Ligang Xia

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.

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.

Efficient wastewater treatment and simultaneously electricity production using a photocatalytic fuel cell based on the radical chain reactions initiated by dual photoelectrodes

Efficient conversion of wastewater into clean energy was achieved by applying a radical chain reaction strategy in a solar responsive photocatalytic fuel cell (PFC) system. The system was constructed with two photoelectrodes where ferrous ions were added to enhance the radical reactions for organic pollutants degradation from the surface of electrodes to the whole solution system via coming into a continuous radical chain reaction. The results indicated that the short-circuit current (Jsc) and the power density (JVmax) obtained in the PFC system is up to 1.41-1.60 and 1.52-2.02 times larger than those of the PFC without ferrous ions. Meanwhile, the degradation rate of refractory organics (methyl orange, methylene blue, congo red and tetracycline) increased to 91.98%, 98.57%, 92.36% and 68.09% from 53.61%, 45.38%, 51.09% and 30.65% respectively after 90min operation. The proposed PFC with a radical chain reaction strategy provides a more economical and efficient way for energy recovery and wastewater treatment and implies a possibility of developing much higher efficient PFC system when applying the other electrodes.

High-efficient energy recovery from organics degradation for neutral wastewater treatment based on radicals catalytic reaction of Fe 2+ /Fe 3+ -EDTA complexes

A high-efficient photo-induced wastewater fuel cell (WFC) for neutral wastewater treatment was proposed in this paper based on radicals catalytic reaction of Fe3+/Fe2+- EDTA complexes in the system which has a lower redox potential than Fe3+/Fe2+ and can accelerate easily the conversion of slow catalytic step from Fe (III) to Fe (II). The results indicated that the WFC shows an excellent performance in a wide pH range of 5-9 and achieves optimal efficiency for organic degradation and electricity generation at pH 7.0. The removal ratio of organic pollutants (Rhodamine b, Phenol, and Methylene Blue) increased to 69.42%, 53.99% and 82.7% from 29.87%, 16.25% and 39% respectively after 3 h operation at an initial pH of 7.0. Meanwhile, the short-circuit current is up to 1.24-2.16 times that of the WFC without EDTA-ferrous complex. Furthermore, the system almost does not produce any sludge. The proposed WFC system can keep stable of Fe3+/Fe2+ in neutral solution and generate more intermediate active free radicals to treat neutral wastewater and recover the abundant chemical energy in organics.

Exhaustive Conversion of Inorganic Nitrogen to Nitrogen Gas Based on a Photoelectro-Chlorine Cycle Reaction and a Highly Selective Nitrogen Gas Generation Cathode

A novel method for the exhaustive conversion of inorganic nitrogen to nitrogen gas is proposed in this paper. The key properties of the system design included an exhaustive photoelectrochemical cycle reaction in the presence of Cl-, in which Cl· generated from oxidation of Cl- by photoholes selectively converted NH4+ to nitrogen gas and some NO3- or NO2-. The NO3- or NO2- was finally reduced to nitrogen gas on a highly selective Pd-Cu-modified Ni foam (Pd-Cu/NF) cathode to achieve exhaustive conversion of inorganic nitrogen to nitrogen gas. The results indicated total nitrogen removal efficiencies of 30 mg L-1 inorganic nitrogen (NO3-, NH4+, NO3-/NH4+ = 1:1 and NO2-/NO3-/NH4+ = 1:1:1) in 90 min were 98.2%, 97.4%, 93.1%, and 98.4%, respectively, and the remaining nitrogen was completely removed by prolonging the reaction time. The rapid reduction of nitrate was ascribed to the capacitor characteristics of Pd-Cu/NF that promoted nitrate adsorption in the presence of an electric double layer, eliminating repulsion between the cathode and the anion. Nitrate was effectively removed with a rate constant of 0.050 min-1, which was 33 times larger than that of Pt cathode. This system shows great potential for inorganic nitrogen treatment due to the high rate, low cost, and clean energy source.

The effect and mechanism of organic pollutants oxidation and chemical energy conversion for neutral wastewater via strengthening reactive oxygen species

Toxic and refractory organic pollutants are continually discharged into the water environment, which has become the crisis for the human living and sustainable development. However, organic pollutants also contain large amounts of chemical energy. In this paper, we studied the effect and mechanism of organic pollutants oxidation and chemical energy conversion for neutral wastewater via strengthening reactive oxygen species (ROS) of HO and O2- in a photocatalytic fuel cell (PFC) system, since ROS has the power to oxidize or even mineralize the organics and is environment-friendly to treat refractory organic pollutants. In our PFC system, the HO was enhanced by the cyclic radical chain reaction via the addition of Fe2+ and tetrapolyphosphate (TPP), while O2- was enhanced by setting an additional bias voltage at the anode which was favorable to O2 production. The results show that the HO and O2- concentration are highly enhanced, showing 8.28 and 8.99 times those of traditional PFC, respectively. Meanwhile, the degradation rate constant is remarkably increased by 6.52 times when methylene blue is used as a model pollutant. Furthermore, the performance of wastewater PFC is so improved that the short-circuit current density (Jsc) and maximum power density (JVmax) have been increased by a factor of 9.05 and 12.67 times in the same experiment, respectively.