Zhuwei Du

Power production enhancement with a polyaniline modified anode in microbial fuel cells.

In this paper, an approach of improving power generation of microbial fuel cells (MFCs) by using a HSO(4)(-) doped polyaniline modified carbon cloth anode was reported. The modification of carbon cloth anode was accomplished by electrochemical polymerization of aniline in 5% H(2)SO(4) solution. A dual-chamber MFC reactor with the modified anode achieved a maximum power density of 5.16 Wm(-3), an internal resistance of 90 Ω, and a start-up time of 4 days, which was respectively 2.66 times higher, 65.5% lower, and 33.3% shorter than the corresponding values of the MFC with unmodified anode. Evidence from X-ray photoelectron spectroscopy and scanning electron microscopy results proved that the formation of biofilm on the anode surface could prevent the HSO(4)(-) doped polyaniline to be de-doped, and the results from electrochemical tests confirmed that the electrochemical activity of the modified anode was enhanced significantly after inoculation. Charge transfer was facilitated by polyaniline modification. All the results indicated that the polyaniline modification on the anode was an efficient approach of improving the performance of MFCs.

Electrochemical treatment of graphite to enhance electron transfer from bacteria to electrodes

In this paper, graphite felts were continuously electrochemically oxidized to increase the current generation in microbial fuel cells (MFCs). The treated and untreated graphite felts were utilized as anodes in MFCs and current production was compared. The current production on electrochemically treated graphite felt anodes was about 1.13 mA, 39.5% higher compared with that of MFCs containing untreated anodes. The results demonstrated that the electronic coupling between graphite felt electrodes and electrogenic bacteria could be enhanced by electrochemical oxidization of the electrodes. Further study showed that the newly generated carboxyl containing functional groups from electrochemical oxidization were responsible for the enhanced electron transfer, due to their strong hydrogen bonding with peptide bonds in bacterial cytochromes.

Conductive polypyrrole hydrogels and carbon nanotubes composite as an anode for microbial fuel cells

Conducting polymer hydrogels, a unique class of materials having the advantageous features of both hydrogels and organic conductors, possess excellent electrochemical properties due to their intrinsic porous structure. Herein, we report a facile and scalable method for synthesizing conductive polypyrrole hydrogels/carbon nanotubes (CPHs/CNTs) using phytic acid as both gelator and dopant, and this composite was used as an anode in a dual-chamber microbial fuel cell (MFC). The high electrocatalytic activity of this material significantly reduced the interfacial charge transfer resistance and facilitated the extracellular electron transfer on the anode surface. The three dimensional porous structure and hydrophilicity of this composite enhanced the biofilm formation on the anode surface. CPHs/CNTs anode increased the maximum power density from 871 ± 33 mW m−2 to 1898 ± 46 mW m−2 and exhibited high stability in the two-chambered MFC. These results demonstrated that the synthesis of the CPHs/CNTs composite offered an effective approach towards enhancing the power production in MFCs.

Calcined polyaniline–iron composite as a high efficient cathodic catalyst in microbial fuel cells

A new type of carbon-nitrogen-metal catalyst, PANI-Fe-C, was synthesized by calcination process. According to the results of FT-IR and XPS analysis, polyaniline chain was broken by calcination. Small nitrogen-contained molecular fragments were gasified during calcination process, while the remaining nitrogen atoms were enchased in the new produced multiple carbon rings by C-N and CN bonds and performed as the catalytic active sites and the covalent centers for soluble iron components. Calculated from the polarization curves, a maximum power density of 10.17W/m(3) for the MFC with the synthetic catalyst was obtained, which was slightly higher than the MFC with Pt/C catalyst of 9.56W/m(3). All the results obtained in this paper proved that the newly synthetic nitrogen-carbon-metal catalyst would be a potential alternative to the expensive Pt/C catalyst in the field of MFC.

Spontaneous modification of graphite anode by anthraquinone-2-sulfonic acid for microbial fuel cells.

In this study, anthraquinone-2-sulfonic acid (AQS), an electron transfer mediator, was immobilized onto graphite felt surface via spontaneous reduction of the in situ generated AQS diazonium cations. Cyclic voltammetry (CV) and energy dispersive spectrometry (EDS) characterizations of AQS modified graphite demonstrated that AQS was covalently grafted onto the graphite surface. The modified graphite, with a surface AQS concentration of 5.37 ± 1.15 × 10(-9)mol/cm(2), exhibited good electrochemical activity and high stability. The midpoint potential of the modified graphite was about -0.248 V (vs. normal hydrogen electrode, NHE), indicating that electrons could be easily transferred from NADH in bacteria to the electrode. AQS modified anode in MFCs increased the maximum power density from 967 ± 33 mW/m(2) to 1872 ± 42 mW/m(2). These results demonstrated that covalently modified AQS functioned as an electron transfer mediator to facilitate extracellular electron transfer from bacteria to electrode and significantly enhanced the power production in MFCs.

Deposition of Fe on graphite felt by thermal decomposition of Fe(CO)5 for effective cathodic preparation of microbial fuel cells.

In this paper, an efficient and cost-effective method to prepare cathodes for microbial fuel cells (MFCs) was developed. Fe(CO)5 was decomposed and Fe was deposited on graphite felts for cathodic preparation. The unmodified, Pt modified and Fe modified graphite felts were utilized as cathodes in MFCs and power generation was compared. The maximum power density of MFCs with unmodified, Pt modified and Fe modified cathodes were respectively 288, 866 and 925 mW/m3. The internal resistance of MFCs with unmodified, Pt modified and Fe modified cathodes were respectively 505, 384 and 278Ω. The results of multiple analyses confirmed that Fe on cathode was Fe2O3 and FeOOH and Fe(III) oxides as cathodic catalysts improved the electrochemical activity and promoted power generation. The greatest advantage of new method for cathodic preparation was the replacing manual brushing and Nafion solution and decreasing the cost.

Fluidized roasting reduction kinetics of low-grade pyrolusite coupling with pretreatment of stone coal

Based on the fluidized roasting reduction technology of low-grade pyrolusite coupling with pretreatment of stone coal, the manganese reduction efficiency was investigated and technical conditions were optimized. It is found that the optimum manganese reduction efficiency can be up to 98.97% under the conditions that the mass ratio of stone coal to pyrolusite is 3:1, the roasting temperature of stone coal is 1000°C, the roasting temperature of pyrolusite is 800°C, and the roasting time is 2 h. Other low-grade pyrolusite ores in China from Guangxi, Hunan, and Guizhou Provinces were tested and all these minerals responded well, giving ∼99% manganese reduction efficiency. Meanwhile, the reduction kinetic model has been established. It is confirmed that the reduction process is controlled by the interface chemical reaction. The apparent activation energy is 36.397 kJ/mol.

Enhanced U(VI) bioreduction by alginate-immobilized uranium-reducing bacteria in the presence of carbon nanotubes and anthraquinone-2,6-disulfonate.

Uranium-reducing bacteria were immobilized with sodium alginate, anthraquinone-2,6-disulfonate (AQDS), and carbon nanotubes (CNTs). The effects of different AQDS-CNTs contents, U(IV) concentrations, and metal ions on U(IV) reduction by immobilized beads were examined. Over 97.5% U(VI) (20 mg/L) was removed in 8 hr when the beads were added to 0.7% AQDS-CNTs, which was higher than that without AQDS-CNTs. This result may be attributed to the enhanced electron transfer by AQDS and CNTs. The reduction of U(VI) occurred at initial U(VI) concentrations of 10 to 100 mg/L and increased with increasing AQDS-CNT content from 0.1% to 1%. The presence of Fe(III), Cu(II) and Mn(II) slightly increased U(VI) reduction, whereas Cr(VI), Ni(II), Pb(II), and Zn(II) significantly inhibited U(VI) reduction. After eight successive incubation-washing cycles or 8 hr of retention time (HRT) for 48 hr of continuous operation, the removal efficiency of uranium was above 90% and 92%, respectively. The results indicate that the AQDS-CNT/AL/cell beads are suitable for the treatment of uranium-containing wastewaters.

Polyaniline and iron based catalysts as air cathodes for enhanced oxygen reduction in microbial fuel cells

The catalyst for oxygen reduction in a cathode is vital for power production in microbial fuel cells (MFCs). In this study, non-precious metal catalysts were prepared by a high-temperature treatment of the iron containing polyaniline as both nitrogen and carbon precursor. These catalysts showed very positive onset potentials and less than 3% yield of hydrogen peroxide in the whole potential range, which matched the state-of-the-art Pt/C. The MFC with a bare cathode only produced a maximum power density of 1.32 W m(-3), while the MFCs with a PANI(900), PANI-Fe-700, and PANI-Fe-900 cathode had a maximum power density of 3.00 W m(-3), 7.45 W m(-3), and 12.54 W m(-3), respectively. Physical and chemical characterizations of the catalysts indicated that iron coordinated with pyridinic nitrogen hosted in micropores was responsible for the high catalytic activity. These results demonstrate that these catalysts are excellent cathodes for MFCs due to their high catalytic activity, strong stability and low cost.

Converting Low-grade Biomass to Produce Energy Using Bio-fuel Cells

Aerobic and anaerobic respiration of microorganisms involves redox reactions that provide energy for cell growth or maintenance. The energy comes from breaking up chemical bonds during the oxidation of organic carbons by the microorganisms. The electrons released from the oxidation are taken up by the reduction of an oxidant such oxygen, sulfate, nitrate, etc. If the oxidation and reduction reactions occur at the same place, for example, the cytoplasm of microbial cells, no electricity is produced. The energy produced will be used for cell growth or maintenance. The rest will be released as low-grade heat that cannot be harvested cost-effectively. Electrochemically, digestion of organic carbons can be split into anodic (organic carbon oxidation) and cathodic (proton reduction) reactions to produce an electric current that can be harvested when electrons from the oxidation reaction is donated to the anode and flow through an external circuit before be utilized by the reduction reaction at the cathode. Bio-fuel cells are classified into two different categories. fie is the so-called microbial fuel cell (MFC) that relies on a microbial biofilm to provide enzyme catalysis to fie anodic reaction while the other utilizes a cell-free enzyme system for catalysis. The recent energy crisis and concerns over global warming have reinvigorated interests in bio-fuel cells because their potential applications in electricity generation and biohydrogen production from renewable sources that are often low-cost or zerocost wastes. Currently, the bottleneck of real-world applications of bio-fuel cells in harnessing energy lies in their low power density and high costs, thus limiting their uses to powering small sensors or devices that require very little power. Numerous interesting and innovative approaches have been reported to increase the performances and to reduce reactor construction and operating costs of biofuel cells. Although significant hurdles remain ahead, new progresses are making bio-fuel cells closer to eventual practical applications utilizing low-grade biomass. This book chapter reviews various recent advances in bio-fuel cell research using various biomass feed stocks.