Photoelectrochemical Electrode Research Articles

Enhanced photoelectrochemical performance of atomic layer deposited Hf-doped ZnO

Generation of hydrogen using photoelectrochemical (PEC) water splitting has attracted researchers for the last two decades. Several materials have been utilized as a photoanode in a water splitting cell, including ZnO due to its abundance, low production cost and suitable electronic structure. Most research attempts focused on doping ZnO to tailor its properties for a specific application. In this work, atomic layer deposition (ALD) was used to precisely dope ZnO with hafnium (Hf) in order to enhance its PEC performance. The resultant doped materials showed a significant improvement in PEC efficiency compared to pristine ZnO, which is linked directly to Hf introduction revealed by detailed optical, structural and electrical analyses. The photocurrent obtained in the best performing Hf-doped sample (0.75 wt% Hf) was roughly threefold higher compared to the undoped ZnO. Electrochemical impedance spectroscopy (EIS) and open-circuit potential-decay (OCPD) measurements confirmed suppression in photocarriers' surface recombination in the doped films, which led to a more efficient PEC water oxidation. The enhanced PEC performance of Hf-doped ZnO and effectiveness of the used metal dopant are credited to the synergistic optimization of chemical composition, which enhanced the electrical, structural including morphological, and optical properties of the final material, making Hf-doping an attractive candidate for novel PEC electrodes.

Freeing the Polarons to Facilitate Charge Transport in BiVO4 from Oxygen Vacancies with an Oxidative 2D Precursor.

The BiVO4 photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost-efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO4 photoanodes by using a highly oxidative two-dimensional (2D) precursor, bismuth oxyiodate (BiOIO3 ), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO4 and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO4 . This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC-PV solar fuel devices.

Freeing the Polarons to Facilitate Charge Transport in BiVO4 from Oxygen Vacancies with an Oxidative 2D Precursor

AbstractThe BiVO4 photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost‐efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO4 photoanodes by using a highly oxidative two‐dimensional (2D) precursor, bismuth oxyiodate (BiOIO3), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO4 and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO4. This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC‐PV solar fuel devices.

Robust Photoelectrochemical Oxygen Evolution with N, Fe-CoS2 Nanorod Arrays.

Photoelectrochemical water splitting is a promising approach to enhance the efficiency of water splitting. However, it is still challenging to develop an efficient oxygen evolution reaction (OER) electrocatalyst that can be coupled with light due to inefficient light utilization. Here, we demonstrate that N, Fe-co-doped CoS2 (N, Fe-CoS2) nanorod arrays can act as a highly efficient photo-coupled electrochemical OER catalyst. In dark conditions, the N, Fe-doped CoS2 on self-supported stainless steel (SS) mesh shows a small OER overpotential (215 mV) at a current density of 10 mA cm-2, a reduced Tafel slope (43.2 mV dec-1), and negligible activity decay after 10 000 cycles. Upon visible-NIR light illumination, the N, Fe-doped anode exhibits superior photoelectrochemical performance because of the enhanced photoresponse, excellent light harvesting ability and promoted interfacial kinetics of charge separation. Our well-designed photoelectrochemical OER electrode can not only serve as a light absorption semiconductor but also the active catalytic sites for the OER reaction; the electrode composed of the single phase can efficiently avoid photocarrier recombination at the grain boundary. This study provides an insight into photoanode synthesis for photoelectrochemical OER and offers guidance on the future electrocatalyst design.

CdS quantum dots/Au nanoparticles/ZnO nanowire array for self-powered photoelectrochemical detection of Escherichia coli O157:H7

In this paper, the hydrothermally grown ZnO nanowire array (NWs) was modified by Au nanoparticles (NPs) and CdS quantum dots (QDs) to construct a high-performance photoelectrochemical (PEC) electrode. The aligned ZnO NWs, which decorated Au NPs and CdS QDs have the effective light absorption range from UV to visible region. This hybrid structure provided a self-powered PEC electrode with a favorable energy-band configuration for fast charge separation and transportation. Meanwhile, the Au NPs and CdS QDs also made increase of the surface area to improve the immobilization of the analytes. After assembling aptamer as recognition element, this composite nanoarray was further developed as a self-powered PEC biosensor by synergizing above multiple enhancement factors. The PEC aptasensor exhibited a rapid response in a wide linear range of 10–107 CFU/mL with the detection limit as low as 1.125 CFU/mL to Escherichia coli O157:H7 (E. coli O157:H7). This approach would offer an alternative PEC transduction for fast environment monitoring and clinical diagnosis related to pathogenic bacteria.

Current progress in Cu 2 BaSn(S, Se) 4 thin film

The inexhaustible solar energy is regarded as a candidate to displace the diminishing fossil fuel resources and reduce greenhouse emissions. Photovoltaic and photoelectrochemical process provide a pathway for directly converting solar light into electricity power and clean hydrogen energy. It is significant to explore a promising and abundant material for utilization the solar energy. Cu2ZnSn(S, Se)4 has a direct bandgap, suitable bandgap (1.0–1.5 eV), high absorption efficient, which has been used as a absorbed layer in thin film solar cell achieving a power conversion efficiency of 12.6% and a photocathode gaining a photocurrent density of 13 mA/cm2. However, the close ionic sizes between Cu+ (0.91 A) and Zn2+ (0.88 A) in Cu2ZnSn(S, Se)4 leads to the antisite disorder and associated band tailing, and limits the performance improvement. According to the theoretical calculation, substituted the Cu or Zn with the large radius atom can efficiently reduce the antisite disorder. The large Ba substitutes Zn in Cu2ZnSn(S, Se)4 forming Cu2BaSn(S, Se)4, which can suppress the antisite defects. According to the Schockley-Queisser theory, the photocurrent density of the photocathode based on bare Cu2BaSn(S, Se)4 thin film is 14.5 mA/cm2 under AM 1.5G illumination and the maximum power conversion efficiency of the thin film solar cell based on a pure Cu2BaSn(S, Se)4 ( E g =2.0 eV) is 22%. Therefore, it has attracted a great deal of attentions in Cu2BaSn(S, Se)4 thin films. From a special perspective, this review summarizes the progress of Cu2BaSn(S, Se)4 thin films in recent years. First, we outline the physical properties of Cu2BaSn(S, Se)4. According to the experimental and theoretical results, it reveals that the Cu2BaSn(S, Se)4 has less cationic disordering and associated band tailing than that in Cu2ZnSn(S, Se)4, which indicates the Cu2BaSn(S, Se)4 will be a promising candidate to Cu2ZnSn(S, Se)4. Moreover, the Cu2BaSn(S, Se)4 has two crystal structures and the phase transition from trigonal ( P3 1 ) to orthorhombic ( Ama 2 ) with a increasing Se/(S+Se) ratio. Due to the phase transition, the bandgap decreases with an increasing Se/(S+Se) ratio, achieved a lowest bandgap, then the bandgap increases with an increasing Se/(S+Se) ratio. In other word, the bandgap of Cu2BaSn(S, Se)4 can be controlled by adjusted the Se/(S+Se) ratio. Meanwhile, the Cu2BaSn(S, Se)4 shows a direct bandgap which is beneficial to the performance of photoelectrical devices. Therefore, Cu2ZnSn(S, Se)4 will be an excellent semiconductor material in photoelectrical field. Second, the methods for preparing Cu2BaSn(S, Se)4 thin films is a hot topic. Here, we classified the methods for growing Cu2BaSn(S, Se)4 thin films to physical deposition approach and chemical solution approach. The advantages and disadvantages of the method are summarized in this review. It is worth to noting, the morphology of the thin films is related with the composition of Cu2BaSn(S, Se)4. Third, we summarized the application field of Cu2BaSn(S, Se)4 thin films. For example, the solar cells based on Cu2BaSn(S, Se)4 get a highest power efficiency conversion of 5.2% (total area 0.425 cm2) and the Cu2BaSn(S, Se)4 applied in photoelectrochemical electrode achieved a current-density of 12.08 mA/cm2 at 0 V vs. reversible hydrogen electrode. Finally, we conclude the prospective and challenge in the future.

Nanostructured boron doped diamond enhancing the photoelectrochemical performance of TiO2/BDD heterojunction anodes

Photoelectrochemical (PEC) water splitting provides a promising way for development of sustainable methods of hydrogen generation and water treatment without chemicals. In this paper, we report on the development of a unique PEC electrode consisting of nanostructured p-type boron doped diamond (BDD) layers covered by n-type TiO2 thin film. The influence of nanostructuring and boron doping level, as well as the thickness of TiO2 film on PEC properties, was investigated. As-grown and plasma-nanostructured BDD thin films with two doping levels (B/C = 1 000 ppm and 10 000 ppm in the gas phase) were utilized as substrates for deposition of 20, 100 and 500 nm TiO2 layers using RF magnetron sputtering. The highest photocurrent (60 μA/cm2 and 3.2 mA/cm2 at 0 and 2 V vs Ag/AgCl respectively) was obtained in the case of structured BDD electrode with B/C ratio in gas phase 1 000 ppm, covered by a 500 nm thick TiO2 layer. The experiment confirmed the favorable impact of both nanostructuring and p-n junction, contributing to the hole injection.

Photoelectrochemical sensing of hydrogen peroxide using TiO2 nanotube arrays decorated with RGO/CdS

Photoelectrochemical (PEC) sensing has great potential in the field of analytical chemistry due to its low cost, high sensitivity, simple equipment, and easy miniaturization. The design and construct of semiconductor materials used for photoanode with superior optoelectronic properties and excellent photoelectrochemical activity are vital for the realization of effective detection toward the analytes. In this paper, RGO/CdS–TiO2 (RGO, reduced graphene oxide) photoanodes were fabricated by two-step electrochemical anodic oxidation to form highly ordered TiO2 nanotube arrays (TNTs) firstly, then modified with RGO/CdS prepared by cyclic voltammetric electrodeposition. The resultant photoanodes were characterized by scanning electron microscope, X-ray diffraction, and UV–vis diffuse reflectance spectrophotometer as well as photoelectrochemical tests. The fabricated RGO/CdS(5)-TNTs PEC electrode exhibited good sensing for H2O2 with a 5-order wide linear range of 0.1 μM–10 mM and low detection limit of 0.002 μM. The obtained excellent PEC performance can be attributed to the synergistic effect of TNTs having high surface area and one-dimensional (1D) transport properties combined with RGO/CdS as electron collectors and transporters, offering efficient charge carrier separation and good electron transport.

Photoelectrochemical Applications of SrNbO2n Thin Films Synthesized Via a Two-Step Process at Reduced Temperatures

Oxynitride materials often exhibit a perovskite structure in which the oxygen and nitrogen occupy the same lattice sites. Such oxynitride perovskites, for example SrNbO2N with a favorable bandgap of 1.8 eV for tandems, are studied as photoanodes for photoelectrochemical (PEC) water splitting applications. These photoanodes are an essential component to the OER side of the water splitting cell. In literature, SrNbO2N PEC electrodes are often prepared using ammonolysis of deposited Sr2Nb2O7 oxide at high temperatures. To transform Sr2Nb2O7 into SrNbO2N, the ammonolysis temperature has to reach over 900 °C for the time period of minutes to hours. This often leads to intermixing and reactions between the layers in the thin film device stack. In this presentation, PEC measurements of photocurrent are presented for SrNbO2N on n-Si in ferro/ferricyanide, at varying thicknesses and Sr:Nb ratios. For the deposition of these films, we show a two-step low-temperature synthesis approach to SrNbO2N on Si for tandem PEC applications. In the first step, combinatorial RF sputtering (sometimes with a nitrogen plasma cracker) is used to deposit Sr1+yNb1-yO2-xN1+x at ambient temperature with varying Sr:Nb and O:N ratios. In the second step, these films are annealed in a nitrogen atmosphere using Rapid Thermal Annealing (RTA). We surveyed a series of temperatures and times to determine the minimum temperatures needed to obtain highly crystalline SrNbO2N for PEC applications without reaction with the Si substrate. The resulting film morphology, crystalline structure, and other characterization across the combinatorial spread was characterized. Photocurrent was observed in these materials over a range of varying thicknesses and compositions using a solar simulator and a standard 3-electrode setup.

Toward Efficient Charge Collection and Light Absorption: A Perspective of Light Trapping for Advanced Photoelectrodes

Sun light driven water splitting is a promising method to produce hydrogen in a clean and sustainable way. The photoelectrochemical (PEC) cell is highly desirable among various solar water splitting techniques as it is potentially robust, cost-effective, and durable. However, arguably the biggest problem to date for sustainable photoelectrodes currently under intensive study is that the carrier diffusion length is always much shorter than the optical length, thus seriously limiting the cell’s power conversion efficiency. Light trapping strategies could enable multiple passes of light through the absorber to enhance the absorption while still keeping the absorber thickness below the transport limitation. Herein we briefly review recent developments of light management strategies in PEC electrodes by focusing on the relevant concepts, materials, and structures. In addition, current shortcomings and outlooks will be discussed in the hope that more attention of the research community will be drawn to this pro...

Realizing super-long Cu2O nanowires arrays for high-efficient water splitting applications with a convenient approach

Nanowire (NW) structures is an alternative candidate for constructing the next generation photoelectrochemical water splitting system, due to the outstanding optical and electrical properties. NW photoelectrodes comparing to traditional semiconductor photoelectrodes shows the comparatively shorter transfer distance of photo-induced carriers and the increase amount of the surface reaction sites, which is beneficial for lowering the recombination probability of charge carriers and improving their photoelectrochemical (PEC) performances. Here, we demonstrate for the first time that super-long Cu2O NWs, more than 4.5 μm, with highly efficient water splitting performance, were synthesized using a cost-effective anodic alumina oxide (AAO) template method. In comparison with the photocathode with planar Cu2O films, the photocathode with Cu2O NWs demonstrates a significant enhancement in photocurrent, from –1.00 to –2.75 mA/cm2 at –0.8 V versus Ag/AgCl. After optimization of the photoelectrochemical electrode through depositing Pt NPs with atomic layer deposition (ALD) technology on the Cu2O NWs, the plateau of photocurrent has been enlarged to –7 mA/cm2 with the external quantum yield up to 34% at 410 nm. This study suggests that the photoelectrode based on Cu2O NWs is a hopeful system for establishing high-efficiency water splitting system under visible light.

Hierarchical porous ZnO films synthesized by sol–gel method using triethylenetetramine stabilizer

Hierarchically porous ZnO films are synthesized through a novel sol–gel method using triethylenetetramine (TETA) as a stabilizer. Highly crystalline hierarchical porous ZnO thin films with different pore sizes are synthesized in various reaction mediums by altering solvents, sol concentration, the molar ratio of TETA to zinc acetate dehydrate (ZAD), and withdrawal speed. FESEM images show the formation of a hierarchical porous film with spherical and agglomerated particles in the optimized condition of ethanol as the solvent, sol concentration of 0.2 M, the molar ratio of [TETA]:[ZAD] = 2, and withdrawal speed of 30 mm/min. Increasing the solvent chain length, increasing the sol concentration, decreasing the TETA content, or increasing the withdrawal speed increases the particle size and porosity. XRD data, UV–Vis, and PL spectroscopy indicate high crystallinity with appropriate optical properties for the optimized sample. The hierarchical porous ZnO film synthesized by this method can be utilized as a photoelectrochemical electrode in devices such as photocatalysis and photoelectrochemical water splitting.

Concatenated Catalytic Hairpin Assembly/Hyperbranched Hybridization Chain Reaction Based Enzyme-Free Signal Amplification for the Sensitive Photoelectrochemical Detection of Human Telomerase RNA.

Human telomerase RNA (hTR), an important biomarker for cancer diagnosis, is the template for the synthesis of telomeric DNA repeats and is found to be 7-fold overexpressed in tumor cells. Herein, we present a photoelectrochemical (PEC) biosensor for hTR detection coupled with a novel amplification strategy based on cascades of catalytic hairpin assembly (CHA) and hyperbranched hybridization chain reaction (HB-HCR). At the electrode surface, thiolated hairpin 1 probes were immobilized on deposited CdS nanoparticles via a Cd-S bond. In the presence of target hTR, a CHA reaction was triggered and the exposing of trigger1 could further initiate an HB-HCR reaction to form abundant hemin/G-quadruplex DNAzymes containing dendritic DNA structure. The DNAzymes' catalytic precipitation of 4-chloro-1-naphthol (4-CN) by H2O2 subsequently took place on the surface of the PEC electrode and efficiently suppressed the photocurrent output. Therefore, the change of photocurrent response had a positive linear relationship with logarithmic value of hTR concentration varying from 200 fM to 20.0 nM with a limit of detection (LOD) of 17.0 fM. The LOD for CHA/HB-HCR was about 8.8-fold lower than that of CHA/linear-branched HCR (CHA/LB-HCR) and 547-fold lower than that of CHA. By coupling the feature of high signal amplification capacity for DNA nanotechnology, a prominently stable, reproducible, and selective PEC biosensor was successfully constructed and applied in hTR detection.

Sn Doping into Hematite Nanorods for High-Performance Photoelectrochemical Water Splitting

Photoelectrochemical water splitting is of great attention due to its environmental friendly generation of clean fuels. Hematite (α-Fe2O3) is considered one of the promising candidates due to its intrinsic properties for the high performance photoelectrochemical electrode such as favourable bandgap (2.0–2.2 eV), a suitable energy band position, non-toxicity, low cost, and excellent chemical stability. Herein, we report about Sn-doped hematite nanorods and their implementation as photoanodes for photoelectrochemical water splitting. We provide the simple but efficient route to incorporate the Sn into the hematite without structural damage in the nanostructure and scrutinize the effect of Sn dopant on the photoelectrochemical activity of the hematite. By the two-step heat-treatment process, Sn can be successfully incorporated into the hematite, which reveals the enhanced photoelectrochemical responses compared with undoped hematite. We elaborate the effect of Sn dopant in the hematite on the photoelectrochemical activities, thereby the optimum concentration of Sn dopant can be suggested. In addition, the catalyst layer of the cobalt phosphate is introduced to further increase the photoelectrochemical performance of Sn-doped hematite nanorods.

Specific electron-transfer and surface plasmon resonance integrated boosting visible-light photoelectrochemical sensor for 4-chlorophenol

Emerging analytical technologies are being developed to provide advanced methods for monitoring 4-chlorophenol (4-CP) in the environment. Herein, a label-free, sensitive, and rapid photoelectrochemical (PEC) 4-CP detection system was constructed based on ternary composites of Ag nanoparticles, graphitic carbon nitride (GCN) and carbon spheres (CS) (Ag/GCN/CS). The proposed ternary composites were synthesized by a simple hydrothermal method. In this process, ascorbic acid (AA) played a crucial role in reducing Ag+ to metallic Ag, and provided a carbon source for CS. Due to synergistic promotion by the surface plasmon resonance (SPR) effect of Ag nanoparticles and electron-transfer behavior of CS, the ternary composites exhibited a broad visible light response and fast charge transfer, leading to a tremendously enhanced PEC response. Based on the promotion of the PEC response, a PEC sensor for 4-CP was designed by detecting the photocurrent signals of the PEC electrode after adding 4-CP to solution. Under optimal conditions, the PEC sensor exhibited a wide linear range for 4-CP from 16 to 1104ngmL−1, with a limit of detection (LOD) of 5.33ngmL−1. In particular, the present work may assistance in better understanding the synergistic effect between the SPR effect of Ag nanoparticles and electron-transfer properties of CS. The results can also be applied to other PEC and photocatalytic systems in conjunction with high-performance photoactive materials.

Transport of photo-generated electrons and holes in TiO2/CdS/CdSe core-shell nanorod structure toward high performance photoelectrochemical cell electrode

The novel photoelectrochemical cell with very high photocurrent density (>35 mA/cm2) is demonstrated by nanoscale architecturing of TiO2/CdS/CdSe multi-core-shell nanorods. While dimensions of constituting layers, i.e. TiO2 nanorod templates, CdS, and CdSe shell layers, are optimized by thorough investigation of optical and photoelectrochemical responses of each layer, high light absorption through the nanorod geometry and facile transport of the photo-generated electrons and holes along the high conduction path of CdSe and CdS result in the high photoelectrochemical performances. In addition, the microscopic model for the electron and hole transport in the core-shell nanorod is elaborated using the energy band diagram. The demonstration of the high performance PEC electrode as well as the platform to optimize PEC electrodes are highlighted in the current work.

Photoelectrochemical determination of the activity of M.SssI methyltransferase, and a method for inhibitor screening.

A photoelectrochemical (PEC) method is describedfor the determination ofthe activity of M.SssI methyltransferase (MTase). The assay relies on enzyme-linkage reactions and a DNA intercalator Ru(bpy)2(dppz)2+ (where bpy is 2,2'-bipyridine, and dppz is dipyrido[3,2-a:2',3'-c]phenazine) which both serves as a PEC signal. The PEC electrode was obtained by immobilizing 5'-amino modified DNA strands (containing the methylation recognition site 5'-CCGG-3') on a polyethylenimine (PEI) coated ITO/SnO2 electrode with glutaraldehyde as crosslinking agent. In the presence of MTase and S-adenosyl-L-methionine, the 5'-CCGG-3' sequence in the DNA on the electrode is methylated. This protects the DNA strands from the shear of the methylation-sensitive restriction endonuclease HpaII. Consequently, more intact DNA strands remain on the surface of the electrode, providing more sites for Ru(bpy)2(dppz)2+ binding which in turn results in a high PEC response. The result demonstrates that the photocurrent increases linearly with the activity of MTase from 5 to 80U·mL-1, and the limit of detection is 0.45U·mL-1. The other MTases does not enhance the photocurrent, suggesting good selectivity of the assay. The method was also applied to rapid evaluate and screen the inhibitors of MTase. This strategy can be utilized to determinate the activity of other DNA MTases with specific DNA sequence. Graphical abstract Schematic presentation of a photoelectrochemical assay based on enzyme-linkage reactions and a photo electrochemical probe combined with the oxalic acid involved cyclic amplification system for the determination of methyltransferase activity.

Synergistic effect of silane and graphene oxide for enhancing the photoelectrochemical water oxidation performance of WO3NS arrays

Photoelectrochemical (PEC) water splitting using semiconductor-based photoelectrodes is a promising approach for renewable solar fuel production. One of the biggest challenge is that semiconductor electrodes suffer from lower utilization of photogenerated-carriers and sluggish surface water oxidation reaction. Herein, we report that a novel composite photoelectrode based on silane molecule/graphene oxide being modified on the surface of well-aligned WO3 nanosheet arrays (WO3 NS/Silane/GO), efficiently harvests holes from the semiconductor and provides more reactive surface for water oxidation owing to the synergistic effect. The results demonstrate that 1.8 times photocurrent enhancement of WO3 NS/Silane/GO electrode (1.25 mA cm−2 at 1.23 V vs RHE) can be obtained compared to that of the pristine WO3 NS (0.69 mA cm−2) electrode, and it is even much higher than the photocurrent sum of WO3 NS/Silane and WO3 NS/GO electrodes. The remarkably enhanced PEC performance mainly stems from the induced external electric field (EEF) created by silane acting as hole-storage spots and the efficient carrier migration channel provided by GO, dramatically suppress the recombination of photogenerated carriers. As a result, the synergistic effect of silane and GO leads to a steady and continuous hole-transfer pathway, and promotes water oxidation kinetic by the increased reactive site quantity and activity. This study indicates that it can be a general design strategy for the preparation of efficient PEC electrodes in solar water splitting.

Conformal growth of few-layer MoS2 flakes on closely-packed TiO2 nanowires and their enhanced photoelectrochemical reactivity

Vertically-standing, few-layer MoS2 flakes were uniformly and conformally grown on closely-packed TiO2 nanowire substrates using metal-organic chemical vapor deposition. The TiO2/MoS2 heterostructures exhibited remarkably improved photoelectrochemical (PEC) performance and long-term stability owing to enhanced photogenerated electron–hole separation and transfer properties across the heterojunction. Due to the built-in heterojunction potential, the onset potential of TiO2/MoS2 heterostructures was cathodic-shifted to −0.3 V, thereby resulting in maximum PEC reactivity at approximately zero potential. In contrast, MoS2 flakes on fluorine-doped tin oxide substrates exhibited an onset potential of approximately 0.3 V. Furthermore, PEC performance was critically affected by the size of the vertically-standing MoS2 flakes, indicating that controlled conformal growth of MoS2 flakes on appropriate nanostructures is essential to exploit these nanostructures as efficient, non-toxic, inexpensive, and earth-abundant PEC electrodes.

Organic Photo‐Electrochemical Transistor‐Based Biosensor: A Proof‐of‐Concept Study toward Highly Sensitive DNA Detection

Organic bioelectronics have shown promising applications for various sensing purposes due to their significant advantages in term of high flexibility, portability, easy fabrication, and biocompatibility. Here, a new type of organic device, organic photo-electrochemical transistor (OPECT), is reported, which is the combination of an organic electrochemical transistor and a photo-electrochemical gate electrode modified with CdS quantum dots (QDs). Thanks to the inherent amplification function of the transistor, the OPECT-based biosensor exhibits much higher sensitivity than that of a traditional biosensor. The sensing mechanism of the OPECT is attributed to the charge transfer between the photosensitive semiconductor CdS QDs and the gate electrode. In an OPECT-based DNA sensor, target DNA is labeled with Au nanoparticles (NPs) and captured on the gate electrode, which can influence the charge transfer on the gate caused by the exciton-plasmon interactions between CdS QDs and Au NPs. Consequently, a highly sensitive and selective DNA sensor with a detection limit of around 1 × 10-15 m is realized. It is expected that OPECTs can be developed as a high-performance platform for numerous biological detections in the future.