• Energy Research

Microbial fuel cells have gained popularity in recent years due to its promise in converting organic wastewater into renewable electrical energy. In this study, a membrane-less MFC with a biocathode was developed to evaluate its performance in electricity generation while simultaneously treating wastewater. The MFC fed with a continuous flow of 2g/day acetate produced a power density of 30 mW/m(2) and current density of 245 mA/m(2). A substrate degradation efficiency (SDE) of 75.9% was achieved with 48.7% attributed to the anaerobic process and 27.2% to the aerobic process. Sequencing analysis of the microbial consortia using 16S rDNA pryosequencing showed the predominance of Bacteroidia in the anode after one month of operation, while the microbial community in the cathode chamber was dominated by Gamma-proteobacteria and Beta-proteobacteria. Coulombic efficiencies varied from 19.8% to 58.1% using different acetate concentrations, indicating power density can be further improved through the accumulation of electron-transferring bacteria.

This paper investigates the heat/mass transfer and electrochemical kinetics in the cathode catalyst layer of polymer electrolyte fuel cells (PEFCs) during cold start below the freezing temperature. A number of key parameters that govern the cold-start operations, such as time constants and the Damkohler number, are defined and their impacts are explored. A lumped parameter model for cell temperature and ice formation is developed and one-dimensional analysis is performed on the reactant transport in the catalyst layer. We found that a dimensionless parameter, defined as ratio of the time constant of cell warmup to that of ice-volume growth, is important for self-startup of fuel cells in subzero conditions, and a high value of tortuosity has profound impact on reactant starvation during cold start. In addition, the reduction in the electrochemical active surface of the catalyst layer due to the ice coverage is found to be a major mechanism leading to cell voltage loss during cold start.

The removal of antibiotics is crucial for improvement of water quality in animal wastewater treatment. In this paper, the performance of microbial fuel cell (MFC) in terms of degradation of typical antibiotics was investigated. Electricity was successfully produced by using sludge supernatant mixtures and synthesized animal wastewater as inoculation in MFC. Results demonstrated that the stable voltage, the maximum power density and internal resistance of anaerobic self-electrolysis (ASE) -112 and ASE-116 without antibiotics addition were 0.574 V, 5.78 W m-3 and 28.06 Ω, and 0.565 V, 5.82 W m-3 and 29.38 Ω, respectively. Moreover, when adding aureomycin, sulfadimidine, roxithromycin and norfloxacin into the reactors, the performance of MFC was inhibited (0.51 V-0.41 V), while the output voltage was improved with the decreased concentration of antibiotics. However, the removal efficiency of ammonia nitrogen (NH3-N) and total phosphorus (TP) were both obviously enhanced. Simultaneously, LC-MS analysis showed that the removal efficiency of aureomycin, roxithromycin and norfloxacin were all 100% and the removal efficiency of sulfadimidine also reached 99.9%. These results indicated that antibiotics displayed significantly inhibitions for electricity performance but improved the quality of water simultaneously.

Lithium-air batteries show a great promise in electrochemical energy storage with their theoretical specific energy comparable to gasoline. Discharge products such as Li2O2 or Li2CO3 are insoluble in several major nonaqueous electrolytes, and consequently precipitate at the reaction sites. These materials are also low in electric conductivity. As a result, the reduced pore space and electrode passiviation increase the reaction resistance and consequently reduce discharge voltage and capability. This work presents a modeling study of discharge product precipitation and effects for lithium-air batteries. Theoretical analysis is also performed to evaluate the variations of important quantities including temperature, species concentrations, and electric potentials. Precipitation growth modes on planar, cylindrical and spherical surfaces are discussed. A new approach, following the study of ice formation in PEM fuel cells, is proposed. Validation is carried out against experimental data in terms of discharge voltage loss.

Laser-induced breakdown spectroscopy (LIBS) is regarded as a very promising technique for fast or online coal analysis. However, the analytical performance is greatly influenced by its moisture content. In the present work, the effects of moisture content variations on the properties of the laser-induced plasma and its spectral signals were investigated using the same coal samples mixed with different moisture contents. Plasma morphology and spatially resolved spectra were also obtained to further investigate the effects, and the mechanism of the effects was also discussed. Results showed that most of the spectral line intensities decreased as the moisture content increased, even including those of H and O. Seen from the spatially resolved spectra, the profile of H intensity over the height of plasma showed a higher peak position with increasing moisture content, and the height of the peak of the H intensity profile was slightly higher than those of other elements such as C and Al. The laser ablation process and mechanism underlying the effects of moisture content were proposed as following: part of the moisture was evaporated first under laser radiation and ablated earlier than those of other coal materials. Consequently, the outside layer of the laser-induced plasma was mostly from the dissociation of moisture. Given the earlier evaporation of moisture, part of the energy was used to dissociate and ionize the surrounding water vapor or even reflected by the splashed particle caused by fast expanding moisture, thereby shielding the further absorption of laser energy to the solid coal material. This phenomenon resulted in less coal mass being actually ablated into the plasma with increasing moisture content, hence emitting smaller line intensities. On the other hand, the decrease in H line intensity may be caused by the fact that these elements were pushed to the outside cooler layer.

A multi-dimensional two-phase model of polymer electrolyte fuel cells is developed and employed to investigate through-plane water profiles with spatially-varying properties of gas diffusion layers (GDL) being accounted for. Both one-dimensional (1-D) and 2-D model predictions of liquid water profiles are presented. We find that the GDL properties can significantly affect the liquid through-plane profiles and local features, for example, liquid water may be trapped due to the spatial variation in GDL properties. Furthermore, land compression can cause GDL property variation in the in-plane direction, altering liquid water distribution. Model predictions are compared with experimental data from both neutron radiography and X-ray imaging. Reasonably good agreements are obtained.

Abstract A novel fabrication technique for micro proton exchange membrane fuel cells (μPEMFCs) based on carbon-MEMS (C-MEMS) was optimized to yield higher performance cells. Polymer manufacturing is relatively easy compared to directly patterning graphite as is typically done to make fuel cell bipolar plates. In a C-MEMS approach, fuel cell bipolar plates are fabricated by first patterning polymer Cirlex ® sheets. By subsequently pyrolyzing the machined polymer sheets at high temperature in an inert atmosphere, carbon bipolar plates with intricate groove structures to distribute the reactants are obtained. Using an improved assembly technique such as polishing the carbonized plates to minimize the contact resistance between gas diffusion layers (GDL) and bipolar plates, better pyrolysis temperature control and a better end plate design, a μPEMFC with a 0.64 cm 2 active surface was fabricated using the newly developed bipolar plates. At 1 atm and 25 °C a maximum power density of ∼76 mW cm −2 was obtained, and at 2 atm and 25 °C ∼85 mW cm −2 was achieved. These data are comparable with data reported in the literature for μPEMFCs and are a dramatic improvement over earlier results reported for the same C-MEMS based fuel cell. Electrochemical Impedance Spectroscopy (EIS) and cyclic voltammetry were carried out to characterize steady-state and transient characteristics of the novel C-MEMS fuel cell.

Additive manufacturing (AM) techniques have been widely used to fabricate structural components with complex geometries. Understanding AM materials under extreme environments is crucial for their implementation in various engineering sectors. In this study, the deformation behavior and irradiation damage of 316 L stainless steel (SS) fabricated by the direct energy deposition (DED) process are investigated. The fabrication-induced nanopores with an average diameter of 200 nm exhibit a core-shell structure with a local tensile strain. The precession electron diffraction (PED) reveals that austenite-to-martensite phase transformation preferentially occurs around the nanopores under tension test at room temperature. Proton irradiation experiments performed at 360 °C to a fluence of 1.09 × 1019 cm−2 and 5.42 × 1019 cm−2 show that the DED fabricated 316 L SS exhibits a stronger void-swelling resistance and lower dislocation loop density than its wrought counterpart. AM-induced features, such as nanopores and sub-grain boundaries, could serve as defect sinks to absorb irradiation-induced defects. The design of microstructure using AM processes opens up new avenues for the development of irradiation tolerant materials for nuclear applications.