Photoelectrode System Research Articles

Coupling Cuprous Oxide with Upconversion Materials: A Holistic Approach to Efficient Solar Water Splitting

Photoelectrochemical (PEC) water splitting is a promising solution for harnessing solar radiation for hydrogen production. This technology combines sunlight capture and water electrolysis processes, resulting in the production of hydrogen and oxygen that can efficiently recombine in fuel cells. However, challenges in materials science still need resolution to establish PEC water splitting as a practical and competitive approach. Copper oxide semiconductors, particularly materials based on cuprous oxide (Cu2O), have attracted attention due to their abundant elemental availability, scalable synthesis methods, and inherent p-type characteristics. To improve the generated photocurrent of the photoelectrode system, photon upconversion (UC) materials can be implemented into water-splitting devices. TTA-based UC is particularly suitable for solar water splitting due to its efficient conversion at low photon intensity. This work highlights the potential application of TTA-based UC in solar-assisted water splitting and highlights the significance of photonic designs and nanointerface engineering to improve the light-harnessing properties of photoactive materials. To the best of our knowledge, our research group was the first to successfully implement the integration of photoactive materials for solar water splitting with an upconversion device based on the TTA mechanism. This strategy allows us to dramatically improve the light-harnessing properties of our photoelectrode by irradiating the photocatalyst from dual perspectives (front and back-side illumination). It has been demonstrated that Cu2O coupled with an upconverter (UC) outperforms bare Cu2O by 56% in terms of produced photocurrent density, namely bare Cu2O produces -0.32 mA·cm-2 at 0V (vs. RHE), whereas Cu2O/UC exhibits a photocurrent of -0.5 mA·cm-2. Figure 1

Copper oxide coupled with photon upconversion for solar water splitting

Photoelectrochemical water splitting is a promising solution for harnessing solar radiation for hydrogen production. Copper oxide semiconductors, particularly materials based on cuprous oxide, have attracted attention due to their abundant elemental availability and scalable synthesis methods. To improve the generated photocurrent of the photoelectrode system, photon upconversion materials can be implemented into water-splitting devices. Here, we demonstrate the potential application of triplet-triplet annihilation-based upconversion in solar-assisted water splitting and highlight the significance of photonic designs to improve the light-harnessing properties of photoactive materials. The triplet-triplet annihilation mechanism is particularly suitable due to its efficient conversion at low photon intensity, namely under 1-sun illumination. Our results show that Cu2O coupled with an upconverter outperforms bare Cu2O by 56% in terms of produced photocurrent density. We construct a hybrid water-splitting device with an extended absorption range by utilizing a semi-transparent 600 nm Cu2O film with a 5 nm Au underlayer.

Dual-photoelectrode photocatalytic fuel cell-assisted self-powered biosensor: An ingenious and sensitive strategy for p53 gene detection

Self-powered sensors have the advantages of no external power supply, energy conversion in the environment and easy miniaturization, making it an attractive choice for building implantable, wearable and portable devices. However, it is difficult to sensitively detect low abundance targets owing to their poor output performance and interference from complicated settings. Herein, a new photocatalytic fuel cell-based self-powered electrochemical biosensor (PFC-SPEB) was proposed for the detection of p53 gene by combining high photocatalytic performance In2S3 and CuInS2 with magnetic nanobeads-assisted signal amplification strategy. In2S3 photoanode and CuInS2 photocathode were combined to form a dual photoelectrode system with an open-circuit potential up to 705.9 mV, which improved the photoelectric conversion efficiency by 1.4–6.9 folds compared with that of single photoelectrode system. Furthermore, the enzyme-assisted signal amplification strategy made a small number of p53 genes trigger the creation of abundant double-stranded DNA (dsDNA). Finally, manganese porphyrin was inserted into dsDNA to stimulate precipitation reactions on surfaces of the photoanode, leading to a sharp drop of signal. The constructed PFC-SPEB exhibited a wide linear detection range from 10 fM to 10 nM with a low detection limit of 1.40 fM, providing new creative inspiration for constructing SPEB for bioanalysis and clinical diagnostics.

Double-sided semitransparent titania photoelectrode with enhanced light harvesting

In this work, unique semitransparent electrodes were prepared by the anodization of titanium layers (540 nm thick) initially deposited on the both sides of glass substrates employing indium-tin oxide interface layers serving as a current collector for the induced photocurrent. The anodization strategy used in this study enables fabrication of semitransparent titanium dioxide nanotube arrays with either aligned or spaced architecture on the two sides of the planar substrate. This study aims to perform a detailed investigation of this novel photoelectrode system (crystal structure, morphology and optical properties) to reveal their photoelectrochemical features. It was found that the photoelectrode exhibits enhanced photocurrent density about 1.9 times higher (4.6 μAcm−2 at +0.5 V) for aligned nanotubes compared to a substrate overgrown symmetrically by separated nanotubes (2.4 μAcm−2 at +0.5 V). This can be effectively explained by the higher tube density in the case of aligned nanostructures, which provide more channels for charge percolation. In addition, both the high donor concentration (6.4 × 1020 cm−3) together with the low charge transfer resistance of the semitransparent electrode of the aligned nanotubes make the material promising for application in photoelectrochemical systems and smart light management.

Piezoelectric Effect Promoted Photoelectrochemical Water Splitting Ability of ZnIn2S4 Photoanode with Highly Exposed Active (110) Facets

AbstractIt is important to design high performance photoelectrode materials in the process of photoelectrochemical (PEC) water splitting. Herein, ZnIn2S4 nanomaterial with highly exposed active (110) facets were prepared by a simple hydrothermal method. Meanwhile, piezoelectric polarization was used to induce the generation of built‐in electric field, which can suppress the compounding of photogenerated charge carriers caused by structural defects at the semiconductor surface. By controlling the crystal facet structure, ZnIn2S4 with a highly exposed active (110) facet shows a better photoelectrochemical water splitting performance under ultrasound, and its photocurrent density increases with the increase of ultrasound frequency, reaching a maximum value of 0.36 mA/cm2 at 1.23 VRHE, which is 2.8 times higher than that without ultrasound. It can be concluded that the (110) facet of ZnIn2S4 can induce a larger internal piezoelectric potential which allows rapid electron transer at the ZnIn2S4 surface, under ultrasonic conditions. And the highly exposed (110) facet also provides more reactive sites, leading to further enhanced catalytic activity. Such nanomaterial with highly exposed active facets will provide inspiration for the construction of photoelectrode systems with high photoelectrochemical water splitting efficiency.

Charge Recombination Deceleration by Lateral Transfer of Electrons in Dye-Sensitized NiO Photocathode.

Control of charge separation and recombination is critical for dye-sensitized solar cells and photoelectrochemical cells, and for p-type cells, the latter process limits their photovoltaic performance. We speculated that the lateral electron hopping between dyes on a p-type semiconductor surface can effectively separate electrons and holes in space and retard recombination. Thus, device designs where lateral electron hopping is promoted can lead to enhanced cell performance. Herein, we present an indirect proof by involving a second dye to monitor the effect of electron hopping after hole injection into the semiconductor. In mesoporous NiO films sensitized with peryleneimide (PMI) or naphthalene diimide (NDI) dyes, dye excitation led to ultrafast hole injection into NiO from either excited PMI* (τ < 200 fs) or NDI* (τ = 1.2 ps). In cosensitized films, surface electron transfer from PMI- to NDI was rapid (τ = 24 ps). Interestingly, the subsequent charge recombination (ps-μs) with NiO holes was much slower when NDI- was generated by electron transfer from PMI- than when NDI was excited directly. We therefore indicate that the charge recombination is slowed down after the charge hopping from the original PMI sites to the NDI sites. The experimental results supported our hypothesis and revealed important information on the charge carrier kinetics for the dye-sensitized NiO photoelectrode system.

Renewable formate from sunlight, biomass and carbon dioxide in a photoelectrochemical cell

The sustainable production of chemicals and fuels from abundant solar energy and renewable carbon sources provides a promising route to reduce climate-changing CO2 emissions and our dependence on fossil resources. Here, we demonstrate solar-powered formate production from readily available biomass wastes and CO2 feedstocks via photoelectrochemistry. Non-precious NiOOH/α-Fe2O3 and Bi/GaN/Si wafer were used as photoanode and photocathode, respectively. Concurrent photoanodic biomass oxidation and photocathodic CO2 reduction towards formate with high Faradaic efficiencies over 85% were achieved at both photoelectrodes. The integrated biomass-CO2 photoelectrolysis system reduces the cell voltage by 32% due to the thermodynamically favorable biomass oxidation over conventional water oxidation. Moreover, we show solar-driven formate production with a record-high yield of 23.3 μmol cm−2 h−1 as well as high robustness using the hybrid photoelectrode system. The present work opens opportunities for sustainable chemical and fuel production using abundant and renewable resources on earth—sunlight, biomass and CO2.

Surface engineering of Ba-doped TiO2 nanorods by Bi2O3 passivation and (NiFe)OOH Co-catalyst layers for efficient and stable solar water oxidation

The rational design of heterostructures as an ideal photoelectrode system for H2 and O2 conversion in photoelectrochemical (PEC) system has been regarded as an essential key to boost PEC performance. In this work, to demonstrate the energetic photoanode cell, deposition of a thin layer of Bi2O3 is utilized to hybridize with the 5 wt% Ba-doped TiO2 nanorod heterostructure under the cascading band diagram, where Ba-doping can enhance the charge transport/separation rate in bulk phase, in terms of increasing the donor density, enhancing the bulk electronic conductivity, and increasing the band bending. Furthermore, with optimizing the thickness (∼15 nm) of Bi2O3, the (NiFe)OOH as a cocatalyst was adapted to improve the interfacial charge transfer rate in the PEC cell, reaching the high photocurrent density (J) of ∼4.1 mA/cm2 at 1.23 V (vs. Reversible Hydrogen Electrode) and stability retention of 100%, even after 15 h at 1 M NaOH under 1 Sun illumination condition. The improvement mainly comes from the extended absorption of visible light from the thin Bi2O3 layer, effective transfer/separation of photogenerated charge carriers, and acceleration of water oxidizing reaction, caused by the narrowed band gap and the favorable charge transfer under the cascading band alignment built by the heterojunction, as well as electrocatalyst, offering the timely consumption of photogenerated holes accumulated at the electrode surface.

Surface-State-Controlled Fluence-Dependent Apce Behavior of p-GaAs-TiO2-Pt Water Reduction Photocathode

The demand for reform in energy production and reduction in carbon dioxide emission lays emphasis on the development and mechanistic study of photocatalytic water splitting photoelectrodes. Understanding the bottlenecks of the photoelectrochemical (PEC) conversion efficiency in photocatalytic water splitting systems is essential to impart guidance to material selection and photoelectrode design. Absorbed photon-to-current conversion efficiency (APCE), which represents the fraction of absorbed photons converted into electrons in photocurrents, is the key metric in the evaluation of PEC performance. A large portion of studies have reported an illumination fluence-independent APCE under continuous wave (CW) illumination with power densities around 10~100 mW/cm2, whereas few cases have reported the fluence-dependent APCE performance. In the present work, we observe a rarely reported fluence-dependent APCE performance in the p-GaAs/5 nm TiO2/2 nm Pt photocathode under a low-excitation intensity regime. The APCE reaches close to unity at 0.005 mW/cm2 and gradually decreases to 60% at 1 mW/cm2. However, a theoretical explanation for this fluence-dependent APCE reduction is not established. We develop a steady-state kinetic model with the least parameters to decipher such a phenomenon. In this model, the surface electrons in the GaAs/TiO2/Pt photocathode are consumed by three pathways: 1) transferred to redox active species in solution via the conduction band, 2) trapped into surface states that serve as the reaction sites, which competes with the electron-hole recombination at such surface states, and 3) directly recombining with the surface holes. The APCE decrease at higher illumination intensity is attributed to the increasing recombination between the GaAs holes and the TiO2 electrons caused by the saturation of surface sites. A detailed parametric survey shows that the interfacial electron transfer rate, ks, from the trap states to solution redox species is the only parameter that tunes the extent of the APCE reduction. With higher ks, APCE displays a smaller reduction in response to increasing fluences. Thus, the fluence-dependent feature of the APCE is an indicator that the surface reaction is the efficiency-determining step.Through this work, we establish a kinetic model for the semiconductor photoelectrode with catalyst layer and successfully explain the cause to the fluence-dependent APCE performance. These significant findings can be universally applied to address the function of catalytic layer (nanoparticle or molecular) and surface modifier in hybrid photoelectrode systems that exhibit fluence-dependent APCE.

Surface State-Assisted Delayed Photocurrent Response of Au Nanocluster/TiO2 Photoelectrodes.

Gold nanoclusters (NCs) can be used as sensitizers to extend the absorption capabilities of TiO2 as photoelectrodes. However, the adsorption of NCs also creates additional surface states on the TiO2 surface, which gives rise to intricacies in the understanding of various interfacial phenomena occurring in NC-sensitized TiO2. One of the complexities that have recently been discovered is the size-dependent hole-transfer mechanism. In this work, we reveal another anomalous behavior in the hole-transfer process that the hole scavenging ability of the electrolyte also plays a role in determining the hole-transfer mechanism in the NC-TiO2 system, which is unprecedented in other photoelectrode systems. In the presence of an efficient hole scavenger (Na2SO3), the hole transfer in Au18-TiO2 occurs directly through the highest occupied molecular orbital (HOMO) of Au18 NCs. However, in the presence of a less efficient hole scavenger (ethylenediaminetetraacetic acid), hole transfer in Au18-TiO2 does not occur through the HOMO and shifts to surface state-assisted hole transfer. Due to surface state charging, this surface state-assisted hole-transfer mechanism results in delayed photocurrent response in Au18-TiO2. Evidence for this exotic hole-transfer mechanism shift is provided by photoelectrochemical electrochemical impedance spectroscopy, and its implications are discussed.

Modifying the Electron-Trapping Process at the BiVO4 Surface States via the TiO2 Overlayer for Enhanced Water Oxidation.

BiVO4 is one of the most promising photoanode candidates to achieve high-efficiency water splitting. However, overwhelming charge recombination at the interface limits its water oxidation activity. In this study, we show that the water oxidation activity of the BiVO4 photoanode is significantly boosted by the TiO2 overlayer prepared by atomic layer deposition. With a TiO2 overlayer of an optimized thickness, the photocurrent at 1.23 VRHE increased from 0.64 to 1.1 mA·cm-2 under front illumination corresponding to 72% enhancement. We attribute this substantial improvement to enhanced charge separation and suppression of surface recombination due to surface-state passivation. We provide direct evidence via transient photocurrent measurements that the TiO2 overlayer significantly decreases the photogenerated electron-trapping process at the BiVO4 surface. Electron-trapping passivation leads to enhanced electron photoconductivity, which results in higher photocurrent enhancement under front illumination rather than back illumination. This feature can be particularly useful for wireless tandem devices for water splitting as the higher band gap photoanodes are typically utilized with front illumination in such configurations. Even though the electron-trapping process is eliminated completely at higher TiO2 overlayer thicknesses, the charge-transfer resistance at the surface also increases significantly, resulting in a diminished photocurrent. We demonstrate that the ultrathin TiO2 overlayer can be used to fine tune the surface properties of BiVO4 and may be used for similar purposes for other photoelectrode systems and other photoelectrocatalytic reactions.

Unassisted selective solar hydrogen peroxide production by an oxidised buckypaper-integrated perovskite photocathode

Hydrogen peroxide (H2O2) is an eco-friendly oxidant and a promising energy source possessing comparable energy density to that of compressed H2. The current H2O2 production strategies mostly depend on the anthraquinone oxidation process, which requires significant energy and numerous organic chemicals. Photocatalyst-based solar H2O2 production comprises single-step O2 reduction to H2O2, which is a simple and eco-friendly method. However, the solar-to-H2O2 conversion efficiency is limited by the low performance of the inorganic semiconductor-based photoelectrodes and low selectivity and stability of the H2O2 production electrocatalyst. Herein, we demonstrate unassisted solar H2O2 production using an oxidised buckypaper as the H2O2 electrocatalyst combined with a high-performance inorganic-organic hybrid (perovskite) photocathode, without the need for additional bias or sacrificial agents. This integrated photoelectrode system shows 100% selectivity toward H2O2 and a solar-to-chemical conversion efficiency of ~1.463%.

Surface‐Structured Cocatalyst Foils Unraveling a Pathway to High‐Performance Solar Water Splitting

AbstractAn ideal catalytic interface for photoelectrodes that enables high efficiency and long‐term stability remains one of the keys to unlocking high‐performance solar water splitting. Here, fully decoupled catalytic interfaces realized using surface‐structured cocatalyst foils are demonstrated, allowing optimized photoabsorbers to be combined with high‐performance earth‐abundant cocatalysts. Since many earth‐abundant cocatalysts are deposited via solution‐based methods, deposition on chemical‐sensitive photoabsorbers is a significant challenge. By synthesizing cocatalyst foils prior to device fabrication, photoabsorbers are completely isolated from corrosive chemical environments and are provided with outstanding protection during operation. Si and GaAs photoelectrodes prepared using Ni‐based cocatalyst foils achieve excellent half‐cell efficiencies and generate stable photocurrents for over 5 days. Furthermore, a GaAs artificial leaf achieves a solar‐to‐hydrogen efficiency of 13.6% and maintains an efficiency of over 10% for longer than nine days, an accomplishment that has not been previously reported for an immersed solar water splitting system. These results, together with theoretical calculations of other photoelectrode systems, demonstrate that cocatalyst foils offer a very attractive method for fabricating high‐performance solar water splitting systems.

Photothermal‐Assisted Triphase Photocatalysis Over a Multifunctional Bilayer Paper

AbstractPhotocatalysis as one of the future environment technologies has been investigated for decades. Despite great efforts in catalyst engineering, the widely used powder dispersion and photoelectrode systems are still restricted by sluggish interfacial mass transfer and chemical processes. Here we develop a scalable bilayer paper from commercialized TiO2 and carbon nanomaterials, self‐supported at gas‐liquid‐solid interfaces for photothermal‐assisted triphase photocatalysis. The photogeneration of reactive oxygen species can be facilitated through fast oxygen diffusion over triphase interfaces, while the interfacial photothermal effect promotes the following free radical reaction for advanced oxidation of phenol. Under full spectrum irradiation, the triphase system shows 13 times higher reaction rate than diphase controlled system, achieving 88.4 % mineralization of high concentration phenol within 90 min full spectrum irradiation. The bilayer paper also exhibits high stability over 40 times cycling experiments and sunlight driven feasibility, showing potentials for large scale photocatalytic applications by being further integrated into a triphase flow reactor.

Photothermal-Assisted Triphase Photocatalysis Over a Multifunctional Bilayer Paper.

Photocatalysis as one of the future environment technologies has been investigated for decades. Despite great efforts in catalyst engineering, the widely used powder dispersion and photoelectrode systems are still restricted by sluggish interfacial mass transfer and chemical processes. Here we develop a scalable bilayer paper from commercialized TiO2 and carbon nanomaterials, self-supported at gas-liquid-solid interfaces for photothermal-assisted triphase photocatalysis. The photogeneration of reactive oxygen species can be facilitated through fast oxygen diffusion over triphase interfaces, while the interfacial photothermal effect promotes the following free radical reaction for advanced oxidation of phenol. Under full spectrum irradiation, the triphase system shows 13 times higher reaction rate than diphase controlled system, achieving 88.4 % mineralization of high concentration phenol within 90 min full spectrum irradiation. The bilayer paper also exhibits high stability over 40 times cycling experiments and sunlight driven feasibility, showing potentials for large scale photocatalytic applications by being further integrated into a triphase flow reactor.

(Invited) Solar-Driven CO2 Reduction By Molecular-Semiconductor Hybrid Systems: Photoelectrodes and Particulate Photocatalysts

For the development of photosystem for CO2 reduction into useful energy-rich chemicals using water as an electron donor operating under sunlight irradiation, the combination of a semiconductor photosensitizer and a metal-complex catalyst is one promising approach. We previously proposed the a hybrid molecular-catalyst/semiconductor system for the visible-light driven CO2 reduction, and demonstrated particulate photocatalyst and photoelectrode systems utilizing Ru-bipyridine complexes and their polymers as catalysts contacted with semiconductors of N-doped Ta2O5[1], GaP:Zn [2], InP:Zn[2], (CuGa)0.8Zn0.4S2[3], (AgIn)0.22Zn1.56S2[3], ZnS:Ni[3], etc. (Fig. 1). As an example, the photoelectrode system demonstrated formate generation with a solar-to-chemical conversion efficiency of 4.6 % by a non-biased tablet-formed device immersed in an aqueous solution [4].One recent topic is a visible-light-driven Z-schematic CO2 reduction using H2O as an electron donor in aqueous particulate suspension system which can be operated in a simple mixture of [Ru(4,4’-diphosphonate-2,2’-bipyridine)(CO)2Cl2] ([Ru(dpbpy)] modified (CuGa)1-xZn2xS2 (CGZS) hybrid photocatalyst as a CO2 reduction, BiVO4 photocatalyst as a water oxidation and Co-complex as an electron mediator [5]. The CO2 reduction activity was significantly dependent on the composition of CGZS, and utilization of [Ru(dpbpy)]/CGZS at x=0.7 (E g = 2.36 eV) showed the highest Z-schematic CO2 reduction activity for CO and HCOO- production accompanying O2 generation under visible-light irradiation. The very high CO2 reduction selectivity beyond 60% under visible light irradiation as the aqueous particulate suspension suggests that particulate Z-schematic system is feasible to construct selective and efficient photocatalytic system for CO2 fixation and solar fuel generation. An electrode system using earth-abundant elements such as Mn[6], Fe[7] and Si will also be presented.[8]- References[1] S. Sato, T. Morikawa, et al, Angew. Chem. Int. Ed. 2010, 49, 5101-5105.[2] S. Sato, T. Arai, T. Morikawa, et al., J. Am. Chem. Soc., 2011, 133, 15240-15243.[3] T. M. Suzuki, A. Kudo, T. Morikawa, Applied Catalysis B: Environ. 2018 , 224, 572–578.[4] T. Arai, S. Sato, T. Morikawa, Energy Environ. Sci., 201 5 , 8 , 1998-2002.[5] T. M. Suzuki, A. Kudo, T. Morikawa, et al., Chem. Commun., 2018, 54, 10199-10202[6] S. Sato, K.Sekizawa, et al, ACS Catal., 2018, 8, 4452-4458.[7] T. M. Suzuki, et al., Bull. Chem. Soc. Jpn, 2018, 91, 778–786.[8] T. Arai, et al., Chem. Commun., 2019, 55,237-240._ Figure 1

Photoelectrocatalytic hydrogen production of heterogeneous photoelectrodes with different system configurations of CdSe nanoparticles, Au nanocrystals and TiO2 nanotube arrays

The different configurations of CdSe nanoparticles, Au nanocrystals and TiO2 nanotube arrays play an important role in the photoelectrochemical behavior and photoelectrocatalytic hydrogen production of this heterogeneous photoelectrode system. It is discovered that the photoelectrocatalytic hydrogen production of the TiO2–CdSe–Au photoelectrode (1.724 mmol g−1 h−1) is about 4 times that of the TiO2–Au–CdSe photoelectrode (0.430 mmol g−1 h−1) under visible light irradiation. From the comprehensive investigation of their photoelectrochemical behaviors, it is illustrated that the interfacial electrical field has distinct effects on the separation and transportation of photogenerated carriers in these heterostructure photoelectrodes. The directions of the interfacial electrical fields formed at TiO2–Au and Au–CdSe interfaces are opposite in the TiO2–Au–CdSe photoelectrode, which hinders the separation of photogenerated electron-hole pairs and subsequent transportation of photogenerated carriers. On the contrary, the directions of the interfacial electrical fields formed at TiO2–CdSe and CdSe–Au interfaces are identical in the TiO2–CdSe–Au photoelectrode, which promotes the separation of photogenerated excitons and subsequently enhances their transportation for enlarged photocurrent density. The results of photoelectrocatalytic hydrogen production also confirm our assumption.

Fabrication of 1D/2D p-g-C3N4@RGO heterostructures with superior visible-light photoelectrochemical cathodic protection performance

A novel photoelectrode system based on one-dimensional g-C3N4 porous nanofibers (1D-p-g-C3N4) heterostructured with 2D-RGO was fabricated by hydrogen bonding self-assembly technology in combination with heat treatment and electrodeposition process. Ascribed to the one-dimensional porous morphology of g-C3N4 and its heterojunction with RGO, the separation efficiency of the photoinduced electrons and holes was dramatically enhanced, leading to its superior PEC cathodic protection performance for 304 stainless steel. Under visible light illumination, the 1D/2D p-g-C3N4@RGO photoelectrode exhibited a photoinduced current density of 10.1 μA cm−2 and a photoinduced polarized potential of − 480 mV, which is 6 and 2.5 times that of g-C3N4, respectively.

High photoelectrochemical performance of reduced graphene oxide wrapped, CdS functionalized, TiO2 multi-leg nanotubes

Absorption of visible light and separation of photogenerated charges are two primary pathways to improve the photocurrent performance of semiconductor photoelectrodes. Here, we present a unique design of tricomponent photocatalyst comprising of TiO2 multileg nanotubes (MLNTs), reduced graphene oxide (rGO) and CdS nanoparticles. The tricomponent photocatalyst shows a significant red-shift in the optical absorption (∼2.2 eV) compared to that of bare TiO2 MLNTs (∼3.2 eV). The availability of both inner and outer surfaces areas of MLNTs, the visible light absorption of CdS, and charge separating behavior of reduced graphene oxide layers contribute coherently to yield a photocurrent density of ∼11 mA cm−2 @ 1 V vs. Ag/AgCl (100 mW cm−2, AM 1.5 G). Such a high PEC performance from TiO2/rGO/CdS photoelectrode system has been analyzed using diffused reflectance (DRS) and electrochemical impedance (EIS) spectroscopy techniques. The efficient generation of charge carriers under light irradiation and easy separation because of favourable band alignment, are attributed to the high photoelectrochemical current density in these tricomponent photocatalyst systems.

Hexagonal phase/cubic phase homogeneous ZnIn2S4 n-n junction photoanode for efficient photoelectrochemical water splitting

One of the most efficient ways to achieve a high performance of photoelectrochemical (PEC) water splitting is to accelerate the separation and transfer of photogenerated carriers. Homojunction has the perfect advantages due to the appropriate band gap and the close combination of interphase similar lattices between the two semiconductors. Herein, we report a rational and low-cost design that hexagonal phase/cubic phase homogeneous ZnIn2S4 n-n junction on FTO conductive substrate is fabricated through a simple two-step hydrothermal method to realize enganced PEC performance. In addition, the chemical reaction process and mechanism are discussed in detail. The hexagonal phase/cubic phase homogeneous ZnIn2S4 n-n junction have an excellent photocurrent density of 0.53 mA/cm2 at 1.23 V vs RHE, which is 1.36 and 1.89 times increased than that of the hexagonal phase ZnIn2S4 and cubic phase ZnIn2S4, respectively. Moreover, this work will be instructive for the design of efficient photoelectrode system which used in the photoelectrochemical water splitting.