Xuejin Li

Visible-Light Responsive Photocatalytic Fuel Cell Based on WO3/W Photoanode and Cu2O/Cu Photocathode for Simultaneous Wastewater Treatment and Electricity Generation

A visible-light driven photocatalytic fuel cell (PFC) system comprised of WO(3)/W photoanode and Cu(2)O/Cu photocathode was established for organic compounds degradation with simultaneous electricity generation. The central idea for its operation is the mismatched Fermi levels between the two photoelectrodes. Under light illumination, the Fermi level of WO(3)/W photoanode is higher than that of Cu(2)O/Cu photocathode. An interior bias can be produced based on which the electrons of WO(3)/W photoanode can transfer from the external circuit to combine with the holes of Cu(2)O/Cu photocathode then generates the electricity. In this manner, the electron/hole pairs separations at two photoelectrodes are facilitated to release the holes of WO(3)/W photoanode and electrons of Cu(2)O/Cu photocathode. Organic compounds can be decomposed by the holes of WO(3)/W photoanode due to its high oxidation power (+3.1-3.2 V(NHE)). The results demonstrated that various model compounds including phenol, Rhodamine B, and Congo red can be successfully decomposed in this PFC system, with the degradation rate after 5 h operation were obtained to be 58%, 63%, and 74%, respectively. The consistent operation for continuous water treatment with the electricity generation at a long time scale was also confirmed from the result. The proposed PFC system provides a self-sustained and energy-saving way for simultaneous wastewater treatment and energy recovery.

Efficient electricity production and simultaneously wastewater treatment via a high-performance photocatalytic fuel cell

A great quantity of wastewater were discharged into water body, causing serious environmental pollution. Meanwhile, the organic compounds in wastewater are important sources of energy. In this work, a high-performance short TiO(2) nanotube array (STNA) electrode was applied as photoanode material in a novel photocatalytic fuel cell (PFC) system for electricity production and simultaneously wastewater treatment. The results of current work demonstrate that various model compounds as well as real wastewater samples can be used as substrates for the PFC system. As a representative of model compounds, the acetic acid solution produces the highest cell performance with short-circuit current density 1.42 mA cm(-2), open-circuit voltage 1.48 V and maximum power density output 0.67 mW cm(-2). The STNA photoanode reveals obviously enhanced cell performance compared with TiO(2) nanoparticulate film electrode or other long nanotubes electrode. Moreover, the photoanode material, electrolyte concentration, pH of the initial solution, and cathode material were found to be important factors influencing the system performance of PFC. Therefore, the proposed fuel cell system provides a novel way of energy conversion and effective disposal mode of organics and serves well as a promising technology for wastewater treatment.

A novel in situ preparation method for nanostructured α-Fe2O3 films from electrodeposited Fe films for efficient photoelectrocatalytic water splitting and the degradation of organic pollutants

A novel method has been developed for the preparation of nanostructured haematite (α-Fe2O3) films for use in photoelectrocatalytic (PEC) water splitting and the degradation of organic pollutants. The method has two stages, the electrodeposition of Fe films in alkalescent aqueous electrolyte with ferrous sulphate and ammonia, and the in situ thermal oxidation of the Fe films to α-Fe2O3. The thickness and crystallinity of the α-Fe2O3 films can be precisely controlled by adjusting the duration and the annealing conditions of the electrodeposition, respectively, avoiding the microstructural defects arising from the traditional electrodeposition of FeOOH films and the unwanted phases of FeO and Fe3O4 produced by thermal oxidation of Fe foils. This facilitates the generation, transportation and collection of photogenerated charges on the α-Fe2O3 film. The optimized α-Fe2O3 film, obtained from a Fe film deposited for 30 s and then annealed at 500 °C for 2 h, showed a stable PEC water oxidation current around 1.35 mA cm−2 at 1.23 V vs. a reversible hydrogen electrode (RHE) under AM 1.5 irradiation. This was the highest current so far obtained using undoped α-Fe2O3 films produced by electrodeposition. When further coated with a cobalt phosphate (Co–Pi) co-catalyst, the optimized Co–Pi/α-Fe2O3 photoanode showed an incident photon-to-current conversion efficiency (IPCE) above 18% at 400 nm and a stable photocurrent of 1.89 mA cm−2. The α-Fe2O3 film also showed excellent stability and degradation efficiency (rate constant 0.9372 h−1) in the PEC degradation of methylene blue (MB) in neutral aqueous solution under a positive bias potential.

Self-Biasing Photoelectrochemical Cell for Spontaneous Overall Water Splitting under Visible-Light Illumination

A self-biasing photoelectrochemical (PEC) cell that could work for spontaneous overall water splitting in a neutral solution was established based on the mismatched Fermi levels between the photoelectrodes. A Pt-catalyst-decorated crystalline silicon photovoltaic cell (Pt/PVC) was prepared and employed as an effective photocathode. This was coupled with a poly(ethylene glycol)-directed WO3/W photoanode prepared by a hydrothermal process. Both of the photoelectrodes showed a response to visible light. The WO3/W photoanode had a positively located valence band edge, the energy level of which was enough for water oxidation, and the Pt/PVC photocathode possessed a negatively located conduction band edge, which was capable of water reduction. More importantly, the Fermi level of the WO3/W photoanode was more positive than that of the Pt/PVC photocathode because of the p-n junction of the PVC that decoupled the band bending and enlarged the photovoltage. Under visible-light irradiation, the WO3/W photoanode provided a negative bias for the Pt/PVC photocathode, and the Pt/PVC photocathode provided a positive bias for the WO3/W photoanode. An interior bias was generated that could relax the strict criteria of overall water splitting by cooperatively separating the hole-electron pairs at both photoelectrodes. In this system, the short-circuit current and the open-circuit voltage increased with increasing light intensity (AM 1.5 illumination) to reach 121 μA cm(-2) and 0.541 V, respectively, at a light intensity of 100 mW cm(-2). Such a combination provides a promising method for the fabrication of self-driven devices for solar-energy storage.

A solar light driven dual photoelectrode photocatalytic fuel cell (PFC) for simultaneous wastewater treatment and electricity generation.

In this paper, a novel dual heterojunction Photocatalytic Fuel Cell (PFC) system based on BiVO4/TiO2 nanotubes/FTO photoanode and ZnO/CuO nanowires/FTO photocathode has been designed. Compared with the electrodes in PFCs reported in earlier literatures, the proposed heterojunction not only enhances the visible light absorption but also offers a higher photoconversion efficiency. In addition, the nanostructured heterojunction owns a large surface area that ensures a large amount of active sites for organics degradation. The performance of the PFC base on the dual photoelectrodes was also studied herein. The results indicated that the PFC in ths paper exhibits a superior performance and its JV(max) reached 0.116 mw cm(-2), which is higher than that in most of reported PFCs with a Pt-free photocathode. When hazardous organic compounds such as methyl orange, Congo red and methylene blue were decomposed, the degradation rates obtained is to be 76%, 83%, and 90% respectively after 80 mins reaction. The proposed heterojunction photoelectrodes provided great potential for cost-effective and high-efficiency organic pollutants degradation and electricity generation in a PFC system.

The Inhibition Effect of Tert-Butyl Alcohol on the TiO2 Nano Assays Photoelectrocatalytic Degradation of Different Organics and Its Mechanism

The inhibition effect of tert-butyl alcohol (TBA), identified as the •OH radical inhibitor, on the TiO2 nano assays (TNA) photoelectrocatalytic oxidation of different organics such as glucose and phthalate was reported. The adsorption performance of these organics on the TNA photoelectrode was investigated by using the instantaneous photocurrent value, and the degradation property was examined by using the exhausted reaction. The results showed that glucose exhibited the poor adsorption and easy degradation performance, phthalate showed the strong adsorption and hard-degradation, but TBA showed the weak adsorption and was the most difficult to be degraded. The degradation of both glucose and phthalate could be inhibited evidently by TBA. But the effect on glucose was more obvious. The different inhibition effects of TBA on different organics could be attributed to the differences in the adsorption and the degradation property. For instance, phthalate of the strong adsorption property could avoid from the capture of •OH radicals by TBA in TNA photoelectrocatalytic process.

WO3/W Nanopores Sensor for Chemical Oxygen Demand (COD) Determination under Visible Light

A sensor of a WO3 nanopores electrode combined with a thin layer reactor was proposed to develop a Chemical Oxygen Demand (COD) determination method and solve the problem that the COD values are inaccurately determined by the standard method. The visible spectrum, e.g., 420 nm, could be used as light source in the sensor we developed, which represents a breakthrough by limiting of UV light source in the photoelectrocatalysis process. The operation conditions were optimized in this work, and the results showed that taking NaNO3 solution at the concentration of 2.5 mol·L−1 as electrolyte under the light intensity of 214 μW·cm−2 and applied bias of 2.5 V, the proposed method is accurate and well reproducible, even in a wide range of pH values. Furthermore, the COD values obtained by the WO3 sensor were fitted well with the theoretical COD value in the range of 3–60 mg·L−1 with a limit value of 1 mg·L−1, which reveals that the proposed sensor may be a practical device for monitoring and controlling surface water quality as well as slightly polluted water.

Adsorption and photoelectrocatalytic characteristics of organics on TiO2 nanotube arrays

The adsorption and photoelectrocatalytic characteristics of four different kinds of organic compounds (d-fructose, glutamic acid, fumaric acid, and nicotinic acid) on TiO2 nanotube arrays (TNAs) were investigated using a thin-layer cell, wherein the compounds were rapidly and exhaustively oxidized. The photogenerated current–time (Iph–t) profiles were found to be related to the adsorption, the degradation rate, and the reaction mechanism. The relationship between the initial organic compounds concentrations and photocurrent peaks (I0ph) fit the Langmuir type adsorption model well, thereby confirming that the adsorption of organic compounds on TNAs was via monolayer adsorption. The adsorption equilibrium constant was obtained from the Langmuir equation. The results indicate that the adsorption performance of the organic compounds on TNAs were in the following order: nicotinic acid < d-fructose < glutamic acid < fumaric acid. The degradation of organic compounds on TNAs was classified as either easy or difficult based on the time of complete mineralization (tend) of the organic samples under an equal holes consumption; the degree of degradation were as follows: fumaric acid < d-fructose < glutamic acid < nicotinic acid. The photoelectrocatalytic characteristics of the organic compounds on TNAs were also discussed by analyzing the changes in the Iph–t profiles.

The Promotion Effect and Mechanism of Methanoic Acid on the Photoelectrocatalytic Degradation of Fulvic Acid

A significant promotion effect of methanoic acid (MA) was proposed in the photoelectrocatalytic (PEC) degradation of fulvic acid (FA) and the degradation mechanism was also discussed. The PEC degradation property of FA and MA was investigated by an assembled thin-layer PEC reactor in which photoanode is TiO2 nanotube arrays (TNAs) material. The result shows that only about 40% of FA was degraded, while MA could be completely degraded at the same condition. When mixing MA with FA, it shows a significant improvement in the degradation of FA. For instance, 50 mg/L FA mixed with 45 mg/L MA could achieve exhausted degradation. The results could be attributed to the promotion effect of MA that enhanced the generation of hydroxyl radicals, which maintain the continuous degradation of both FA and the intermediate products during the PEC process. This study proposed a new way of promoting the PEC degradation of FA as well as removing humus from the polluted water.