High-performance imidazole-containing polymers for applications in high temperature polymer electrolyte membrane fuel cells

This work focuses on the development of high temperature polymer electrolyte membranes(HT-PEMs)as key materials for HT-PEM fuel cells(HT-PEMFCs).Recognizing the challenges associated with the phosphoric acid(PA) doped polybenzimidazole(PBI) membranes,including the use of carcinogenic monomers and complex synthesis procedures,this study aims to develop more cost-effective,readily synthesized,and high-performance alternatives.A series of superacid-catalyzed polyhydroxyalkylation reactions have been carefully designed between p-terphenyl and aldehydes bearing imidazole moieties,resulting in a new class of HT-PEMs.It is found that the chemical structure of aldehyde-substituted N-heterocycles significantly impacts the polymerization reaction.Specifically,the use of 1-methyl-2-imidazole-formaldehyde and 1 H-imidazole-4-formaldehyde monomers leads to the formation of high-viscosity,rigid,and ether-free polymers,denoted as PTIm-a and PTIm-b.Membranes fabricated from these polymers,due to their pendent imidazole groups,exhibit an exceptional capacity for PA absorption.Notably,PTIm-a,carrying methylimidazole moieties,demonstrates a superior chemical stability by maintaining morphology and structural stability during 350 h of Fenton testing.After being immersed in 75 wt% PA at 40℃,the PTIm-a membrane reaches a PA content of 152%,maintains a good tensile strength of 13.6 MPa,and exhibits a moderate conductivity of 50.2 mS cm^(-1) at 180℃.Under H_(2)/O_(2) operational conditions,a single cell based on the PTIm-a membrane attains a peak power density of 732 mW cm^(-2) at 180℃ without backpressure.Furthermore,the membrane demonstrates stable cycle stability over 173 h within 18 days at a current density of 200 mA cm^(-2),indicating its potential for practical application in HT-PEMFCs.This work highlights innovative strategies for the synthesis of advanced HT-PEMs,offering significant improvements in membrane properties and fuel cell performance,thus expanding the horizons of HT-PEMFC technology.

High-performance and robust high-temperature polymer electrolyte membranes with moderate microphase separation by implementation of terphenyl-based polymers

Acid loss and plasticization of phosphoric acid(PA)-doped high-temperature polymer electrolyte membranes(HT-PEMs)are critical limitations to their practical application in fuel cells.To overcome these barriers,poly(terphenyl piperidinium)s constructed from the m-and p-isomers of terphenyl were synthesized to regulate the microstructure of the membrane.Highly rigid p-terphenyl units prompt the formation of moderate PA aggregates,where the ion-pair interaction between piperidinium and biphosphate is reinforced,leading to a reduction in the plasticizing effect.As a result,there are trade-offs between the proton conductivity,mechanical strength,and PA retention of the membranes with varied m/p-isomer ratios.The designed PA-doped PTP-20m membrane exhibits superior ionic conductivity,good mechanical strength,and excellent PA retention over a wide range of temperature(80–160°C)as well as satisfactory resistance to harsh accelerated aging tests.As a result,the membrane presents a desirable combination of performance(1.462 W cm^(-2) under the H_(2)/O_(2)condition,which is 1.5 times higher than that of PBI-based membrane)and durability(300 h at 160°C and 0.2 A cm^(-2))in the fuel cell.The results of this study provide new insights that will guide molecular design from the perspective of microstructure to improve the performance and robustness of HT-PEMs.

Multi-objective optimization of the cathode catalyst layer micro-composition of polymer electrolyte membrane fuel cells using a multi-scale,two-phase fuel cell model and data-driven surrogates

Polymer electrolyte membrane fuel cells(PEMFCs)are considered a promising alternative to internal combustion engines in the automotive sector.Their commercialization is mainly hindered due to the cost and effectiveness of using platinum(Pt)in them.The cathode catalyst layer(CL)is considered a core component in PEMFCs,and its composition often considerably affects the cell performance(V_(cell))also PEMFC fabrication and production(C_(stack))costs.In this study,a data-driven multi-objective optimization analysis is conducted to effectively evaluate the effects of various cathode CL compositions on Vcelland Cstack.Four essential cathode CL parameters,i.e.,platinum loading(L_(Pt)),weight ratio of ionomer to carbon(wt_(I/C)),weight ratio of Pt to carbon(wt_(Pt/c)),and porosity of cathode CL(ε_(cCL)),are considered as the design variables.The simulation results of a three-dimensional,multi-scale,two-phase comprehensive PEMFC model are used to train and test two famous surrogates:multi-layer perceptron(MLP)and response surface analysis(RSA).Their accuracies are verified using root mean square error and adjusted R^(2).MLP which outperforms RSA in terms of prediction capability is then linked to a multi-objective non-dominated sorting genetic algorithmⅡ.Compared to a typical PEMFC stack,the results of the optimal study show that the single-cell voltage,Vcellis improved by 28 m V for the same stack price and the stack cost evaluated through the U.S department of energy cost model is reduced by$5.86/k W for the same stack performance.

Polymer Electrolyte Membrane Fuel Cells (PEMFC) in Automotive Applications: Environmental Relevance of the Manufacturing Stage

This study presents a state of the art of several studies dealing with the environmental impact assessment of fuel cell (FC) vehicles and the comparison with their conventional fossil-fuelled counterparts, by means of the Life Cycle As-sessment (LCA) methodology. Results declare that, depending on the systems characteristics, there are numerous envi-ronmental advantages, but also some disadvantages can be expected. In addition, the significance of the manufac-turing process of the FC, more specifically the Polymer Electrolyte Membrane Fuel Cell (PEMFC) type, in terms of environmental impact is presented. Finally, CIEMAT’s role in HYCHAIN European project, consisting of supporting early adopters for hydrogen FCs in the transport sector, is

Effects of Freeze/Thaw Cycles and Gas Purging Method on Polymer Electrolyte Membrane Fuel Cells

At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.

Recent developments in electrocatalysts and future prospects for oxygen reduction reaction in polymer electrolyte membrane fuel cells

The main difficulty in the extensive commercial use of polymer electrolyte membrane fuel cells （PEMFCs） is the use of noble metals such as Pt-based electrocatalyst at the cathode, which is essential to ease the oxygen reduction reaction （ORR） in fuel cells （FCs）. To eliminate the high loading of Pt-based electrocatalysts to minimize the cost, extensive study has been carried out over the previous decades on the non-noble metal catalysts. Development in enhancing the ORR performance of FCs is mainly due to the doped carbon materials, Fe and Co-based electrocatalysts, these materials could be considered as probable substitutes for Pt-based catalysts. But the stability of these non-noble metal electrocatalysts is low and the durability of these metals remains unclear. The three basic reasons of instability are： （i） oxidative occurrence by H2O2, （ii） leakage of the metal site and （iii） protonation by probable anion adsorption of the active site. Whereas leakage of the metal site has been almost solved, more work is required to understand and avoid losses from oxidative attack and protonation. The ORR performance such as stability tests are usually run at low current densities and the lifetime is much shorter than desired need. Therefore, improvement in the ORR activity and stability afe the key issues of the non-noble metal electrocatalyst. Based on the consequences obtained in this area, numerous future research directions are projected and discussed in this paper. Hence, this review is focused on improvement of stability and durability of the non-noble metal electrocatalyst.

High temperature polymer electrolyte membrane fuel cell

One of the majorissuesli mitingtheintroduction of polymer electrolyte membranefuel cells(PEMFCs) is thelowtemperature ofoperation which makes platinum-based anode catalysts susceptible to poisoning by the trace amount of CO,inevitably present in reformedfuel.In order to alleviate the problemof COpoisoning andi mprove the power density of the cell,operating at temperature above 100 ℃ispreferred.Nafion-type perfluorosulfonated polymers have been typically used for PEMFC.However,the conductivity of Nafion-typepolymers is not high enoughto be usedfor fuel cell operations at higher temperature(>90 ℃) and atmospheric pressure because they dehy-drate under these condition.An additional problem which faces the introduction of PEMFCtechnology is that of supplying or storing hydrogen for cell operation,especially for vehicular applications.Consequently the use of alternative fuels such as methanol and ethanol is of interest,especially if thiscan be used directlyinthe fuel cell,without reformationto hydrogen.Ali mitation of the direct use of alcohol is thelower activity of oxida-tionin comparison to hydrogen,which means that power densities are considerably lower.Hence to i mprove activity and power outputhigher temperatures of operation are preferable.To achieve this goal,requires a newpolymer electrolyte membrane which exhibits stabilityand high conductivityin the absence of liquid water.Experi mental data on a polybenzi midazole based PEMFC were presented.Asi mple steady-stateisothermal model of the fuel cell is alsoused to aidin fuel cell performance opti misation.The governing equations involve the coupling of kinetic,ohmic and mass transport.Thispaper also considers the advances madeinthe performance of direct methanol and solid polymer electrolyte fuel cells and considers theirli mi-tations in relation to the source and type of fuels to be used.

Study on durability of Pt supported on graphitized carbon under simulated start-up/shut-down conditions for polymer electrolyte membrane fuel cells

The primary issue for the commercialization of proton exchange membrane fuel cell（PEMFC） is the carbon corrosion of support under start-up/shut-down conditions. In this study, we employ the nanostructured graphitized carbon induced by heat-treatment. The degree of graphitization starts to increase between 900 and 1300 ℃ as evidenced by the change of specific surface area, interlayer spacing, and ID/IG value. Pt nanoparticles are deposited on fresh carbon black（Pt/CB） and carbon heat-treated at 1700 ℃（Pt/HCB17） with similar particle size and distribution. Electrochemical characterization demonstrates that the Pt/HCB17 shows higher activity than the Pt/CB due to the inefficient microporous structure of amorphous carbon for the oxygen reduction reaction. An accelerating potential cycle between 1.0 and 1.5 V for the carbon corrosion is applied to examine durability at a single cell under the practical start-up/shutdown conditions. The Pt/HCB17 catalyst shows remarkable durability after 3000 potential cycles. The Pt/HCB17 catalyst exhibits a peak power density gain of 3%, while the Pt/CB catalyst shows 65% loss of the initial peak power density. As well, electrochemical surface area and mass activity of Pt/HCB17 catalyst are even more stable than those of the Pt/CB catalyst. Consequently, the high degree of graphitization is essential for the durability of fuel cells in practical start-up/shut-down conditions due to enhancing the strong interaction of Pt and π-bonds in graphitized carbon.

Effects of Freeze/Thaw Cycles and Gas Purging Method on Polymer Electrolyte Membrane Fuel Cells

At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell PEMFC deteriorates markedly. The object of this work is to study the degradation mechanism of key compo- nents of PEMFC—membrane-electrode assembly MEA and seek feasible measures to avoid degradation. The ef- fect of freezethaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freezethaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable per- formance under subzero temperature and gas purging is proved to be the effective operation.

Water-induced electrode poisoning and the mitigation strategy for high temperature polymer electrolyte membrane fuel cells

Engineering failure of membrane electrode assembly caused by increasingly fuel poisoning in the high temperature polymer electrolyte membrane fuel cells fed with humidified reformate gases is firstly demonstrated herein this work. Based on the results of the in-situ environmental scanning electron microscope, electrochemical analyses, and limiting current method, a water-induced phosphoric acid invasion model is constructed in the porous electrode to elucidate the failure causations of the hindered hydrogen mass transport and the enhanced carbon monoxide poisoning. To optimize the phosphoric acid distribution under the inevitably humidified circumstance, a facile and effective strategy of constructing acid-proofed electrode is proposed and demonstrates outstanding stability with highly humidified reformate gases as anode fuel. This work discusses a potential defect that was rarely studied previously under practical working circumstance for high temperature polymer electrolyte membrane fuel cells, providing an alternative opinion of electrode design based on the fundamental aspects towards the engineering problems.

A comprehensive review of the modeling of transport phenomenon in the flow channels of polymer electrolyte membrane fuel cells

Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optimum level for proton conductivity.Water management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and degradation.This process requires the study and understanding of internal two-phase flows.Different experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel cells.However,the experiments have limitations in in situ measurements;they are also expensive and time exhaustive.In contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel cells.This paper introduces the recent design of flow channels.It reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop models.Furthermore,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected aspects.Finally,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.

Numerical Analysis of Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell when Operated in Elevated Temperature Range

Abstract： The purpose of this study is to analyze the temperature distribution on the interface between the polymer electrolyte membrane and catalyst layer at the cathode in single cell of polymer electrolyte fuel cell when operated in elevated temperature range than usual. In this study, the interface between the polymer electrolyte membrane and catalyst layer at the cathode is named as reaction surface. This study has considered the 1D multi-plate heat transfer model estimating the temperature distribution on the reaction surface and verified with the 3D numerical simulation model solving many governing equations on the coupling phenomena of the polymer electrolyte fuel cell. The 3D numerical simulation model coverers a half size of actual cell including three straight parts and two turn-back corners, which can display the essential phenomena of single cell. The results from both models/simulations agreed well. The effects of initial operation temperature, flow rate, and relative humidity of supply gas on temperature distribution on the reaction surface have been investigated. Though the effect of flow rate of supply gas on temperature distribution on reaction surface has been small, low relative humidity of supply gas has caused higher temperature on the reaction surface compared to high relative humidity of the supply gas. The temperature rise of reaction surface from initial operation temperature has increased with the increasing in initial operation temperature of cell.

Novel phosphonated polymer without anhydride formation for proton exchange membrane fuel cells

Proton exchange membrane fuel cells(PEMFCs)are regarded as one of the most promising clean energy technology because of their high energy density,silent emission-free operation,and wide applications[1].Recently,anion exchange membrane fuel cells(AEMFCs)has emerged as an alternative to PEMFCs.

Impact of Separator Thickness on Temperature Distribution in Single Polymer Electrolyte Fuel Cell Based on 1D Heat Transfer

It is known from the New Energy and Industry Technology Development Organization (NEDO) roam map Japan, 2017 that the polymer electrolyte fuel cell (PEFC) power generation system is required to operate at 100°C for application of mobility usage from 2020 to 2025. This study aims to clarify the effect of separator thickness on the distribution of the temperature of reaction surface (Treact) at the initial temperature of cell (Tini) with flow rate, relative humidity (RH) of supply gases as well as RH of air surrounding cell of PEFC. The distribution of Treact is estimated by means of the heat transfer model considering the H2O vapor transfer proposed by the authors. The relationship between the standard deviation of Treact-Tini and total voltage obtained in the experiment is also investigated. We can know the effect of the flow rate of supply gas as well as RH of air surrounding cell of PEFC on the distribution of Treact-Tini is not significant. It is observed the wider distribution of Treact-Tini provides the reduction in power generation performance irrespective of separator thickness. In the case of separator thickness of 1.0 mm, the standard deviation of Treact-Tini has smaller distribution range and the total voltage shows a larger variation compared to the other cases.

Atomic layer deposition of ultrathin layered TiO_2 on Pt/C cathode catalyst for extended durability in polymer electrolyte fuel cells

This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells（PEFCs）. Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 2000 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.

CFD Analysis of Spiral Flow Fields in Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells(PEMFCs)are largely used in various applications because of their pollution-free products and high energy conversion efficiency.In order to improve the related design,in the present work a new spiral flow field with a bypass is proposed.The reaction gas enters the flow field in the central path and diffuses in two directions through the flow channel and the bypass.The bypasses are arranged incrementally.The number of bypasses and the cross-section size of the bypasses are varied parametrically while a single-cell model of the PEMFC is used.The influence of the concentration of liquid water and oxygen in the cell on the performance of different flow fields is determined by means of Computational fluid dynamics(COMSOL Multiphysics software).Results show that when the bypass number is 48 and its cross-sectional area is 0.5 mm^(2),the cell exhibits the best performances.

Temperature Distributions in Single Cell of Polymer Electrolyte Fuel Cell Simulated by an 1D Multi-plate Heat-Transfer Model and a 3D Numerical Simulation Model

The purpose of this study is to verify an 1D multi-plate heat-transfer model estimating the temperature distribution on the interface between polymer electrolyte membrane and catalyst layer at cathode in single cell of polymer electrolyte fuel cell, which is named as reaction surface in this study, with a 3D numerical simulation model solving many governing equations on the coupling phenomena in the cell. The results from both models/simulations agreed well. The effects of initial operation temperature, flow rate, and relative humidity of supply gas on temperature distribution on the reaction surface were also investigated. It was found in both 1D and 3D simulations that, the temperature rise （i.e., Treact-Tini） of the reaction surface from initial operation temperature at 70℃ was higher than that at 80℃ irrespective of flow rate of supply gas. The effect of relative humidity of supply gas on Treact- Tini near the inlet of the cell was small. Compared to the previous studies conducted under the similar operation conditions, the Treact - Tini calculated by 1D multi-plate heat-transfer model in this study as well as numerical simulation using 3D model was reasonable.

Particle Swarm Optimization based predictive control of Proton Exchange Membrane Fuel Cell (PEMFC)

Proton Exchange Membrane Fuel Cells (PEMFCs) are the main focus of their current development as power sources because they are capable of higher power density and faster start-up than other fuel cells. The humidification system and output performance of PEMFC stack are briefly analyzed. Predictive control of PEMFC based on Support Vector Regression Machine (SVRM) is presented and the SVRM is constructed. The processing plant is modelled on SVRM and the predictive control law is obtained by using Particle Swarm Optimization (PSO). The simulation and the results showed that the SVRM and the PSO re-ceding optimization applied to the PEMFC predictive control yielded good performance.

Phosphorus induced activity-enhancement of Fe-N-C catalysts for high temperature polymer electrolyte membrane fuel cells

Fe-N-C materials with atomically dispersed Fe–N_(4) sites could tolerate the poisoning of phosphate,is regarded as the most promising alternative to costly Pt-based catalysts for the oxygen reduction in high temperature polymer electrolyte membrane fuel cells(HT-PEMFCs).However,they still face the critical issue of insufficient activity in phosphoric acid.Herein,we demonstrate a P-doping strategy to increase the activity of Fe-N-C catalyst via a feasible one-pot method.X-ray absorption spectroscopy and electron microscopy with atomic resolution indicated that the P atom is bonded with the N in Fe–N_(4) site through C atoms.The as prepared Fe-NCP catalyst shows a half-wave potential of 0.75 V(vs.reversible hydrogen electrode(RHE),0.1 M H_(3)PO_(4)),which is 60 and 40 mV higher than that of Fe-NC and commercial Pt/C catalysts,respectively.More importantly,the Fe-NCP catalyst could deliver a peak power density of 357 mW·cm^(−2)in a high temperature fuel cell(160℃),exceeding the non-noble-metal catalysts ever reported.The enhancement of activity is attributed to the increasing charge density and poisoning tolerance of Fe–N_(4) caused by neighboring P.This work not only promotes the practical application of Fe-N-C materials in HT-PEMFCs,but also provides a feasible P-doping method for regulating the structure of single atom site.

Water spatial distribution in polymer electrolyte membrane fuel cell: Convolutional neural network analysis of neutron radiography

Polymer electrolyte membrane(PEM)fuel cells produce water as byproduct,which may cause electrode“flooding”and reduce cell performance.In operation,water usually builds up downstream in the gas flow channel due to the water production by the oxygen reduction reaction(ORR),leading to a water spatial dis-tribution.In this study,a convolutional neural network(CNN)is presented to analyze neutron radiography images to obtain water spatial variation under various operating conditions.5 and 10 segments of a fuel cell are analyzed for spatial variations.Image pre-processing treatments are carried out to improve the convolutional neural network accuracy to 96.6%.The results show that liquid water emerges at a position around 55%downstream for 50%relative humidity while the entire cell is subject to two-phase flow for 100%relative hu-midity under a co-flow configuration.Large water content is present in most of the segments and the near-outlet segment for the counter-flow and co-flow configurations,respectively.In addition,the quad-serpentine cell exhibits more water accumulation than the single serpentine one in most downstream segments.The convolu-tional neural network results agree well with the data obtained from a pixelation image processing method with an accuracy of 91.8%.Compared with conventional pixelation methods,the convolutional neural network method performs better in speed for high-resolution images.It also shows that the current CNN tool fails to predict local water for small spatial scales,such as 10 segments,which leads to a large error(>27%)in prediction.