NiFe-LDH-Decorated Ti-Doped Hematite Photoanode for Enhancing Solar Water-Splitting Efficiency.

Ti-doped α-Fe2O3 nanorods were prepared by a facile hydrothermal method, followed by a NiFe-LDH catalyst that was electrodeposited on the doped α-Fe2O3 nanorods to structure an integrating photoanode Ti:Fe2O3/NiFe-LDH for improving solar PEC water-splitting efficiency. The structure and properties of electrode materials were characterized and the PEC properties of photoanodes were measured. The results show that the photocurrent density of the photoanode enhances 11.25 times at 1.23 V (vs RHE) and the IPCE value enhances 4.10 times at 420 nm compared with pristine α-Fe2O3. The enhancement is attributed to the separating of photogenerated electron-hole, the increase of carrier density, and the acceleration of the carrier transfer rate due to the dual action of doping and catalysis.

Facile one-step synthesis of a WO3/ZnWO4 heterojunction modified using ZnFe LDH enhances the PEC water splitting efficiency.

Photoelectrochemical water splitting represents a promising approach for directly converting solar energy into green hydrogen, offering a potential solution to the challenges of energy shortages and environmental pollution. In this work, a WO3/ZnWO4 binary heterojunction was synthesised by a simple and effective one-step drop casting method to enhance the charge separation efficiency; ZnFe LDH was deposited on the surface of the heterojunction with the aim of accelerating water oxidation and synergising with the heterojunction to enhance the photoelectrochemical performance of the photoanode. The photocurrent density of the WO3/ZnWO4/ZnFe LDH electrode can reach 2.1 mA cm-2 at 1.23 V (vs. RHE). This value is approximately 4 times greater than that observed for pure WO3 (0.53 mA cm-2). The IPCE and ABPE were able to improve by 3.1 times and 6 times, respectively.

Synthesis of quantum-sized ZnO nanoparticles in different medium and their application to NO2 sensors.

Quantum-sized ZnO nanoparticles were synthesized using zinc acetate dihydrate through a sol-gel process in different mediums: water, ethanol and methanol. Three types of modifiers: tetraethyl orthosilicate (TEOS), sodium dodecyl sulfate (SDS) and oleic acid (OA) were added to control the growth of the ZnO nanoparticles and inhibit Ostwald ripening. X-ray Diffraction (XRD) analyses revealed that ZnO have a hexagonal crystal structure, the estimated average crystallite sizes of modified ZnO are in the range of 4.5-10 nm, while the crystallite sizes of non-modified ZnO are large than 20 nm. X-ray photoelectron spectroscopy (XPS) analyses obtained the surface composition and chemical states of the products of ZnO. In this paper, the obtained quantum-sized ZnO nanoparticles as a novel sensing material were used to detect NO2 in environment. The sensing tests indicated that the ZnO based sensors not only have high response to NO2 but also exhibited high selectivity to CO and CH4 at low operating temperature of 290 degrees C.

NiFePB-modified ZnO/BiVO4 photoanode for PEC water oxidation.

Photoelectrochemical (PEC) water splitting has been recognized as the most promising approach for directly converting solar energy into chemical energy, and substantial efforts have been made to develop a highly efficient and low-cost photoanode for enhancement of PEC water splitting efficiency due to sluggish water oxidation reaction kinetics. A ternary NiFePB-modified ZnO/BiVO4 heterojunction photoanode was simply assembled by low-temperature hydrothermal, metal-organic decomposition and electrodeposition methods to improve the water splitting efficiency; its photocurrent density for water oxidation reached 1.66 mA cm-2 at 1.23 V (vs. RHE); in comparison, that of ZnO is only 0.4 mA cm-2. The onset potential manifests a cathodic shift of ∼283 mV compared to ZnO. The IPCE and the ABPE respectively are 3.1 and 6.4 times those of ZnO, respectively. This improvement is ascribed to the efficient separation of photogenerated electrons and holes by the formation of a heterojunction between ZnO and BiVO4 and the enhancement in the oxygen evolution reaction kinetics by the decoration of the co-catalyst NiFePB as a hole acceptor.

Bi nanoparticles modified the WO3/ZnWO4 heterojunction for photoelectrochemical water splitting.

The novel ternary photoanode was successfully prepared by Bi nanoparticles (Bi NPs) modified on type II heterojunction of WO3-ZnWO4 using the simple and effective drop casting and chemical impregnation methods. The photoelectrochemical (PEC) experimental tests revealed that the photocurrent density of the ternary photoanode of WO3/ZnWO4(2)/Bi NPs reaches 3.0 mA/cm2 at 1.23 V (vs. RHE), which is 6 times of the WO3 photoanode. The incident photon-to-electron conversion efficiency (IPCE) at 380 nm wave length reaches 68%, which increases 2.8 times compared to WO3 photoanode. The observed enhancement can be attributed to the formation of type II heterojunction and modification of Bi NPs. The former broadens the absorption range for visible light and improves the carrier separation efficiency, while the latter enhances the light capture ability through the local surface plasmon resonance (LSPR) effect of Bi NPs and the generation of hot electrons.

rGO decorated ZnO/CdO heterojunction as a photoanode for photoelectrochemical water splitting.

A ternary photoanode of ZnO/CdO heterojunction decorated with reduced graphene oxide (rGO) was firstly fabricated by electrochemical deposition and thermal decomposition that is simple and effective compared with other method reported in literature. The structure and morphology of the photoanode were systematically characterized by various spectrum technologies. The photoanode expands the visible light absorption range to 428 nm, the photocurrent density reaches 1.15 mA·cm-2 at 1.23 V (vs. RHE) that is 3 times and 1.85 times of pure ZnO (0.38 mA·cm2) and ZnO/CdO (0.62 mA·cm2) photoanodes. The highest IPCE value reaches 42.63% at 380 nm. The enhancement is attributed to the architecture of semiconductor heterojunctions and the decoration of rGO nanosheets, the former promotes charge separation, while the latter accelerates electron transfer thus both synergistically enhance PEC water splitting efficiency. Here fabricated photoanode has never been reported before, only Cd and other metal elements doped ZnO photoanodes were reported in the literature.

Pine dendritic bismuth vanadate loaded on reduced graphene oxide for detection of low concentration triethylamine.

The volatile gas of Triethylamine (TEA) can cause environment pollution and lead to the serious hurt of the human respiratory system. Therefore, it is necessary to detect low concentrations of TEA in our daily lives rapidly. The hybrid of pine dendritic BiVO4/reduced graphene oxide (rGO) has been synthesized firstly by one step hydrothermal process. The gas sensing tests show that the 13.0 wt% rGO hybrid not only exhibits high response of 5.9 and rapid response of 11.4 s, but also exclusive selectivity and long-term stability to 10 ppm of TEA at the operating temperature of 180 °C. The formation of heterojunction and the incoporation of rGO are responsible for the improving sensing properties of the hybrid to TEA, the former results in reduction of the electron depletion layer at interface in hybrid, while the latter enhances the specific surface of the hybrid and accelerates the transfer of electrons. The research is expected to have wide application in the development of composite based gas sensors made of rGO/metal oxide semiconductors.

Synthesis of novel BiVO4/Cu2O heterojunctions for improving BiVO4 towards NO2 sensing properties.

To develop a high sensitive and low temperature NO2 gas sensor, the novel BiVO4/Cu2O heterojunctions were synthesized by a modified metal organic decomposition method to decorate BiVO4 nanoplates using Cu2O nanoparticles for enhancement of BiVO4 sensing performance to NO2. The structure and morphology of BiVO4, Cu2O and BiVO4/Cu2O composites were characterized by XRD, SEM and TEM spectra. The results indicate that the BiVO4/Cu2O heterojunctions are composed of monoclinic BiVO4 nanoplates with the thickness about 1.0-1.2 µm and 30-40 nm diameters of cubic Cu2O nanoparticles. The gas-sensing tests display that the composite exhibits rapid and linear responses to low concentration NO2 (from 100 ppb to 8.0 ppm), the highest response reaches 4.2 towards 4 ppm NO2 at 60 °C and relative humidity of 28.3%, which is more than 2 times of pure BiVO4 at the same condition. The enhanced sensing properties benefit from the novel p-n heterojunction between BiVO4 and Cu2O, which forms a depletion layer at the interface, leading to resistance increase of composites in NO2. The work demonstrates the as-synthesized BiVO4/Cu2O is a promising sensing material to detect NO2 gas.

rGO modified nanoplate-assembled ZnO/CdO junction for detection of NO2.

The triadic composite of ZnO/CdO heterojunction decorated with reduced graphene oxide (rGO) was prepared using a one-step hydrothermal method. The characterizations of morphology, structure and composition to the composite were undertaken by XRD, Raman, SEM, TEM, XPS, UV-vis spectra. The sensing experimental data indicate that the highest response of the ZnO/CdO/rGO (1.0 wt%) composite to ppm-level NO2 is 8 times and 2 times higher than pure ZnO and ZnO/CdO junction, respectively. The composite not only exhibits fast response time and recovery time, high response, but also reveals outstanding stability and repeatability at an operating temperature of 125 °C. The sensing mechanism also has been discussed in detail in the work. The enhancement in gas sensing properties is credited to the development of ZnO/CdO heterojunction and the decoration of rGO with high conductivity. The logarithm of sensitivity in the range of 0.4-2.4 ppm NO2 shows good linear dependence, indicating that the composite based sensor can be used to quantificationally detect low concentration of NO2.

Effect of Mo doping and NiFe-LDH cocatalyst on PEC water oxidation efficiency.

The NiFe-layered double hydroxide (LDH) nanosheets were decorated on the surface of doped BiVO4 to structure an integrating photoanode for improving solar photoelectrochemical (PEC) water splitting efficiency, which is a dynamic research topic to solve the energy crisis and remit environmental pollution caused by fossil fuel combustion. The fabricated photoanode exhibits rapid response to visible light, enhances photocurrent density and shows significant cathodic shift compared to BiVO4. Moreover, the measured incident photon-to-current efficiency (IPCE) of the photoanode is comparable to that reported in the literature. The amount of evolution oxygen was measured and the faradaic efficiency produced oxygen was also obtained by comparing the theoretical calculation value. The enhancement is attributed to the increase of the carrier density, the effective separation of photogenerated electron-hole and consuming of the photogenerated holes accumulated at the electrode surface, which has been confirmed by electrochemical impedance spectra (EIS) and the intensity modulated photocurrent spectra (IMPS). The work may offer a promising method for designing a high efficiency and low-cost photoanode.

An integrating photoanode consisting of BiVO4, rGO and LDH for photoelectrochemical water splitting.

The low carrier mobility of BiVO4 is a bottleneck that limits its charge transfer in bulk or on the surface. Herein, reduced graphene oxide (rGO) nanosheets as an effective electron mediator were successfully loaded on BiVO4 and NiFe-layered double hydroxides (NiFe-LDHs) were decorated on BiVO4/rGO heterojunctions by two facile electrodeposition methods to construct a triadic photoanode of BiVO4/rGO/NiFe-LDH for improvement of photoelectrochemical (PEC) water splitting efficiency of BiVO4. This photoanode significantly extends the absorption region of visible light, increases the photocurrent density, exhibits an onset potential with a significant cathodic shift, and enhances photon-to-electron conversion efficiency (IPCE) compared with the pristine BiVO4 photoanode. The enhancement of PEC properties benefits from the formation of p-n heterojunctions between rGO and BiVO4 and the use of NiFe-LDH as a cocatalyst for accelerating the kinetics of oxygen evolution from water.

Two-step electrodeposition to fabricate the p-n heterojunction of a Cu2O/BiVO4 photoanode for the enhancement of photoelectrochemical water splitting.

A Cu2O/BiVO4 p-n heterojunction based photoanode in photoelectrochemical (PEC) water splitting is fabricated by a two-step electrodeposition method on an FTO substrate followed by annealing treatment. The structures and properties of the samples are characterized by XRD, FESEM, HRTEM, XPS and UV-visible spectra. The photoelectrochemical activity of the photoanode in water oxidation has been investigated and measured in a three electrode quartz cell system; the obtained maximum photocurrent density of 1.72 mA cm-2 at 1.23 V vs. RHE is 4.5 times higher than that of pristine BiVO4 thin films (∼0.38 mA cm-2). The heterojunction based photoanode also exhibits a tremendous cathodic shift of the onset potential (∼420 mV) and enhancement in the IPCE value by more than 4-fold. The enhanced photoelectrochemical properties of the Cu2O/BiVO4 photoelectrode are attributed to the efficient separation of the photoexcited electron-hole pairs caused by the inner electronic field (IEF) of the p-n heterojunction.

Ultrasensitive room temperature NH3 sensor based on a graphene-polyaniline hybrid loaded on PET thin film.

This research was motivated by the need to develop a smart ammonia (NH3) sensor based on a flexible polyethylene terephthalate (PET) thin film loaded with a reduced graphene oxide-polyaniline (rGO-PANI hybrid) using in situ chemical oxidative polymerization. The sensor not only exhibited high sensitivity, good selectivity and a fast response at room temperature but was also flexible, cheap and had wearable characteristics.