Proton Electrolyte Membrane Fuel Cell Research Articles

Theoretical analysis of a biogas-fed PEMFC system with different hydrogen purifications: Conventional and membrane-based water gas shift processes

This study presents a thermodynamic analysis of biogas reforming and proton electrolyte membrane fuel cell (PEMFC) integrated process with different hydrogen purifications: conventional and membrane-based water gas shift processes. The aim is to determine the optimal reforming process for hydrogen production from biogas in the PEMFC system. The formation of carbon is concerned in the hydrogen production. The simulation results show that increases in the steam-to-methane ratio and reformer temperature can improve the hydrogen yield and reduce the carbon formation. From the performance analysis, it is found that when the PEMFC is operated at high temperature and fuel utilization, the overall system efficiency enhances. The performance of the PEMFC system with the installation of a water gas shift membrane unit in the hydrogen purification step is slightly increased, compared with a conventional process.

HRTEM Characterization of Non-Precious Metal-Based Catalyst Cathode Electrodes in PEM Fuel Cells

In Proton Electrolyte Membrane Fuel Cells (PEMFCs) the structure and morphology of the electrode layer play an important role in the reduction of the electrochemical resistance, which impacts the single cell performance. In the cathode layer, specifically, the oxygen reduction reaction takes place, involving complex mass and charge transport processes (diffusion of oxygen, migration and diffusion of protons, migration of electrons, water transport by diffusion, permeation, electroosmotic drag, as well as vaporization/condensation of water) 1.An understanding of the structure of the electrode layer at the various hierarchical levels, and furthermore, of its influence on the cell performance is far from complete 2. Moreover, factors like the type of the supported catalyst, the type and amount of ionomer added, the type of dispersion medium used during ink preparation, and the fabrication conditions (temperature, pressure) have proved to influence the properties of this microstructure1.Over the last four decades, intensive research has been devoted to the replacement of the platinum catalyst with non-precious metals, posing a new challenge in terms of electrode layer structure and properties. Given the lower activity of these materials compared to Pt and Pt-based materials, achievement of comparable results requires an increase in the ~10µm current state-of-the-art electrode thickness, leading to mass-transport limitations 3.In previous studies performed in our lab, catalysts based on Cu, Co, Ni, Mn and Fe complexes of substituted triazoles supported on BP2000 carbon black have been synthetized. The higher activity towards the oxygen reduction were obtained with the Co and Cu based catalysts 4.The main objective of this study is to evaluate the microstructure characteristics of Co and Cu-based cathodes for its application in PEMFCs operation. To achieve this goal, membrane electrodes assemblies (MEA) were prepared using cathodes with different catalyst loading and ionomer-catalyst ratio. Platinum electrodes with a 0.2 mg/cm2 loading were used as anodes. The performance of the MEAs was evaluated in single cell, and the structure and morphology were analyzed before and after testing through Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM).

The Effects of Compression Pressure Applied on the Manufacture of Carbon Composite Bipolar Plate for PEMFC by Utilizing Graphite Waste Products

Proton electrolyte membrane fuel cells (PEMFC) have near zero carbon dioxide and hazardous pollutant emission. Thus, it is considered as one of energy sources for transportation and other application which can improve environmental performance by decreasing the emission of greenhouse gases and other air pollutant. In accordance with its environmental preservation values, graphite waste product from electric arc furnace (graphite EAF) was chosen as a potential candidate material for bipolar plate for PEMFC. The utilization of graphite waste product is expected to result in light-weight and cost-effective bipolar plates. In this paper, we used graphite EAF as a filler together with carbon black and epoxy resin as a binder. We examined the effects of differential pressure applied on compression molding process on density, porosity, flexural strength and electrical conductivity of the resulting carbon polymer composite bipolar plate. Pressure was applied from 30 MPa - 60 MPa in increments of 5 MPa while maintaining constant temperature operation at 700C for 4 hours. Maximum value of bipolar plate density was achieved at application 55 MPa, of 1.69 g/cm3. At this condition, the flexural strength was measured to be 48 MPa with the porosity of 0.7%, and electrical conductivity of 1.03 S/cm. Taken together, we demonstrated that graphite EAF is a good candidate for the manufacturing of polymer composite bipolar plates.

Greenhouse Gas Emission Mitigation Potential of Different Technologies Used for Converting Biogas into Effective Energy in Germany

The upgrading of biogas to achieve natural gas quality for direct feeding into the supply grid has been frequently discussed as an alternative to its utilization for local energy production in block heat power plants (BHPP) using cogeneration. In this study, we compared the local use of upgraded biogas for producing electricity and heat with its energetic conversion at a distance away from the biogas plant under the conditions present in Germany. A total of seven systems were compared theoretically with the direct feeding of upgraded biogas into the grid. These systems involved either a BHPP or one of three types of fuel cell [molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), proton electrolyte membrane fuel cell (PEMFC)] or a hybrid system consisting of a SOFC and a gas turbine. The degree of efficiency in direct gas feeding was essentially better (71.3% secondary energy out of primary energy) than the decentralized forms of energetic conversion [45.7 (BHPP) -57.8% (hybrid system)]. The reason for this is that in Germany, natural gas, which is substituted through direct gas feeding, is primarily used for heating purposes. In comparison, however, the greenhouse gas emissions (GHG) reduction potential of local cogeneration (254-360 g CO2/kWhbiogas) was much higher than that of direct gas feeding (187- to 228-g CO2/kWhbiogas). This was found to be true even when no useful heat could be used on the site of the biogas plant. The best results were achieved with the hybrid system. By considering the effects of a reduction in the CO2 production of the German power supply mix on the potential emissions reduction of all eight systems investigated, it could also be shown that the hybrid system again had the greatest GHG emissions reducing potential. These results indicate that the direct feeding of upgraded biogas is not the best option for the utilization of this commodity with regards to climate protection in the German situation. Indeed, the results indicate that the application of innovative and efficient technologies, such as the hybrid system consisting of SOFC and a gas turbine, can generate essential improvements in emissions reductions in biogas plants in comparison to the presently used BHPPs. For this reason, the use of fuel cells in German biogas plants should be promoted.

Transient Analysis of Proton Electrolyte Membrane Fuel Cells (PEMFC) at Start‐Up and Failure

AbstractA two‐dimensional, transient, single‐phase computational model, incorporating water transport in the membrane and the flow and transport of species in porous gas diffusion electrodes is developed to evaluate the transient performance of a PEMFC with interdigitated gas distributors. The co‐flow and counter‐flow of the anode and cathode reactants are discussed to address their effects on PEMFC performance and transients. The important role of water transport in the membrane on the transients is demonstrated. The membrane's water intake or outtake determines the duration of the transients. The effect of the operating conditions on steady state and transient performances is outlined. Overshoots and undershoots are observed in the average current density, due to a step change in the cell voltage and the cathode pressure under start‐up conditions. Simulation results are used to address the role of auxiliary components in the failure modes of the PEMFC.

Technical design and economic evaluation of a PEM fuel cell system

The main objectives of this study are to develop the economic models and their characterization trends for the common unit processes and utilities in the fuel cell system. In this study, a proton electrolyte membrane fuel cell (PEMFC) system is taken as a case study. The overall system consists of five major units, namely auto-thermal reformer (ATR), water gas shift reactor (WGS), membrane, pressure swing adsorber (PSA) and fuel cell stack. Besides that, the process utilities like compressor, heat exchanger, water adsorber are also included in the system. From the result, it is determined that the specific cost of a PEM fuel cell stack is about US$ 500 per kW, while the specific manufacturing and capital investment costs are in the range of US$ 1200 per kW and US$ 2900 per kW, respectively. Besides that the electricity cost is calculated as US$ 0.04 kWh. The results also prove that the cost of PEM fuel cell system is comparable with other conventional internal engine.

Inverse gas chromatographic investigation of the effect of hydrogen in carbon monoxide adsorption over silica supported Rh and Pt–Rh alloy catalysts, under hydrogen-rich conditions

Selective CO oxidation (SCO) has attracted scientific and technological interest due to its application to the operation of proton electrolyte membrane fuel cells (PEM-FCs). CO adsorption, being an elementary step of SCO, is studied over silica supported monometallic Rh and Rh 0.50 + Pt 0.50 alloy catalysts, under various hydrogen atmospheres, namely: 25% H 2 + 75% He, 50% H 2 + 50% He and 75% H 2 + 25% He carrier gas mixture compositions. The investigation of CO adsorption is done by utilizing reversed-flow gas chromatography (RF-GC). As a result rate constants for the adsorption ( k 1), desorption ( k −1) and irreversible CO binding ( k 2) over the studied catalysts as well as the respective activation energies are determined. The variation of the rate constants and the activation energies against the nature of the used catalyst (monometalic or alloy) and the amount of hydrogen in the carrier gas gives useful information for the selectivity as well as the activity of CO oxidation over group VIII noble metals. At low temperatures and under H 2-rich conditions compatible with the operation of PEM fuel cells the activity of the monometallic and the alloy catalysts is expected to be similar, however the selectivity of Rh 0.50 + Pt 0.50 alloy catalyst is expected to be higher, making Pt–Rh alloy catalyst as a better candidate for CO preferential oxidation (PROX). The low energy barrier values found in the present work, most likely are referred to high surface amounts of CO. The desorption barriers determined are in any case much lower than the respective activation energies found for CO desorption in the absence of hydrogen indicating a H 2-induced desorption, which can explain the observed in the literature rate enhancement of SCO oxidation.

Optimization of 5-kW Mobile and Portable PEMFC System via Energy Integration

he main objective of this study is to design an energy recovery system for the Proton Electrolyte Membrane Fuel Cell (PEMFC) that will optimize energy use through heat integration. A PEMFC system with a power output of 5 kW was used in the case study. Methanol, which served as primary fuel source of the autothermal reformer (ATR) system, was fed together with steam and oxygen. Based on the conceptual design, the ATR product contains about 73% H2' 2% CO, and 25% C02' The hydrogen-rich reform ate produced by reforming primary fuels in the fuel proC€t::30r ystem, which scontains a significant amount of CO, was reduced further via Water Gas Shift (WGS) reactor, Tubular Ceramic Membrane (TCM), and Pressure Swing Adsorber (PSA) in series. From the plots, the pinch point was determined at 540°C,the minimum process heating requirement from hot utilities QH mon at 140 W, and the minimum process cooling requirement from cold utilities Qc. at 96 W. Furthermore, energy recovery for both heating and cooling purposes aft~; heat integration registered at 92% and 95%, respectively. Also, the number of heat exchangers reduced from 7 to 4 after heat integration.

Design of a fuel processor unit for PEM fuel cell via shortcut design method

The objective of this paper is to conceptually design a fuel processor system for a 5 kW proton electrolyte membrane fuel cell (PEMFC) system for mobile and portable application. The first section describes the auto-thermal reformer (ATR) system while the second section demonstrates the significance of the water gas shift (WGS) reaction in the system. Shortcut design methods are used for the process units and the characterization curve for each unit is also presented. Kinetic parameters for steam reforming and WGS reactions are also shown. The 5 kW PEMFC requires about 0.08 m 3/min (3.74 mol/min) of H 2 fuel at the fuel cell stack. The primary fuel source to the ATR system is methanol 0.1 m 3/min (4 mol/min), which is fed together with steam and oxygen with the ratio of S/C and O 2/C at 1.3:1 and 1:4, respectively. The conceptual design indicates that if the mole ratio of O 2/C is 0.20–0.25, then the hydrogen selectivity is around 2.5–2.6 for complete methanol. Steam is fed at excess condition in both units, ATR and WGS, to avoid reverse WGS reaction. The conceptual design also proved the significance of WGS reaction in the reduction of CO produced in the ATR and indicated the importance of pressure to reduce the bulk size of WGS reactor. Finally from the overall mass balance for fuel processor unit, the ATR product contains H 2: 73%, CO: 2%, and CO 2: 25%. The CO level is then further reduced to less than 2000 ppm after the WGS reactor. In addition, this paper also studied the performance of preferential oxidation (PROX) in removing the CO and it was observed that the PROX could reduce the CO to less than 100 ppm and performed better than WGS reaction in terms of water management. However, the main problem with PROX is to decide a good catalyst that can give a good selectivity for CO oxidation rather than water formation.

Design of a Tubular Ceramic Membrane for Gas Separation in a PEMFC System

AbstractThe objective of this study is to introduce a shortcut in the method of design for a tubular ceramic membrane (TCM) for gas separation. Generally, it explains the permeation of the multi component gas using cross flow models in a porous membrane and the surface area of the membrane required. The novel aspect of this method is that the expression for the length of the membrane is simplified to a number unit (NTU) and a height of transfer unit (HTU). The HTU term for porous membranes is characterised by the physical properties of the membrane; the feed flow rate, nF, membrane thickness, lM, feed pressure, PF, K the permeability of gas and the diameter of the membrane, DM. The integral for NTU of a porous membrane is the solution for the local permeate along the length of the membrane. It is found that, NTU mainly depends on the rejection stream, xR,, along the membrane and it describes the relative degree of separation. The Proton Electrolyte Membrane Fuel Cell (PEMFC) system is taken as the case study. CO is the main culprit in reducing the performance of the PEMFC and will act as a catalyst poison for the fuel cell anode at a concentration as low as 100 ppm. Thus, the reformate, from primary reforming, contains a significant amount of CO and must be purified. The effect of some important parameters such as temperature, pressure and the thickness of membrane to the degree of separation are presented in this paper. From the results, it can be seen that the system could reduce the CO concentration from 2000 – 500 ppm. Basically the TCM will operate, in series, with a pressure swing adsorber in order to further reduce the concentration of CO to less than 10 ppm before entering the fuel cell stack. However, this paper only focuses on the design of the TCM. Besides this, it is observed that the purity of the hydrogen increased from 72.8 – 96% (at θ = 0.5) after the membrane.

Evaluation of a Sol-Gel Derived Nafion/Silica Hybrid Membrane for Proton Electrolyte Membrane Fuel Cell Applications: I. Proton Conductivity and Water Content

Sol-gel derived Nafion®/silica hybrid membranes were investigated as a potential polymer electrolyte for fuel cell applications. Membrane proton conductivity and water content were measured as a function of temperature, water vapor activity, and silica content. The hybrid membranes have a higher water content at 25 and 120°C, but not at 150 and 170°C. Despite the higher water content, the proton conductivities in the hybrid membranes are lower than, or equal to, that in unmodified Nafion membranes under all conditions investigated. The proton conductivity of the hybrid membrane decreases with increasing silica content under all conditions. © 2001 The Electrochemical Society. All rights reserved.

Biological variability of serum 5′ nucleotidase and cholinesterase activities: G.C. Moses, James F. Tuckerman, and A. Ralph Henderson, Dept. Clin. Biochemistry, University Hospital, London, Ontario, N6A 5A5

Proton electrolyte membrane fuel cell (PEMFC) is one of the most popular clean energy systems, which has attracted attention in a few recent years. However, due to the sluggish oxygen reduction reaction (ORR) in acid media, platinum-based catalysts are highly required in the-state-of-the-art PEMFC. Also, the low durability and scarcity of novel metals significantly limit its wide application. This study applied a novel plasma engineering route to fabricate molecular transition metal macrocycles (M-N4 where M = Fe, Co, Mn) in situ into nitrogen-carbon support. CoN4 showed the highest ORR onset (Eonset) and halfwave potential (E1/2) of 0.78 and 0.67 V vs. RHE, respectively, which was only slightly inferior by 100 mV in ORR onset compared to the benchmark 20 wt.% Pt/C. On the other hand, CoN4 presented extremely high durability (E1/2 = −15 mV after 3000 cycles) and outperformed 20 wt.% Pt/C (E1/2 = −140 mV after 3000 cycles). This study presented a novel plasma engineering to fabricate molecular transitional metal-N4 doped carbon as a highly durable and economic ORR electrocatalyst to replace current benchmark Pt-based metal for PEMFC.