethylpentane: comparison with .gamma.-ray irradiation

The ionization quantum yield and thermalization range parameter of photoelectrons were extracted by a three-parameter adjustment from experimental curves of the photocurrent as a function of an applied electric field. Results were obtained at VUV photon energies of 0.5-2 eV above the threeshold energy in 2,2-dimethyl butane and at 10.03 eV in 2,2,4-trimethylpentane. These values were compared to those obtained when electron quenchers were added to the solvent. The same technique was carried out when excess electrons were produced by Co 60 γ-ray irradiation. With VUV irradiation, the drop in photocurrent arises mainly from the drop in the ionization quantum yield, whereas with γ-rays it is rather the thermalization distance that is affected