Fang-Bor Weng, Bo-Shian Jou, Pei-Hung Chi et al.

Journal of Fuel Cell Science and Technology • 2009

A micro-fuel-cell stack of six cells with an active area of 2.73 cm2 and 2.5 W output power has been designed and fabricated in-house. It can go with mini hydrogen storage and provide enough power for portable electric products. Under polarization curve measurement, when the voltage was scanning to low voltage, the performance was quickly decayed by the low fuel concentration. This result was contributed by a limited fuel supply of metal hydride hydrogen tank. The voltage declined to very low voltage in some of the cell stacks when the current output was at high current. This phenomenon is attributed to the self-breath of air in the cathode. At the higher current of 0.9 A condition, the stack voltage was decreased even though the high hydrogen flow rate was increased. The solution to prevent the decrease in voltage is adding the airflow in the cathode. The fuel cell performances respond to the transient of load changes influenced by the hydrogen flow rate and step increase in current. The flow change can decrease the high resistance in the transient of the current output, which prevents membrane electrode assembly (MEA) degradation caused by being operated for many times. After a series of experiments in this study, the micro-fuel-cell system demonstrates the ability of offering a stable power to a cell phone or robot with reliability.

Elizabeth Aleman-Gama, Alan J. Cornejo-Martell, Sathish Kumar Kamaraj et al.

Journal of Electrochemical Science and Technology • 2022

The high internal resistance (Rint) that develops across the sediment microbial fuel cells (SMFC) limits their power production (~4/10 mW m−2) that can be recovered from an initial oil-contaminated sediment (OCS). In the anolyte, Rint is related to poor biodegradation activity, quality and quantity of contaminant content in the sediment and anode material. While on the catholyte, Rint depends on the properties of the catholyte, the oxygen reduction reaction (ORR), and the cathode material. In this work, the main factors limiting the power output of the SMFC have been minimized. The power output of the SMFC was increased (47 times from its initial value, ~4 mW m−2) minimizing the SMFC Rint (28 times from its initial value, 5000 ohms), following the main modifications. Anolyte: the initial OCS was amended with several amounts of gasoline and kerosene. The best anaerobic microbial activity of indigenous populations was better adapted (without more culture media) to 3 g of kerosene. Catholyte: ORR was catalyzed in birnessite/carbon fabric (CF)-cathode at pH 2, 0.8M Na2SO4. At the class level, the main microbial groups (Gammaproteobacteria, Coriobacteriia, Actinobacteria, Alphaproteobacteria) with electroactive members were found at C-anode and were associated with the high-power densities obtained. Gasoline is more difficult to biodegrade than kerosene. However, in both cases, SMFC biodegradation activity and power output are increased when ORR is performed on birnessite/CF in 0.8 M Na2SO4 at pH 2. The work discussed here can focus on bioremediation (in heavy OCS) or energy production in future work.

Sri Rachmania Juliastuti, Fitria Nur Laily, Raden Darmawan

Bulletin of Chemical Reaction Engineering & Catalysis • 2024

The generation of electricity via MFC is subject to alteration by the concentration of the substrate. The objective of this study was to examine the performance of MFCs using both theoretical and experimental methods to ascertain the kinetic parameters associated with the addition of cobalt, with the aim of enhancing electricity generation via MFCs. The study demonstrated the impact of varying substrate concentrations and the composition of food waste and water, with formulas 0:5, 1:4, 2:3, 3:2, 4:1, and 5:0 (w/v). The kinetics of biochemical reactions were determined by employing the Monod and Gates-Marlar equations. The Monod equations were evaluated using three distinct representation methods. The Langmuir, Lineweaver-Burk, and Eadie-Hofstee models were employed. Conversely, the electrochemical reaction rate is evaluated through the Butler-Volmer equation. The current density derived from the theoretical approach exhibited a comparable pattern to that observed in the experimental data. The maximum power density was attained at a substrate concentration of 4:1 (w/v) exceeding 25,000 mW/m². The presented model facilitated the enhancement and optimization of MFC performance. Substrate concentration and biomass concentration exert a significant influence on MFC performance, as evidenced by the analysis of variance (ANOVA) and response surface methodology (RSM). Copyright © 2025 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Tian‐shun Song, Wei‐min Tan, Xia‐yuan Wu et al.

Journal of Chemical Technology & Biotechnology • 2012

Abstract BACKGROUND: Sediment microbial fuel cells (SMFCs) could be used as power sources and one type of new technology for the removal of organic matters in sediments. Various types of materials have been used as electrodes. Nevertheless, there is still room to improve electrode materials and enhance their effect on the performance of SMFCs. In this work, performances of SMFCs with activated carbon fiber felt (ACFF) and with nitric acid‐treated ACFF were compared with graphite felt (GF) materials. RESULTS: The maximum power density of the SMFC with ACFF electrode was the highest (33.5 ± 1.5 mW m −2 ). Nitric acid‐treated GF electrode slightly increased the maximum power density of SMFC, while the nitric acid treated‐ACFF resulted in significant decline in the maximum power density of SMFC. The maximum power density further increased to 74.5 ± 7.5 mW m −2 in SMFC using GF cathode and ACFF anode. CONCLUSIONS: ACFF as anode can enhance the transport of electrons from the oxidation of organic matter in the sediment, while the output power was found to reduce in SMFC with ACFF cathode. Further efforts are needed to study the formation conditions of the biocathode and new electrode modification technology. Copyright © 2012 Society of Chemical Industry

Yu-Hsuan Hung, Tzu-Yin Liu, Han-Yi Chen

ECS Meeting Abstracts • 2019

Microbial fuel cells (MFCs), an unique type of fuel cell, have deeply attracted scientists’ attention as new sustainable energy devises in the past several years. They can transform chemical energy into bioelectricity by utilizing active microorganisms as biocatalyst in the anode compartment. Carbon materials including carbon paper, graphite plates, carbon cloth, and carbon nanotubes are the most commonly used electrodes because of their high surface area, good electric conductivity, and well biocompatibility. In this study, biowaste-derived activated carbon was fabricated with different activating agent ratios and characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR). The MFCs with biowaste derived activated carbon electrodes exhibited well cell performance with a power density more than 1600 mW/cm 2 . It demonstrates that the biowaste-derived activated carbon is a promising MFC electrode for sustainable bioelectricity generation. Keywords: Microbial fuel cells, biowaste derived activated carbon, nitrogen-doped carbon

Irdawati, Shintia Hendriany

Jurnal Biogenerasi • 2025

The increasing global energy demand and the negative impact of the use of fossil energy on the environment encourage the use of environmentally friendly renewable energy sources, one of which is through Microbial Fuel Cell technology. This study aims to measure or analyze bioelectrical production by utilizing a consortium of thermophilic bacterial bicultures (SSA 14 and SSA 16) in an MFC system arranged in a series circuit configuration. The research method was carried out experimentally in the laboratory using a dual-chamber reactor arranged in a series of two and three series, with voltage measurements carried out every 2 hours for 24 hours. The results showed that the series three series produced a higher average voltage (0.823 V) than the series two series (0.744 V). This study indicates that the addition of the number of fermenter units in the series series significantly increases the electrical voltage produced.

You-xian Gao, Ping Yang

E3S Web of Conferences • 2019

Aerobic granular sludge(AGS) is a special biofilm formed by the self-aggregation of sludge material. In this study, AGS was cultivated in the biocathode of a continuous flow microbial fuel cell (MFC). During the formation of AGS, changes in sludge concentration, extracellular polymers (EPS), pollutants removal and power generation were examined. The results showed that, MLVSS kept above 5 g/L, the PS, PN and PN/PS of TB-EPS showed a gradually increasing trend, the removal efficiency of COD and ammonia nitrogen was 94.46% and 93.03%, respectively. A maximum voltage output of 350 mV was achieved.

Yifeng Zhang, Irini Angelidaki

Biotechnology and Bioengineering • 2011

Abstract A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm‐colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm‐colonized anode showed linear relationship with BOD content, to up to 250 mg/L (∼233 ± 1 mA/m 2 ), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine‐triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m 2 ) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol‐ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers. Biotechnol. Bioeng. 2011;108: 2339–2347. © 2011 Wiley Periodicals, Inc.

Aashray Narla, Dhruv Upadhyaya, Sivakumar Amaravati et al.

ECS Meeting Abstracts • 2016

Microbial fuel cells (MFCs) are a hybrid bioelectrochemical system, which converts biosubstrates directly into electricity by effectively oxidizing those using bacteria under ambient temperature/pressure condition. The potential, developed between the bacterial metabolic activity and electron acceptor, was separated by a membrane (Perfluro sulphonic acid membrane in this case) manifesting bioelectricity generation. The achievable power output from MFCs can be tuned by modifying the system design, such as optimization of the Membrane Electrode Assembly (MEA) structure, cell operating conditions, and the choice of biocatalyst. MFC’s are good candidates for implantable applications. The advantages for implantable application are biocompatibility and natural, safe and light, amenability to sterilization, continuous power output, minimal invasiveness, long life cycle, easy to integrate electronics. Selection of the anode-cathode electrodes materials and structure is one of the critical challenges of MFC and more so for the implantable application. These can affect the power density and Coulombic efficiency. The electrochemical characteristics of MFC are studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and polarization profiles. Carbon and blends with graphene are used for developing the electrode diffusion structure. The anode is filled with bacteria which is E.Coli where luria bertani medium is used to grow the bacteria. The cathode is coated with manganese dioxide. The achievable cell potential is around 0.7-0.8V. For implantable application a power density of, in vitro > 10 μW / cm² and in vivo > 5 μW / cm² is targeted. Complete characterisation and optimisation parameters of the cell will be presented.

Ryan Yow Zhong Yeo, Wei Lun Ang, Mimi Hani Abu Bakar et al.

Fuel Cells • 2024

ABSTRACT Using microbial fuel cells (MFCs) as biosensors ensures a sustainable method for water quality detection. However, the research on MFC‐based biosensors with a tubular setup is still scarce. In this study, a tubular multi‐array MFC‐based biosensor setup with air‐cathodes was assembled under the membrane electrode assembly configuration. Three different materials, including carbon black (CB), Pt/C (PtC), and polyaniline (PANI), were synthesized and coated on the membrane‐facing side of the air‐cathode to demonstrate the effects of modified air‐cathodes on the overall performance of the MFC‐biosensors. Unmodified carbon cloths were used as anodes. Three days of startup period were required by the biosensors before producing an electrical signal output. The highest current density was obtained by the polytetrafluoroethylene (PTFE)/CB/PtC (0.31 A m −2 ) sample followed by PTFE/CB/PANI (0.09 A m −2 ), and lastly PTFE/CB (0.05 A m −2 ). The control (PTFE only) sample did not generate any noticeable electrical signal. The electrochemical impedance spectroscopy analysis showed that the incorporation of PtC on the PTFE/CB sample lowered the charge transfer resistance ( R ct ), whereas the addition of PANI increased the R ct . Despite the differences in R ct values, both PTFE/CB/PtC and PTFE/CB/PANI samples demonstrated a better current density production than the PTFE/CB sample. Thus, modified air‐cathodes further elevated the biosensor's performance.

Verjesh Kumar Magotra, T.W. Kang, S.J. Lee et al.

• 2020

Abstract Background: This paper provides an overview of the present advances in renewable and sustainable energy resources used for new energy demand in the world. Aiming to address, Urea, Urine resources are abundant like urea-containing wastewater, industrial urea, wastewater treatment plants, becoming an attractive option as anodic fuel for the application in urea fuel cells. And as a hydrogen-rich chemical fuel, urea can also be hydrolysis and electrolyzed to produce hydrogen for energy storage in the near future. Results: We report a novel, urea-hydrogen based compost soil microbial fuel cell (UH-CSMFC). As compost soil is a rich source of bacteria, enzymes, and organic matter, soil provided the necessary ingredients for the operation of the device. While bacteria and enzymes that hydrolysed by urea powered by the fuel cell. The compost soil was also found to exhibit partial electrocatalytic activity itself. This novel UH-CSMFC shows power density of 18.26 mW/m 2 . For continuous operation of the device, and cleaning of the excess of nitrogen compounds from urea fuel (urine, containing different wastewater energy resources). Conclusion: The constant state is the most desirable, where the device behaviour is entirely irreversibly, which helps to feed the device. Thus, the results of electrochemical studies show that the system is suitable for cleaning, hydrogen, power generation by consuming urea as fuel. This multifunctional device is sustainable, cheap, and eco-friendly for the environment.

Mehroze Iqbal, Amel Benmouna, Frederic Claude et al.

Energies • 2023

Mainstream power-conditioning devices such as boost converters are frequently utilized for developing a compatible interface between a fuel cell, electrical storage, and high power loads. The conventional power stage comprising a unique boost converter suffers from low efficiency and poor reliability due to excessive power losses, particularly in high-power applications. Additionally, the presence of high ripple contents can reduce the lifespan of the fuel cell itself. With this background, this paper proposes and experimentally validates a physical components-assisted equivalent power-sharing strategy between parallel-coupled boost converters (PCCs) that is subjected to a wide spectrum of low-voltage–high-power conditions. The operation of PCCs is bottlenecked by several practical limitations, such as the presence of inner circulating currents (ICCs) and stability issues associated with the equivalent sharing of power. To overcome these limitations, a module of reverse blocking diodes is suggested to avoid ICCs between the PCCs. Further, an equalization filter is properly placed to improve the equivalent power-sharing capability. The proposed strategy is theoretically assessed in a MATLAB/Simulink environment with a 6 kW proton exchange membrane fuel cell (PEMFC) as the main power source. A scaled-down laboratory setup consisting of an 810 W PEMFC stack, an electronic load, three boost converters, and a filter circuit is then designed and critically evaluated. A consistent agreement is observed between the experimental findings and the simulation results under realistic operating conditions.

Aryama Raychaudhuri, Manaswini Behera

Research Square • 2021

Abstract An innovative design approach was employed in the present study to enhance the electricity generation and wastewater treatment in a microbial fuel cell (MFC). A dual-chambered MFC with a ceramic separator was coupled with an acidogenic chamber. Acidogenic bioconversion of rice mill wastewater into volatile fatty acid (VFA) represents an interesting approach for wastewater valorization. The VFA containing effluent could be used as an effective substrate for bioelectricity generation in MFCs. A short hydraulic retention time (HRT) can be used for the two-stage anaerobic process (acidogenesis and electrogenesis), thus preventing the proliferation of methanogens. The effect of pH (5.5–7.5) and HRT (0.5 d–0.75 d) were investigated to understand the influence of operational parameters on the performance of the integrated system. The maximum VFA concentration of 1065.15 ± 5.08 mg COD/L was achieved at pH 7.5 and HRT 0.5 d. Under these operating conditions, the general activity of acid-forming microorganisms and exoelectrogens improved remarkably, and the power density obtained from the system was 4.72 ± 0.10 W/m 3 . The current research indicates excellent potential for simultaneous treatment and electricity production from rice mill wastewater. The use of low-cost, locally manufactured, and customized membranes and the two-stage treatment can pave the way for the practical application of this technology.

Marzia Quaglio, Daniyal Ahmed, Giulia Massaglia et al.

Fuels • 2021

Sediment microbial fuel cells (SMFCs) are energy harvesting devices where the anode is buried inside marine sediment, while the cathode stays in an aerobic environment on the surface of the water. To apply this SCMFC as a power source, it is crucial to have an efficient power management system, leading to development of an effective energy harvesting technique suitable for such biological devices. In this work, we demonstrate an effective method to improve power extraction with SMFCs based on anodes alternation. We have altered the setup of a traditional SMFC to include two anodes working with the same cathode. This setup is compared with a traditional setup (control) and a setup that undergoes intermittent energy harvesting, establishing the improvement of energy collection using the anodes alternation technique. Control SMFC produced an average power density of 6.3 mW/m2 and SMFC operating intermittently produced 8.1 mW/m2. On the other hand, SMFC operating using the anodes alternation technique produced an average power density of 23.5 mW/m2. These results indicate the utility of the proposed anodes alternation method over both the control and intermittent energy harvesting techniques. The Anode Alternation can also be viewed as an advancement of the intermittent energy harvesting method.

Xuan Yang, Cong Li, Cheng Li et al.

New Journal of Chemistry • 2024

Through a one-step hydrothermal method, we synthesized CCS- M ( M = Cu/Co ratio) catalysts, with M = 0.5 showing optimal ORR performance. As an MFC cathode, it achieved 200.08 mW m −2 power density and stable 345 mV output.

I. A. Ieropoulos, J. You, I. Gajda et al.

Fuel Cells • 2018

Abstract Microbial fuel cells (MFCs) are energy transducers, which through the metabolic reactions of facultative anaerobic microorganisms, transform the energy in organic matter directly into electricity. Extrinsic parameters such as hydraulic retention time, fuel quality (type and concentration) and physicochemical environment of electrodes and biofilms (e.g., temperature, pH, salinity, and redox), can all influence system efficiency. This work proposes that MFCs can be “fine‐tuned” by adjustment of any of the physicochemical conditions including redox potential; in this context, an entirely novel method was investigated as a practical means of tuning, modulating and monitoring the redox potential within the electrode chambers. The method uses additional electrodes – known as 3 rd and 4 th ‐pins for anode and cathode chambers, respectively – which can be used in individual units, modules, cascades or stacks, for optimising the production of a large variety of chemicals, as well as biomass, water and power. The results have shown that the power output modulation resulted in an up to 79% and 33% increase, when connected via 3 rd and 4 th pins, respectively. Apart from power improvement, this study also demonstrated a method of open circuit potential (OCP) sensing, by using the same additional electrodes to both monitor and control the MFC signal in real time.

Pinkhas Rapaport, Yeh-Hung Lai, Chunxin Ji

ASME 2006 Fourth International Conference on Fuel Cell Science, Engineering and Technology, Parts A and B • 2005

This paper reports on the study of gas diffusion media (GDM) intrusion into reactant gas channels and its effect on the performance of the proton exchange membrane (PEM) fuel cell. The PEM fuel cell under consideration consists of a membrane electrode assembly (MEA) sandwiched between two layers of gas diffusion media commonly made of carbon paper or cloth. The GDM/MEA/GDM assembly is then compressed between two adjacent bi-polar plates. In this configuration, the compression pressure is transmitted under the lands of the reactant gas flow-field onto GDMs on which the portion over the channels remain unsupported. Because of the relatively low bending and compressive stiffness, it is found that GDMs can easily intrude into the reactant gas channels. The direct consequence of GDM intrusion is the pressure drop increase in the reactant gases in the intruded channels. This is further compounded by cell-to-cell or channel-to-channel variation in GDM thickness and mechanical properties, which results in non-uniform reactant gas flow distribution and ultimately negatively impacts the fuel cell performance. In this study, we have developed a GDM intrusion model based on the finite element method (FEM. We have also devised an experimental setup to measure the GDM intrusion, in which we found good agreement between the model prediction and experimental measurement. Combining the FEM based intrusion model and a flow redistribution model we have investigated the effect of GDM channel intrusion on the reactant flow distribution and the impact on the fuel cell performance. It is found that a 20% reduction of reactant flow can be induced with a 5% additional blockage in channels by GDM intrusion. Based on the findings from the current study, we attribute the significant performance variation in a 30-cell fuel cell stack to the variation in reactant flow induced by the variation in GDM intrusion. The results from the analytical study and fuel cell testing both suggested that the product variations in GDM would need to be significantly reduced and the stiffness of the GDM would need to be increased if the PEM fuel cells of high power density were to be used reliably at a relatively low stoichiometry.

Seok-Beom Yun, Youn-Jea Kim

Volume 6: Ceramics and Ceramic Composites; Coal, Biomass, Hydrogen, and Alternative Fuels; Microturbines, Turbochargers, and Small Turbomachines • 2021

Abstract Renewable energy such as hydrogen or solar energy is promising due to issues surrounding environmental pollution. In particular, hydrogen only produces water and generates electric energy in a fuel cell when reacting electrochemically with air. A fuel cell consists of many parts such as a cell stack, an ejector, a hydrogen tank, and a regulator, and so on. In this study, the ejector, a device that supplies hydrogen to proton exchange membrane fuel cell (PEMFC), is studied. The ejector recirculates unreacted hydrogen in proton exchange membrane fuel cells by the Venturi effect. Since the ejector is related to energy efficiency, many researchers have conducted research to improve the performance of the ejector. Therefore, it is most desirable that hydrogen recirculation in the ejector is increased. The present research investigates how the configuration of the ejector affects the hydrogen recirculation. A concave configuration of the ejector is considered. This concave having a helical pattern is dependent on a pitch ratio and the number of grooves. The results are compared with numerical analysis data from existing publications using computational fluid dynamics (CFD). The influence of the configuration was analyzed by performing numerical simulations with three-dimensional grid systems. A poly-hex-core mesh type was applied to reduce errors caused by convection and diffusion in the computational domain. Considering the configurations of the ejector, turbulence dissipation rate, static pressure, and tangential velocity inflow were analyzed graphically. Consequently, it was determined that the model displays a 7% increase in recirculation ratio over the reference model.

Mahak Jain, Partha Sarathi Ghosal, Ashok Kumar Gupta

• 2023

In recent times, the research trend has shifted towards identifying sustainable energy resources. Bioenergy generation employing wastewater and micro-organisms might be a potential solution to achieve this goal. In microbial fuel cells (MFC), the energy stored in the chemical bonds of contaminants present in wastewater is utilized by the micro-organisms for their metabolism in redox conditions. Furthermore, in this process, free electrons are released into the system, which are captured by the electrodes resulting in the generation of electricity in the external circuit. Hence, the system provides wastewater treatment along with bioenergy generation. However, the system finds difficulty in degrading recalcitrant organic compounds, such as pharmaceuticals and other emerging contaminants, which is possible in constructed wetland (CW) systems. However, CWs require a large footprint area. Recently, combined CW and MFC systems are being used for this purpose due to their resilience and capacity to produce electricity and provide a high level of wastewater treatment. Combined CW-MFC has been found to be more useful than either system alone by complimenting their issues as the redox conditions required for the proper functioning of the MFC system are available in the CW system. Furthermore, the high diversity of micro-organisms present in MFC improves the treatment efficiency of the CW system. This study involves the application of a combined CW-MFC system for the treatment of wastewater and the production of bioelectricity using Lemna minor as macrophyte species. Graphite plates were used as the anode and cathode for electricity production. In order to test the system's effectiveness in terms of removing recalcitrant organic compounds, synthetic wastewater was spiked with 5 mg/L of sulfamethoxazole. The influence of various parameters, such as electrode spacing, the substrate to water depth ratio, and the initial COD concentration of wastewater, was studied. Considerably high removal of around 99% for sulfamethoxazole and 90% for COD removal were observed, along with the production of 133 mV of voltage. It was observed that with the increase in initial COD concentration and substrate to water depth ratio, COD removal also increased. However, an increase in electrode spacing and substrate to water depth ratio after a certain limit showed a negative effect on voltage generation. The entire system could effectively generate bioenergy and treat the sulfamethoxazole-contaminated wastewater.Keywords- Constructed wetlands, Microbial fuel cell, Lemna minor, Emerging contaminants, Bioelectricity

Md. Abdul Halim, Md. Owaleur Rahman, Mohammad Ibrahim et al.

Journal of Chemistry • 2021

Finding sustainable alternative energy resources and treating wastewater are the two most important issues that need to be solved. Microbial fuel cell (MFC) technology has demonstrated a tremendous potential in bioelectricity generation with wastewater treatment. Since wastewater can be used as a source of electrolyte for the MFC, the salient point of this study was to investigate the effect of pH on bioelectricity production using various biomass feed (wastewater and river water) as the anolyte in a dual-chambered MFC. Maximum extents of power density (1459.02 mW·m−2), current density (1288.9 mA·m−2), and voltage (1132 mV) were obtained at pH 8 by using Bhairab river water as a feedstock in the MFC. A substantial extent of chemical oxygen demand (COD) removal (94%) as well as coulombic efficiency (41.7%) was also achieved in the same chamber at pH 8. The overall performance of the MFC, in terms of bioelectricity generation, COD removal, and coulombic efficiency, indicates a plausible utilization of the MFC for wastewater treatment as well as bioelectricity production.

Ademola Adekunle, Vijaya Raghavan

Waste Management & Research: The Journal for a Sustainable Circular Economy • 2016

In a number of energy-poor nations, peel from cassava processing represents one of the most abundant sources of lignocellulosic biomass. This peel is mostly discarded indiscriminately and eventually constitutes a problem to the environment. However, energy can be extracted from this peel in a microbial fuel cell. In this study, the viability of cassava peel extract as a substrate in a single-chamber air cathode microbial fuel cell is demonstrated, and optimum performance conditions are explored. The effects of different pretreatments on the extract are also discussed in the context of observed changes in the internal resistances, conductivity and Coulombic efficiencies. At the best conditions examined, the extract from cassava peel fermented for 168 h and adjusted to a pH of 7.63 attained a peak voltage of 687 mV ± 21 mV, a power density of 155 mW m −3 of reactor volume and a Coulombic efficiency of 11 %. Although this energy is limited to direct use, systems exist that can effectively harvest and boost the energy to levels sufficient for supplementary energy usage in cassava producing regions.

Rachel C Wagner, Sikandar Porter-Gill, Bruce E Logan

AMB Express • 2012

Abstract Current-generating (exoelectrogenic) bacteria in bioelectrochemical systems (BESs) may not be culturable using standard in vitro agar-plating techniques, making isolation of new microbes a challenge. More in vivo like conditions are needed where bacteria can be grown and directly isolated on an electrode. While colonies can be developed from single cells on an electrode, the cells must be immobilized after being placed on the surface. Here we present a proof-of-concept immobilization approach that allows exoelectrogenic activity of cells on an electrode based on applying a layer of latex to hold bacteria on surfaces. The effectiveness of this procedure to immobilize particles was first demonstrated using fluorescent microspheres as bacterial analogs. The latex coating was then shown to not substantially affect the exoelectrogenic activity of well-developed anode biofilms in two different systems. A single layer of airbrushed coating did not reduce the voltage produced by a biofilm in a microbial fuel cell (MFC), and more easily applied dip-and-blot coating reduced voltage by only 11% in a microbial electrolysis cell (MEC). This latex immobilization procedure will enable future testing of single cells for exoelectrogenic activity on electrodes in BESs.

V. Mounica, Y. P. Obulesu

Energies • 2022

The power management strategy (PMS) is intimately linked to the fuel economy in the hybrid electric vehicle (HEV). In this paper, a hybrid power management scheme is proposed; it consists of an adaptive neuro-fuzzy inference method (ANFIS) and the equivalent consumption minimization technique (ECMS). Artificial intelligence (AI) is a key development for managing power among various energy sources. The hybrid power supply is an eco-acceptable system that includes a proton exchange membrane fuel cell (PEMFC) as a primary source and a battery bank and ultracapacitor as electric storage systems. The Haar wavelet transform method is used to calculate the stress σ on each energy source. The proposed model is developed in MATLAB/Simulink software. The simulation results show that the proposed scheme meets the power demand of a typical driving cycle, i.e., Highway Fuel Economy Test Cycle (HWFET) and Worldwide Harmonized Light Vehicles Test Procedures (WLTP—Class 3), for testing the vehicle performance, and assessment has been carried out for various PMS based on the consumption of hydrogen, overall efficiency, state of charge of ultracapacitors and batteries, stress on hybrid sources and stability of the DC bus. By combining ANFIS and ECMS, the consumption of hydrogen is minimized by 8.7% compared to the proportional integral (PI), state machine control (SMC), frequency decoupling fuzzy logic control (FDFLC), equivalent consumption minimization strategy (ECMS) and external energy minimization strategy (EEMS).

J.C. Carrillo-Rodriguez, I.L Alonso-Lemus, R. Pérez-Hernández et al.

ECS Meeting Abstracts • 2017

Nanostructured Pd-CeO 2-NR /G, synthesized with NaBH 4 as reducing agent, was evaluated as cathode catalyst for the Oxygen Reduction Reaction (ORR) in 0.5 M KOH and in a Microbial Fuel Cell (MFC) with pH=9.6. Previously, ceria nanorods (CeO 2-NR ) were synthesized by a hydrothermal method, while graphene (G) was obtained by mechanical milling. Morphological characterization showed agglomerated Pd nanoparticles and CeO 2-NR dispersed over graphene. Evaluation of catalytic activity for the ORR in half cell showed a higher mass activity of Pd-CeO 2-NR /G relative to Pd/C. The MFC was of the two-chamber type, separated by a Nafion(R) 117 membrane. In the anode, residual water directly from a pharmaceutical company (pH=9.6) was the electrolyte with an anode containing commercial Pt/C. The Bacilus Subtilis microorganism was used to form a biofilm over Pt/C and promote the bioelectrochemical reactions in N 2 atmosphere. In the cathode chamber, KOH with pH=9.6 was the electrolyte, which was saturated with O 2 . The polarization curves from the MFC demonstrated a higher catalytic activity of Pd-CeO 2-NR /G than Pd/C. The former delivered an open circuit voltage of 0.26 V and a maximum power density of 12.47 mW m -2 .

Yueping Ren, Danyun Pan, Xiufen Li et al.

Journal of Chemical Technology & Biotechnology • 2013

Abstract BACKGROUND The limitation on output power is a great challenge for the practical application of sediment microbial fuel cells ( SMFC ). One of the effective strategies to overcome this problem is to develop better‐performing cathodes . RESULTS Polyaniline (PANI)‐graphene nanosheets (GNS) modified cathodes were fabricated and applied as the cathodes of SMFCs to improve their electricity generation capacity. PANI‐GNS cathodes were fabricated through situ‐polymerization of aniline in a solution containing homogeneously dispersed GNS . The mass ratio between aniline and GNS in the polymerized solution was the key factor controlling the properties of the modified cathode and the optimum ratio was 9:1. Because of the outstanding electrical conductivity of GNS , PANI‐GNS cathodes outperform the control (blank) and PANI cathodes. The PANI‐GNS 0 .1 ‐ SMFC exhibited the highest output voltage of 640 mV , 5 times that of the blank SMFC ; the maximum power density was improved from 0.85 mW m ‐2 with the blank SMFC to 99 mW m ‐2 of the optimal PANI‐GNS 0 .1 ‐ SMFC . CONCLUSIONS This study provides a simple electrode modifying method to enable an as‐synthesized PANI‐GNS cathode to dramatically promote the performance of an SMFC . © 2013 Society of Chemical Industry

S. A. Abbasi, Tabassum Abbasi, Pratiksha Patnaik

Nature Environment and Pollution Technology • 2021

Studies are presented in the context of the past attempts at finding nanocatalysts that can boost the performance of microbial fuel cells (MFCs) ? in terms of waste treatment and energy generation. Given the great potential of biomimetically synthesized nanoparticles (BMNPs) in providing less expensive and more environmentally friendly alternatives to NPs synthesized by physical and chemical methods, as well as a near-total lack of previous work in this area, the current research was undertaken. Effect of gold and silver nanoparticles (NPs), synthesized biomimetically using five freely available weeds, was assessed as catalysts in the MFCs. In all cases, the nanoparticles were seen to enhance the coulombic efficiency (reflective of the reduction in the waste’s organic carbon load), maximum attainable power density, and overall energy yield of the MFCs by >200% relative to the uncatalyzed MFCs. Gold nanoparticles were more effective than silver nanoparticles by ? 20%. The results reveal that biomimetically synthesized NPs can be highly effective in reducing the operational costs as well as ecological footprints of MFCs and further work should be focused on NPs of non-precious metals.

Rishi Gurjar, Manaswini Behera

Fermentation • 2022

Performance evaluation of a ceramic microbial fuel cell (CMFC) by varying organic strength, hydraulic retention time (HRT) and anode electrode surface area (AESA) to treat leachate generated from acidogenesis of kitchen waste (KW) was studied by the central composite design of experiment. The increase in organic loading rate (OLR) positively affected power density (PD) while negatively influencing organic removal and coulombic efficiency (CE). This behavior is possible due to substrate inhibition and the coercive effect of low HRT, i.e., substrate washout, biofilm abrasion, and reduced contact period, while at high HRT, the volatile fatty acid (VFA) degradation improved. Since acetic acid is the final product of long-chain VFAs degradation, a pseudo consumption order for VFAs was obtained: butyric > propionic > acetic. The AESA aided organics removal and PD but had a negligible effect on CE. According to ANOVA, the COD removal was linearly modeled, while PD and CE were quadratic. The validation runs (VR) proved efficient as the highest COD removal was for VR2 (83.7 ± 3.6%), while maximum PD and CE values obtained were 0.224 ± 0.02 W/m3 and 2.62 ± 0.33%, respectively, for VR3, supported by the lower anode potential.

Iliya Krastev Iliev, Antonina Andreevna Filimonova, Andrey Alexandrovich Chichirov et al.

Energies • 2024

Currently, the process of creating industrial installations is associated with digital technologies and must involve the stage of developing digital models. It is also necessary to combine installations with different properties, functions, and operational principles into a single system. Some tasks require the use of predictive modeling and the creation of “digital twins”. The main processes during the fuel cell modeling involve electrochemical transformations as well as the movement of heat and mass flows, including monitoring and control processes. Numerical methods are utilized in addressing various challenges related to fuel cells, such as electrochemical modeling, collector design, performance evaluation, electrode microstructure impact, thermal stress analysis, and the innovation of structural components and materials. A digital model of the membrane-electrode unit for a solid oxide fuel cell (SOFC) is presented in the article, incorporating factors like fluid dynamics, mass transfer, and electrochemical and thermal effects within the cell structure. The mathematical model encompasses equations for momentum, mass, mode, heat and charge transfer, and electrochemical and reforming reactions. Experimental data validates the model, with a computational mesh of 55 million cells ensuring numerical stability and simulation capability. Detailed insights on chemical flow distribution, temperature, current density, and more are unveiled. Through a numerical model, the influence of various fuel types on SOFC efficiency was explored, highlighting the promising performance of petrochemical production waste as a high-efficiency, low-reagent consumption fuel with a superior fuel utilization factor. The recommended voltage range is 0.6–0.7 V, with operating temperatures of 900–1300 K to reduce temperature stresses on the cell when using synthesis gas from petrochemical waste. The molar ratio of supplied air to fuel is 6.74 when operating on synthesis gas. With these parameters, the utilization rate of methane is 0.36, carbon monoxide CO is 0.4, and hydrogen is 0.43, respectively. The molar ratio of water to synthesis gas is 2.0. These results provide an opportunity to achieve electrical efficiency of the fuel cell of 49.8% and a thermal power of 54.6 W when using synthesis gas as fuel. It was demonstrated that a high-temperature fuel cell can provide consumers with heat and electricity using fuel from waste from petrochemical production.

Fumihiko Yoshiba

Journal of Fuel Cell Science and Technology • 2008

A module part of a 7MW class centralized molten carbonate fuel cell/gas turbine (GT) combined system has been tested. Since the designed (GT) working pressure is 1.2MPa, the operating pressure of the module was high (1.2MPa). In order to realize a high steam-reforming efficiency of the fuel gas under high-pressure operation, the module has an additional adiabatic reformer, which changes the CH4 remaining in the exhausted anode gas to H2. Using a 125-cell stack, the module was operated and the performance of the stack was evaluated; the CO2 partial pressure of the cathode inlet gas was kept low during the operation. The maximum operating current density of the stack was limited to 1600A∕m2; however, the maximum total steam-reforming efficiency of the fuel gas was 96% in the module. The heat loss of the module was evaluated in the pressure swing test. Using these operation results, the efficiency of the module, at the designed operating current density of 2000A∕m2, was estimated; the result was 39.6% low heating value (LHV) by applying the normal cell performance, whereas 44.4% LHV by applying the best performance cell. The module efficiency of 44.4% LHV corresponds to the system’s net efficiency of 48% high heating value in the 7MW system.

Willie Prasidha, Akmal Irfan Majid

Jurnal Penelitian Saintek • 2020

This study was aimed at evaluating the performance of non-aerated and aerated double chamber microbial fuel cells from food waste leachate. The value of open circuit voltage (OCV) and close circuit voltage (CCV) were taken to analyze power density and current density of both configurations. Two double chamber microbial fuel cells (MFC) with different configurations were developed to produce electricity from food waste leachate and studied for 30 days. Anode and catode were made by uncoated carbon felt and graphite rod. Food waste and water were incubated inside a reactor. After 30 days, the electricity production characteristics between the two configurations were obtained. Both configurations reached the same maximum power density and maximum current density but the aerated MFC showed higher performance of maximum open-circuit voltage (OCV), average power density, and current density than non-aerated MFC. The results show that the supplying continuous dissolved air in the cathode chamber resulted in higher voltage, higher average power density, and higher average current density in double chamber microbial fuel cell.

Seyed Hesam‐Aldin Samaei, Gholamreza Bakeri, Mohammad Soleimani Lashkenari

Journal of Applied Polymer Science • 2020

Abstract In this research, the preparation of low cost proton exchange membranes (PEMs) based on sulfonated poly ether ether ketone (SPEEK) for application in the microbial fuel cells (MFCs) is studied. Sulfonated polystyrene (SPS) and phosphotungstic acid (PWA) were employed to improve the performance of PEM through the creation of more proton pathways. At first, the sulfonation of PEEK and polystyrene were performed through two modified methods to obtain uniform and high degree of sulfonation (DS) of the polymers and then, the PEMs were prepared through the solution casting method. Accordingly, the formation of uniform skin layer was confirmed by the SEM micrographs. Blending the aforementioned additives to the SPEEK polymer solution significantly enhanced the proton conductivity, water uptake and durability of the modified membranes. The proton conductivities of SPEEK/SPS and SPEEK/PWA membranes at additive/SPEEK weight ratio of 0.15 were 45.3% and 26.2% higher than that of the commercial Nafion117 membrane, respectively. Moreover, the degradation times for the abovementioned modified membranes were 140 and 350 min which indicated satisfactory oxidation stability. Besides, the aforementioned membranes exhibited two times more water uptake compared to the neat SPEEK membrane. Finally, SPEEK/SPS and SPEEK/PWA membranes produced 68% and 36% higher maximum power in the MFC, compared to the commercial Nafion117 membrane. Therefore, the fabricated PEMs are potentially suitable alternatives to be used in the fuel cell applications.

Hao-Ming Chang, Min-Hsing Chang

Journal of Fuel Cell Science and Technology • 2013

In this study, the performance of a polymer electrolyte membrane fuel cell with double-side microporous layer (MPL) coating on gas diffusion layer (GDL) is investigated experimentally. A standard commercial SGL® 10BA carbon paper is used as the substrate and it is coated with MPL on both sides of the paper with different composition. Three different carbon powders are used in the experiments, including Vulcan XC-72R, Acetylene black, and Black Pearls 2000. The effect of polytetrafluoroethylene (PTFE) content is also considered. A single cell testing apparatus is constructed to measure the cell performance and evaluate the effect of GDL with double-side MPL coating. Accordingly, the optimal fabrication parameters of double-side MPL are determined. The result shows that under the same operating conditions, the performance of fuel cell using GDL with double-side MPL is better than that using general single-side MPL. The Acetylene black is found to give the best cell performance than the others. The optimal composition of MPL on the surfaces facing to the catalyst layer and flow-channel plate are 1.25 mg/cm2 and 0.25 mg/cm2, respectively. Besides, the optimal PTFE content is the same on both sides of MPL which is found to be 20 wt%.

Susanta K. Das, K. J. Berry

ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology • 2016

In this paper, using patented nano-additive based polymer synthesis technology, a novel approach to the design and fabrication of high temperature proton exchange membrane (PEM) has been developed. The presence of sulfonated octaphenyl POSS (S-POSS) in a PBI-PA (polybenzimidazole-phosphoric acid) membrane results in a 40–50% increase in conductivity at 120–200$deg relative to non-sulfonated silica or POSS control fillers at comparable weight percent filler loadings and PBI molecular masses, and also relative to unfilled PBI-PA membranes. In addition, the presence of S-POSS and silica both result in physical reinforcement of the membrane and increased its modulus and mechanical integrity, but only S-POSS offers the benefits of both increased conductivity and increased modulus. Isophthalic acid and 3,3’-diaminobenzidine (DAB) were polymerized in the presence of polyphosphoric acid (PPA) and S-POSS nanoadditive, and the degree of polymerization was monitored by viscosity and torque change measurements. Molecular mass was determined by inherent viscosity measurements of samples removed from the reaction solution. Membranes were prepared by casting the reaction solution and allowing PPA to hydrolyze to PA under ambient conditions. The membranes were characterized for acid content, in-plane conductivity, tensile modulus and shear modulus, and were roll-milled to achieve the desired thickness for membrane electrode assembly (MEA) fabrication.

M Amirul Islam

IIUM Engineering Journal • 2017

Microbial fuel cell (MFC) is a bioelectrochemical system that uses bacteria as biocatalyst to oxidize organic substrates as well as release electrons, which can be harvested in an external circuit to produce electrical energy. In this study, a proteolytic biocatalyst Bacillus cereus (B. cereus) has been employed for the first time in a microbial fuel cell (MFC). The wild type pure culture was isolated from municipal wastewater and identified using Biolog Gen III analysis. The MFCs were fueled with palm oil mill effluent (POME) and attained the maximum power density of about 3.88 W/m3. The electrochemical behavior of MFC operated by B. cereus was evaluated using polarization curve, electrochemical impedance spectroscopy (EIS) and cyclic voltammetery (CV) analysis. B. Cereus excreated electron shuttling compound which significantly reduced the anode charge transfer resistance (52.95%). The FESEM result shows that B. Cereus has the capability of effective biofilm formation. These results revealed the electrocatalytic potentiality of B. cereus and which makes it a promising candidate to be used in MFCs. Therfore, this biocatlyst can be used to generate electricity through the wastewater valorization.

Hong Song, Wei Guo, Menglin Liu et al.

Water Science and Technology • 2013

The microbial fuel cells (MFCs) are the focus of extensive investigation as one of the promising technologies for renewable energy generation and wastewater treatment. Two-chambered MFCs were designed to investigate the removal of metronidazole and to quantify the effect of antibiotic on the efficacy of energy generation. Using 1,000 mg glucose L−1 containing different concentrations of metronidazole (0, 10, 30, 50 mg L−1) as the fuels, the corresponding power densities were 141.94, 99.23, 25.44, 16.26 mW m−2, respectively. The adverse effect on the performance of the MFCs was reversible. The removal of metronidazole achieved 85.4% within 24 hours in MFCs, while only 35.2% in open circuit. Current generation could account for the improved removal efficiency at these tested concentration levels. The findings of this paper indicated that antibiotics such as metronidazole could be removed in MFCs, which has implications for general wastewater treatment.

Jakub Dziegielowski, Mirella Di Lorenzo

E3S Web of Conferences • 2021

Soil microbial fuel cell (SMFC) is a carbon-neutral energy harvesting technology that exploits the use of electroactive bacteria naturally present in soil to directly generate electricity from organic compounds. Given the simplicity of the system design, SMFCs have great potential to be used for decentralised solutions, especially in areas where access to conventional energy sources is limited. Yet, the high cost to power ratio severely limits the translation of this technology into the market. With the aim of reducing the capital cost, in this study we explore the effect of decreasing the amounts of current collector (CC) on the performance. The results demonstrate that increasing the amount of current collector per surface area of the electrode is not a feasible way of enhancing power densities, as to increase the performance by 20% and 35%, the amount of current collector would have to be increased by 150% and 300%, respectively. This highlights the importance of economic evaluations when optimising the design of a SMFC.

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Biointerface Research in Applied Chemistry • 2021

Hospital waste is a type of hazardous waste that contains a wide range of dangerous substances, including radioactive materials. Radiation-tolerant microbes have shown an interest in treating this liquid waste. Radiation-resistant microorganisms were chosen from irradiated fermented sausage in this investigation. The activity of enzymes such as protease, lipase, and laccase was studied. For hospital wastewater treatment, a single chamber microbial fuel cell (sMFC) with a radiation-tolerant bacterial consortium was deployed. The microbial structure analysis showed the selected consortium was similar to Acinetobacter sp. The COD was removed at a rate of 90.10±0.30%, and the power density (PD) was 168.91±3.89 mW/m2. This was the first study to use the radiation-resistant Acinetobacter sp. bacterial consortia to treat hospital waste and generate power simultaneously.

Julian Ferdinand, Adhi Yuniarto

Sainteknol : Jurnal Sains dan Teknologi • 2024

Chromium ions is notably a hazardous heavy metal due to its toxic and carcinogenic nature, particularly in its hexavalent form, Cr(VI). One of the major Cr(VI) pollution source is from electroplating industry effluent, which may contain high concentrations that pose a risk of contamination of aquatic and soil ecosystems if not treated carefully. One of the alternative method known to be able to treat Cr(VI) wastewater is by using microbial fuel cell (MFC). This research focused on on the removal of Cr(VI) from synthetic electroplating wastewater using a 4L dual-chamber MFC under fed-batch condition, as well as investigating the impact of mixed liquor suspended solids (MLSS) and chemical oxygen demand (COD) concentrations to its performance. Observed parameters include the efficiency of Cr(VI) removal and power density. Septage sludge and acetate were both used as biomass and substrate source respectively. Based on this research, it can be concluded that the highest Cr(VI) removal efficiency and power density were achieved using specific MLSS and COD concentration that resulting in F/M ratio of 0,459 to 0,489 gCOD/gMLSS. From initial Cr(VI) concentration of 50 mg/L, the highest removal was obtained by MFC running with initial MLSS and COD concentrations of 3.500 and 1.500 mg/L respectively, achieving 62,17% over 312 hours. This setup also produced the highest power density of 48,22 mW/m².

M N I M Sabri, N A Shamsuddin, M F A Alias et al.

IOP Conference Series: Earth and Environmental Science • 2021

Abstract Water and energy security are gaining high interest of many researchers and intensive exploration took place around the global. Membrane-less microbial fuel cell (ML-MFC) has been emerging as one of the popular wastewater treatment-based technology to provide clean water and green energy. MFC are bio-electrical devices that harness the natural metabolism of electrogenic bacteria (EB) to produce electrical energy. In this study, Bacillus subtilis (BS) was used to catalyst the transformation of carbon source in dewatered sludge into renewable energy. From the study, the MFCs were tested to see the robustness of the MFC by exposing them to the ambient temperature (25± 1°C) with the parameter of pH (6), electrode distance (6 cm), initial moisture content (30 % vol/wt) were set as constant. The result focused on the performance of the ML-MFC during noon (8-10 am and 4-6 pm) as these were the periods which BS recorded actively growth (increment of ±5.167 × 10 -3 mg/L of biomass per day). The ML-MFCs were carried out for 7 days incubation period and the BS growth reflected significantly on the voltage and power generated. The highest voltage and power density were recorded which were 90 mV and 8.793Watt/m 2 (at morning on 6th day), respectively. Moreover, observation gram staining of BS under a light microscope indicated a purple appearance due to thick peptidoglycan layer of the cell wall. Obviously, this study could be the bench mark of the practicality of the MFC technology which projected to be implemented in remote area where the natural environment condition is the surrounding parameter of the MFC same like in current study.

Tsvetomila Ivanova Parvanova-Mancheva, Elena Razkazova-Velkova, Martin Martinov et al.

Food Science and Applied Biotechnology • 2018

Traditional methods for wastewater treatment are associated with high energy consumption. This is why biological treatment of water is more appropriate at the moment. In our previous study, oxidation and reduction of pollutants have been proposed to be carried out in a microbial fuel cell (MFC) designed by our laboratory that simultaneously purifies wastewater from sulfide and nitrate ions and generates electricity. The experiments were carried out with two types of electrodes, graphite rods and paddling of activated carbon using a Fumapem® FFA-3-PK-75 (OH- form) membrane. The results show that the cell has higher energy output when using paddling of activated carbon as an electrode.