Heterostructure Photoelectrodes Research Articles

A photoelectrochemical sensor based on In2S3/AgInS2 in situ Z-type heterojunction with “photo-modulated interface charge” for sensitive detection of Programmed Death-Ligand 1

The construction of heterostructure photoelectrodes can enhance the performance of photoelectrochemical (PEC) sensors. However, it is still a critical challenge to achieve efficient transfer of interface carriers. In this paper, we propose a strategy of “photo-modulated interface charge” to design a PEC sensor based on a hollow hexagonal tubular In2S3/AgInS2 in situ Z-type heterojunction for the susceptible detection of Programmed Death-ligand 1 (PD-L1). The hollow structured In2S3/AgInS2 is ingeniously synthesized employing indium-sourced MIL-68 as a sacrificial template and in situ cation exchange technique. This composite material has close contact interfaces due to in situ growth, which facilitates the spontaneous establishment of a robust and stable built-in electric field between the interfaces. Moreover, the inner cavity structure promotes multiple light refractions and scatterings, significantly enhancing light trapping capability. Under the influence of both light irradiation and electric field force, the migration direction of the interfacial charge is reversed, forming a Z-transfer path, which effectively delays the compounding of the electron-hole pairs (e-/h+) and further improves the sensitivity of the sensor. The minimum detection threshold of the PEC sensor is 26.58 fg/mL, and the feasibility of real samples is investigated, providing new insights for early diagnosis and prognostic treatment of diseases.

A 3D hierarchical TiO2/CaIn2S4/C3N4 arrays photoanode with dual-heterojunction for enhanced photoelectrochemical performance

A novel 3D hierarchical TiO2/CaIn2S4/C3N4 arrays with dual heterojunctions photoanode is constructed by stepwise deposition of CaIn2S4 nanosheets and ultrathin C3N4 onto the well-aligned TiO2 nanorods arrays. Integrating the merit of the superior ability of CaIn2S4 and C3N4 to harvest visible light, dual type-Ⅱ heterojunction band structure and one-dimensional ordered nanostructures, the TiO2/CaIn2S4/C3N4 photoanode exhibits simultaneous significant improvements in visible-light harvesting, charge separation and electron transfer capability. At 1.23 V (versus reversible hydrogen electrode) under AM 1.5 G irradiation, the TiO2/CaIn2S475/C3N4 photoanode exhibits a photocurrent density of 4.5 mA cm−2, which is 5.2 and 51.1-fold higher than that of TiO2/CaIn2S475 and pristine TiO2 photoanode, respectively. Moreover, the applied bias photo-to-current efficiency (ABPE) of the TiO2/CaIn2S475/C3N4 photoanode reaches 3.5% at 0.36 V (versus reversible hydrogen electrode). These results are helpful for fabricating more efficient heterostructure photoelectrodes.

Nanostructured Semiconductor Photoelectrodes Complexed with Natural Photosystems I and II for Bias-Free Tandem Biophotovoltaics

Natural photosynthesis can offer attractive models for light-harvesting antennae, electron- and proton-transfer units, and catalytic clusters for photovoltaics and solar fuel production. However, photoelectrodes with natural photosystems exhibit relatively low performances due to poor interfacial electron transfer. Here, we present efficient bias-free biophotovoltaics (BPVs) based on dual heterostructure photoelectrodes comprising natural photosystems and semiconductor nanostructures. The photocathode and photoanode were prepared using photosystem I (PSI)-protonated carbon nitride (p-C3N4) nanosheet complexes and a photosystem II (PSII)–TiO2 nanoparticle film, respectively. The linker-free complexation of PSI and PSII with nanostructured semiconductors efficiently suppressed the recombination of photogenerated charges for efficient light harvesting and photoconversion. In particular, the oriented coupling of the negatively charged luminal side of PSI to protonated carbon nitride synergistically increased the photoelectron generation and charge transfer, resulting in the generation of a photocurrent density 28 times higher than that of randomly oriented PSI. Under one-sun simulated illumination, the BPV cell with the PSI-p-C3N4 and PSII–TiO2 tandem structure exhibited a photocurrent of 7.7 μA cm–2 without any external bias and a cell power up to 0.9 μW cm–2. This work provides a simple self-assembly method to construct efficient nanobio complex photoelectrodes based on natural photosystems coupled with semiconductor nanostructures in a favorable orientation for efficient and stable interfacial electron transfer.

Easy method to prepare copper oxides with good photocurrent values

The influence of thermal annealing on the microstructure of copper oxide thin films has been investigated. The copper hydroxide (Cu(OH)2) nanowires were synthesized using a wet chemical (immersion) method. The aqueous solution was prepared by mixing 1 M NaOH and 0.1 M (NH4)2S2O8 and 30 ml of distilled water. The copper substrate was well polished, then immersed into the growth solution for 10 min, rinsed with distilled water, then dried in air, and finally annealed at different temperatures for 1 h in air. This structure can be used for many applications such as photoelectrochemical water splitting and photo-catalysis.The obtained materials were characterized by X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM).The results revealed the formation of cupric oxide (CuO) and cuprous oxide (Cu2O), observed on the surface of the thin films annealed at different temperatures. The morphology of these two oxides was found to depend on annealing temperature. The resulting of a copper-oxide (CuO) photoelectrode exhibited an enhanced photocurrent density under light illumination compared to the heterostructure (CuO and Cu2O) photoelectrode. This result indicates a good conductivity of the CuO phase and a good charge separation due to the band structure realignement at the interface.

Efficient heterostructure of MoS2/Ti-doped Fe2O3 nanorods for high-performance photoelectrochemical activity

The unique nanoflakes/nanorods heterostructure of MoS2/Ti-Fe2O3 was designed to boost the photoelectrochemical (PEC) performance of Fe2O3 nanorods through Ti doping and MoS2 nanoflake coating. The MoS2/Ti-Fe2O3 heterostructure photoelectrode exhibited significantly improved PEC performance, with a photocurrent density 15-fold higher than that of the Fe2O3 photoelectrode. Along with the concordance of band gap and band edge levels between Fe2O3 and MoS2, the enhanced PEC performance can be explained by the efficient charge separation and transfer in the MoS2/Ti-Fe2O3 heterostructure. These results offer new opportunities for Fe2O3-based nanostructures in constructing high-performance solar energy-driven devices.

Direct growth of Bi2S3 nanorods onto the Bi2MoO6 nanoflakes: A promising heterostructure for efficient photoelectrochemical water-splitting application

Fabrication of heterostructure promises a potential approach to increase the hydrogen production performance of photoelectrodes under solar light irradiation. Herein, a two-step hydrothermal method was introduced to grow directly Bi2S3 nanorods onto the Bi2MoO6 nanoflakes to form Bi2MoO6/Bi2S3 heterostructure. This work is aimed to synthesize heterostructure photoelectrode for photoelectrochemical water splitting application. The as-prepared photoelectrodes were analyzed by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, and UV–vis spectroscopy. As a result, the heterostructure Bi2MoO6/Bi2S3 indicated a dramatic improvement in the PEC properties (1.41 mA/cm2). From the X-ray photoelectron spectroscopy valence band measurement, the suitable bandgap between Bi2MoO6 and Bi2S3 can promote charge transfer across the junction interface and suppress electron-hole recombination. Furthermore, coupling a narrow bandgap material Bi2S3 with Bi2MoO6 can form a type II- heterostructure, leading to enhancement of the light absorption under visible light irradiation. This work provides a promising and efficient photoanode for light harvesting and hydrogen production.

Dynamic Photocurrent Response of CuO-Nanoarray-Based Photoelectrodes: Heterostructure and Small Electric Field Effects

CuO nanoarrays were synthesized by using a hydrothermal method, and TiO2 nanocrystals were deposited on the surface of CuO nanoarrays to form bulk heterostructure photoelectrodes. The current-time curve revealed that TiO2 nanocrystals can enhance the photocurrent of CuO nanoarrays, resulting from the higher charge separation efficiency and transfer rate. In addition, the effects of small biases (–0.1 and 0.1 V) on the photocurrent and photogenerated charge dynamics in the aforementioned photoelectrodes were evaluated. A small bias was found to not influence the macroscopic dynamical process during charging and discharging of the CuO photoelectrode, but it was more correlated with the microscopic dynamics. Additionally, the built-in electric field in the CuO nanoarray/TiO2 heterojunction could be affected by a small external bias, thereby influencing the charge separation and charge diffusion concentration, which, subsequently, influenced the charge diffusion length, L. In contrast, L in the pristine CuO nanoarray was not improved under a small reverse bias, because the small reverse bias could not efficiently improve the diffusion concentration owing to the lack of a built-in electric field to dissociate electron-hole pairs. These kinetic mechanisms are helpful in understanding the photoelectric conversion process in heterogeneous photoelectrodes.

Epitaxial Grown Sb2Se3@Sb2S3 Core-Shell Nanorod Radial-Axial Hierarchical Heterostructure with Enhanced Photoelectrochemical Water Splitting Performance.

Antimony selenide (Sb2Se3) as a light-harvesting material has gradually attracted the attention of researchers in the field of photoelectrocatalysis. Uniquely, the crystal structure consists of one-dimensional (Sb4Se6)n ribbons, with an efficient carrier transport along the ribbon [001] direction. Herein, a novel Sb2Se3@Sb2S3 core-shell nanorod radial-axial hierarchical heterostructure was successfully fabricated by epitaxial growth strategy. Taking advantage of the isomorphous and anisotropic binding modes of (Sb4S(e)6)n ribbons for Sb2Se3 and Sb2S3, the epitaxially grown core-shell heterostructure forms a van der Waals heterojunction across the radial direction and covalently bonded heterojunction along the axial direction. A photocurrent of 1.37 mA cm-2 was achieved at 0 V vs RHE for the hierarchical Sb2Se3@Sb2S3 nanorod photoelectrode with [101] preferred orientation, up to 40 times higher than for pure Sb2Se3. Moreover, the FeOOH was introduced as a cocatalyst. The photoelectrode decorated with FeOOH shows better stability with a H2 generation rate of 18.9 μmol cm-2 h-1 under neutral conditions. This study provides a new insight into the design of antimony chalcogenide heterostructure photoelectrodes for photoelectrochemical water splitting.

Homogeneous Photoelectrochemical Aptasensors for Tetracycline Based on Sulfur-Doped g-C3N4/n-GaN Heterostructures Formed through Self-Assembly.

The complex synthesis of photoelectric materials and the difficulty of fixing the identification elements on the photoelectrode are long-standing problems in the field of photoelectrochemical (PEC) biosensing. In this work, a simple PEC aptasensor construction strategy based on a sulfur-doped g-C3N4 (SCN)/n-GaN heterostructure photoelectrode was proposed. The SCN/n-GaN heterostructure can be formed through self-assembly in solution since SCN can be uniformly dispersed in solution. In addition, as a dual-function mediate, an aptamer can be fixed on an SCN substrate automatically because of the good adsorption performance of SCN. Therefore, tedious steps of PEC electrode preparation and the fixing of recognition elements were both avoided. Compared with the traditional ones, the construction difficulty and time cost of the prepared PEC aptasensors are greatly reduced. The simplified experimental process improves the stability and reproducibility of the aptasensor. Finally, tetracycline (TET) was used as a model target to verify the sensing performance of the proposed PEC strategy. TET can consume the photogenerated holes of the SCN/n-GaN heterostructure, promote carrier migration, and result in the change in the photocurrent. The linear relationship between the change in the photocurrent intensity and the TET concentration can be used to detect TET. The aptasensor has a linear range of 0.10-10.0 nmol L-1 and the detection limit is 0.030 nmol L-1 (3S/N). The aptasensor was applied to the detection of TET in milk samples with satisfactory results.

Construction of ZnO@NiO heterostructure photoelectrodes for improved photoelectrochemical performance

In this report, a p-n junction has been constructed using ZnO/NiO heterostructured photoelectrode by spin coating NiO layers over vertically aligned ZnO nanorod arrays to demonstrate its potential in water splitting applications. Before investigating their PEC performance, we thoroughly studied the introduction of NiO layers on the structure, morphology and light absorption property of ZnO nanorods. 9 layered NiO coated ZnO nanorods exhibited optimum photocurrent density of 0.251 mA/cm2 at 0.8 V vs. Ag/AgCl which is attributed to its high absorbance and better charge transfer as recorded from UV–Vis and EIS data. Furthermore, we also studied the effect of (cation (Mg) and anion (Cl)) doping in PEC performance of ZnO nanorods on this optimized sample. Cl_ZnO/NiO showed high Jph of 1.282 mA/cm2 at 1.2 V vs. Ag/AgCl under visible light illumination. The reason behind better photoresponse is its enhanced absorption and well-defined p-n heterojunction between Cl_ZnO and NiO which favoured the separation and transfer of the photocarriers. The results displayed in this work provides a suitable approach of building p-n junction for high performance PEC water oxidation.

Photogenerated Hole-Induced Chemical-Chemical Redox Cycling Strategy on a Direct Z-Scheme Bi2S3/Bi2MoO6 Heterostructure Photoelectrode: Toward an Ultrasensitive Photoelectrochemical Immunoassay.

To achieve high sensitivity for biomolecule detection in photoelectrochemical (PEC) bioanalysis, the ideal photoelectrode and ingenious signaling mechanism play crucial roles. Herein, the feasibility of the photogenerated hole-induced chemical-chemical redox cycling amplification strategy on a Z-scheme heterostructure photoelectrode was validated, and the strategy toward enhanced multiple signal amplification for advanced PEC immunoassay application was developed. Specifically, a direct Z-scheme Bi2S3/Bi2MoO6 heterostructure was synthesized via a classic hydrothermal method and served as a photoelectrode for the signal response. Under the illumination, the PEC chemical-chemical redox cycling (PECCC) among 4-aminophenol generated by the enzymatic catalysis from a sandwich immunoassay, ferrocene as a mediator, and tris (2-carboxyethyl) phosphine as a reducing agent was run on the Z-scheme Bi2S3/Bi2MoO6 heterostructure photoelectrode. Exemplified by interleukin-6 (IL-6) as the target, the applicability of the strategy was studied in a PEC immunoassay. Thanks to the multiple signal amplification originating from the high efficiency of the PECCC redox cycling system, the enzymatic amplification, and the fine performance of the Z-scheme Bi2S3/Bi2MoO6 heterostructure photoelectrode, the assay for IL-6 exhibits a very low detection limit of 2.0 × 10-14 g/mL with a linear range from 5.0 × 10-14 to 1.0 × 10-8 g/mL. This work first validates the feasibility of the PECCC redox cycling on the Z-scheme heterostructure photoelectrode and the good performance of the strategy in PEC bioanalysis. We envision that it would provide a new prospective for highly sensitive PEC bioanalysis on the basis of a Z-scheme heterostructure.

Flexible BiVO4/WO3/ITO/Muscovite Heterostructure for Visible-Light Photoelectrochemical Photoelectrode

Flexible electronics has recently captured extensive attention due to its intriguing functionalities and great potential for influencing our daily life. In addition, with the increasing demand for green energy, photoelectrochemical (PEC) water splitting is a clean process that directly converts solar energy to chemical energy in the form of hydrogen. Thus the development of flexible green energy electronics represents a new domain in the research field of energy harvesting. In this work, we demonstrate the BiVO4 (BVO)/WO3/ITO/muscovite heterostructure photoelectrode for water splitting with flexible characteristics. The performance of BVO was modified by specific crystal facets, and the BVO/WO3 bilayer exhibited superior performance of 33% enhanced PEC activity at 1 V vs Ag/AgCl compared with pure BVO due to the proper staggered band alignment. Moreover, excellent mechanical stability was verified by a series of bending modes. This study demonstrates a pathway to a flexible photoelectrode for developing innovative devices for solar fuel generation.

Arrays of needle-like TiO2/CdS nanorod heterostructure photoelectrodes with enhanced photoelectrochemical properties fabricate by pulsed laser deposition

To improve the photoelectrochemical properties of TiO 2 /CdS composite nanorod electrodes, we developed a one-step quantum dot (QD) synthesis and assembly process based on pulsed laser deposition (PLD). An advantage of this method is that it does not involve ligand-exchange processing or wet chemical methods that might destabilize the QD attachment. By using PLD, CdS QDs were successfully grown on a dense array of TiO 2 nanorods, forming needle-like heterostructures whose photophysics depends on the laser pulse energy. The XRD results indicated that the products were composed of the tetragonal rutile, TiO 2 and hexagonal CdS. The TiO 2 /CdS heterostructures fabricated with this method are very stable and exhibit promising photoelectrochemical characteristics for photovoltaic applications. The best results are obtained for a PLD laser pulse energy of 300 mJ, which produces TiO 2 /CdS heterostructure nanorod electrodes that, when illuminated at AM 1.5 G, have a photocurrent density exceeding 4.7 mA cm −2 at 0 V versus a saturated calomel electrode. • Pulsed laser deposition (PLD) is a promising technique for fabricating quantum dot (QD) without ligand-exchange. • We grow CdS QDs on a dense array of TiO 2 nanorods, forming needle-like heterostructures. • TiO 2 /CdS( N ) electrodes exhibit a stable photocurrent when illuminated with 100 mW cm −2 of simulated sunlight.

Synchronous etching and W-doping for 3D CdS/ZnO/TiO2 hierarchical heterostructure photoelectrodes to significantly enhance the photoelectrochemical performance

Herein, the three-dimensional ZnO nanorod/TiO2 nanosheet films are constructed and optimized by synchronous etching and W-doping, which is demonstrated as an effective strategy to improve the photoelectrochemical performance of CdS/ZnO/TiO2 photoelectrodes. Notably, the ZnO nanorods preferentially grow on the {101} facet of TiO2 nanosheets, which can extend light scattering path-ways for light absorption, and effectively improve the electron transport due to the lower conduction band edge of {101} facet than that of highly exposed {001} facet for TiO2 nanosheets. Moreover, through the effects of synchronous etching and W-doping, the ZnO nanorods become ZnO nanotubes and the rough etched layers with W-doping are formed on the surface of ZnO/TiO2 films, which can improve the light absorption due to the enhanced light scattering, accelerate the photogeneratedcharges separation and transport owing to the introduction of W-doped energy level, and increase the electron density becauseof the different valences between W6+ and Zn2+. Benefiting by these superior properties, the CdS quantum-dots are densely and uniformly loaded on the surface of ZnO/TiO2 films, which can effectively improve the visible light absorption, heterojunction areas and charge injection efficiency. Therefore, the optimal photocurrent density (5.6 mA cm−2) of etched and W-doped CdS/ZnO/TiO2 photoelectrodes is remarkably enhanced.

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.

Recent progress of heterostructure-based photoelectrodes in photoelectrochemical biosensing: a mini review

Photoelectrochemical (PEC) biosensing has received increasing attention due to its great potential in the analysis of biomarkers. The performance of a PEC biosensor depends largely on photosensitive materials. The photoactive materials with excellent properties are of great importance to realize advanced PEC bioassays. Recently, as a special class of nanocomposites, heterostructures consisting of different types of semiconductors with potential applications in PEC systems have witnessed the rapid development to improve the performance of PEC biosensors. In this review, the research progress on the promising heterostructures has been introduced and summarized, and the applications of such heterostructures in PEC bioassays are provided. The future development of heterostructures pertaining to PEC biosensing systems has also been briefly discussed.

In Situ Integration of ReS2/Ni3S2 p-n Heterostructure for Enhanced Photoelectrocatalytic Performance.

The excellent light absorption, low electron-hole recombination rate, and fast reaction kinetics of photogenerated charges are urgently needed for photoelectrochemical (PEC) water splitting. Herein, a novel p-n heterostructure photoelectrode (ReS2/Ni3S2) is constructed via a one-step hydrothermal method, which shows remarkable HER activity under illumination such as a low overpotential (η10) of 106 mV, high IPCE of 10-15%, and good stability. High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) reveal that the intimate interface and strong electron interaction between ReS2 and Ni3S2 can enhance the light adsorption and provide abundant active sites. The transient absorption (TA) spectroscopy and impedance spectroscopy analyses (EIS) demonstrate the prolonged carrier lifetime and fast charge transfer. All of these are responsible for the improvement of reaction kinetics. This work provides a brand new avenue to explore efficient photoelectrocatalysts for water splitting.

Improvement of an Al2O3/CuO heterostructure photoelectrode by controlling the Al2O3 precursor concentration

An Al2O3 capping layer was grown on a CuO photoelectrode using microwave-chemical bath deposition. We investigated the effects of the concentration of the Al2O3 precursor solution on the morphological, structural, optical, electrical and photoelectrochemical properties of the Al2O3/CuO heterostructure photoelectrode. XPS analysis confirmed that the CuO was structurally stabilized by the Al2O3 capping layer. In addition, we found that the morphology, (020) XRD peak intensity, (020) XRD peak full width at half maximum, optical energy band gap, flat-band potential and acceptor density values of the Al2O3/CuO heterostructure photoelectrode were strongly dependent on the concentration of the Al2O3 precursor solution. Among the photoelectrodes evaluated in this study, the Al2O3/CuO heterostructure photoelectrode obtained with an Al2O3 precursor concentration of 3mM had the highest crystallinity, flat-band potential and acceptor density. It also exhibited a photocurrent density of -2.64mA/cm2 (vs. SCE at −0.55V) and a photostability of approximately 55%. In contrast, bare CuO had a photocurrent density of −1.8mA/cm2 (vs. SCE at −0.55V) and a photostability of 25%. Based on our results, the photocurrent density and photostability of the CuO photoelectrode could be dramatically improved by capping with an Al2O3 layer using a 3mM precursor concentration.

Effect of directional light dependence on enhanced photoelectrochemical performance of ZnIn2S4/TiO2 binary heterostructure photoelectrodes

This work focuses on dependence of incident light illumination direction on the photoelectrochemical performance of hydrothermally prepared two dimensional ZnIn2S4 nanosheets/one dimensional rutile TiO2 nanorod arrays (2D ZIS NS's/1D R-TNR's) heterostructure photoelectrodes. The 2D ZIS NS's are grown on the 1D R-TNR's/FTO substrates by varying the concentration of ZIS precursor in the hydrothermal method, forming 2D ZIS NS's/1D R-TNR's heterostructure. One dimensional rutile TiO2 nanorod arrays (1D R-TNR's) provide excellent electron transfer pathway and role of the 2D ZIS NS's is to offer effective visible light absorbing surface onto the 1D R-TNR's and extended the absorbance spectrum from ultraviolet to visible region; bathochromic shift occurs. This binary heterostructure provides the lower resistance, shortest electron transport time and less recombination under the back side illumination (BSI) and effectively contributed to charge separation and transport in 2D ZIS NS's/1D R-TNR's heterostructure. However, the results demonstrate that the front side illumination (FSI) results in poor PEC performance; because of blockage of light at the surface of 2D ZIS NS's. Further, these results show that BSI could also be applicable for other heterostructures, where the low band gap sulfide materials need to be engineered on large band gap metal oxide for energy harvesting in future prospect.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.