High Photoelectrochemical Performance Research Articles

Core-shell nanorods film of p-CuZnS/n-TiO2 with boosting interfacial charge separation for sensitive photoelectrochemical photodetector

Copper zinc sulphide (CZS) due to high conductivity, fast photoresponse and good stability has attracted rising attention in optoelectronic field. Constructing heterojunctions with rational energy bands alignment can accelerate carrier separation to improve the performance of CZS-based photoelectric device. Herein, p-CZS/n-TiO2 core-shell nanorods heterojunction film was successfully fabricated for the first time. CZS nanoparticles (NPs) were directly loaded on the surface of TiO2 nanorods (NRs) through a simple chemical bath deposition. Photoelectrochemical (PEC) photodetector based on CZS/TiO2 composite film was designed and interfacial charge kinetics has also been investigated. The CZS/TiO2 PEC device exhibits fast response speed of 95/56 ms, high responsivity of 7.1 mA W-1 and detectivity of 5.6 × 1012 Jones at a bias voltage of 1 V. The light on/off ratio of self-powered CZS/TiO2 PEC device achieves 5.6 × 103, nearly 30.4 times higher than bare CZS PEC device. Furthermore, the photodetection performance of the CZS/TiO2 PEC device can be effectively regulated by light power density and environment conditions, promoting its adaptability in multifarious practical applications. The findings suggest that CZS/TiO2 heterostructure film devices have great potential for high-performance and energy-efficient PEC photodetectors.

Progress on Si‐based photoelectrodes for industrial production of green hydrogen by solar‐driven water splitting

AbstractSolar power has been regarded as the ultimate green‐energy source because of its inexhaustibility and eco‐friendliness. The solar‐driven water‐splitting technology for green hydrogen production is considered to be one of effective ways for solar energy harvesting and storage, which may provide solutions for the energy crisis and environmental issues. In the past decades, great progress has been achieved in this area. Photoelectrochemical (PEC) water splitting is especially promising for the production of solar fuels because of expected large‐scale industrial application. Silicon (Si), as an ideal candidate for the photoelectrode, is the most suitable material for the PEC device in industrial photocatalytic water splitting because of its abundance, mature fabrication technology, and suitable band gap. Here, we give a systematic review on the recent progress for Si‐based photoelectrodes for water splitting with a focus on the industrial application. Particularly, the strategies, such as band‐alignment control, morphology design, and surface engineering, are summarized to enhance the PEC performance and durability for practical application. Furthermore, the perspective for the design of commercial Si‐based PEC devices with high PEC performance, long‐term stability, large‐size, and low cost are given at the end, which shall guide the development of PEC water splitting for industrial application.

Incorporation of Perovskite Quantum Dot Passivated by Ultrathin SiO2 on WO3 for Boosting Solar Water Splitting

Photoelectrochemical (PEC) water splitting stands as a promising strategy for sustainable hydrogen (H2) production, driven by renewable solar energy conversion. However, the lack of highly efficient photoanodes has constrained high-performance PEC water splitting due to poor light absorption, charge transportation, and sluggish catalytic kinetics of the oxygen evolution reaction (OER). Extensive efforts have focused on developing transition metal oxide (TMO)-based semiconductors as highly efficient photoanodes, owing to their favorable band structure, eco-friendliness, abundance on Earth, and good stability in aqueous environments. However, TMO-based materials encounter challenges such as undesired rapid charge recombination, insufficient surficial reaction kinetics, and low light absorption coefficients. To address these limitations, a systematic design of heterostructured TMO-based photoanodes has been considered a potential strategy. On the other hand, lead halide perovskite quantum dots (PQDs), including all-inorganic CsPbX3 (where X represents one of the halogens), have been extensively investigated for optical energy conversion systems due to their high absorption coefficient, defect tolerance, moderate carrier mobility, and cost-effective preparation. However, the significant instability of PQDs against polar solvents, even under anodic reaction conditions, leading to critical self-oxidation and deformation, has hindered their practical application in solar water splitting. To overcome these restrictions, numerous investigations have explored methods such as encapsulation, ligand modification, and surface engineering to prevent PQD decomposition and modulate charge dynamics based on interfacial characteristics. Constructing a core-shell structure for PQDs with an oxide-based passivation layer has been proposed as an efficient approach to protect PQDs from water molecules and tune the dynamics of photogenerated charges. However, charge extraction from PQDs could be hindered by the high dielectric properties of the oxide-based passivation layer. Thus, a conformal and sub-nanometer scale introduction of the passivation layer can facilitate successful PQD incorporation on TMO-based photoanodes. In this study, we propose a rational heterostructured photoanode for boosting solar water splitting, and we report for the first time that PQDs exposed to an aqueous electrolyte demonstrate excellent stability even under oxidation reaction conditions. We demonstrate a core-shell structured CsPbBr3 PQDs with an ultrathin SiO2 passivation layer (CS-PQDs), less than 1 nm thick, incorporated on a WO3 nanoflake photoanode (CS-PQD/WO3). The SiO2 passivation prevents undesirable recombination of CsPbBr3, and the extraction of photogenerated charges is prominently promoted, indicating not only improved stability of CsPbBr3 PQDs but also manipulated charge dynamics of the CS-PQD/WO3 photoanode. The heterostructured photoanode achieves a 2.2-fold improvement in photocurrent density at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun illumination, attributed to enhanced interfacial catalytic kinetics with improved light harvesting and efficient charge migration facilitated by the built-in electric field. Additionally, the CS-PQD/WO3 exhibits moderate durability over 12 hours and excellent Faraday efficiency for H2 production through solar water splitting. This study provides insight into the rational heterostructure of PQDs and TMO, in the presence of an ultrathin oxide passivating layer, raising the potential of perovskite-based nanomaterials as a facilitator for manipulating photogenerated charge dynamics for solar energy conversion in aqueous media.

Ligand-free Cs2PdBr6 perovskite microcrystals with narrow bandgap and high photoelectrochemical performance in aqueous solution

The exploration of efficient lead-free perovskite photoelectric active materials to develop high-performance photoelectrochemical (PEC) systems in aqueous solution is crucial to expand their PEC applications. Herein, we successfully constructed a high-performance PEC platform using ligand-free perovskite Cs2PdBr6 microcrystals (MCs) as the photoactive substance. The Cs2PdBr6 MCs showed narrow bandgap, wide absorption range, high electronic mobility and good stability in aqueous solutions. Particularly, the Cs2PdBr6 MCs exhibited an excellent photoresponse, the photocurrent density could reach as high as 98 μA/cm2 under 10.18 mW/cm2 light irradiation in the absence of other electron acceptors. In addition of the extremely wide range of response wavelength, wide pH range and accelerated interfacial carrier transfer, the Cs2PdBr6 MCs demonstrated the significant potential of photocathode active material for applications in PEC sensors and optoelectronic devices. Therefore, this work indicates that Cs2PdBr6 MCs design is a highly efficient way to solve the intrinsic issues of perovskite material, predicting a promising strategy for high performance PEC application in aqueous ambience.

Systematic Constructing FeOCl/BiVO4 Hetero-Interfacial Hybrid Photoanodes for Efficient Photoelectrochemical Water Splitting.

Bismuth vanadate (BiVO4), as a promising photoanode for photoelectrochemical (PEC) water splitting, suffers from poor charge separation efficiency and light absorption efficiency. Herein, iron oxychloride (FeOCl) is introduced as a novel cocatalyst simply grafted on BiVO4 to construct an integrated photoanode, enhancing PEC performance. The optimized FeOCl/BiVO4 photoanode exhibits a superior photocurrent density value of 5.23mAcm-2 at 1.23V versus reversible hydrogen electrode (RHE) under AM 1.5G illuminations. From experimental analysis, such high PEC performance is ascribed to the unique properties of FeOCl, facilitating charge transport, increasing light absorption efficiency, and promoting water oxidation kinetics. Density functional theory calculations further confirm that FeOCl optimizes the Gibbs free energy of H and O-containing intermediates (OOH*) during PEC processes, boosting the catalytic kinetics of PEC water splitting. This work presents FeOCl as a promising catalyst for constructing high efficient PEC water-splitting photoanodes.

Work function-tunable graphene/WO3 heterojunctions for high-performance photoelectrochemical cell: UV-treatment effect and defective graphene

Designing hybrid photoelectrodes with graphene capable of efficient charge-carrier transfer and excellent chemical stability is an effective strategy for developing high-performance photoelectrochemical (PEC) cells. However, it remains unclear how the PEC properties are enhanced and how to control the junction properties in graphene/metal oxide heterojunction-based photoelectrodes. Here, we develop a deterministic junction to enhance PEC performance in graphene/tungsten trioxide (WO3)-based photoelectrodes by tuning the work function of graphene. It reveals that the band structure of graphene/WO3 heterojunctions can be modified by ultraviolet (UV) treatment on WO3 thin films. This modification is supported by the observation that a single-layer graphene/UV-treated WO3 photoelectrode exhibits significantly enhanced PEC activities toward the oxygen evolution reaction (OER) (evidenced by features like a threefold increase in photocurrent, an onset potential shift, and improved stability), whereas the single-layer graphene/untreated WO3 electrode demonstrates improved properties for the hydrogen evolution reaction (HER). Additionally, defects in the graphene layer formed during PEC water splitting contribute to high catalytic activities of the graphene/WO3 photoelectrode due to a decrease in the Gibbs free energy for OER and HER. These results emphasize that band structure engineering via work function tuning in graphene/WO3 heterostructures can provide multiple benefits for high PEC performance and long-term stability.

High-Performance Self-Powered Photoelectrochemical Ultraviolet Photodetectors Based on an In2O3 Nanocube Film.

Ultraviolet photodetectors (UV PDs) have attracted significant attention due to their wide range of applications, such as underwater communication, biological analysis, and early fire warning systems. Indium oxide (In2O3) is a candidate for developing high-performance photoelectrochemical (PEC)-type UV PDs owing to its high UV absorption and good stability. However, the self-powered photoresponse of the previously reported In2O3-based PEC UV PDs is unsatisfactory. In this work, high-performance self-powered PEC UV PDs were constructed by using an In2O3 nanocube film (NCF) as a photoanode. In2O3 NCF photoanodes were synthesized on FTO by using hydrothermal methods with a calcining process. The influence of the electrolyte concentration, bias potential, and irradiation light on the photoresponse properties was systematically studied. In2O3 NCF PEC UV PDs exhibit outstanding self-powered photoresponses to 365 nm UV light with a high responsivity of 44.43 mA/W and fast response speed (20/30 ms) under zero bias potential, these results are superior to those of previously reported In2O3-based PEC UV PDs. The improved self-powered photoresponse is attributed to the higher photogenerated carrier separation efficiency and faster charge transport of the in-situ grown In2O3 NCF. In addition, these PDs exhibit excellent multicycle stability, maintaining the photocurrent at 98.69% of the initial value after 700 optical switching cycles. Therefore, our results prove the great promise of In2O3 in self-powered PEC UV PDs.

Modulating Interfacial Charge Transfer Behavior through the Construction of a Hetero-Interface for Efficient Photoelectrochemical Water Splitting

Surface-coupled transition metal oxyhydroxide (TMOOH) on semiconductor (SC)-based photoanodes are effective strategies for improving photoelectrochemical (PEC) performance. However, there is a substantial difference between the current density and theoretical value due to the inevitable interfacial charge recombination of SC/TMOOH. Here, we employ BiVO4/FeNiOOH as a model, constructing the BiVO4/MnOx/CoOx/FeNiOOH integrated system by introducing a novel hetero-interface regulation unit, i.e., MnOx/CoOx. As expected, the optimized integrated system demonstrates a photocurrent density as high as 5.0 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun AM 1.5G illumination, accompanied by 12-h stability. The detailed electrochemical analysis and intensity modulated photocurrent spectroscopy (IMPS) have confirmed that the high PEC performance mainly originates from the hetero-interface structure, which not only suppresses the interfacial charge recombination by accelerating the photogenerated hole transfer kinetics from BiVO4 to FeNiOOH but promotes the kinetics of surface oxygen evolution reaction (OER). Notably, these findings can also be extended to other structures (CeOx/CoOx), reflecting its universality. This finding has provided a new insight into the highly efficient solar energy conversion in the SC/TMOOH system.

A signal amplification strategy based on hexametaphosphate-stabilized BiVO4@CdS heterojunction with Mg2+-modulated surface charge for CEA detection

An ultrasensitive sensor with excellent photoelectrochemical (PEC) properties was developed based on the combination of electrostatic interactions between the hexametaphosphate (HMP)-coated BiVO4@CdS novel photoelectric material and the electron donor. Compared with the conventional BiVO4@CdS photoactive material, the HMP-modified BiVO4@CdS not only increases the stability, but also utilizes the electrostatic interactions between the negative charge carried by the phosphate group and the electron donor, which results to a significant increase in the photoelectric conversion ability after Mg2+ incubation. Specifically, carcinoembryonic antigen (CEA)-targeted immunorecognition was combined with MgCO3 antibody labelling inspired by the ability of HMP to complex with Mg2+. The released Mg2+ from the MgCO3 tag could neutralize the negative charge on the surface of BiVO4@CdS-HMP, and the electrostatic repulsion with the electron donor was suppressed, accelerating the electron transfer, and thus improving the electron-hole separation efficiency. A sensitive detection capability was demonstrated with CEA as the model target. Featuring a wide linear detection range with a detection limit as low as 60 fg/mL, this work provides a fresh perspective on the development of high-performance PEC biosensors.

High-Sensitivity Photoelectrochemical Ultraviolet Photodetector with Stable pH-Universal Adaptability Based on Whole Single-Crystal Integrated Self-Supporting 4H-SiC Nanoarrays.

Emerging photoelectrochemical (PEC) photodetectors (PDs) have notable advantages over conventional PDs and have attracted extensive attention. However, harsh liquid environments, such as those with high corrosivity and attenuation, substantially restrict their widespread application. Moreover, most PEC PDs are constructed by assembling numerous nanostructures on current collector substrates, which inevitably contain abundant interfaces and defects, thus greatly weakening the properties of PDs. To address these challenges, a high-performance pH-universal PEC ultraviolet (UV) PD based on a whole single-crystal integrated self-supporting 4H-SiC nanopore array photoelectrode is constructed, which is fabricated using a two-step anodic oxidation approach. The PD exhibits excellent photodetection behavior, with high responsivity (218.77mAW-1), detectivity (6.64×1013Jones), external quantum efficiency (72.47%), and rapid rise/decay times (17/48ms) under 375nm light illumination with a low intensity of 0.15mWcm-2 and a bias voltage of 0.6V, which is fall in the state-of-the-art of the wide-bandgap semiconductor-based PDs reported thus far. Furthermore, the SiC PEC PD exhibits excellent photoresponse and long-term operational stability in pH-universal liquid environments. The improved photodetection performance of the SiC PEC PD is primarily attributed to the synergistic effect of the nanopore array structure, integrated self-supporting configuration, and single-crystal structure of the whole photoelectrode.

Unveiling the effect of the structural transformation of CoZn-MOF on BiVO4 photoanode for efficient photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting has been widely investigated for solar-to-hydrogen conversion. However, issues like high charge recombination rate and slow surface water oxidation kinetics severely hinder its (PEC) conversion efficiency. Herein, we constructed MOF-derived CoOOH cocatalyst on BiVO4 photoanode, using a feasible electrochemical activation strategy. The BiVO4-based photoanode obtained shows a high photocurrent density of 3.15 mA/cm2 at 1.23 VRHE and low onset potential. Detailed experiments and theoretical calculations show that during the activation of CoZn-MOFs, there was a partial breakage of 2-methylimidazole (mIM) linker, an increase in the oxidation state of Cobalt ion (Co), and increased O2–. The high PEC performance is mainly attributed to the MOF-derived CoOOH, which provides rich active sites for hole extraction and reduces the overpotential for oxygen evolution reaction. Furthermore, when CoZnNiFe-LDHs were decorated on BiVO4 using the ions exchange method, the photocurrent density of BiVO4/CoZnNiFe-LDHs photoanode got to 4.0 mA/cm2 at 1.23 VRHE, accompanied with high stability. This study provides insights into understanding the key role played by the structural transformation of MOF cocatalyst in PEC water splitting processes.

Self-powered photoelectrochemical immunosensing platform for sensitive CEA detection using dual-photoelectrode synergistic signal amplification

Self-powered photoelectrochemical (PEC) sensing, as an emerging sensing mode, can effectively solve the problems such as weak anti-interference ability and poor signal response of individual photoanode or photocathode sensing. In this work, an ITO/Co–CuInS2 photocathode and ITO/WO3@CdS photoanode based self-powered cathodic PEC immunosensor was developed, which integrated dual-photoelectrode to synergistic amplify the signal for highly sensitive and specific detection of carcinoembryonic antigen (CEA). The self-powered PEC sensor could drive electrons transfer through the difference in Fermi levels between the two photoelectrodes without an external bias voltage. The photoanode was introduced to amplify the photoelectric signal, and the photocathode was only designed for the construction of sensing interfaces. The proposed sensor quantitatively determined the target CEA with the detection limit of 0.23 pg/mL and a linear correlation confine of 0.1 pg/mL ∼100 ng/mL. The constructed immunosensing platform exhibited high sensitivity, satisfactory stability and great biological detection selectivity, providing a feasible and effective strategy for the manufacture of new self-powered sensors in high-performance PEC bioanalytical applications.

Universal photoelectrochemical aptasensing platform for antibiotic based on CuInS2/rGO and triplex DNA

In this work, a universal and convenient photoelectrochemical (PEC) biosensor was proposed to detect antibiotic on the basis of CuInS2/rGO and triplex DNA molecular switch. High performance photoactive structure was formed via p-type CuInS2 nanosphere complexed with rGO, which was employed to enhance the cathode photocurrent. Capture probe (CP) was conjugated onto the photoactive interface through covalent bonding. In the absence of target, the triplex DNA (THMS) was in a closed state. After introducing a target, the interaction between the target and the specific ring part DNA fragment leaded to the dissociation of the THMS and thereby liberated the single strand DNA (SP). The above identification process was completed in the homogeneous solution. Then, SP was captured to the electrode by CP and hybridized to form dsDNA. The steric effect of dsDNA hindered the interfacial charge transfer, resulting in signal-off photocurrent output. By only altering the specific loop section sequence of THMS, different targets can release the same SP, and can be detected on the same sensing platform under the same testing conditions. As proof of principle, three kinds of antibiotics amoxicillin (AMOX), ampicillin (AMP) and tobramycin (TOB) was detected, achieving limit of detection values of 3.17 pM, 0.63 nM and 2.81 fM, respectively. This approach was also used to detect antibiotic residues in food and environmental samples, which provides a promising paradigm for developing universal, high-performance and convenient PEC biosensing platform.

Enhanced photoelectrochemical water splitting performance of α-Fe2O3 photoanodes through Co-modification with Co single atoms and g-C3N4.

The practical application of α-Fe2O3 in water splitting is hindered by significant charge recombination and slow water oxidation. To address this issue, a CoSAs-g-C3N4/Fe2O3 (CoSAs: cobalt single atoms) photoanode was fabricated in this study through the co-modification of CoSAs and g-C3N4 to enhance photoelectrochemical (PEC) water splitting. The coupling between g-C3N4 and α-Fe2O3 resulted in the formation of a heterojunction, which provided a strong built-in electric field and an additional driving force to mitigate charge recombination. Moreover, g-C3N4 served as a suitable carrier for single atoms, which effectively anchored CoSAs through N/C coordination. The highly dispersed CoSAs provided abundant active sites, which further promoted surface holes extraction and oxidation kinetics, resulting in higher PEC performance and photostability. This study indicates the benefits of these collaborative strategies and provides more efficient designs for solar energy conversion in PEC systems.

Study of the Hydrogen Evolution Reaction on Macroscopic Snse-Based Photoelectrodes

Conversion of solar energy to valuable chemicals by using photoelectrochemical (PEC) techniques such as water splitting, carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (N2RR), are promising methods to solve the issues of energy crisis and global warming [1-2]. Two-dimensional (2D) and layered semiconductors, for example, transition metal chalcogenides (TMCs), metal oxides and MXenes have attracted great attention for PEC applications because of their unique properties, such as high carrier mobility, tunable bandgap, anisotropic carrier transport, and high specific surface area [3]. Our review indicates that, i) 2D and layered semiconductors can be applied for different PEC applications, both in oxidation and reduction reactions, and have ability to give higher performance in water reduction (i.e., hydrogen evolution reaction, HER) than in the other ones. ii) TMCs have been the most studied material with higher performance than the others. However, high PEC performance was achieved only on single crystal TMCs or in microelectrochemical cells, implying a limitation in the scalability of this solar energy conversion approach [4]. There is a clear need to study macroelectrodes prepared from polycrystalline semiconductors and identify the opportunities and barriers for their applications. In our study [5], tin(II) selenide (SnSe) was used as a photoelectrode for PEC HER since it has not been widely investigated for this PEC application. We fabricated SnSe macroscopic photocathodes by depositing SnSe flakes, made from commercial SnSe crystals using a liquid phase exfoliation (LPE) method, on glassy carbon. The as-received SnSe crystals were exfoliated in isopropanol/water mixtures (IPA/H2O) and pure IPA, respectively. Pure IPA was found to be the optimal solvent to prepare flakes and for achieving the highest PEC activity. An additional size separation to make three different size fractions of SnSe crystals served to further optimize the LPE process. Electrodes prepared from the largest flakes showed the highest photocurrent density of 2.44 ± 0.65 mA cm–2 at –0.74 V vs. RHE. The photodeposited Pt co-catalyst on SnSe surface further accelerated the PEC HER activity to 4.39 ± 0.15 mA cm–2. Intensity modulated photocurrent spectroscopy results manifested that the Pt co-catalyst enhanced the charge transfer process and suppressed charge carrier recombination. Overall, the solvent for exfoliation, the edge density of SnSe nanoflakes, immobilization method, and Pt co-catalyst affected the PEC HER performance of SnSe. These results indicate the merit of employing SnSe electrodes for PEC HER and inspire us to explore other photoelectrocatalytic reactions on the macroscopic exfoliated SnSe electrodes.

Enhanced performance of self-powered ZnO-based PEC type UV photodetectors by loading GQDs to construct heterojunctions

The construction of semiconductor heterojunctions is an effective approach to enhance the performance of optoelectronic devices. In this study, graphene-quantum-dots (GQDs) were grown on ZnO nanorods arrays in-situ to form intimate heterojunctions. The fabricated photoelectrochemical (PEC) photodetector based on ZnO/GQDs heterojunctions displayed good self-powering characteristics, with an on/off current ratio of approximately 21 at zero bias, which was almost seven-fold higher than that of the bare ZnO device. The responsivity and detectivity of the ZnO/GQDs-based photodetector were also enhanced compared with those of bare ZnO devices. A unique type-II band alignment was established at the ZnO/GQDs heterojunction interface, which facilitated the carrier transfer. Moreover, the ZnO/GQDs heterojunction reduced the passivation of the surface states, resulting in large energy-band bending and an internal electric field at the semiconductor/electrolyte interface, which provided a powerful driving force for the separation and transport of photogenerated carriers. These combined effects enhance the performance of the photodetector, indicating that this approach can be used to fabricate high-performance PEC optoelectronic devices.

Surface restructuring Ni0.85Se/ZnSe catalyst shows large boosting electrocatalytic and photoelectrochemical performance

Catalytic performance is often affected by electronic band structure. Here, it is demonstrated that though loading ZnSe on the surface of Ni0.85Se to build Ni0.85Se/ZnSe heterojunction catalysts. The electronic band structure of Ni0.85Se/ZnSe heterojunction can be adjusted by the loading ZnSe, which largely affects the electrocatalytic and photoelectrochemical performance. Compared with pristine Ni0.85Se (1.49 eV) and ZnSe (2.50 eV), the bandgap of Ni0.85Se/ZnSe change from 1.28 to 1.60 eV, which is even lower than that of Ni0.85Se and ZnSe. Meanwhile, the positions of the conduction and valence bands of composites also show unusual changes: NZS2 has the highest conduction band of −0.78 eV which is higher than that of Ni0.85Se (−0.62 eV) and ZnSe (−0.66 eV) while NZS3 shows the lowest valence band of 0.88 eV which is also little lower than that of Ni0.85Se (0.87 eV). The characteristics of this adjustable electronic band structure bring obvious changes in catalytic performance. In the hydrogen evolution reaction tests, NZS2 has the lowest overvoltage of 209 mV and Tafel slope of 56 mV/dec, and NZS3 shows the lowest overvoltage of 318 mV and Tafel slope of 89 mV/dec in the oxygen evolution reaction. As compared, the Ni0.85Se has an overvoltage of 247 mV and Tafel slope of 77 mV/dec in hydrogen evolution reaction, and cannot achieve current density of 10 mA/cm2 in oxygen evolution reaction. It is considered that the higher conduction band is beneficial for reduction reaction and lower valence band means higher oxidation capacity. Moreover, the loading of ZnSe enhances the carrier's separation efficiency which causes higher photoelectrochemical performance.

Dense/nanoporous bilayer BiVO4 photoanode with outstanding light-absorption efficiency for high-performance photoelectrochemical water splitting

This study designs a dense/porous bilayer-structured BiVO4 photoanode to achieve a high photoelectrochemical (PEC) performance. Monolayer photoanodes have their respective limitations; the dense monolayer BiVO4 (d-BVO) photoanode has high reflectance, and the porous monolayer (p-BVO) photoanode has high transmittance, which limits light absorption. Conversely, the dense/porous bilayer structure maximizes the light-absorption and increases PEC efficiency by combining these layers. The dense and porous layers of the bilayer photoanode (b-BVO) were manufactured using the simple processes of sputtering deposition and solution spin coating, respectively. The light absorption of b-BVO increased to approximately 92 % (at wavelengths of 300–500 nm). This resulted in an increase in the absorption efficiency (ηabs) to 81.4 %, which was 21.9 % and 24.5 % higher than those of d-BVO and p-BVO, respectively. The photocurrent density of b-BVO was 2.43 mA cm−2 at 1.23 V versus a reversible hydrogen electrode, which was 31.4 % and 102.5 % higher than those of d-BVO and p-BVO, respectively.

Construction of type-II SnO2/InGaN nanorods heterostructure toward high photoelectrochemical performance

Exploring highly efficient and stable photoelectrode material is essential for high-performance photoelectrochemical (PEC) water-splitting applications. III-nitride semiconductors, particularly InGaN, have been considered as prospective materials for PEC hydrogen evolution. However, their surface states and other recombination centers, which enhance the charge recombination kinetics, are bottlenecks for the high PEC performance. In this work, we report the construction of type-II heterojunction by sputter depositing SnO2 on InGaN nanorods (NRs) to promote interfacial carrier transport and thereby enhance PEC performance. The energy band offsets at the SnO2/InGaN NRs interface were analyzed by x-ray photoelectron spectroscopy. Type-II heterojunction was defined at the SnO2/InGaN NRs interface with a valence band offset of 0.77 eV and conduction band offset of 0.25 eV. The photocurrent density of the SnO2/InGaN NRs photoanode is 7.09 mA/cm2 at 0.77 V vs Ag/AgCl electrode with 80 nm SnO2 thickness, which is ∼14-fold higher than that of the pristine InGaN NRs photoanode. Furthermore, the applied bias photo-to-current efficiency of SnO2/InGaN NRs photoanode records 3.36% at 0.77 V vs Ag/AgCl electrode. The enhanced PEC performance is mainly ascribed to the formation of high-quality SnO2/InGaN NRs heterojunction that enforces the directional charge transfer and substantially boosts the separation of photogenerated electron–hole pairs at the interface of InGaN NRs and SnO2. Overall, this work sheds light on the promising strategy to design and fabricate III-nitride nanostructures-based photoelectrodes for feasible PEC water-splitting applications.

Insights into Chemical Bonds for Eliminating the Depletion Region and Accelerating the Photo-Induced Charge Efficient Separation toward Ultrasensitive Photoelectrochemical Sensing.

The empty-space-induced depletion region in photoelectrodes severely exacerbates the recombination of electron-hole pairs, thereby reducing the photoelectrochemical (PEC) analytical performance. Herein, the chemical bond that can suppress the potential barrier and overcome the high energy barrier of out-of-plane Ohmic or Schottky contact is introduced into the PEC sensor to eliminate the depletion region and dramatically promote the separation of electron-hole pairs. Specifically, three-dimensional (3D) hierarchically wheatear-like TiO2 (HWT) nanostructures featuring a large surface area to absorb incident light are crafted as the substrate. The facile carbonized strategy is further employed to engineer the Ti-C chemical bond, serving as the touchstone. The average PL lifetime of HWT-C (4.14 ns) is much shorter than that of the 3D HWT (8.57 ns) due to the promoting effect of the chemically bonded structure on carrier separation. Consequently, the 3D HWT-C covalent photoelectrode (600 μA/cm2) exhibits a 3.6-fold increase in photocurrent density compared with the 3D HWT (167 μA/cm2). Ultimately, the model analyte of the tumor marker is detected, and the linear range is 0.02 ng/mL-100 ng/mL with a detection limitation of 0.007 ng/mL. This work provides a basic understanding of chemical bonds in tuning charge separation and insights on strategies for designing high-performance PEC sensors.