Photoeletrochemical Research Articles

Ultrathin metal Ni layer on ZnO/TiO2 photoelectrodes with excellent photoeletrochemical performance in multiple electrolyte solutions

It is well known that the oxygen vacancy (Ovac) as the electron-donor dopant in semiconductor can increase the electron-holes separation in photoeletrochemical (PEC) water splitting. Furthermore, the metal Ni can promote the hydrogen evolution reaction (HER) on the surface of semiconductor. In this paper, the ZnO/TiO2 photoelectrodes with rich Ovac was synthesized by electrostatic adsorption through using ZIF-8 as the precursor. Then the ultrathin Ni layer with about 7 nm was deposited on the surface of ZnO/TiO2 (Ni/ZnO/TiO2) by vacuum thermal evaporation method. The Ni/ZnO/TiO2 photoelectrodes showed the highest photocurrent than ZnO/TiO2, Ni/ TiO2 and pure TiO2 photoelectrodes. The durability of Ni/ZnO/TiO2 photoelectrodes was keeping for 10 h in multiple electrolyte solutions under AM 1.5 G illumination and the photocurrent decline can be ignored. The UV–vis absorption spectra demonstrated that the ultrathin Ni layer showed plasma with ZnO/TiO2 for enhancing the water splitting performance. Furthermore, the ultrathin Ni layer enhanced the photogenerated charges transfer for improving the PEC performance. This work provides a new method for ultrathin metal Ni layer with Ovac semiconductor photoelectrode to improve the PEC performance in multiple electrolyte solutions.

High-performance self-powered photodetector based on Bi2O2Se nanosheets

2D layered material Bi2O2Se nanosheets, due to its high carrier mobility, near-ideal subthreshold swing, and high air-stability, which have shown great potential for applications in high-performance field-effect transistors and photodetector. Here, we have been successfully synthesized Bi2O2Se nanosheets via a facile one-step hydrothermal method. The Bi2O2Se nanosheets were characterized by scanning electron microscopy (SEM), Raman spectra and X-ray diffraction (XRD) patterns, which confirm an excellent crystallized of Bi2O2Se nanosheets. The as-prepared Bi2O2Se nanosheets were used to fabricate electrodes for a self-powered photodetector and exhibit preferable photoresponse activity. At 0 V, the photoeletrochemical (PEC) tests demonstrate that the responsivity and the response time of Bi2O2Se nanosheets can reach up to 20 μA W−1 and 0.12 s. Furthermore, the time stability and cycle stability also were measured. After a long time of testing, the photocurrent of Bi2O2Se nanosheets remained around 300 nA, and after processing 100 and 200 cycles, the photocurrent exhibits slight distinction. These findings indicate that Bi2O2Se nanosheets have great prospects for future applications in self-powered photodetector devices.

Using PbS–Au heterodimers as signal quencher for the sensitive photoelectrochemical immunoassay of amyloid β-protein

By using PbS–Au heterodimers as the signal quencher, TiO2/BiOI as matrix, a novel sandwich-type photoeletrochemical (PEC) biosensor for sensitive determination of amyloid β-protein (Aβ, ∼4 KDa) was developed. BiOI was attached to the surface of TiO2 and formed a heterogeneous structure (p-n junction), which enlarged the light harvest range and enhanced the electron transfer rate of TiO2. In order to quench the PEC signal, PbS–Au heterodimers were used as the labels to combine with Aβ. Owing to the competitively light energy harvesting and electron donor consuming effect of PbS–Au heterodimers, less light energy and electron donor arrived at TiO2/BiOI. In addition, Au directly contacted with PbS could enhance the electron seperation and transfer rate, and lead to improved competitiveness consumption of the electron donor. PbS–Au integrated with secondary antibodies formed PbS–Au-Ab2 bioconjugate, which would further obstruct the electron transfer and impede the interreaction between electron donor and photoelectrode surfaces. Owing to the unique PbS–Au heterodimer structure and the quenching effect of PbS–Au-Ab2 bioconjugate, the fabricated immunosensor for Aβ detection exhibited good stability, high sensitivity, and a low detection limit of 0.028 pg/mL (S/N = 3).

A nanostructured CuWO4/Mn3O4 with p/n heterojunction as photoanode toward enhanced water oxidation

In this paper, we report a novel photoanode fabricated by spin-coating n-type CuWO4 nano-ovoids on the surface of fluorine-doped tin oxide (FTO) glass and then modified with p-type Mn3O4 nanospheres using a deposition-annealing method. A novel nanocomposite (CuWO4/Mn3O4) with p/n heterojunction formed on the surface of FTO glass. The characterazation results of the nanocomposite indicate that the two moieties of the nanocomposite intimately contact with each other. The photoelectrochemical tests of the prepared CuWO4/Mn3O4 photoanode reveal that the electrode can produce larger anodic photocurrent and show enhanced incident photon-to-current efficiency (IPCE) than the bare CuWO4 photoanode does. Moreover, the PEC tandem cell assembled by using the CuWO4/Mn3O4 electrode as photoanode and Pt plate as counter electrode demonstrates enhanced photocatalytic activity and stability for photoeletrochemical (PEC) water splitting. The amount of hydrogen and oxygen, collected from the counter chamber and the photoanode chamber, separately, reached to 5.0 μmol and 2.3 μmol, respectively, under 2 h simulated sunlight irradiation at 1.20V vs. RHE bias without any sacrificial agent. The remarkable performance of the nanocomposite anode owe to the formed heterojunction structure in the nanocomposite, leading to high photoexcited charge transfer and separation.

Nanoflower like SnO2-TiO2 nanotubes composite photoelectrode for efficient photocathodic protection of 304 stainless steel

In this study, titanium dioxide nanotube arrays (TiO2-NTs) were prepared on titanium plates through a two-step anodization method and then the SnO2 nanoparticles were deposited onto TiO2-NTs by electrodeposition method to produce SnO2-TiO2-NTs. The electrodeposition time has a great influence on the photoeletrochemical (PEC) performance of SnO2-TiO2-NTs composite photoelectrode. The photocurrent density of SnO2-TiO2-NTs electrode increased up to 4 times as compared to pristine TiO2-NTs photoelectrode. Furthermore, open circuit potential and tafel curves were measured to evaluate the photocathodic protection properties of SnO2-TiO2-NTs. The corrosion potential dropped to -730 mV and the corrosion current density reached to 259.8 μA/cm−2. The results indicate that SnO2 deposition into the TiO2-NTs photo-electrode is a simple and effective way to protect stainless steel (304SS) from corrosion.

Enhanced Photoelectrochemical Water Oxidation by Fabrication of p-LaFeO3/n-Fe2O3 Heterojunction on Hematite Nanorods

The LaFeO3 film exhibits interesting p-type behavior and stable photocatalytic hydrogen production in aqueous solution, and we combine it with α-Fe2O3 nanorods to form a p-LaFeO3/n-Fe2O3 heterojunction to improve the photoeletrochemical (PEC) water oxidation performance of hematite. An atomic layer deposition (ALD) technique is adopted to deposit La2O3 controllably on β-FeOOH nanorods, and the p-LaFeO3/n-Fe2O3 heterojunction is achieved by post-thermal treatment, which is evidenced by the XRD, XPS, and HRTEM images. Due to the well-matched band levels of LaFeO3 and α-Fe2O3, the onset potential for photocurrent is negatively shifted by ∼50 mV. Meanwhile, the photocurrent density is promoted from 0.37 to 0.58 mA/cm2 at 1.23 V versus RHE owing to the accelerated charge separation within the space depletion layer induced by the build-in potential. Furthermore, the heterojunction is further modified by CoOx cocatalyst to improve the surface water oxidation kinetics, and the photocurrent density is promoted to ...

3D WO3 /BiVO4 /Cobalt Phosphate Composites Inverse Opal Photoanode for Efficient Photoelectrochemical Water Splitting.

A novel 3D WO3 /BiVO4 /cobalt phosphate composite inverse opal is designed for photoeletrochemical (PEC) water splitting, yielding a significantly improved PEC performance.

Effect of hydrothermal growth time on ZnO nanorod arrays photoelectrode performance

High density and vertically aligned zinc oxide nanorod arrays (ZnO NRs) have been prepared directly on indium-doped tin oxide (ITO) substrates via two-steps preparation: sol-gel spin coating and hydrothermal process. The nanostructured ZnO was characterized for its morphology, crystalline structure and optical properties by using field emission scanning electron microscopy (FESEM), X-ray diffractometry, and ultraviolet-visible spectroscopy respectively. In addition, the photoeletrochemical (PEC) properties were investigated through photocurrent measurements. The ZnO NRs/ITO had wurtzite-structured (hexagonal) ZnO and preferred growth along (0001) direction. When the growth time was 4h, ZnO NRs/ITO showed impressive photoresponse. The PEC analysis verified that the ZnO NRs gave better photocurrent response and photoconversion efficiency with approximately 42 times greater than seed layer.

Hydrogenated TiO2 nanotube arrays with enhanced photoelectrochemical property for photocathodic protection under visible light

The hydrogenated TiO2 nanotube arrays (H-TiO2 NTs) were prepared by annealing anodized TiO2 NTs in hydrogen atmosphere, and then used as photoanodes for photocathodic protection of 304 stainless steel (304SS) under visible light and simulated solar light. The effects of hydrogenated temperature and time on the photoeletrochemical (PEC) performance of H-TiO2 NTs were studied in details. The PEC tests showed that the photocurrent density of H-TiO2 NTs was up to 270.8μA/cm2 and 1.20mA/cm2 under visible and simulated solar light with good stability, which is about 23 times and 4.5 times than that of pristine TiO2 NTs. Furthermore, photo-induced open circuit potential (OCP) and Tafel curves were measured to evaluate the photocathodic protection effect of H-TiO2 NTs. Salient visible light responses and sharp decline of the OCP made H-TiO2 NTs a promising photocathodic protection material and could be applied to protect the coupled 304 stainless steel from corrosion.

Correlation between SSM substrate effect and physical properties of ZnO nanowires electrodeposited with or without seed layer for enhanced photoelectrochemical applications

ZnO nanowires (NWs) were grown vertically by electrodeposition technique on a stainless-steel mesh (SSM) substrate in the presence and absence of seed layer. A new contribution to the knowledge of both substrate nature and seed layer dependence on structural, morphological, optical properties is reported. X-ray diffraction revealed that all the samples are mainly crystallized in the wurtzite ZnO phase. In the presence of seed layer onto the SSM substrate, the crystalline nature of ZnO NWs is improved by the enhancement of intensity in (002) peak, which indicates a preferential orientation along this peak. The scanning electron microscopy (SEM) images show that, in the presence of seed layer, nanowires appear uniform and stand perpendicular to the substrate with hexagonal shape, implying the occurrence of the wurtzite ZnO crystal structure. According to optical measurements, the decrease of the band-gap energy is due mainly to the seed layer effect and the SSM substrate contribution. To investigate the effect of seed layer and SSM substrate, a photoeletrochemical (PEC) analysis of ZnO NWs is performed. The photocurrent density produced by the ZnO NWs/ZnO/SSM electrode reached 0.2mA·cm^-2, about two times higher than that measured on the ZnO NWs/SSM electrode. These results indicate that both seed layer and substrate have great potential in photoelectrochemical devices.

Concurrent photoelectrochemical reduction of CO2 and oxidation of methyl orange using nitrogen-doped TiO2

This study employed a novel material, nitrogen-doped TiO2 thin film (NTTF), as a photoanode for the concurrent photoeletrochemical (PEC) reduction of CO2 and oxidation of methyl Orange (MO). Under illumination, the onset potential of the total current was approximately 1.5V (vs. SCE) and the maximum total current was around 0.65mA at 2V (vs. SCE). The photocurrent can be effectively driven to the counter electrode at this positive potential, which will decrease the recombination of photo-generated holes and electrons, leading to more electrons available for CO2 reduction in the cathodic chamber and more holes for the oxidation of hazardous chemicals in the anodic chamber simultaneously. Formic acid, formaldehyde, methanol and methane were detected as the CO2 reduction products at a Cu electrode in the KHCO3 electrolyte. The first-order kinetic model was successfully applied to simulate the NTTF PEC reduction of CO2. The reaction rate constant were 6.68×10−7, 2.18×10−4, 8.62×10−4 and 2.27×10−4s−1, for the formation of formic acid, formaldehyde, methanol, and methane, respectively. The maximum Faradaic efficiency was 5.01, 1.04, 5.41 and 7.83% for the generation of formic acid, formaldehyde, methanol, and methane, individually. In addition, the effect of initial CO2 concentration on CO2 reduction was also conducted in the presence of methanol (0, 20 and 40%). Results showed that methanol-containing electrolyte enhanced CO2 solubility thereby suppressing hydrogen generation and favoring CO2 reduction. Finally, the degradation of methyl orange was compared using PEC, photocatalytic (PC), electrochemical (EC) and direct photolysis (P) processes. The PEC process was able to achieve a 10-log versus less than 1-log of methyl orange degradation by all other methods studied within 60min under otherwise similar conditions of pH, temperature, intensity and wavelength of light source. Results clearly demonstrated the potential of a sustainable technology for the concurrent reduction of CO2 and oxidation of hazardous chemicals by the PEC process using solar energy.

InGaN-based light-emitting solar cells with a pattern-nanoporous p-type GaN:Mg layer

InGaN-based light-emitting solar cells (LESCs) with a nanoporous micro-pattern array (NMPA) p-type GaN:Mg structures were fabricated through a photoeletrochemical (PEC) process. The photovoltaic property of these NMPA devices was analyzed. The higher light output power and light absorption properties were observed from the NMPA structure compared with the standard devices. The nanoporous structures acted as an anti-reflection layer to increase the light-coupling process at the light propagation surface. The light output power of the NMPA-LESCs had a 41% enhancement at 20-mA operating current, compared to standard LESCs (ST-LESCs). The peak external quantum efficiencies (EQE) were measured as the values of 42% (at 365 nm) and 27% (at 370 nm) for the NMPA-LESCs and the ST-LESCs structures, respectively. The photovoltaic device structure with the NMPA structure had the higher EQE at the ultraviolet (UV) region for higher efficiency nitride-based solar cell devices applications.