Application of proton exchange membrane fuel cells for the monitoring and direct usage of biohydrogen produced by Chlamydomonas reinhardtii

Photo-biologically produced hydrogen by Chlamydomonas reinhardtii is integrated with a proton exchange (PEM) fuel cell for online electricity generation. To investigate the fuel cell efficiency, the effect of hydrogen production on the open circuit fuel cell voltage is monitored during 27 days of batch culture. Values of volumetric hydrogen production, monitored by the help of the calibrated water columns, are related with the open circuit voltage changes of the fuel cell. From the analysis of this relation a dead end configuration is selected to use the fuel cell in its best potential. After the open circuit experiments external loads are tested for their effects on the fuel cell voltage and current generation. According to the results two external loads are selected for the direct usage of the fuel cell incorporating with the photobioreactors (PBR). Experiments with the PEM fuel cell generate a current density of 1.81 mA cm⁻² for about 50 h with 10 Ω load and 0.23 mA cm⁻² for about 80 h with 100 Ω load.     

Multi-electrode microbial fuel cell (MEMFC): A close analysis towards large scale system architecture

Microbial fuel cells are capable of producing electricity through the treatment of wastewater, however, the low power density poses main hurdles towards their wide application. In present work, microbial fuel cell based on multiple anodes, acting as baffle is constructed for achieving higher performance which can be scaled up for real life application. It is investigated for continuous sixty two days using distillery wastewater (WW) in three batches under ambient condition. During first batch, the WW is maintained under stagnant condition inside the anode chamber where as in the rest of the two batches WW is recirculated in the chamber. A maximum power density 427 mW m⁻², is achieved under stagnant condition which is further enhanced to 597 mW m⁻² under recirculation mode. Recirculation of WW reduces the internal resistance arising from the mass transfer by 50%. Maximum COD removal and Coulombic efficiency obtained is 43% and 23%. Biofouling on the surface of the membrane facing anode chamber is observed.     

Hydrogen generation by alcohol reforming in a tandem cell consisting of a coupled fuel cell and electrolyser

The performance of a novel electro-reformer for the production of hydrogen by electro-reforming alcohols (methanol, ethanol and glycerol) without an external electrical energy input is described. This tandem cell consists of an alcohol fuel cell coupled directly to an alcohol reformer, negating the requirement for external electricity supply and thus reducing the cost of operation and installation. The tandem cell uses a polymer electrolyte membrane (PEM) based fuel cell and electrolyser. At 80 °C, hydrogen was generated from methanol, by the tandem PEM cell, at current densities above 200 mA cm⁻², without using an external electricity supply. At this condition the electro-reformer voltage was 0.32 V at an energy input (supplied by the fuel cell component) of 0.91 kWh/Nm³; i.e. less than 20% of the theoretical value for hydrogen generation by water electrolysis (4.7 kWh/Nm³) with zero electrical energy input from any external power source. The hydrogen generation rate was 6.2 × 10⁻⁴ mol (H₂) h⁻¹. The hydrogen production rate of the tandem cell with ethanol and glycerol was approximately an order of magnitude lower, than that with methanol.     

Performance comparison of up-flow microbial fuel cells fabricated using proton exchange membrane and earthen cylinder

Continuous bioelectricity generation was studied in a novel up-flow bio-cathode microbial fuel cell (MFC). The performance of MFC-1, employing commercially available proton exchange membrane (PEM), was evaluated under different organic loading rates (OLRs). Maximum volumetric power density of 10.04 W m⁻³ was obtained in MFC-1 at the OLR of 0.923 kg COD m⁻³ d⁻¹. Overall chemical oxygen demand (COD) removal efficiency more than 90% was achieved under all the OLRs. The performance of MFC-1 was compared with MFC-2, in which the inner anode chamber was made up of earthen cylinder, without employing polymer membrane. MFC-2 generated maximum volumetric power density of 14.59 W m⁻³ at OLR of 0.923 kg COD m⁻³ d⁻¹, which was 46% higher than that produced in MFC-1. The internal resistance of MFC-1 (96 Ω) was higher than MFC-2 (69 Ω). The earthen cylinder MFC demonstrated better COD removal and power generation than the MFC employing PEM.     

Inoculation procedures and characterization of membrane electrode assemblies for microbial fuel cells

Membrane electrode assemblies were prepared following procedures adopted in the fabrication of polymer electrolyte membrane (PEM) fuel fells and used in microbial fuel cells (MFCs) with Shewanella oneidensis MR-1 as a single culture and sodium lactate as the electron donor. Improved inoculation procedures were developed and fuel cell performance with the biofilm density of microbes over the anode is discussed. A novel procedure to condition the membrane is also presented. Polarization measurements were carried out and power density plots were generated. Power density values of 300 mW m⁻² are typically obtained while a maximum value of 600 mW m⁻² is demonstrated indicating good performance for a single cell culture.     

Characterization of nitrogen gas crossover through the membrane in proton-exchange membrane fuel cells

Gas crossover phenomenon through a membrane is inevitable in a proton-exchange membrane fuel cell (PEMFC). For nitrogen, the concentration at the cathode side is usually higher than that at the anode side, so N₂ permeates to the anode side. Nitrogen gas crossover (NGC) may cause fuel starvation, if N₂ gas accumulates in the hydrogen recirculation loop. Thus, it is important to determine the NGC under various PEMFC operating conditions. In this study, characterization of NGC under both open circuit voltage (OCV) and power generation conditions is investigated using a mass spectrometer. Under OCV conditions with the PEMFC membrane fully hydrated, N₂ concentration in the anode exit stream increases as cell temperature increases. Nitrogen permeability coefficients (NPC) are calculated based on the obtained N₂ concentration data. The results show that NPC exhibits an Arrhenius type relationship. Under OCV conditions, the maximum NPC is 5.14 × 10^?13 mol m^?1 s^?1 Pa^?1 with an N₂ activation energy of 19.83 kJ. Under power generation conditions, the NGC increases with increasing current density, which is the result of elevated membrane temperature and increased water content. When the anode stoichiometric ratio (SR_A) is lowered, the N₂ concentration increases under all tested current densities. A low hydrogen flow rate, along with a low SR_A at low current density, significantly increases N₂ concentration at the anode outlet.     

Modification of graphite felt using nano polypyrrole and polythiophene for microbial fuel cell applications-a comparative study

Microbial fuel cells (MFC) are bio-electrochemical devices used for the generation of electricity from biomass. A single chamber membrane less air-breathing cathode microbial fuel cell (SCMFC) with two different anode configurations was investigated for energy generation using shewanella putrifaciens as bio-catalyst. The graphite felt (GF) anode was modified with 0.008 g/cc polypyrrole nanoparticles (Ppy-NPs) and 0.024 g/cc polythiophene nanoparticles (PTh-NPs) by conventional method. The nanoparticles coating improved the properties such as thermal characteristics and electron transfer capabilities of the anodes, which was confirmed by Thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS) and cyclic voltametry (CV). The variation in the cell potential with time under open circuit condition resulted in voltages of 0.842V and 0.644 V for Ppy-NP and PTh-NP modified GF respectively. A maximum power density (1.22 W/m²) was obtained for Ppy-NP modified GF than PTh-NP modified GF (0.8 W/m²). The results showed that GF coated with nano conductive polymers such as Ppy and PTh are the promising candidates for the best performance of a MFC.     

Construction and operation of a microbial fuel cell for electricity generation from wastewater

The increase in the global energy demand every year and the over-consumption of nonrenewable sources of energy has led to the identification and use of renewable and cost effective sources of energy. In this context, wastewater, which contains high levels of easily degradable organic material, has gained importance as a source of electricity generation using a microbial fuel cell.A microbial fuel cell comprising of Pseudomonas sp., mediator, and potassium ferricyanide as the oxidizing agent was developed for generation of electricity using wastewater, as substrate, obtained from wastewater treatment plant. The cells were connected in series with the anodic and cathodic solutions being introduced in batch and continuous modes. A maximum open-circuit potential of 2.2 V was obtained with the anode in batch-fed and cathode in continuous mode of operation. Methylene blue, when used as the mediator was found to produce a higher output from the cell when compared to neutral red. The maximum power output and current density obtained were 979 μW/m² and 1.15 mA/m² respectively. A 10% reduction in COD was observed when the microbial fuel cell was operated using the wastewater as the substrate.     

Effects of mediator producer and dissolved oxygen on electricity generation in a baffled stacking microbial fuel cell treating high strength molasses wastewater

The effects of Pseudomonas aeruginosa, pyocyanin, and influent dissolved oxygen (DO) on the electricity generation in a baffled stacking microbial fuel cell (MFC) treating high strength molasses wastewater were investigated. The result shows that the influent chemical oxygen demand (COD) of 500–1000 mg l⁻¹ had the optimal substrate-energy conversion rate. The addition of a low density of P. aeruginosa (8.2 mg l⁻¹) or P. aeruginosa with pyocyanin improved the COD removal and power generation. This improvement could be attributed to the enhancement of electron transfer with the help of redox mediators. Influent DO at a concentration of up to 1.22 mg l⁻¹ did not inhibit the electricity generation. Large proportions of COD, organic-N and total-N were removed by the MFC. The MFC effluent was highly biodegradable. Denaturing gradient gel electrophoresis analysis shows that the added pyocyanin resided in the MFC for up to 14 days. An analysis of anode voltage reveals that microbial proton transport to the cathode was importantly responsible for the internal resistance.     

Electricity generation from rice straw using a microbial fuel cell

This study demonstrated electricity generation from rice straw without pretreatment in a two-chambered microbial fuel cell (MFC) inoculated with a mixed culture of cellulose-degrading bacteria (CDB). The power density reached 145 mW/m² with an initial rice straw concentration of 1 g/L; while the coulombic efficiencies (CEs) ranged from 54.3 to 45.3%, corresponding to initial rice straw concentrations of 0.5–1 g/L. Stackable MFCs in series and parallel produced an open circuit voltage of 2.17 and 0.723 V, respectively, using hexacyanoferrate as the catholyte. The maximum power for serial connection of three stacked MFCs was 490 mW/m² (0.5 mA). In parallelly stacked MFCs, the current levels were approximately 3-fold (1.5 mA) higher than those produced from the serial connection. These results demonstrated that electricity can be produced from rice straw by exploiting CDB as the biocatalyst. Thus, this method provides a promising way to utilize rice straw for bioenergy production.     

Natural degradation and stimulated recovery of a proton exchange membrane fuel cell

In this paper, the stimulated recovery of a proton exchange membrane (PEM) fuel cells after natural degradation has been investigated. The performance degradation of a 63-cell PEM fuel cell stack over a storage interval of 40,000 h at temperature 24 °C and relative humidity 65% was analyzed by static and dynamical tests. The average cell voltage degradation rate was 309 μV h⁻¹, averaged over a range of currents. The performance was then partially recovered by application of a high frequency pulsing procedure after which the effective average degradation rate (from the commencement of storage to after the recovery) was approximately 170 μV h⁻¹. This indicates the existence of both recoverable and irrecoverable degradations in the fuel cell. Furthermore, the equivalent circuit model and membrane resistance were used to investigate the degradation mechanisms, suggesting that the natural degradation of the fuel cell is mainly caused by the increase of the resistance, which is most likely caused by membrane dehydration.     

Process engineering for stable power recovery from dairy wastewater using microbial fuel cell

Microbial fuel cells (MFCs) are one of the sustainable technologies that can effectively treat wastewater with concomitant generation of electricity. The present study investigated the treatment of real dairy wastewater (RDW) using Shewanella algae (MTCC-10608) within a single chamber microbial fuel cell (SCMFC). The study was conducted in both batch and fed-batch modes with initial chemical oxygen demand (COD) of 4000 mg/L and 2000 mg/L, respectively, in 0.2 L working volume of RDW for 15 days. However, the fed-batch strategy involved subsequent feeding of dairy wastewater with 6000 mg/L and 8000 mg/L COD on the 5th and 10th day, respectively. This two-step feeding strategy resulted in a maximum open-circuit voltage of 666 mV at 286 h of incubation with a COD removal efficiency of 92.21% and a columbic efficiency of 27.45%. The kinetic studies predicted the saturation constant of 55.83 mg COD/L and current density of 143.3 mA/m², which are similar to the findings from the experiments and polarization curve obtained. The maximum current density and power density from experiments were found to be 141 mA/m² and 50 mW/m² respectively. Thus, this study successfully indicates the utilization of dairy wastewater as a potential substrate for the sustainable power generation using Shewanella algae as a biocatalyst in the microbial fuel cell.     

Performance of an anion exchange membrane in association with cathodic parameters in a dual chamber microbial fuel cell

Performance of two-chambered microbial fuel cells (MFCs) using anion exchange membrane (AEM) was evaluated under batch mode with Shewanella putrefaciens in Luria broth. Maximum voltage and power density using Nafion and Ralex AEM were 0.676 V and 0.729 V and 39.2 ± 7.39 mW/m² and 57.8 ± 5.509 mW/m² respectively. Cathodic half cell potential was monitored along with cathodic pH and the results revealed that low power density was achieved in case of Nafion as compared to Ralex AEM mainly due to pH imbalance associated voltage losses using small external resistance of the same. Metabolite loss in AEM was found at higher current density which limits the Coulombic efficiency and power generation. A three parameters optimization showed that surface area of cathode had significant effect on the power generation. Effect of anode surface area, dissolve oxygen (DO) in catholyte and electrode spacing on power production were evaluated using AEM membrane.     

Novel design of a multitube microbial fuel cell (UM2FC) for energy recovery and treatment of membrane concentrates

A two-stage treatment process, consisting of a flat sheet membrane system and a novel upflow multitube microbial fuel cell (UM²FC), was investigated to simultaneously treat concentrate streams—as well as produce electricity. This study tested the treatment of the retained part (i.e membrane concentrate) of the membrane process and electricity production using an air-cathode UM²FC inoculated with sediment sample collected from Golden Horn, Istanbul. The electrochemical behaviors were investigated using electrochemical methods to identify how membrane concentrates effects the reactor performance. The treatment of domestic wastewater was performed using a lab-scale cross-flow filtration apparatus with a UH050 membrane and the chemical oxygen demand (COD) removal efficiency as a result of membrane treatment was 87%. Then the UM²FC was fed sequentially from the feed tank when desired retained ratios (25% and 50%) observed. The maximum power density obtained was 25.138 mW m⁻² in the 50% concentrate or a volume concentration ratio (VCR) of 2 fed UM²FC which was 244% higher than that achieved using raw wastewater (7.303 mW m⁻²) and COD removal was >65% in UM²FC. The contribution of different resistances such as ohmic, charge transfer and mass transfer resistances of the reactor under different stages was ascertained through the measurements using electrochemical impedance spectroscopy (EIS) and the results showed that an increasing organic loading reduced the internal resistance and enhanced power. On the whole, study reported new findings such as a new treatment technology for membrane concentrate treatment and gives insight to literature on reactor design.     

Physically stable proton exchange membrane with ordered electrolyte for elevated temperature PEM fuel cell

Dimensional change and humidity-induced stress of the proton exchange membrane were demonstrated to be main reasons for membrane physical failure during the long-term fuel cell operation. In this work, UV laser ablation was proposed to prepare physically stable polyimide supports to reduce the dimensional swelling and humidity-induced stress of the proton exchange membrane under variable humidities. Long-range ordered straight holes with definable open pattern and diameter of 50–200 μm were formed through the polyimide support. Composite proton exchange membrane prepared from the straight-hole polyimide support presented desirable performance and high durability in fuel cells. When Nafion fraction in the composite membrane increased to 48.67%, the proton conductivities of the composite membranes were equal to or greater than that of the conventional Nafion membrane with activation energies lower than that of the Nafion 211 membrane. The dimensions of the composite membranes are very stable in both low and elevated temperature conditions. The proportion of humidity-induced stress to the yield strength for the composite membrane is 0.20%–0.21%, much lower than that of the conventional Nafion membrane (24.77%). As a result, the composite proton exchange membrane prepared from the straight-hole polyimide presented high durability in the fuel cell operation. In the open circuit voltage accelerated test under in situ accelerating RH cyclic test, the irreversible OCV reduction rate of the composite membranes was 2.41–2.72 × 10⁻⁵ V/cycle, 37.1%–41.8% lower than that of the conventional Nafion 211 membrane.     

Performance evaluation of a fuel processing system based on membrane reactors technology integrated with a PEMFC stack

The development of fuel cells is promised to enable the distributed generation of electricity in the near future. However, the infrastructure for production and distribution of hydrogen, the fuel of choice for fuel cells, is currently lacking. Efficient production of hydrogen from fuels that have existing infrastructure (e.g., natural gas, gasoline or LPG) would remove a major drawback to use fuel cells for distributed power generation.The aim of this paper is to define the better operating conditions of an innovative hydrogen generation system (the fuel processing system, FP) based on LPG steam reforming, equipped with a membrane shift reactor, and integrated with a PEMFC (Proton Exchange Membrane Fuel Cell) stack of 5 kWel.With respect to the conventional hydrogen generation systems, the use of membrane reactors (MRs) technology allows to increase the hydrogen generation and to simplify the FP-PEMFC plant, because the CO removal system, needed to reduce the CO content at levels required by the PEMFC, is avoided.Therefore, in order to identify the optimal operating conditions of the FP-PEMFC system, a sensitivity analysis on the fuel processing system has been carried out by varying the main operating parameters of both the reforming reactor and the membrane water gas shift reactor. The sensitivity analysis has been performed by means of a thermochemical model properly developed.Results show that the thermal efficiency of the fuel processing system is maximize (82.4%, referred to the HHV of fuels) at a reforming temperature of 800 °C, a reforming pressure of 8 bar, and an S/C molar ratio equal to 6. In the nominal operating condition of the PEMFC stack, the FP-PEMFC system efficiency is 36.1% (39.0% respect to the LHV).     

Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Investigation of the effect of cathode stoichiometry of proton exchange membrane fuel cell using localized electrochemical impedance spectroscopy based on print circuit board

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm² multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100  mA cm⁻², 500  mA cm⁻² and 900 mA cm⁻²) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.     

Influence of growth curve phase on electricity performance of microbial fuel cell by Escherichia coli

The microbial fuel cell of Escherichia coli can convert microorganism biochemistry energy into electrical energy. To realize the influence of the growth curve phase with respect to different culture times on electricity performance, three kinds of E. coli (BCRC No. 10322, 10675, 51534) are selected, and it is both required and important to improve the performance of the microbial fuel cell (MFC). Results show that the BCRC No. 51534 of E. coli would be a better choice because a larger open-circuit voltage of 0.88 V and a limiting current of 10.1 mA possessed by it would result in an excellent power density of 547 mW/m². In addition, the selection of culture timing set as at the middle of the logarithmic phase and phase transition from logarithmic to stationary is suggested because the growth curve is suitable for electricity generation of the MFC. These observations would be useful for the improvement of the MFC.     

Electricity harvest from nitrate/sulfide-containing wastewaters using microbial fuel cell with autotrophic denitrifier, Pseudomonas sp. C27

Toxicity prevents the bioenergy content of certain industrial effluents from being recovered. In operation of microbial fuel cell (MFC), microorganisms can be inhibited with high levels of sulfide. This study applied a pure culture, an autotrophic denitrifier, Pseudomonas sp. C27, to start up a two-chambered MFC using sulfide as the sole electron donor. The MFC can successfully convert sulfide to elementary sulfur with electricity generation at a maximum power density of 40 mW m⁻². The addition of acetate interfered biofilm activity to convert sulfide to electricity. Nitrate was revealed as the more powerful electron acceptor than anode in the MFC. The present device introduces a route for treating sulfide laden wastewaters with electricity harvest.