Synergies of co-doping in ultra-thin hematite photoanodes for solar water oxidation: In and Ti as representative case

Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. The challenge is to develop corrosion resistant and chemically stable semiconductors that absorb sunlight in the visible region and, at the same time, have the band edges matching with the redox level of water. In this work, hematite (α-Fe₂O₃) thin films were prepared onto an indium-doped tin oxide (ITO; In:SnO₂) substrate by e-beam evaporation of Fe, followed by air annealing at two different temperatures: 350 and 500 °C. The samples annealed at 500 °C show an in situ diffusion of indium from the ITO substrate to the surface of α-Fe₂O₃, where it acts as a dopant and enhances the photoelectrochemical properties of hematite. Structural, optical, chemical and photoelectrochemical analysis reveal that the diffusion of In at 500 °C enhances the optical absorption, increases the electrode–electrolyte contact area by changing the surface topology, improves the carrier concentration and shifts the flat band potential in the cathodic direction. Further enhancement in photocurrent density was observed by ex situ diffusion of Ti, deposited in the form of nanodisks, from the top surface to the bulk. The in situ In diffused α-Fe₂O₃ photoanode exhibits an improved photoelectrochemical performance, with a photocurrent density of 145 μA cm⁻² at 1.23 V_RHE, compared to 37 μA cm⁻² for the photoanode prepared at 350 °C; it also decreases the photocurrent onset potential from 1.13 V to 1.09 V. However, the In/Ti co-doped sample exhibits an even higher photocurrent density of 290 μA cm⁻² at 1.23 V_RHE and the photocurrent onset potential decreases to 0.93 V_RHE, which is attributed to the additional doping and to the surface becoming more favorable to charge separation.

Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. In this work, hematite (α-Fe₂O₃) thin film were modified by In³⁺ and Ti⁴⁺ co-doping for enhanced PEC performance.     

Efficient solar light-driven hydrogen generation using an Sn3O4 nanoflake/graphene nanoheterostructure

Herein, we report Sn₃O₄ and Sn₃O₄ nanoflake/graphene for photocatalytic hydrogen generation from H₂O and H₂S under natural “sunlight” irradiation. The Sn₃O₄/graphene composites were prepared by a simple hydrothermal method at relatively low temperatures (150 °C). The incorporation of graphene in Sn₃O₄ exhibits remarkable improvement in solar light absorption, with improved photoinduced charge separation due to formation of the heterostructure. The highest photocatalytic hydrogen production rate for the Sn₃O₄/graphene nanoheterostructure was observed as 4687 μmol h⁻¹ g⁻¹ from H₂O and 7887 μmol h⁻¹ g⁻¹ from H₂S under natural sunlight. The observed hydrogen evolution is much higher than that for pure Sn₃O₄ (5.7 times that from H₂O, and 2.2 times from H₂S). The improved photocatalytic activity is due to the presence of graphene, which acts as an electron collector and transporter in the heterostructure. More significantly, the Sn₃O₄ nanoflakes are uniformly and parallel grown on the graphene surface, which accelerates the fast transport of electrons due to the short diffusion distance. Such a unique morphology for the Sn₃O₄ along with the graphene provides more adsorption sites, which are effective for photocatalytic reactions under solar light. This work suggests an effective strategy towards designing the surfaces of various oxides with graphene nanoheterostructures for high performance of energy-conversion devices.

Herein, we have demonstrated the synthesis of the two-dimensional hierarchical Sn₃O₄/graphene nanostructure by a facile solvothermal method. The nanostructure has been used as a photocatalyst for hydrogen production under solar light.     

Photoelectrochemical study of carbon-modified p-type Cu2O nanoneedles and n-type TiO2−x nanorods for Z-scheme solar water splitting in a tandem cell configuration

Nanostructured photoelectrodes with a high surface area and tunable optical and electrical properties can potentially benefit a photoelectrochemical (PEC) water splitting system. The PEC performance of a nanostructured photoelectrode is usually quantified in a standard three-electrode configuration under potential-assisted conditions because of the additional overpotentials for the two half-reactions of water splitting. However, it is a necessity to fully recognize their potential to split water under unassisted conditions by designing a tandem cell that can provide sufficient voltage to split water. Herein, we present a tandem cell consisting of carbon-modified cuprous oxide (C/Cu₂O) nanoneedles and oxygen-deficient titanium dioxide (TiO_2−x) nanorods for unassisted solar water splitting. The synthesized photoelectrodes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) techniques. The tandem cell performance was analyzed by measuring the current–voltage responses in various photoelectrode configurations to validate the collective contributions of both photoelectrodes to unassisted solar water splitting. The PEC properties of C/Cu₂O nanoneedles coupled with TiO_2−x nanorods in a tandem configuration exhibited a photocurrent density of 64.7 μA cm⁻² in the absence of any redox mediator and external bias. This photocurrent density can be further enhanced with an application of external bias. Moreover, the heterojunction formed by the above-mentioned nanostructured photoelectrodes in intimate contact and in the absence of water exhibited 2 μA cm⁻² UV photoresponsivity at 1.5 V with promising rectifying characteristics of a diode.

Nanostructured photoelectrodes with high surface-area and tunable optical-electrical properties can potentially benefit a Z-scheme photoelectrochemical water splitting systems to generate solar fuels at no external bias.     

Photoelectrochemical enzymatic sensor for glucose based on Au@C/TiO2 nanorod arrays

In this work, a photoelectrochemical (PEC) glucose biosensor was synthesized on the basis of a type of Au@C/TiO₂ composite by using an unsophisticated secondary hydrothermal strategy. The compounded Au@C/TiO₂ material was characterized by XRD, SEM, TEM, UV-vis, and XPS to identify the composition and the purity of the phase. Glucose oxidase (GODx) was immobilized on the Au@C/TiO₂. The PEC biosensor presented satisfactory stability and outstanding reproducibility. The range and the sensitivity of the linear measurement were 0.1–1.6 mM and 29.76 μA mM⁻¹ cm⁻², respectively, and the detection limit was low (0.049 mM). The GODx/Au@C/TiO₂/FTO biosensor presented excellent efficiency in detecting glucose, suggesting the great potential application of this synthesized material in PEC biosensors.

In this work, a photoelectrochemical (PEC) glucose biosensor was synthesized on the basis of a type of Au@C/TiO₂ composite by using an unsophisticated secondary hydrothermal strategy.     

Enhanced photoelectrochemical performance of LaFeO3 photocathode with Au buffer layer

Due to an appropriate band gap of 2.07 eV, perovskite LaFeO₃ (LFO) is an alternative candidate for high-efficiency photoelectrochemical (PEC) systems. However, the photocurrent of the LFO photocathode is too low to be practical. Herein, we prepared a LFO film with high crystal quality by inserting an Au thin layer between LFO and FTO in the LFO/FTO photocathode. Accordingly, an effective improvement PEC performance could be obtained and the photocurrent density of the FTO/Au/LFO electrode was increased to −19.60 μA cm⁻² at 0.6 V vs. RHE, which is 4.1 times higher than that of pristine FTO/LFO electrode. Based on the experimental and theoretical analysis, the enhancement of the photocurrent was attributed to the strong light harvesting, enhanced charge separation, and increased charge-collection efficiency of the Au/LFO structure. This work provides a promising strategy to develop high-efficiency PEC electrodes, and has potential to be applied in the visible-light water splitting area.

Au/LFO obtained by facile magnetron sputtering and sol–gel process presents a remarkable improvement in photocurrent up to −19.60 μA cm⁻².     

Efficient photoelectrochemical water oxidation using a TiO2 nanosphere-decorated BiVO4 heterojunction photoanode

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting. In this work, we fabricated a highly efficient TiO₂/BiVO₄ heterojunction photoanode for PEC water oxidation via a simple hydrothermal method. The resulting heterojunction photoanodes show enhanced PEC performance compared to the bare BiVO₄ due to the simultaneous improvements in charge separation and charge transfer. Under simulated sunlight illumination (AM 1.5G, 100 mW cm⁻²), a high photocurrent of 3.3 mA cm⁻² was obtained at 1.23 V (vs. the reversible hydrogen electrode (RHE)) in a neutral solution, which exceeds those attained by the previously reported TiO₂/BiVO₄ heterojunctions. When a molecular Co–cubane catalyst was immobilized onto the electrode, the performance of the TiO₂/BiVO₄ heterojunction photoanode can be further improved, achieving a higher photocurrent density of 4.6 mA cm⁻² at 1.23 V, an almost three-fold enhancement over that of the bare BiVO₄. These results engender a promising route to designing an efficient photoelectrode for PEC water splitting.

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting.     

A significant enhancement of bulk charge separation in photoelectrocatalysis by ferroelectric polarization induced in CdS/BaTiO3 nanowires

Efficient charge separation, in particular bulk charge separation (BCS), is one of the most critical factors in determining the performance of photoelectrochemical (PEC) water-splitting. The BCS enhancement of CdS/BaTiO₃ (CdS/BTO) nanowires (NWs) in photoelectrocatalysis has rarely been reported. This paper describes a remarkable PEC properties promotion of the CdS/BTO NWs, which is confirmed to be a result of the enhanced BCS efficiency induced by the ferroelectric polarization. The vertical arrays of BTO NWs endow fast transfer of carriers. Meanwhile, CdS is decorated uniformly on the surface of BTO NWs, which ensures a wide range of light absorption. After two negative polarizations, the CdS/BTO NWs have successfully obtained a remarkable photocurrent density, achieving 459.53 μA cm⁻² at 1.2 V_(vs.RHE), which is 2.86 times that of the unpolarized sample. However, after two positive polarizations, the photocurrent density dramatically decreases to 40.18 μA cm⁻² at 1.2 V_(vs.RHE), which is merely 0.25 times the original value. More importantly, the photocurrent density reaches up to a prominent value of −71.09 mA cm⁻² at −0.8 V_(vs.RHE) after two successive negative polarizations, which is a 40.87 mA cm⁻² enhancement with respect to the sample without poling. Significantly, at −0.8 V_(vs.RHE), the BCS efficiency of the CdS/BTO NWs is as high as 91.87% after two negative polarizations. The effects of ferroelectric polarization on the PEC performance of CdS/BTO NWs have been systematically studied. The results demonstrate that ferroelectric polarization, especially negative polarization, results in an internal electric field to tune band bending of CdS/BTO NWs, thus prominently enhancing the PEC performance.

Efficient charge separation, in particular bulk charge separation (BCS), is one of the most critical factors in determining the performance of photoelectrochemical (PEC) water-splitting.     

Constructing a TiO2/PDA core/shell nanorod array electrode as a highly sensitive and stable photoelectrochemical glucose biosensor

Developing stable PEC glucose biosensors with high sensitivity and low detection limit is highly desirable in the biosensor field. Herein, a highly stable and sensitive enzymatic glucose photoelectrochemical biosensor is rationally designed and fabricated by constructing TiO₂/PDA core/shell nanorod arrays. The TiO₂ nanorod as the core has the advantages of increasing charge transportation towards interfaces and enhancing the absorption of incident sunlight due to its single-crystal nature and one dimensional array structure. The PDA shell not only induces a rapid charge transfer across the interfaces but also stabilizes the biosensor performance by avoiding the decomposition of enzymes induced by the strong oxidizing holes from the TiO₂ core. A remarkable performance with an ultrahigh sensitivity of 57.72 μA mM⁻¹ cm⁻², a linear range of 0.2–1.0 mM, a glucose detection limit of 0.0285 mM (S/N = 3) and a high sensitivity of 8.75 μA mM⁻¹ cm⁻² in a dynamic range of 1.0–6.0 mM were obtained for the glucose detection. This study might provide a strategy for constructing inorganic/organic core/shell structures with a satisfactory PEC performance.

Developing stable PEC glucose biosensors with high sensitivity and low detection limit is highly desirable in the biosensor field.     

Sn-doped 3D ATO inverse opal/hematite hierarchical structures: facile fabrication and efficient photoelectrochemical performance

The coupling of hematite with a three-dimensional (3D) conductive inverse opal (IO) skeleton provides an efficient route to enhance the photoelectrochemical (PEC) properties of hematite without changing its chemical composition. In this work, novel 3D antimony-doped SnO₂ (ATO) IO/hematite heterostructures were facilely fabricated, and their PEC properties were thoroughly studied. Analysis of the morphologies and photocurrent densities of the 3D ATO IO//Fe₂O₃ heterostructures reveals that the high conductivity of the ATO skeleton as well as the high specific area and good light harvesting properties of the 3D IO structures greatly enhance their PEC performance. In particular, further morphology tuning by changing the diameters of the ATO IO skeletons could optimize the optical and electrical properties of the as-prepared heterostructures, demonstrating the important influence of morphology engineering on PEC performance. Moreover, after a simple Sn-doping process, the PEC properties of the as-prepared structure could be further enhanced; a photocurrent density of 1.28 mA cm⁻² at 1.23 V vs. RHE was obtained under AM 1.5G illumination.

We report the rational design, morphology engineering and enhanced photoelectrochemical properties of Sn-doped ATO IO/hematite heterostructures.     

TiO2–Au composite nanofibers for photocatalytic hydrogen evolution

TiO₂-based materials for photocatalytic hydrogen (H₂) evolution have attracted much interest as a renewable approach for clean energy applications. TiO₂–Au composite nanofibers (NFs) with an average fiber diameter of ∼160 nm have been fabricated by electrospinning combined with calcination treatment. In situ reduced gold nanoparticles (NPs) with uniform size (∼10 nm) are found to disperse homogenously in the TiO₂ NF matrix. The TiO₂–Au composite NFs catalyst can significantly enhance the photocatalytic H₂ generation with an extremely high rate of 12 440 μmol g⁻¹ h⁻¹, corresponding to an adequate apparent quantum yield of 5.11% at 400 nm, which is 25 times and 10 times those of P25 (584 μmol g⁻¹ h⁻¹) and pure TiO₂ NFs (1254 μmol g⁻¹ h⁻¹), respectively. Furthermore, detailed studies indicate that the H₂ evolution efficiency of the TiO₂–Au composite NF catalyst is highly dependent on the gold content. This work provides a strategy to develop highly efficient catalysts for H₂ evolution.

The H₂ production rate of TiO₂–Au nanofibers is dramatically improved to 12 440 μmol g⁻¹ h⁻¹, 10 times that of pure TiO₂.     

Surface plasmon-driven photoelectrochemical water splitting of a Ag/TiO2 nanoplate photoanode

A silver/titanium dioxide nanoplate (Ag/TiO₂ NP) photoelectrode was designed and fabricated from vertically aligned TiO₂ nanoplates (NP) decorated with silver nanoparticles (NPs) through a simple hydrothermal synthesis and electrodeposition route. The electrodeposition times of Ag NPs on the TiO₂ NP were crucial for surface plasmon-driven photoelectrochemical (PEC) water splitting performance. The Ag/TiO₂ NP at the optimal deposition time of 5 min with a Ag element content of 0.53 wt% demonstrated a remarkably high photocurrent density of 0.35 mA cm⁻² at 1.23 V vs. RHE under AM 1.5G illumination, which was 5 fold higher than that of the pristine TiO₂ NP. It was clear that the enhanced light absorption properties and PEC performance for Ag/TiO₂ NP could be effectively adjusted by simply controlling the loading amounts of metallic Ag NPs (average size of 10–30 nm) at different electrodeposition times. The superior PEC performance of the Ag/TiO₂ NP photoanode was attributed to the synergistic effects of the plasmonic Ag NPs and the TiO₂ nanoplate. Interestingly, the plasmonic effect of Ag NPs not only increased the visible-light response (λ_max = 570 nm) of TiO₂ but also provided hot electrons to promote photocurrent generation and suppress charge recombination. Importantly, this study offers a potentially efficient strategy for the design and fabrication of a new type of TiO₂ hybrid nanostructure with a plasmonic enhancement for PEC water splitting.

A hybrid nanostructure Ag/TiO₂ photoelectrode for PEC water splitting with a remarkable high photocurrent density, 0.35 mA cm⁻² (5 fold higher than that of the pristine TiO₂ photoeletrode) was fabricated by a facile one-pot hydrothermal and electrodeposition method.     

Preparation and photoelectrochemical properties of BiFeO3/BiOI composites

BiFeO₃ thin films were spin coated onto FTO. BiFeO₃/BiOI composites have been successfully synthesized by an electrochemical deposition method. The morphology, structure and optical absorption properties of the as-synthesized samples were characterized via XRD, SEM, and UV-Vis DRS. The effect of the BiOI electrodeposition cycles on the photoelectrochemical properties of the BiFeO₃/BiOI composites were investigated. The results showed that the photoelectrochemical properties were enhanced under simulated solar light. The composite could achieve an optimum photocurrent density of 16.03 μA cm⁻² at 0 V (vs. Ag/AgCl), which is more than twice that of pure BiFeO₃ thin films (6.3 μA cm⁻²). In addition, the Mott–Schottky curves indicate an improvement in the carrier density of the composite. The enhanced photoelectrochemical properties of the composites can be attributed to the formation of a heterojunction at the interface and the band bending of the ferroelectric material BiFeO₃.

We report the preparation, optical absorption and enhanced photoelectrochemical properties of novel BiOI-decorated BFO thin films heterostructures.     

Growth of narrow-bandgap Cl-doped carbon nitride nanofibers on carbon nitride nanosheets for high-efficiency photocatalytic H2O2 generation

Heterojunction construction has been proved to be an effective way to enhance photocatalysis performance. In this work, Cl-doped carbon nitride nanofibers (Cl–CNF) with broadband light harvesting capacity were in situ grown on carbon nitride nanosheets (CNS) by a facile hydrothermal method to construct a type II heterojunction. Benefiting from the joint effect of the improved charge carriers separation efficiency and a broadened visible light absorption range, the optimal heterostructure of Cl–CNF/CNS exhibits a H₂O₂ evolution rate of 247.5 μmol g⁻¹ h⁻¹ under visible light irradiation, which is 3.4 and 3.1 times as much as those of Cl–CNF (72.2 μmol g⁻¹ h⁻¹) and CNS (80.2 μmol g⁻¹ h⁻¹), respectively. Particularly, the heterojunction nanostructure displays an apparent quantum efficiency of 23.67% at 420 nm. Photoluminescence spectra and photocurrent measurements both verified the enhanced charge carriers separation ability. Our work provides a green and environmentally friendly strategy for H₂O₂ production by elaborate nanostructure design.

The Cl-CNF/CNS heterostructure can efficiently boost the photocatalytic H₂O₂ generation activity.     

MOF-derived (MoS2, γ-Fe2O3)/graphene Z-scheme photocatalysts with excellent activity for oxygen evolution under visible light irradiation

Constructing Z-scheme heterojunctions is considered as an effective strategy to obtain catalysts of high efficiency in electron–hole separation in photocatalysis. Unfortunately, suitable heterojunctions are difficult to fabricate because the direct interaction between two semiconductors may lead to unpredictable negative effects such as electron scattering or electron trapping due to the existence of defects which causes the formation of new substances. Furthermore, the van der Waals contact between two semiconductors also results in bad electron diffusion. In this work, a MOF-derived carbon material as a Z-scheme photocatalyst was synthesized via one-step thermal treatment of MoS₂ dots @Fe-MOF (MIL-101). Under visible light irradiation, the well-constructed Z-scheme (MoS₂, γ-Fe₂O₃)/graphene photocatalyst shows 2-fold photocatalytic oxygen evolution activity (4400 μmol g⁻¹ h⁻¹) compared to that of γ-Fe₂O₃/graphene (2053 μmol g⁻¹ h⁻¹). Based on ultraviolet photoelectron spectrometry (UPS), Mott–Schottky plot, photocurrent and photoluminescence spectroscopy (PL) results, the photo-induced electrons from the conduction band of γ-Fe₂O₃ could transport quickly to the valence band of MoS₂via highly conductive graphene as an electron transport channel, which could significantly enhance the electron–hole separation efficiency as well as photocatalytic performance.

The heterojunction between MoS₂ and γ-Fe₂O₃ was constructed via linking by in situ formed graphene, which resulted in a good photocatalyst for the oxygen evolution reaction, showing O₂ evolution activity of 4400 μmol g⁻¹ h⁻¹.     

Structure of Ni(OH)2 intermediates determines the efficiency of NiO-based photocathodes – a case study using novel mesoporous NiO nanostars

We report the wet chemical synthesis of mesoporous NiO nanostars (NS) as photocathode material for dye-sensitized solar cells (DSSCs). The growth mechanism of NiO NS as a new morphology of NiO is assessed by TEM and spectroscopic investigations. The NiO NS are obtained upon annealing of preformed β-Ni(OH)₂ into pristine NiO with low defect concentrations and favorable electronic configuration for dye sensitization. The NiO NS consist of fibers self-assembled from nanoparticles yielding a specific surface area of 44.9 m² g⁻¹. They possess a band gap of 3.83 eV and can be sensitized by molecular photosensitizers bearing a range of anchoring groups, e.g. carboxylic acid, phosphonic acid, and pyridine. The performance of NiO NS-based photocathodes in photoelectrochemical application is compared to that of other NiO morphologies, i.e. nanoparticles and nanoflakes, under identical conditions. Sensitization of NiO NS with the benchmark organic dye P1 leads to p-DSSCs with a high photocurrent up to 3.91 mA cm⁻² whilst the photoelectrochemical activity of the NiO NS photocathode in aqueous medium in the presence of an irreversible electron acceptor is reflected by generation of a photocurrent up to 23 μA cm⁻².

NiO nanostructures prepared from β-Ni(OH)₂ intermediates exhibit favorable electronic properties for functional photocathodes for solar energy conversion devices.     

Enhanced photocatalytic water splitting of a SILAR deposited α-Fe2O3 film on TiO2 nanoparticles

We have investigated the effect of deposition of a α-Fe₂O₃ thin layer on a substrate of TiO₂ nanoparticles for photoelectrochemical (PEC) water splitting. The TiO₂ layer was coated on an FTO substrate using the paste of TiO₂ nanoparticles. The α-Fe₂O₃ layer was deposited on the TiO₂ thin film, using the method of Successive Ionic Layer Adsorption and Reaction (SILAR) with different cycles. Various characterizations including XRD, EDX and FE-SEM confirm the formation of α-Fe₂O₃ and TiO₂ nanoparticles on the electrode. The UV-visible absorption spectrum confirms a remarkable enhancement of the absorption of the α-Fe₂O₃/TiO₂/FTO composite relative to the bare TiO₂/FTO. In addition, the photocurrents of the composite samples are remarkably higher than the bare TiO₂/FTO. This is mainly due to the low band gap of α-Fe₂O₃, which extends the absorption spectrum of the α-Fe₂O₃/TiO₂ composite toward the visible region. In addition, the impedance spectroscopy analysis shows that the recombination rate of the charge carriers in the α-Fe₂O₃/TiO₂ is lower than that for the bare TiO₂. The best PEC performance of the α-Fe₂O₃/TiO₂ sample was achieved by the sample of 70 cycles of α-Fe₂O₃ deposition with about 7.5 times higher photocurrent relative to the bare TiO₂.

Optimization of photoelectrochemical water splitting by a composite of SILAR-deposited α-Fe₂O₃ thin film on a substrate of TiO₂ nanoparticles.     

A Cu2+-doped two-dimensional material-based heterojunction photoelectrode: application for highly sensitive photoelectrochemical detection of hydrogen sulfide

In this work, on the basis of a Cu²⁺-doped two-dimensional material-based heterojunction photoelectrode, a novel anodic photoelectrochemical (PEC) sensing platform was constructed for highly sensitive detection of endogenous H₂S. Briefly, with g-C₃N₄ and TiO₂ as representative materials, the sensor was fabricated by modifying g-C₃N₄/TiO₂ nanorod arrays (NAs) onto the surface of fluorine-doped tin oxide (FTO) and then doping Cu²⁺ as a Cu_xS (x = 1, 2) precursor. After the binding of S²⁻ with surface-attached Cu²⁺, the signal was quenched owing to the in situ generation of Cu_xS which offers trapping sites to hinder generation of photocurrent signals. Since the photocurrent inhibition was intimately associated with the concentration of S²⁻, a highly sensitive PEC biosensor was fabricated for H₂S detection. More importantly, the proposed sensing platform showed the enormous potential of g-C₃N₄/TiO₂ NAs for further development of PEC bioanalysis, which may serve as a common basis for other semiconductor applications and stimulates the exploration of numerous high-performance nanocomposites.

In this work, on the basis of a Cu²⁺-doped two-dimensional material-based heterojunction photoelectrode, a novel anodic photoelectrochemical (PEC) sensing platform was constructed for highly sensitive detection of endogenous H₂S.     

Deposition of platinum on boron-doped TiO2/Ti nanotube arrays as an efficient and stable photocatalyst for hydrogen generation from water splitting

An efficient photocatalyst of boron-doped titanium dioxide/titanium nanotube array-supported platinum particles (Pt–B/TiO₂/Ti NTs) was fabricated for photocatalytic water splitting for hydrogen production through a two-step route. First, B/TiO₂/Ti NTs were prepared by anodic oxidation using hydrofluoric acid as electrolyte and boric acid as a B source. Then, Pt particles were deposited on the surface of B/TiO₂/Ti NTs by photo-assisted impregnation reduction. The structure and properties of Pt–B/TiO₂/Ti NTs were characterized by various physical measurements which showed the successful fabrication of Pt–B/TiO₂/Ti NTs. The Pt–B/TiO₂/Ti NTs, with a B-doping content of 15 mmol L⁻¹, showed the highest photocatalytic activity and exhibited a photocatalytic hydrogen-production rate of 384.9 μmol g⁻¹ h⁻¹, which was 9.2-fold higher than that of unmodified TiO₂/Ti NTs (41.7 μmol g⁻¹ h⁻¹). This excellent photocatalytic performance was ascribed mainly to the synergistic effect of Pt and B, which could enhance the photocatalytic activity of TiO₂/Ti NTs.

Pt–B/TiO₂/Ti NTs, prepared by anodic oxidation and photo-deposition methods, showed excellent photocatalytic activity.     

Enhanced photoelectrochemical activity of Co-doped β-In2S3 nanoflakes as photoanodes for water splitting

This work is primarily focused on indium sulfide (β-In₂S₃) and cobalt (Co)-doped β-In₂S₃ nanoflakes as photoanodes for water oxidation. The incorporation of cobalt introduces new dopant energy levels increasing visible light absorption and leading to improved photo-activity. In addition, cobalt ion centers in β-In₂S₃ act as potential catalytic sites to promote electro-activity. 5 mol% Co-doped β-In₂S₃ nanoflakes when tested for photoelectrochemical water splitting exhibited a photocurrent density of 0.69 mA cm⁻² at 1.23 V, much higher than that of pure β-In₂S₃.

Doped indium sulfide as an efficient photocatalyst for water oxidation.     

Materials characterization of TiO2 nanotubes decorated by Au nanoparticles for photoelectrochemical applications

The structural and chemical modification of TiO₂ nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1–2 × 10⁻⁸ mbar) on TiO₂ nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO₂ NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of “hot spots”, the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO₂ NTs annealed at 650 °C was found to be much greater (14.7 μA cm⁻²) than the corresponding value (∼0.2 μA cm⁻²) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO₂ NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide (E_g ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials.

The structural and chemical modification of TiO₂ NTs by the deposition of a well-controlled Au deposit (0.01 mg cm⁻¹) was investigated using a combination of microscopic (SEM, STEM), analytical measurements (XPS, SERS, UV-Vis, XRD) and photoelectrochemical investigations.