Power Density Curves Research Articles

Development of a novel carbon-based conductive membrane with in-situ formed MnO2 catalyst for wastewater treatment in bio-electrochemical system (BES)

A new carbon-based RGO/PVDF/MnO2 conductive membrane was developed to treat high load wastewater and recovery energy through bio-electrochemical system (BES), combining Membrane bioreactor (MBR) and Microbial fuel cell (MFC). The conductive membrane dual functions as the cathode of MFC and the filtration medium of MBR simultaneously. The structures of the conductive membrane were investigated by SEM, EDX and XPS, the existence of manganese dioxide catalyst, the high porosity and smooth surface morphology were confirmed. During operation, the membrane always maintained distinct ORR and electrochemical activity, exhibited excellent anti-fouling and flux recovery property, also better COD removal property than the control membrane without MnO2. Replacing proton exchange membrane (PEM) using Quartz sand chamber (QSC), the BES power density was 228mW/m3 higher than using PEM. The internal resistance, calculated in accordance with the power density curve using QSC was lower than that of the control group (respectively 752Ω and 937Ω). The results confirmed that it was feasible to replace the expensive PEM with cheap materials. The novel carbon-based conductive membrane with in-situ formed MnO2 catalyst and constructed BES with QSC were promising and beneficial for the future scale-up of BES.

Investigation of Spiral Flow‐Field Design on the Performance of a PEM Fuel Cell

AbstractPolymer exchange membrane fuel cells (PEMFCs) are promising energy converters due to their unique features with an application potential for many sectors. The performance of PEM fuel cells depends on a number of factors, one of which is suitable flow‐field design. In this study, the effect of spiral flow‐field design is investigated with computational fluid dynamics (CFD) method. The model consists of the transport phenomena in a fuel cell. Electrochemical reactions, mass, heat, energy, species transport, and potential fields equations are solved by ANSYS‐FLUENT. The polarization and power density curve, temperature, pressure, and distributions of the gases inside the flow‐fields were obtained. The results were compared with the reference geometry. Although the spiral flow‐field has considerable ohmic losses, the velocity and pressure distributions of the gases are found to be uniform. Furthermore, it is shown that the spiral flow‐field reduces the pressure drop per unit length of the flow‐field. When compared to other flow‐field designs, the spiral flow‐field is found to be quite efficient by means of auxiliary power consumption.

Novel Fuel Cell MEA Based on Pt-C Deposited by Magnetron Sputtering

The presented research is focused on Pt-C composite catalysts for proton exchange membrane fuel cell (PEMFC) applications. Nanostructured Pt-C thin films (thickness 25-150 nm, Fig 1d) were deposited on carbon paper gas diffusion layer (Sigracet 29 BC) substrates by magnetron sputtering method. Total Pt loading in the thin films varied in the range 5.5-30 µg/cm2as determined by XPS. These catalysts were examined for their activity in hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). A fuel cell with a membrane electrode assembly (MEA) based on Nafion 212 membrane with our Pt-C anode (Pt loading 5.5-30 µg/cm2) and a commercial state-of-the-art Pt/C cathode (Pt loading 300µg/cm2) generated output power up to 1.0 W/cm2 (Fig 1a), value comparable to MEA with commercial powder anode using much higher Pt loading 200-300 µg/cm2. This result demonstrates significant improvement in platinum utilization for HOR due to high dispersion of Pt provided by the magnetron sputtering deposition method. Similarly, a MEA with the commercial Pt/C cathode and our Pt/C thin film (Pt loading 5.5-30 µg/cm2) as anode yielded stable power up to 0.73W/cm2(Fig 1 b), proving its high efficiency for ORR. Based on the above findings, a MEA with both magnetron sputtered Pt/C electrodes using total Pt loading 20 µg/cm2 was tested with a 4 cm2 cell operating at 70˚C in H2/O2-feed regime for 24 hours. The platinum content on cathode and anode side was chosen 14.4 µg/cm2 and 5.5 µg/cm2, providing highest efficiency for HOR and ORR, respectively. I-V polarization and power density curves were measured with fresh catalyst as well after a 24-hour duration test without any significant lost of efficiency during this period of time (Fig 1c). The magnetron sputtered Pt-C with fine metal dispersion proved to be a promising catalytic material with high Pt utilization for hydrogen-feed PEMFC applications. An additional significant benefit of the Pt-C composite is its lower requirement with respect to feed humidity. Figure 1

A 1D+1D Model of Direct Ethanol Fuel Cells Based on an Optimized Kinetic Mechanism for Ethanol Electro-Oxidation Involving Free and Adsorbed Intermediate Species

A 1D+1D model for liquid-feed direct ethanol fuel cells with detailed ethanol electro-oxidation kinetics is presented. One-dimensional convective transport along the flow channels is coupled to a one-dimensional description for species transport across the MEA accounting for the effect of the electrochemical reactions and the mixed potential due to ethanol and acetaldehyde crossover. The model, validated against previous experimental data, provides the variation of the concentrations of the free species and the output and parasitic current densities along the flow channels. The downstream evolution of ethanol and acetaldehyde affects the anode reaction rates and the ethanol and acetaldehyde crossover fluxes, which in turn impacts on the cathode reaction rates. Polarization curves obtained at different positions along the flow channels show the effect of ethanol consumption and acetaldehyde upstream production and downstream consumption. Power density, parasitic current, fuel utilization and product selectivity curves are presented and discussed for different ethanol feed concentrations and flow rates.

A unified design for lightweight robotic arms based on unified description of structure and drive trains

This article presents a unified design for lightweight robotic arms based on a unified description of structure and drive trains. In the unified design, the drive trains and structural dimensions are parameterized as design variables, and a major objective minimizes the total mass of robotic arms satisfying the constraint conditions and design criteria. To implement the optimization problem, a mapping relationship between mass and torque of drive trains is introduced as their power–density curves, which enable a unified description of structure and drive trains combining with the dynamics of robotic arms. In this implementation of unified design, there are two modules: structure optimization and drive trains design. The finite element method with nonlinear programming by quadratic Lagrange algorithm is adopted to implement the structure optimization. Moreover, the dynamic analysis in MSC ADAMS is achieved to design the drive trains of robotic arms. This method could uniformly evaluate all components of robotic arms in mass and continuously search the global optimal results. Finally, a design example on this unified design is compared with a referenced design to illustrate the validity and advantage of the proposed scheme.

Photocoupled Bioanode: A New Approach for Improved Microbial Fuel Cell Performance

AbstractMicrobial fuel cells (MFCs) received considerable attention because of their ability to provide dual advantages of electricity generation and wastewater treatment. However, their performance is primarily limited by the slow oxygen reduction reaction (ORR). To alleviate this problem, we describe a hybrid MFC in which a conventional bioanode is coupled with a TiO2 photoanode. The photocatalytic photoanode utilizes light to provide additional photogenerated electrons to the external circuit of the MFC, which promotes the ORR, as confirmed by power density curves and electrochemical impedance spectra, resulting in improved power generation (1284±20 mW m−2) compared to that of a normal MFC (850±12 mW m−2). Furthermore, the ability of the TiO2 photoanode to reduce CO2 to methane is demonstrated.

Influence of Cell Design on the Performance of Direct Ammonia-Fueled Solid Oxide Fuel Cell: Anode- vs. Electrolyte-Supported Cell

In this study, the performance of anode-supported and electrolyte-supported cells was compared under similar operating conditions for direct ammonia-fueled solid oxide fuel cells (SOFCs); the cell configuration of both types of cells was as follows, Ni‒YSZ|YSZ|GDC|LSCF. The anode-supported cell (ASC) showed better performance as compared with that of the electrolyte-supported cell (ESC). The influence of the humidity of inlet gas on the performance of ASC was investigated at 700 oC. The cell performance did not change substantially under different humidified conditions. In addition, the long-term discharge operation of direct ammonia-fueled ASC was conducted at 600 oC for ca. 235 h. The durability of ASC under polarization was evaluated on the basis of the measured current-voltage and power density curves. The cell showed slight degradation in current density and power density after discharge operation. Furthermore, the formation temperature of Ni3N under ammonia-fueled SOFC conditions was investigated in detail.

Graphene-Based Electrocatalysts to Boost Electrocatalytic Reduction of Oxygen in Bioelectrochemical Systems

Microbial fuel cells (MFCs) can be considered as an efficient and flexible platform for integrated waste treatment and energy recovery [1]. The extensive research work devoted to this technology over the past decade demonstrates the promising outlook of MFCs, but practical application is still limited by the high costs associated to the materials used for device assembly, such as cathode materials which accounts for over 50% of the overall MFC capital cost. The sluggish kinetics of oxygen reduction reaction (ORR) has led to the use of expensive catalysts, such as platinum, which is not suitable to be applied to sustainable technologies. Hence, a great variety of materials have been developed for MFC cathodes, including nitrogen-doped activated carbons and non platinum group metal catalysts. Such materials allow achieving ORR rate comparable to Pt, the morphology and structure of the catalysts playing an important role on the efficiency and durability of ORR active sites [2,3]. The development of new carbon nanostructures with highly tunable morphology and structure has led to the use of graphene for several applications, including as component for MFC cathodes [4,5]. However, challenges, such as complexity in synthesis and costs, still limit the applicability of graphene as cathode component of MFCs. Therefore, a facile and efficient approach to develop graphene based catalysts can be considered a promising direction to achieve sustainable wastewater treatment and bioenergy production by BESs. In this work, we report a facile method for large-scale preparation of ORR catalysts based on graphene oxide (GO) obtained by electrochemical oxidation of graphite in aqueous solutions of inorganic salts. We developed different strategies to include nitrogen functionalities in GO structure, including post treatments based on annealing with ammonia gas and one-step nitrogen-doping of GO. By combining the use of atomic force microscopy with electrochemical and spectroscopic techniques, we correlated the different morphology and surface chemistry of GO with catalytic activity towards ORR. Differences in catalytic activity obtained by supporting iron on GO surface were also elucidated, investigating the nature of ORR active sites. The applicability of GO-based materials as ORR cathodes of MFCs was evaluated by assembling single chamber air-cathodes MFCs operating with sodium acetate in phosphate buffer solution. Coulombic efficiency, polarization and power density curves, and voltage generation cycles over time were acquired. The body of results demonstrated the potential ability of GO electrocatalysts to substitute platinum for ORR in MFCs. Acknowledgements. The present work was carried out with the support of the “European Union's Horizon 2020 research and innovation programme” (under H2020-FTIPilot-2015-1, Grant Agreement n. 720367-GREENERNET), the University of Rome Tor Vergata (under the Research Call “Consolidate the Foundations”, project name: BEST WATER), and CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil. References. [1] A. Rinaldi, B. Mecheri, V. Garavaglia, S. Licoccia, P. Di Nardo, E.Traversa. Energ. Environ. Sci., 1 (2008) 417-429. [2] C. Santoro, A. Serov, L. Stariha, M. Kodali, J. Gordon, S. Babanova, O. Bretschger, K. Artyushkova, P. Atanassov, Energ. Environ. Sci. 9 (2016) 2346-2353. [3] A. Iannaci, B. Mecheri, A. D'Epifanio, M. J. Lázaro Elorri, S. Licoccia. Int J Hydrogen Energ. 41 (2016) 19637-19644. [4] H. Yuan, Z. He. Nanoscale 7 (2015) 7022-7029. [5] K. Parvez, S. Yang, Y. Hernandez, A. Winter, A. Turchanin, X. Feng, K. Müllen. ACS Nano. 6 (2012) 9541-9550.

Estimation of Cell Voltage and Power Density for Alcohols Electro-Oxidation on Modified Platinum Surface

Fuel cell performance was studied with regard to alcohols electro-oxidation on modified platinum under different conditions such as temperature and modification time. This research is aimed to estimate each of cell voltages and power densities as a function of current densities and the other cell parameters. The electrochemical cells operated on the electro-oxidation of methanol and ethanol in both HClO4 as an acidic medium and KOH as an alkaline medium. Applying the definition of electromotive force combined with Ohm’s law on the oxidation reaction, power density curves are constructed. Optimum parameters for cell voltage and power density had been determined.

Design and simulation of a novel bipolar plate based on lung-shaped bio-inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung-shaped bipolar plate was modeled. Simulations in this research showed that the lung-shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung-shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.

The comparison of direct borohydride-hydrogen peroxide fuel cell performance with membrane electrode assembly prepared by catalyst coated membrane method and catalyst coated gas diffusion layer method using Ni@Pt/C as anodic catalyst

Carbon supported Ni@Pt nanoparticles are synthesized using sodium dodecyl sulphate (SDS) and sodium borohydride (NaBH4) as a structure-directing and reducing agents, respectively. The metal loading in synthesized nanocatalyst is 20 wt% and the ratio of Ni:Pt in the nanocatalyst is 1:1. The structural characterizations and morphologies of Ni@Pt/C nanocatalyst are investigated by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The electrocatalytic activity of Ni@Pt/C catalyst toward borohydride (BH4−) oxidation in alkaline medium is studied by means of cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA). The results show that Ni@Pt/C catalyst has superior catalytic activity toward borohydride oxidation (8825.38 mA mg Pt−1). The Membrane Electrode Assembly (MEA) used in fuel cell set-up is fabricated with catalyst-coated membrane (CCM) and catalyst coated gas diffusion medium (CCG) techniques. The effect of two MEA performances on current–voltage (I–V) and current–power density (I–P) curves in the direct borohydride-hydrogen peroxide fuel cell was investigated using Pt/C 0.5 mg cm−2 as cathode catalyst and Ni@Pt/C 1 mg cm−2 as anode catalyst. The influence of cell temperature, sodium borohydride and hydrogen peroxide concentration on the I–V and I–P is determined. The results show that the maximum power density in MEA prepared using CCM method (CCM-MEA) is 68.64 mW cm−2 at 60 °C, 1 M sodium borohydride and 2 M hydrogen peroxide (H2O2) that is higher than MEA prepared using CCG method (CCG-MEA). The impedance results show that with increasing temperature and discharging current, the overall anodic and cathodic charge transfer resistances reduce.

Full cell simulation and the evaluation of the buffer system on air-cathode microbial fuel cell

Abstract This paper presents a computational model of a single chamber, air-cathode MFC. The model considers losses due to mass transport, as well as biological and electrochemical reactions, in both the anode and cathode half-cells. Computational fluid dynamics and Monod-Nernst analysis are incorporated into the reactions for the anode biofilm and cathode Pt catalyst and biofilm. The integrated model provides a macro-perspective of the interrelation between the anode and cathode during power production, while incorporating microscale contributions of mass transport within the anode and cathode layers. Model considerations include the effects of pH (H + /OH − transport) and electric field-driven migration on concentration overpotential, effects of various buffers and various amounts of buffer on the pH in the whole reactor, and overall impacts on the power output of the MFC. The simulation results fit the experimental polarization and power density curves well. Further, this model provides insight regarding mass transport at varying current density regimes and quantitative delineation of overpotentials at the anode and cathode. Overall, this comprehensive simulation is designed to accurately predict MFC performance based on fundamental fluid and kinetic relations and guide optimization of the MFC system.

Impacts of process parameters optimization on the performance of the annular single chamber microbial fuel cell in wastewater treatment.

Energy harvest from optimized annular single chamber microbial fuel cell (ASCMFC) with novel configuration, which treats chocolate industry wastewater, was investigated. In this study, optimization of operational parameters of the ASCMFC in terms of efficiency water-soluble organic matter reduction and capability of electricity generation was evaluated. During the experiment, effluent from the anode compartment was examined through current and power density curves for variation in temperature and pH, chemical oxygen demand (COD), and turbidity removal, and substrate concentration. The performance analyzed at different temperature ranges such as 25, 30, 35, and 40°C, which showed 88% increase by uprising temperature from 25 to 35°C. The ASCMFC was used to produce electricity by adjusting pH between 5 and 9 at resistance of 100 Ω. Under the condition of pH 7 power density (16.75 W/m3) was highest, which means natural pH is preferred to maximize microbial activities. Wastewater concentration with COD of 700 and 1400 mg/L were investigated to determine its affection on current production. Reduction of current density was observed due to decrease in wastewater concentration. Significant reduction in COD and turbidity of effluent were 91 and 78%, respectively. The coulombic efficiency of 45.1% was achieved.

Enhanced stability of symmetrical polymer electrolyte membrane fuel cell single cells based on novel hierarchical microporous-mesoporous carbon supports

Fuel cell electrodes were prepared from Pt nanocluster activated hierarchical microporous-mesoporous carbon powders. The carbon supports were synthesized from molybdenum carbide applying the high-temperature chlorination method. Six different synthesis temperatures within the range from 600 to 1000 °C were used for preparation of carbon supports. Thermogravimetric analysis, X-ray diffraction, low-temperature nitrogen sorption, and high-resolution scanning electron microscopy methods were used to characterize the structure of the electrode materials and symmetrical membrane electrode assemblies (MEAs). The MEAs prepared were used to conduct the proton exchange membrane fuel cell (PEMFC)single-cell measurements. The polarization and power density curves for single cells were calculated to evaluate the activity of the catalyst materials synthesized. The electrochemically active surface area (from 2.4 to 11.9 m2 g−1) was obtained in order to estimate the contact surface areas of platinum and Nafion® electrolyte. The values of the electrolyte resistance, polarization resistance, and cell degradation rate were calculated from electrochemical impedance spectroscopy data. The carbon materials synthesized within temperature range from 600 to 850 °C were found to be the most suitable supports for PEMFCs, having higher maximum power density values and better stability (cell potential degradation 240 μV h−1) than commercial carbon-based (Vulcan XC72; 670 μV h−1) single cells.

Surface Ce Decorated Exsolved Ni Nanoparticles Pinned Titanate Based Perovskite for Solid Oxide Fuel Cells

Tremendous endeavor has been devoted to synthesizing highly active supported nanoparticles (NPs) catalysts for energy conversion and storage devices. Specifically, planting NPs has been proven to be a promising approach to enhance both the catalytic activity and durability of the state-of-the-art perovskite oxide catalysts for solid oxide fuel cells. Unlike traditional impregnation method, the exsolution process provides a promising pathway to design and synthesize NPs with better thermal stability and dispersion, which can usually drive B-site cations exsolution from their parent lattice. This study demonstrated that the transitional metals exsolved on diverse perovskites exhibited special properties and desirable activities. It is also believed that the functionality of such exsolved particle pinned perovskite can be further optimized and altered through the decoration of other surface promoters. Herein, we developed a surface Ce decorated exsolved Ni NPs pinned titanate based perovskite (LSCNT) for solid oxide fuel cells via a modified sol–gel method. The exsolution of nano Ni particles with the uniformly dispersed nanoscale Ce over material surface could be obtained by sintering the material in consecutive atmospheres. The SOFC with the prepared anode shows promising electrochemical performance and stability in both sour H2 and dry CH4. In addition, the material also exhibited excellent long term stability with good carbon deposition and sulfur resistance. The detailed characterization results including SEM-EDX, O2 and CH4 pulses, H2-TPR and O2-TPO demonstrate that the presence of exsolved metallic Ni can be regarded as the active sites for the fuel oxidation reaction. Simultaneously, the presence of widely dispersed Ce species enclosing the Ni particles had oxygen storage ability and redox properties. This provided more active oxygen ions to promote the electrochemical reaction and to facilitate the removal of carbon deposits formed on Ni. The synergistic effect between Ni and Ce over LST scaffold enabled the fabricated material to be a potential anode candidate operating in various fuels. The obtained precursor was sintered at 1200 oC for 10 h in consecutive atmospheres of air and 10% H2/Ar for 10 h, respectively. The SEM image demonstrates the exsolved particles widely dispersed on the surface of the material. The composition of these particles on LSCNT was analyzed by EDX mapping analysis. Here, in order to quantitatively describe the variation in concentration of each element, five zones corresponding to the dramatic changes in the signal intensity for each element (La, Sr, Ce, Ni, Ti) were selected for detailed investigation. The EDX mapping scan results support the conclusion that the exsolved Ni particles with high concentration were well dispersed. And the other elements, including Ce, were also widely and uniformly dispersed. The voltage-current and power density curves of the single fuel cells with LSCNT anode operating at the temperatures from 800 to 900 oC in 5000 ppm H2S-H2 were shown in Figure 1. As the temperature increased, the maximum power density sharply increased from 260 mW/cm2 to 660 mW/cm2 and the maximum current density from 1100 mA/cm2 to 2600 mA/cm2, respectively. The corresponding electrochemical impedance spectra (EIS) data for LSCNT under OCV condition were demonstrated in the figure below. At 900 oC, for example, the cell with LSCNT anode shows the ohmic resistance of 0.21 Ω cm2 and activation polarization resistance of 0.19 Ω cm2, indicating its comparable performance to the traditional Ni/YSZ cermet anode. Figure 1. Current density vs. voltage and power density curves and Electrochemical impedance spectra (EIS) of fuel cells with LSCNT in 5000 ppm H2S-H2 Figure 1

On the Design of a Comb-Shaped, Poly(phenylene oxide)-Based Anodic Binder for Anion-Exchange Membrane Direct Methanol Fuel Cell (AEM-DMFC)

Anion-exchange ionomers are used in wide range of applications such as water treatment (desalination, purification, decontamination), chromatography and fuel cells. They consist of polymer chains functionalized with cationic groups to carry anionic molecules and can therefore be used as membrane and catalyst binder in anion-exchange membrane fuel cells (AEMFCs). In the last years there were many improvements related to alkaline stability and ion conductivity of anion-exchange membranes making these fuel cells more feasible. Anion-exchange membrane direct methanol fuel cells (AEM-DMFCs) are a subcategory of AEMFCs and convert the chemical energy of methanol into electric current by oxidizing methanol and reducing oxygen on the anode and cathode, respectively. Advantages of the alkaline over the acidic environment are enhanced methanol oxidation kinetics, lower overpotentials for oxygen reduction reaction, usage of cheaper catalysts than platinum, no need of highly alloyed steels due to less corrosive medium and possible usage of alcohol tolerant oxygen reduction reaction catalysts. It was recently demonstrated that AEM-DMFCs free from platinum reach power densities of up to 0.1 W cm-2 [1,2] making them an interesting alternative as power source for mobile and back-up power applications. In AEM-DMFCs, an ionomeric binder is needed to fix the carbon supported catalyst onto the liquid/gas diffusion layer. The catalyst layer consisting of the ionomer and the catalyst is supposed to build a three-phase boundary (TPB). The TPB facilitates the simultaneous transport of hydroxide ions, electrons and reactants/products. Research groups working on AEM-DMFCs currently rely on highly stable polytetra-fluoroethylene (PTFE) as binder as it is forming a microporously structured catalyst layer. On the downside, PTFE is non-anion conductive polymer. Hence, AEM-DMFCs with PTFE as binder need KOH added to the anodic fuel as electrolytic supplement to reach high current densities. As most anion-exchange membranes are not stable in highly alkaline media at elevated temperatures the addition of KOH to the fuel is considered to be problematic leading to the failure of the cell. Besides this, the addition of KOH is not consumer friendly and could therefore lead to problems in commercialization of the AEM-DMFCs. Thus, it is favorable to eliminate KOH as a fuel supplement. To reach this, ionomeric binders have to be designed for the needs of the AEM-DMFC especially on the anode compartment as the liquid methanolic fuel and the methanol oxidation reaction demand special properties from the ionomeric binder: Anionic conductivity, low swelling in water/methanol, high stability in alkaline environment and formation of a microporous catalyst layer structure. We herein present the synthesis, characterization and implementation in single cells of a comb-shaped anion-conductive ionomer with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as backbone polymer for the use as anodic binder in AEM-DMFCs. To synthesize the ionomer, PPO was brominated to further functionalize it. The comb-shaped ionomer resulted from a subsequent reaction of linking (2-methylimidazole, 2MIm), side chain (octafluoro-1,4-diiodobutane, DIFB) and quaternization (1,2,4,5-tetramethylimidazole, TMIm) agents. Successful synthesis was confirmed by 1H-NMR-spectroscopy. In Figure 1 the alkaline stability of comb-like PPO-2MIm-DIFB-TMIm is compared with a non-comb-shaped ionomer (PPO-TMIm). It is observed that the alkaline stability is greatly enhanced especially at high temperatures when the cationic group is not directly linked to the PPO backbone. Besides this, the comb-shaped ionomer shows several other advantageous properties over PPO-TMIm like lower swelling ratios while having similar water/methanol uptakes, higher thermal stability and higher ionic conductivity. Further investigations were done by implementing the ionomer as anodic binder in membrane electrode assemblies and conducting CO stripping and performance experiments on single cell level. Resulting UI and power curves (Fig. 2) showed a significant performance gain for the single cells with the comb-shaped ionomer used as binder. Fig. 1 (A) Loss of ionic conductivity of PPO-TMIm (black) and PPO-2MIm-DIFB-TMIm membranes (red) immersed in 3M KOH solution for 10 days at room temperature (straight lines), 60 °C (dashed lines) and 80 °C (dotted lines). (B) UI and power density curves of single cells fed with 4M CH3OH and O2 as anodic and cathodic fuels in dependency of the ionomer content in the anodic catalyst layers. Anodes consisted of various amounts of comb-like ionomer or PTFE and 2 mgPt cm-2 Pt/C. Cathodes consisted of 2 mgPt cm-2 Pt/C and 12.5wt% PTFE binder. Membrane: Tokuyama A201.

Sodium Cobalt Oxide As a Non-Platinum Cathode Catalyst for Microbial Fuel Cells

Microbial fuel cell is a device that can achieve wastewater treatment and power generation simultaneously. For the practical application of microbial fuel cell, development of alternative cathode catalyst for platinum is necessary. In this study, a kind of sodium cobalt oxide, NaCo2O4was investigated, because estimated cobalt reserve is 100 times higher than platinum, and its price is about one thousandth. Catalyst ink was prepared by mixing NaCo2O4powder with carbon black powder and Nafion dispersion. Then cathode was fabricated by applying the ink to PTFE treated carbon paper. Cathode with Pt catalyst and that with activated carbon (NORIT SX PLUS) were also prepared for comparison.ORR activity of the cathodes was measured by linear sweep voltammetry (LSV). Oxygen reduction reaction (ORR) activity of NaCo2O4 cathode increased 15-25 times by the addition of carbon black as conductive assistant material in catalyst ink. Two kinds of carbon black were tested, and a cathode with Ketjen black showed better ORR activity than that with Vulcan XC-72. By increasing coating amount of catalyst ink from 2mg/cm2 (NaCo2O4) to 4mg/cm2, ORR activity increased 1.6 - 1.7 times, which was equivalent to 50-60% of Pt catalyst (Fig) . Gram based ORR activity of this catalyst was higher than that of activated carbon (NORIT SX PLUS) catalyst (Fig). The NaCo2O4 cathode having highest ORR activity was built into a pre-acclimated MFC, and then used for the treatment of synthetic wastewater. The current density was about 3A/m2, which was a little lower than the value during the operation equipped with a Pt cathode (about 4A/m2). However, any problems such as a decrease in electricity generation were not observed in several days of operation. Power density curve of the MFC equipped with the NaCo2O4 cathode was obtained by the LSV measurement , and the maximum current density was 0.58 W/m2, which is about a half of the density achieved by a Pt cathode. Further research on the preparation condition of the cathode, such as the amount of conductive assistant material, the amount of binder, and the coating amounts of the catalyst ink, would probably contribute to further improve the cathode ORR activity, which would improve electricity generation performance of a MFC. Figure 1

Iron-Based Electrocatalysts Supported on Nanostructured Carbon to Enhance Oxygen Reduction in Microbial Fuel Cells

Sustainable waste management and energy supply can find a concrete answer in the technology of microbial fuel cells (MFCs). One of the major barriers to the widespread diffusion of this technology is the high cost of materials, among which the platinum-based cathode accounts for about 50 % of the total cell cost. Although platinum is a highly effective oxygen reducing catalyst, its activity is decreased by a variety of poisoning substances present in wastewater [1]. Latest development on nanostructured carbon for energy storage and conversion has brought to light carbon nanofibers (CNF), carbon nanotubes (CNT) and activated carbon (AC) as good candidates to replace costly Pt. These materials have high surface area and conductivity, and nitrogen doping has been demonstrated to be an effective approach to modulate their electronic properties [2]. Moreover, recent advances on non platinum group metal (NPGM) catalysts demonstrated the possibility to replace Pt with earth-abundant elements, such as Mn, Fe, Co, and Cu [3]. Among all, iron based catalysts supported on carbon have being used at cathodes of MFCs, active sites arising from Fe/N/C coordination. Aim of this study is to evaluate and compare catalytic activity towards oxygen reduction reaction (ORR) of catalysts based on iron phthalocyanine (FePc) supported over different carbon substrates with physical and morphological differences. Commercial carbon black, carbon nanotubes, and black pearls were used as catalyst support. Furthermore, the use of different advanced nanostructured carbon materials, such as carbon nanofibers and carbon xerogels was also investigated, owing to their porous structure and surface properties which can be tailored according to catalytic requirements [4, 5]. To facilitate catalyst dispersion and obtain effective ORR active sites, the supports were modified by a two-step treatment with nitric acid and ammonia gas. The treatment allowed introducing oxygen and nitrogen functionalities on the carbon surface while maintaining an extensively developed porous structure, as demonstrated by elemental analysis, BET, and X-ray photoelectron spectroscopy (XPS). Electrocatalysts derived from iron phthalocyanine (FePc) and the different carbon supports were prepared and their electrochemical activity towards ORR was assessed by cyclic voltammetry and rotating disk voltammetry experiments. The electrochemical results demonstrated that the prepared electrocatalysts are all active towards ORR at neutral pH; the higher the density of pyridinic nitrogen on the sample surface, the greater is the performance, as indicated by XPS. The applicability of FePc-based materials as ORR cathodes of MFCs was evaluated by assemblying FePc cathodes in single chamber air-catodes MFCs operating with sodium acetate in phosphate buffer solution, which coulombic efficiency, polarization and power density curves, and voltage generation cycles over time were acquired. The body of results demonstrated the potential ability of FePc-electrocatalysts to substitute platinum for ORR in MFCs.

Performance of Polymer Electrolyte Membrane Fuel Cell Single Cells Prepared Using Hierarchical Microporous-Mesoporous Carbon Supported Pt Nanoparticles Activated Catalysts

Hierarchical microporous-mesoporous carbon supports were prepared from molybdenum carbide using the high temperature chlorination method at six different synthesis temperatures within the range from 600°C to 1000°C. The platinum nanoparticles were deposited onto the carbon support using the sodium borohydride method. Thermogravimetric analysis, X-ray diffraction, low temperature nitrogen sorption and high resolution transmission electron microscopy methods were used to characterize the structure of materials. The synthesized catalysts were used as cathodes in the polymer electrolyte membrane fuel cell (PEMFC) single cell measurements. The polarization and power density curves were used to evaluate the activity of the materials synthesized. The electrochemically active surface area has been obtained in order to estimate the contact surface areas of platinum and Nafion® electrolyte. The values of the electrolyte resistance, polarization resistance and the activation energy were calculated from electrochemical impedance spectroscopy data. The carbon support material synthesized at 750°C was found to be the best for PEMFC cathode.

Multi-variable mathematical models for the air-cathode microbial fuel cell system

This research adopted the version control system into the model construction for the single chamber air-cathode microbial fuel cell (MFC) system, to understand the interrelation of biological, chemical, and electrochemical reactions. The anodic steady state model was used to consider the chemical species diffusion and electric migration influence to the MFC performance. In the cathodic steady state model, the mass transport and reactions in a multi-layer, abiotic cathode and multi-bacteria cathode biofilm were simulated. Transport of hydroxide was assumed for cathodic pH change. This assumption is an alternative to the typical notion of proton consumption during oxygen reduction to explain elevated cathode pH. The cathodic steady state model provided the power density and polarization curve performance results that can be compared to an experimental MFC system. Another aspect considered was the relative contributions of platinum catalyst and microbes on the cathode to the oxygen reduction reaction (ORR). Simulation results showed that the biocatalyst in a cathode that includes a Pt/C catalyst likely plays a minor role in ORR, contributing up to 8% of the total power calculated by the models.