High Temperature Proton Exchange Membrane Fuel Cell Research Articles

Effect of phosphoric acid purity on the electrochemically active surface area of Pt-based electrodes

• H 3 PO 4 should be purified before ORR measurements to remove impurities which can be oxidized. • H 3 PO 3 was suggested as one of the impurities in the unpurified H 3 PO 4 solution. • ESCA HUPD analysis is more accurate than ESCA CO in the presence of H 3 PO 3. • H 3 PO 3 and CO compete for Pt surface active sites. • Commercial “crystalline H 3 PO 4 ” contains low amount of reduced phosphorus impurities. In this work, the effect of H 3 PO 4 purity on the activity of Pt/C thin film catalysts towards the oxygen reduction reaction (ORR) was investigated. H 3 PO 4 is routinely introduced in the electrolyte during rotating disk electrode (RDE) measurements to simulate the existing environment within high-temperature proton exchange membrane fuel cells (HT-PEMFC). Three different purity grades were tested: crystalline (99.99% purity), commercial H 3 PO 4 solution (85 wt%), hereafter, designated as non-purified H 3 PO 4 , and commercial H 3 PO 4 solution (85 wt%) purified with H 2 O 2 . H 3 PO 4 and/or its anions are known to strongly adsorb and interact with Pt surfaces. The presence of H 3 PO 4 negatively affected the electrochemically active surface area (ECSA) measured by H upd (ECSA H ), and by CO stripping (ECSA CO ), kinetic parameters in the high current density region and the limiting current density ( j lim ) of ORR. One major finding was that the crystalline and purified H 3 PO 4 solutions have similar effects on the Pt/C catalyst activity while the non–purified H 3 PO 4 showed a significantly more negative effect on the ECSA as well as on the ORR measurements. This was found to be due to the presence of H 3 PO 3 in the non-purified H 3 PO 4 solution. Adsorption isotherms of H 3 PO 3 were also measured using H upd and CO stripping in order to evaluate its adsorption on the catalyst surface. From these investigations, the purity level of H 3 PO 4 was shown to be an important factor in reliable ORR testing.

Speciation and Proton Conductivity of Phosphoric Acid Confined in Mesoporous Silica.

Phosphoric acid (PA) confined in a commercial mesoporous silica (CARIACT G) with porous size in the range of 3 to 10 nm was studied in relation to its coordination with the silanol groups on the silica surface as a function of temperature, up to 180 °C, using 31P and 29Si MAS NMR spectroscopy. As the temperature increases, the coordination of Si and P in the mesopores depends on the pore size, that is, on the area/volume ratio of the silica matrix. In the mesoporous silica with the higher pore size (10 nm), a considerable fraction of PA is nonbonded to the silanol groups on the surface, and it seems to be responsible for its higher conductivity at temperatures above 120 °C as compared to the samples with a smaller pore size. The electrical conductivity of the functionalized mesoporous silica was higher than that reported for other silico-phosphoric composites synthesized by sol-gel methods using soft templates, which require high-temperature calcination and high-cost reagents and are close to that of the best PA-doped polybenzimidazole membranes used in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). The rate of PA release from the mesoporous silica matrix when the system is exposed to water has been measured, and it was found to be strongly dependent on the pore size. The low cost and simplicity of the PA-functionalized mesoporous silica preparation method makes this material a promising candidate to be used as an electrolyte in HT-PEMFCs.

Performance and Durability of HT-PEMFC Enhanced By One-Step Electrochemical Exfoliated Phosphonated Graphene Oxide

The high-temperature proton exchange membrane fuel cell (HT-PEMFC) conducts protons through the hydrogen bond network established by the polymer and phosphoric acid (PA), which reduces the dependence on humidity and allows its operating temperature to be higher than 100°C [1]. A higher operating temperature is conducive to improve catalyst activity, reducing carbon dioxide adsorption on the catalyst thus reducing the requirement for hydrogen purity, and convenient water management [2]. As the most widely commercialized HT-PEMFC proton exchange membrane material, the performance and durability of Polybenzimidazole (PBI) still need to be improved. In particular, it has insufficient proton conductivity, insufficient mechanical properties, and phosphoric acid leaching issues under high acid doping level [3] [4] [5].The doping of functionalized graphene oxide in the PBI membrane can build additional proton transfer channels, promote proton hopping and act as a trap for PA to reduce its leaching by virtue of abundant functional groups of functionalized GO [6] [7] [8]. Among the groups that can be used for functionalization, the phosphoric acid group has become one of the most promising due to its strong hydrogen bonding and water retention ability [9] [10] [11]. Phosphonated graphene oxide (PGO) is usually synthesized by further phosphonation of GO obtained by chemical exfoliation [6] [7]. Chemical exfoliation methods usually require the long-term action of strong acids and strong oxidants [12]. The safety and environmental issues caused by those methods can not be underestimated. And the two-step synthesis method of PGO has a long reaction period.This work achieved the rapid, safe, and large-yield production of electrochemically exfoliated PGO by using a 3D printed reactor, ammonium dihydrogen phosphate as the electrolyte and natural graphite flakes as the raw material. The two-step electrochemical exfoliation method of producing GIC with concentrated sulfuric acid as the first electrolyte is also used to synthesize electrochemical exfoliated (E)GO. 1.5wt% EGO or PGO was doped in the PBI membrane to explore the effect of different GO on the performance and durability of the PBI- membrane-based HT-PEMFC. Compared with pure PBI, the doping of EGO and PGO increases the peak power density of HT-PEMFC by 17.4% and 35.4%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Journal of The Electrochemical Society 2004, 151, A8.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, International Journal of Hydrogen Energy 2013, 38, 11370.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, International Journal of Hydrogen Energy 2013, 38, 6469.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Journal of Synchrotron Radiation 2014, 21, 1319.[5] Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Physical Chemistry Chemical Physics 2010, 12, 12544.[6] J. Yang, C. Liu, L. Gao, J. Wang, Y. Xu, R. He, RSC Advances 2015, 5, 101049.[7] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.[8] Y. Cai, Z. Yue, S.X.-J. of A.P. Science, undefined 2017, Wiley Online Library 2017, 134, 44986.[9] E. Abouzari-Lotf, H. Ghassemi, A. Shockravi, T. Zawodzinski, D. Schiraldi, Polymer 2011, 52, 4709.[10] E. Abouzari-Lotf, M. Zakeri, M.M. Nasef, M. Miyake, P. Mozarmnia, N.A. Bazilah, N.F. Emelin, A. Ahmad, Journal of Power Sources 2019, 412, 238.[11] S. Some, I. Shackery, S.J. Kim, S.C. Jun, Chemistry - A European Journal 2015, 21, 15480.[12] C. Xu, Y. Cao, R. Kumar, X. Wu, X. Wang, K. Scott, Journal of Materials Chemistry 2011, 21, 11359.

Single-Layer-Graphene and Electrochemical Exfoliated Graphene Oxide for HT-PEMFC

High-temperature proton exchange membrane fuel cell (HT-PEMFC) is promising with its low demand for hydrogen purity, simple water management, and high waste heat utilization [1][2]. Although polybenzimidazole (PBI), as a typical high-temperature fuel cell membrane, has been developed for a long period, it still has defects such as phosphoric acid leaching and insufficient mechanical properties under high acid doping level [3][4]. With its unique 2D hexagonal grid structure and its electron cloud arrangement, single-layer graphene (SLG) can block the passage of any atoms [5]. However, hydrogen protons can easily penetrate SLG through a unique intermediate state mechanism to make it have excellent proton conductivity [6]. SLG's high proton conductivity combined with its excellent mechanical properties and thermal conductivity make it an ideal material for blocking phosphoric acid leaching. The SLG prepared by the chemical vapor deposition (CVD) method was transferred to the surface of catalyst layer of electrodes by the wet chemical transfer method. Due to the rupture and incompleteness of the SLG during the transfer process, the coverage rate of the SLG on the electrode surface is about 55%. This incomplete coverage facilitates small quantities of phosphoric acid leaching from PBI membrane to electrodes, which increases the three-phase boundary area and improves the performance of the HT-PEMFC. After 70 hours of accelerated stress testing (AST), the peak power density of membrane-electrode-assembly (MEA) with SLG on both sides of the cathode and anode can reach 480 mW cm-2, while the peak power density of MEA based on pure PBI membrane is only 249 mW cm-2. The quantification of phosphoric acid in the electrode by Lab based X-ray micro-computed tomography and the Raman spectroscopic mapping of the MEA cross-section shows that SLG can mitigate the leaching of phosphoric acid in the PBI film and improve the durability of HT-PEMFC. Graphene oxide (GO) is a low-cost application of graphene. Its doping in the PBI membrane can also reduce the leaching of phosphoric acid through enhancing the interaction between phosphoric acid and the PBI membrane [7]. A reactor based on 3D printing was designed so that natural graphite flakes can be used for electrochemical exfoliation to achieve rapid, safe, environmentally friendly, and mass production of GO. The electrochemically exfoliated (E)GO is doped in the PBI membrane. The 0.5%, 1% and 2% EGO loadings in the PBI membrane increased the peak power density by 13.8%, 24.4% and 29.2%, respectively.[1] Y.-L. Ma, J.S. Wainright, M.H. Litt, R.F. Savinell, Conductivity of PBI Membranes for High-Temperature Polymer Electrolyte Fuel Cells, Journal of The Electrochemical Society. 151 (2004) A8. https://doi.org/10.1149/1.1630037/XML.[2] H. Su, S. Pasupathi, B. Bladergroen, V. Linkov, B.G. Pollet, Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer, International Journal of Hydrogen Energy. 38 (2013) 11370–11378. https://doi.org/10.1016/J.IJHYDENE.2013.06.107.[3] S. Galbiati, A. Baricci, A. Casalegno, R. Marchesi, Degradation in phosphoric acid doped polymer fuel cells : A 6000 h parametric investigation, International Journal of Hydrogen Energy. 38 (2013) 6469–6480. https://doi.org/10.1016/j.ijhydene.2013.03.012.[4] S.H. Eberhardt, F. Marone, M. Stampanoni, F.N. Büchi, T.J. Schmidt, Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy, Journal of Synchrotron Radiation. 21 (2014) 1319–1326. https://doi.org/10.1107/S1600577514016348.[5] S. Hu, M. Lozada-Hidalgo, F.C. Wang, A. Mishchenko, F. Schedin, R.R. Nair, E.W. Hill, D.W. Boukhvalov, M.I. Katsnelson, R.A.W. Dryfe, I. V. Grigorieva, H.A. Wu, A.K. Geim, Proton transport through one-atom-thick crystals, Nature. 516 (2014) 227–230. https://doi.org/10.1038/nature14015.[6] S.M. Holmes, P. Balakrishnan, V.S. Kalangi, X. Zhang, M. Lozada-Hidalgo, P.M. Ajayan, R.R. Nair, 2D Crystals Significantly Enhance the Performance of a Working Fuel Cell, Advanced Energy Materials. 7 (2017) 1–7. https://doi.org/10.1002/aenm.201601216.[7] J. Li, X. Zeng, T. Ren, E. van der Heide, The Preparation of Graphene Oxide and Its Derivatives and Their Application in Bio-Tribological Systems, Lubricants 2014, Vol. 2, Pages 137-161. 2 (2014) 137–161. https://doi.org/10.3390/LUBRICANTS2030137.

(Energy Technology Division Research Award) Interplay between Synthesis, Mechanisms and Performance of Electrocatalysts and Ionomers for Ion-Exchange Membrane Fuel Cells

Ion-exchange membrane fuel cells (IEMFCs) are a family of electrochemical energy conversion and storage devices characterized by several attractive features, including outstanding energy conversion efficiency and a clean operation. IEMFCs are a cornerstone of the “hydrogen economy”, one of the most promising avenues to decarbonize the energy sector, with the ultimate purpose to curtail the emissions of greenhouse gases and mitigate global warming. Therefore, a goal of great practical relevance is to devise highly performing, durable and inexpensive IEMFCs .IEMFCs consist of an electrolyte membrane sandwiched between two electrodes. At the membrane-electrode interfaces are located electrocatalytic layers (EC layers) comprising suitable electrocatalysts (ECs) able to promote the redox processes exploited by the IEMFC operation. The IEMFC sub-families are distinguished by the attributes of the membrane, especially in terms of: (i) chemical features (e.g., polymeric backbone); (ii) mobile ion(s) (e.g., protons for proton-exchange membrane fuel cells, PEMFCs, OH- anions for anion-exchange membrane fuel cells, AEMFCs); and (iii) operation temperature. In the environment modulated by the ionomer, the properties of the ECs , with particular reference to the chemical composition of the active sites and support morphology, are correlated to their performance. Hence, to obtain an IEMFC exhibiting a high performance and durability is imperative to rationally design membranes and ECs that are: (i) highly compatible with one another; and (ii) able to express their best performance and durability in the same set of operating conditions.This contribution overviews our research activities aimed at the development of ECs and membranes for application in PEMFCs, high-temperature PEMFCs and AEMFCs. The topics include: (i) the innovative approaches for the synthesis of the functional components; (ii) the aspects of their physicochemical characterization, together with the unique and comprehensive frameworks contrived for the integration and interpretation of the experimental outcomes; and (iii) the steps to integrate the functional components in high-performing IEMFC prototypes.The ECs considered here are meant to promote the oxygen reduction reaction (ORR), a sluggish electrochemical process that is a major bottleneck in the operation of IEMFCs fueled with hydrogen. State-of-the-art ORR ECs are based on Pt nanoparticles supported on carbon (“Pt/C” ECs). Pt/C ECs warrant a sufficient performance, but suffer from a poor durability and require a high loading of platinum, a strategic element that is prone to trigger supply bottlenecks especially in the event of a large-scale rollout of IEMFCs. The ECs devised in our research laboratory are aimed at addressing all of these issues with materials exhibiting a number of unique features, as follows. (i) Active sites with either an intrinsic ORR kinetics much improved above the Pt baseline or completely “Pt-free”, consisting of an “active metal” (e.g., Pt, Fe) whose performance is boosted by one or more “co-catalyst” (e.g., Co, Ni, Cu, Sn). (ii) Strong, covalent interactions between the active sites and the C-/N- ligands of the “coordination nests” on the surface of the EC support, warranting a high durability. (iii) A support featuring a “core-shell” morphology, wherein a “core” consisting of suitable carbon system(s) is covered by a carbon nitride (CN) “shell”, bestowing facile charge and mass transport features (Figure 1(a)). The resulting ECs bestow the IEMFC a high performance with a minimized loading of Pt. Specifically, the PEMFC prototypes mounting the ECs here described yielded more than 20 kW∙gPt -1.The second main topic of this overview is the development and the study of the conductivity mechanism of separator membranes for IEMFCs. The latter consist mainly of ionomer matrices (e.g., perfluorinated systems such as Nafion™, SPEEK and developmental anion-exchange block copolymers), both pristine and doped with suitable nanofillers (e.g., conventional ceramic oxoclusters, “core-shell” oxocluters, among many others). The matrix-nanofiller interactions modulate the physicochemical features of the resulting hybrid inorganic-organic membrane, allowing to improve crucial features for applications in IEMFCs such as: (i) mechanical stability; and (ii) conductivity in dry conditions and high temperature. Other separator membranes are overviewed, including: (i) anion-exchange ionomers based on polyketone matrices (Figure 1(b)); (ii) hybrid inorganic-organic membranes for HT-PEMFCs based on oxocluster nanofillers and polybenzimidazole-like matrices; and (iii) membranes swollen with proton-conducting ionic liquids. These membranes underwent a thorough characterization elucidating their morphology, structure, thermal properties, thermomechanical relaxations and electric response (Figure 1(c)). The integration of all the above knowledges yielded a unique, comprehensive and general framework which proved crucial to elucidate the interplay between the physicochemical properties of the different phases within each membrane and their overall conductivity mechanism. This allowed to trigger the development of new high-performing separator membranes for application in IEMFCs. Figure 1

Performance analysis and optimization of a novel vehicular power system based on HT-PEMFC integrated methanol steam reforming and ORC

In this paper, a novel vehicular high temperature proton exchange membrane fuel cell (HT-PEMFC) power system integrated with methanol steam reforming (MSR) and Organic Rankine Cycle (ORC) is proposed. The system uses waste heat from the HT-PEMFC to provide the MSR subsystem for hydrogen production, and the ORC subsystem recovers the remaining heat to generate electrical power. The thermodynamic model of the system and multi-criteria evaluation are established. Numerical results show that increasing the current density and decreasing the cathode pressure and stoichiometry is favorable for improving the net output power of the system, but also increasing the levelized cost of energy and carbon mass specific emission of the system. Higher operating temperatures and anode pressures are beneficial to overall performance. Moreover, the system is optimized using the NSGA-II algorithm to obtain the three-dimensional (3D) Pareto solution and the optimal set of operating parameters. The optimized system net output power, levelized cost of energy and carbon mass specific emission at the Final Optimal Point are 36.98 kW, 0.2138 $/kWh and 0.5583 kg/kWh, respectively. Compared to the un-optimized system, the system working at optimal parameters has better thermodynamic, economic and environmental performance.

Numerical Study of the Flow Field Distributor in High-temperature Proton-exchange Membrane Fuel Cells

Numerical Study of the Flow Field Distributor in High-temperature Proton-exchange Membrane Fuel Cells

Real-Time Monitoring of the Temperature, Flow, and Pressure Inside High-Temperature Proton Exchange Membrane Fuel Cells.

The proton exchange membrane fuel cell (PEMFC) system is a highly efficient and environmentally friendly energy conversion technology. However, the local temperature, flow, and pressure inhomogeneity within the fuel cell during the electrochemical reaction process may lead to depletion of PEMFC material and uneven fuel distribution, thus affecting the performance and service life of high-temperature PEMFCs. In this study, micromachining technology is used to develop a three-in-one flexible micro-sensor that is resistant to a high-temperature electrochemical environment (120~200 °C). Appropriate materials and process parameters are used to protect the micro-sensor from failure or damage under long-term testing, and to conduct a real-time micro-monitor of the local temperature, flow, and pressure distribution inside high-temperature PEMFCs.

Implementation of different Fe–N–C catalysts in high temperature proton exchange membrane fuel cells – Effect of catalyst and catalyst layer on performance

Fe–N–Cs are an alternative to Pt/C catalysts as they show promising activity towards the oxygen reduction reaction. While several studies are based on thin-film analysis in diluted electrolytes, only few reports show the application of Fe–N–Cs in gas diffusion electrodes (GDE) and their tests under high temperature proton exchange membrane fuel cell (HT-PEMFC) conditions. Here, a series of Fe–N–Cs with different physical properties are analyzed. GDEs are fabricated using ultrasonic spray and doctor blade coating to investigate the effect of coating method on the morphology and performance. Morphological analysis identified thinner catalyst layers for spray coating and inhomogeneous PTFE distribution for doctor blade coated GDEs. Electrochemical characterization in the HT-PEM half-cell displays significantly lower performance for ultrasonic spray-coated GDEs, possibly due to more pronounced phosphoric acid penetration. On the contrary, implementation of GDEs as cathodes in the HT-PEMFC yields comparable performances for both coating methods but differences in ORR and proton transport resistances determined by distribution of relaxation times analysis. Moreover, it was shown that inhomogeneous PTFE distribution caused by high amounts of hydrophilic O-/N-functionalities negatively affects HT-PEMFC performance. This study helps to understand the impact of GDE fabrication and Fe–N–C catalyst properties in HT-PEM half- and single-cell application.

Numerical study of carbon monoxide poisoning effect on high temperature PEMFCs based on an elementary reaction kinetics coupled electrochemical reaction model

High-temperature proton exchange membrane fuel cells have received lots of attention due to their high tolerance of impurities in the fuel gas. Many researchers have conducted experimental and numerical investigations to study the influence of carbon monoxide on performance of the high-temperature proton exchange membrane fuel cell. However, most numerical models use an empirical formula to consider the effect of adsorption and desorption of hydrogen and carbon monoxide. To more accurately study the influence mechanism of carbon monoxide as an impurity, a novel three-dimensional non-isothermal model considering elementary reactions of hydrogen and carbon monoxide for high-temperature proton exchange membrane fuel cells is developed in this study. The elementary reaction kinetics of the anodic catalytic layer adopts a six-step global reaction, and the adsorption processes, desorption processes, as well as electrochemical reactions are taken into account. This model is able to accurately predict the steady polarization curve of a high-temperature proton exchange membrane fuel cell fed by hydrogen containing different amounts of carbon monoxide. The sensitivities of elementary reaction rates in the voltage range of 0.4–0.9 V for the fuel cell fed by pure hydrogen or a mixture of hydrogen and carbon monoxide are analyzed. The rate-determination step is studied at different voltages. In addition, the distributions of gaseous species, surface species and reaction rates of all elementary reactions along different directions of the anode catalytic layer are presented. Finally, the influences of carbon monoxide content in the fuel gas and the operating temperature of a high-temperature proton exchange membrane fuel cell fed by a mixture of hydrogen and carbon monoxide are numerically studied.

Modeling and analysis of water vapor dynamics in high-temperature proton exchange membrane fuel cell coupling gas-crossover phenomena

A 3-D numerical model coupling gas-crossover phenomena for high-temperature proton exchange membrane fuel cell (HT-PEMFC) is developed to investigate the water vapor behavior. After model validation, sensitivity analysis of the water vapor diffusion coefficient is carried out, which does not further affect the water vapor behavior, when the order of magnitude of diffusion coefficient is higher than 10−5m2/s. It is also found that the water vapor transport flux decreases with increasing membrane thickness. However, the flux increases slightly with increasing the catalyst layer. In addition, Increasing the pressure and humidity on the anode side will cause water vapor to diffuse from the anode to the cathode, while increasing the current density or the pressure of cathode, the rate of water vapor transport from the cathode to the anode is enhanced. In the dead-end mode, the accumulation of water vapor at the anode outlet is the main cause for the reversible performance decline, which can be restored through reasonable purge strategies. This work contributes to improve the water management strategy of HT-PEMFC operating in dead-end mode.

Thermodynamic, Exergetic and Thermoeconomic Analyses of Double-Effect LiBr–Water Absorption Refrigeration Systems with a 5 kW High Temperature PEMFC as Heat Source for Data Center Applications

Thermodynamic, exergetic and thermoeconomic analyses were performed on two types of double-effect LiBr–water absorption refrigeration systems (ARS) for use with a 5-kW high-temperature proton exchange membrane fuel cell (HT-PEMFC) as a heat source. Proper temperatures of the high-pressure generator, combined generator and condenser, condenser, absorber and evaporator were determined to meet the requirements of constant cooling demands for data center operations. The heat balance of the combined unit of generator and condenser in the industrial double-effect LiBr-water ARS is important for determining the flow rate of the primary vapor refrigerant from the high-pressure generator. The industrial double-effect ARS system, whose analysis has not been studied analytically, outperformed the series double-effect system and provided 6.5 kW of cooling capacity with a coefficient of performance of 0.99. The unit cost of chilled water estimated by the modified productive structure analysis (MOPSA) method is approximately 7.18 USD/GJ (=0.026 US$/kWh). Effective exergetic efficiency of HT-PEMFC with the industrial ARS increases to 57.6% from 47.0%.

Voltage Readjustment Methodology According to Pressure and Temperature Applied to a High Temperature PEM Fuel Cell

The operating conditions can have uncontrolled effects on the voltage of a High-Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC). For instance, the HT-PEMFC can be used at ambient pressure, i.e., without having a back pressure regulator. In this case, the variation in the atmospheric pressure directly affects pressures inside the fuel cell, which induces voltage variation. Moreover, in transient phases, several coupled phenomena can have an uncontrolled effect on the voltage. For example, following a change in the current operating point, thermal conditions in the fuel cell can vary, and the temperature stabilization then leads to a voltage variation. This article introduces a readjustment method for the fuel cell voltage to compensate for the effects of the pressure and temperature variations that are undergone and to decouple their effects. This methodology is based on the realization of a design of experiments to characterize the voltage sensitivity to pressure ([1; 1.5 bar]) and temperature ([120; 180 °C]) between 0.2 and 1 A/cm2 of an Advent PBI MEA (formerly BASF Celtec®-P 1100 W). The data obtained allowed identifying an empirical model that takes into account the aging caused by the experiment. Finally, the methodology is criticized before proposing an alternative method.

Utilizing coke oven gases as a fuel for a cogeneration system based on high temperature proton exchange membrane fuel cell; energy, exergy and economic assessment

Based on a high temperature proton exchange membrane fuel cell (HT-PEMFC), a cogeneration system is proposed to produce heat and power. The system includes a coke oven gas steam reformer, a water gas shift reactor, and an afterburner. The system is analyzed in detail considering the energy, exergy and economic viewpoints. The analyses reveal the importance of HT-PEMFC in the system and according to the results, 9.03 kW power is generated with energy and exergy efficiencies of 88.2% and 26.2%, respectively and the total product unit cost is calculated as 91.8 $/GJ. Through a parametric study the effects on system performance are studied of such variables as the current density, fuel cell and reformer operating temperatures, and cathode stoichiometric ratio. It is found that an increase in the fuel cell temperature and/or a decrease in the reformer temperature enhance the exergy efficiency. The exergy efficiency is also maximized at the cathode stoichiometric ratio of 2.4. By performing a two-objective optimization using genetic algorithm, the best operating point is determined at which the exergy efficiency is (32.86%) and the total product unit cost is (78.68 $/GJ).

Tröger's base polymer blended with poly(ether ketone cardo) for high temperature proton exchange membrane fuel cell applications

Developing membrane electrolyte materials with high performance and low cost is a key factor in promoting the application and commercialization of the high temperature proton exchange membrane fuel cell (HT-PEMFC). In this work, a Tröger's base (TB) polymer is synthesized from commercially available and low-cost 4,4′-diamine-3,3′-dimethyl-biphenyl (DMBP) and dimethoxy methane in trifluoroacetic acid via a one-pot TB polymerization reaction under mild conditions. The obtained polymer is composited by TB unit and DMBP moiety (named as DMBP-TB), which occupies a good organic solubility, high thermal stability and excellent chemical resistance. Due to the built-in bicyclic amine rings and intrinsic microporous structure, the pure DMBP-TB membrane exhibits a remarkable phosphoric acid (PA) doping content as high as 1077% in 85 wt% PA solution at room temperature. However, the excessive swelling and poor mechanical integrity hinder the PA doped DMBP-TB membrane as the HT-PEM. Thus, the commercial and low-cost engineering thermoplastic of poly(ether ketone cardo) (PEKC) is employed as the enhanced material to prepare DMBP-TB blend membranes. The DMBP-TB/50%PEKC/149%PA membrane displays an anhydrous conductivity of 0.061 S cm−1 at 180 °C and a tensile strength of 8.7 MPa at room temperature, which enables H2–O2 fuel cell with a peak power density of 536 mW cm−2 at 180 °C without backpressure, suggesting the utility for HT-PEMFCs.

Thermodynamic analysis and optimization of a novel hybrid system using thermoacoustic cycle to harvest waste heat of high temperature PEMFC

The high temperature proton exchange membrane fuel cell (HTPEMFC) shows multiple advantages over the traditional PEMFC. To achieve the waste heat effective utilization of the fuel cell, a novel hybrid system mainly including a HTPEMFC and a thermo-acoustic cycle (TAC) is proposed. By considering the major irreversible losses, such as ohmic, concentration and activation losses, regenerative loss, heat transfer loss between the HTPEMFC and the TAC, and heat leak loss from the HTPEMFC to the environment, the expressions for the output power and energy efficiency of the proposed system are obtained. Based on typical conditions, the maximum power density for the proposed system increases by 33.3% compared with a single HTPEMFC system, and the corresponding energy efficiency also improves by 34.5%. The sensitive analysis is represented, and coupling a TAC unite to recover the HTPEMFC waste heat shows significant advantages by comparing with other available HTPEMFC-based hybrid systems. Finally, the proposed system is optimized using ideal point method based on the multi-objective optimization. The optimal power density is 6147.8 W m−2, and the optimal efficiency is 53.9%. This work proves the feasibility of the HTPEMFC-TAC system, and hints the broad prospect of low-grade heat collections through a TAC.

Dispersing Agents Impact Performance of Protonated Phosphonic Acid High-Temperature Polymer Electrolyte Membrane Fuel Cells

The microstructure of ionomers plays a significant role in the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Here, we establish direct correlations between the properties of dispersing agents and the microstructure of a protonated phosphonic acid ionomer. Most importantly, the formation of the porous structure of a protonated phosphonic acid ionomer depends on the pKa of the liquid media. Namely, the acid–base interaction between the charged polymer and dispersing agents determines the porosity in the ionomer thin films. The HT-PEMFC performance increases with the level of porosity of the ionomer, as the pores enable fast reactant gas accessibility. This study concludes the importance of the pKa of ionomers’ dispersing media for the HT-PEMFC performance.

Enhancing proton conductivity on polybenzimidazole (PBI) membrane doped acid

Abstract This study provides various condition for acid doped polybenzimidazole (PBI) membrane which giving the best proton conductivity result with respect to the High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC). A highly phosphonated polymer membrane based on acid-base complex membrane system was introduced where phytic acid (PyA) was chosen as an acid doping instead of phosphoric acid (PA) due to its properties of having high phosphate group content and ability to participate in H bonding interactions with the functionalities in PBI matrix. By introducing this PBI/phytic acid membrane helped to overcome the issues arise from PBI/PA membrane system especially on acid leaching problem. In this study, a simple and cost effective technique on porous PBI membrane fabrication and acid doping condition were employed to search an optimum acid-doping level and to further improve the stability and durability of the membrane.

Surface Modification of Polybenzimidazole (PBI) with Microwave Generated Vacuum Ultraviolet (VUV) Photo-oxidation

Background: Polybenzimidazole (PBI) is used in high temperature proton exchange membrane fuel cells (HT-PEMFCs) and redox flow batteries, where proton transfer occurs with the nitrogen-containing groups in PBI, and in aerospace applications exposed to oxygen and radiation. Objective: The objective is to investigate VUV photo-oxidation of PBI for the first time in order to incorporate polar functional groups on the surface to potentially enhance proton conductivity in HT-PEMFCs. Methods: A low-pressure microwave discharge of Ar generated 104.8 and 106.7 nm vacuum UV (VUV) radiation to treat PBI with VUV photo-oxidation. Analysis was done with X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), water contact angle (WCA) and Thermal Gravimetric Analysis (TGA) to detect changes in chemistry, surface roughness, hydrophilicity, and adhesion, respectively. Results : XPS showed: an increase in the O concentration up to a saturation level of 15 ± 1 at %; a decrease of the C concentration by about the same amount; and little change in the N concentration. With increasing treatment time, there were significant decreases in the concentrations of C-C sp2, C-C sp3 and C=N groups, and increases in the concentration of C=O, O-C=O, O-(C=O)-O, CN, and N-C=O containing moieties. The water contact angle decreased from 83° for pristine PBI down to 43°, making the surface more hydrophilic, primarily due to the oxidation, since AFM detected no significant changes in surface roughness. TGA analysis showed an improvement of water adhesion to the treated surface. Conclusion: Microwave generated VUV photo-oxidation is an effective technique for oxidizing the surface of PBI and increasing hydrophilicity.

The Pt–Co alloying effect on the performance and stability of high temperature PEMFC cathodes

High temperature (HT) PEMFC technology offers a number of advantages over its low temperature counterpart, including high tolerance to fuel impurities, system simplifications and generation of high-quality waste heat. Nevertheless, the operating temperature and the presence of phosphoric acid necessitate the use of high amounts of platinum metal at the electrodes, especially the cathodic one. In this work, we report the facile preparation of a Pt–Co alloy supported on multi-wall carbon nanotubes. Using the rotating disk electrode method in HClO4, the activity of this catalyst towards the oxygen reduction reaction, as well as its tolerance to phosphoric acid is evaluated. A comparison is made with two electrocatalysts with similar characteristics (support, nanoparticle size and spatial distribution), where one is based on Pt and the other is a physical mixture of the aforementioned metals (Pt and Co). The superior behavior of the alloyed electrocatalyst urged its electrochemical characterization in-situ, at the cathode of a HT-PEMFC, where performance and, very importantly, stability are thoroughly evaluated and discussed. A comparison with a commercial state-of-the-art electrocatalyst shows the potential to decrease the metal loading of HT-PEMFC electrodes without compromising performance.