Development of innovative materials used in electrochemical devices for the renewable production of hydrogen and electricity

<i>Harvesting Energy using Biocatalysts</i>

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.

Effect of ionic strength, cation exchanger and inoculum age on the performance of Microbial Fuel Cells

Microbial fuel cell represents an emerging technology to attain electrical energy from wastewater. There are several alternative methods available for wastewater treatment; Microbial fuel cell is one of them, which generates green energy from wastewater for making a contribution to renewable sources of energy. This study states the performance of microbial fuel cell with different parameters i.e., catholyte, electrodes, and initial COD concentration. Sodium chloride was used as catholyte and graphite rods were used as both electrodes. The sodium chloride concentrations in the cathode and initial chemical oxygen demand have also been optimized. The optimum sodium chloride of 70 mM in the cathode solution generates the maximum power density of 408.98μW/m2. As the sodium chloride concentration increases in catholyte, the capacity for power production also increases. The voltage output of Microbial fuel cell increases when the initial concentration of chemical oxygen demand increases to a peak value of 1500 mg/l and if the value exceeds this limit, the performance of Microbial fuel cell (in terms of voltage) starts decreasing. The chemical oxygen demand removal efficiency of a microbial fuel cell with simple graphite electrode and graphite electrodes with coated iron were 79% and 90% respectively.

Electrode modifications employing conductive and nanostructured polyaniline (PANI) have been acknowledged as an effective strategy to enhance the interaction between electrode surfaces and bacteria, thereby augmenting the performance of Microbial Fuel Cells (MFCs). However, the specific influence of PANI morphology on power generation in MFCs remains unknown. In this study, two nanostructures of polyaniline, viz., polyaniline nanofiber (PANI-NF) and polyaniline nanoparticle (PANI-NP), were electro-polymerized on a peanut shell biochar (PSB) electrode by chronoamperometry. The physico-chemical properties of PSB, PSB/PANI-NF, and PSB/PANI-NP were analyzed using scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), and Fourier transform infrared spectroscopy (FT-IR). The electrochemical performance of the electrodes was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Remarkably, the PSB/PANI-NP composite exhibited notably heightened electrochemical activity and superior electrode-electrolyte interaction, leading to a significant enhancement in MFC performance. MFCs equipped with PSB/PANI-NP electrodes achieved a power output of 600 mW/m2 surpassing the performance of MFCs utilizing PSB/PANI-NF and PSB electrodes by 2.8 and 25 times, respectively. This investigation elucidates the pivotal role of PANI morphology on power production in MFC.

Enhancement of gaseous chlorobenzene biodegradation and power generation in a microbial fuel cell by bifunctional Acinetobacter sp. HY-99C

ABSTRACTAir-cathode microbial fuel cells (MFCs) are widely tested to recover electrical energy from waste streams containing organic matter. When high-strength wastewater, such as liquid animal manure, is used as a medium, inhibition on anode and cathode catalysts potentially impairs the effectiveness of MFC performance in power generation and pollutant removal. This study evaluated possible inhibitive effects of liquid swine manure components on MFC power generation, improved liquid manure-fed MFCs performance by pretreatment (dilution and selective adsorption), and modeled the kinetics of organic matter and nutrients removal kinetics. Parameters monitored included pH, conductivity, chemical oxygen demand (COD), volatile fatty acids (VFAs), total ammoniacal nitrogen (TAN), nitrite, nitrate, and phosphate concentrations. The removals of VFA and TAN were efficient, indicated by the short half-life times of 4.99 and 7.84 d, respectively. The mechanism for phosphate decrease was principally the salt precipitation on cathode, but the removal was incomplete after 42-d operation. MFC with an external resistor of 2.2 kΩ and fed with swine wastewater generated relatively small power (28.2 μW), energy efficiency (0.37%) and Coulombic efficiency (1.5%). Dilution of swine wastewater dramatically improved the power generation as the inhibitory effect was decreased. Zeolite and granular activated carbon were effective in the selective adsorption of ammonia or organic matter in swine wastewater, and so substantially improved the power generation, energy efficiency, and Coulombic efficiency. A smaller external resistor in the circuit was also observed to promote the organic matter degradation and thus to shorten the treatment time. Overall, air-cathode MFCs are promising for generating electrical power from livestock wastewater and meanwhile reducing the level of organic matter and nutrients.

The current study was performed to evaluate the beneficial effect in the power output of microbial fuel cells (MFCs) through supplementation of dried red pepper (Capsicum annuum) powder into the anodic chamber. Mediator-less H-type MFCs were set up where the anode chamber contained rumen microorganisms as inocula on cellulose (Avicel) and the cathode chamber of phosphate buffered saline (pH 7.4), both separated by cation exchange membrane. Electrical power generation in MFC was monitored daily over a 10-day period and the accumulated amounts and components of gaseous byproducts were measured at the end of 10 d operation of MFC. For both groups of MFCs with red pepper and the control, the head space gases collected were methane and CO2, and its volume and composition were similar between treatments. Methane and CO2 produced for 10 d operation were 210.7 and 106.5 mL, respectively, in MFC. The addition of red pepper powder caused an average power density to increase from 24.0 mW/m2 to 39.6 mW/m2 (P 2 for control and bellflower, respectively. This study provides the strong evidence that red pepper (Capsicum annuum) supplementation might modify the anaerobic fermentation characteristics of rumen microorganisms in anode chamber and improve the cellulosic bioenergy production in MFC.

Advances in Understanding Carbon Composite Catalysts Based on Cathode for Microbial Fuel Cells

Billions of dollars are spent on wastewater treatment each year, and the worldwide energy crisis makes green technologies increasingly more attractive. Microbial fuel cells (MFCs) can potentially be used to digest organic matter in wastewaters and reduce its solids by up to 90%. MFCs generate electricity by harvesting the electrons donated to the anode from organic carbon oxidation in an anaerobic anodic chamber mediated by bacteria in biofilms. The electrons flow through an external circuit to reach the cathode where they are used to react with oxygen and protons to form water in the cathodic chamber. Instead of using oxygen in the cathodic chamber, which requires expensive catalytic cathodes, alternate oxidants such as nitrate and nitrite in wastewaters can also be used as electron acceptors with a biocathode. It was claimed that MFCs have the potential to reduce power consumption in wastewaters by as much as 50%. By operating MFCs in electrolysis mode, known as microbial electrolysis cells (MECs), biohydrogen can be produced by applying a much lower external voltage than that for the direct water electrolysis. In laboratory investigations, MECs have been used to treat many kinds of hazardous wastes and wastewaters. Recently, there is a growing interest in producing value-added bioproducts from MFCs or MECs, as well as microbial desalination cells. Significant technical hurdles need to be overcome before large-scale MFCs become practical. Recent advances such as genetically engineered, dispersion-deficient microbes that bind tenaciously to an electrode, electrogenic hyperpilated bacteria, new anodic materials, more efficient mediators, and membrane-less MFCs make the feasibility of MFCs for wastewater treatment more promising than ever. This review discusses new advances in MFC operation, design, and optimization for wastewater treatment with concomitant bioenergy production.

Microbial fuel cells (MFCs) are bioelectrochemical systems that exploit microbial respiration for the conversion of organic compounds into electrical energy. Within a typical system, electrochemically active microorganisms extracellularly transfer electrons released during the oxidation of organic compounds to the anode surface. The electrons travel from the anode, across an external load to the cathode, where they react with the terminal electron acceptor (e.g. oxygen from air). MFCs are a promising means for wastewater treatment and as a source of renewable energy. The operational mode of the MFC can directly control microbial metabolism and respiration and thus define the wastewater treatment rate, energy recovery and final products from wastewater treatment. Despite the advantages, MFCs are not yet a viable solution for large-scale wastewater treatment and energy generation. Extensive research must still be conducted to optimize the system including MFC start-up time, stability and treatment rates. MFC start-up time is widely variable depending on external conditions, inoculum source and substrate. There are challenges associated with stability and reproducibility of the system. Finally, wastewater treatment rates using MFCs still are not comparable to conventional wastewater treatment methods, and the magnitude of energy recovery is not at a meaningful scale. In this study, we evaluated different enrichment and operational strategies to optimize MFC performance. At the beginning of the experiment, during the enrichment phase, the anode potential was modulated either by an external resistor or an applied voltage. It has been previously shown that the anodic community composition and biomass formation changes according to the external resistor or potential applied [1,2]. Under such operational conditions, a faster start up time can also be achieved [3]. In addition, start-up time and overall performance will also be impacted by inoculum source and substrate selection. Previous reports addressed MFC performance as a function of operation and startup time using either a defined media and single carbon substrate [2] or a single enrichment strategy with primary clarifier effluent as the single inoculum and substrate [1]. Therefore our evaluations addressed a highly diverse inoculum source including lagoon sediment and swine waste and different methodologies for enrichment to expand the knowledge base about what enrichment strategies may be best for a given wastewater treatment application. Varying ranges of external resistors and applied voltages were tested. A periodically induced open circuit condition was also evaluated to study its effect on MFC output. With these experimental conditions, we are aiming to identify an optimal strategy for MFC start-up and operation, and evaluate the long-term effects on MFC performance including the electrochemical performance, community taxonomic dynamics, biomass formation, and wastewater treatment rate.

Microbial fuel cell (MFC) represents a new method for producing electricity from the oxidation of organic matter. In addition, MFC offers an effective wastewater treatment. The feasibility of using POME wastewater as a substrate was investigated through a two-chambered MFC operated in batch mode for 12 days. The performance of MFC was evaluated under three different anode pH microenvironments of acidic (pH 4), neutral (pH 7) and alkaline (pH 8). Results of experiments indicated that the MFC reactor was able to generate electricity and treat POME wastewater that acted as substrate for MFC. The performance of MFC was found to be dependent on the anode pH microenvironments. Higher power density was observed at neutral condition compared to acidic and alkaline conditions. Furthermore, significant reductions in chemical oxygen demand (COD) in anode chambers were found due to the changes of pH in anode microenvironment. This indicated that effective wastewater treatment of POME in MFC batch experiments. In conclusion, MFC provides an alternative, sustainability and effective method to generate electricity and effectively treat wastewater.

Probing mechanisms for microbial extracellular electron transfer (EET) using electrochemical and microscopic characterisations

Formation of methane in the anodic chamber of a microbial fuel cell (MFC) indicates an energy inefficiency in electricity generation as the energy required for electrogenesis gets redirected to methanogenesis. The hypothesis of this research is that inhibition of methanogenesis in the mixed anaerobic anodic inoculum is associated with an enhanced activity of the electrogenic bacterial consortia. Hence, the primary objective of this investigation is to evaluate the ability of chloroform to inhibit the methanogenesis at different dosing to enhance the activity of electrogenic consortia in MFC. A higher methane inhibition and hence an enhanced performance of MFC was achieved when mixed anaerobic sludge, collected from septic tank, was used as inoculum after pre-treatment with 0.25% (v/v) chloroform dosing (MFC-0.25CF). The MFC-0.25CF attained a maximum power density of 8.51W/m3, which was more than twice as that of MFC inoculated with untreated sludge. Also, a clear correlation between the chloroform dosing, methane inhibition, wastewater treatment, and power generation was established, which demonstrated the effectiveness of the technique in enhancing power generation in MFC along with adequate biodegradation of organic matter present in wastewater at an optimum chloroform dosing of 0.25% (v/v) to inhibit methanogenesis.

The use of catalysts and membranes in microbial fuel cells (MFCs) is rather controversial. Platinum is the best catalyst to improve the oxygen reduction reaction and the implementation of an ion exchange membrane may help to avoid the oxygen leakages from the cathode to the anode compartments and, therefore, the losses of efficiencies associated to the use of oxygen by microorganisms as the immediate electron acceptor. In this work, it is studied the influence of the platinum loading in the cathode and the implementation of membrane on the performance of an air-breathing MFC. To do this, four cells were operated for 50 days in order to clarify the effect of the platinum loading contained in the cathode (0.25, 0.50, 1.00, and 2.00 mg Pt cm−2) and two additional MFCs for more than 100 days in order to evaluate the effect of the membrane on the performance of the MFC. The results obtained point out that the performance of the MFC, in terms of maximum current density and power density from the polarization curves, depends strongly on the Pt content of the cathode. This indicates that under open-circuit conditions the cathode controls the performance. Nonetheless, during the closed-circuit operation (under 120 Ω resistance), the performance is not cathodically limited as there are no significant changes between the four cells. This suggests that the performance of the MFC is limited by the anodic process. Likewise, the separation of the anode and cathode by a membrane attains a faster stabilization of the MFC and a slight improvement in the production of electricity, although for air-breathing MFC, this element does not seem to be as crucial as for other types of MFCs.