Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising technology for clean and efficient power generation in the twenty-first century. Proton exchange membranes (PEMs) are the ...key components in fuel cell system. The researchers have focused to reach the proton exchange membrane with high proton conductivity, low electronic conductivity, low permeability to fuel, low electroosmotic drag coefficient, good chemical/thermal stability, good mechanical properties and low cost. These are classified into the “iron triangle” of performance, durability, and cost. Current PEMFC technology is based on expensive perflourinated proton-exchange membranes (PEMs) that operate effectively only under fully hydrated conditions. There is considerable application-driven interest in lowering the membrane cost and extending the operating window of PEMs. PEMFC system complexity could be reduced by the development of ‘water-free’ electrolytes that do not require hydration. It also enables the PEMFC to be operated under ‘warm’ conditions (i.e. above 100 °C) thus further improving its efficiency. Capital cost could also be further reduced because at warmer conditions less Pt could be used. This paper presents an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements. A number of possible alternative candidates are reviewed and presented in this paper. Also discussed are some of the new materials, technologies, and research directions being pursued to try to meet the demanding performance and durability needs of the PEM fuel cell industry. The alternative PEMs are classified into three categories: (1) modified Nafion
® composite membranes; (2) functionalized non-fluorinated membranes and composite membranes therein; and (3) acid–base composite membranes. Several commonly used inorganic additives are reviewed in the context of composite membranes. Finally, the general methods of the measuring and evaluating of proton exchange membrane properties have been investigated such as proton conductivity, ion exchange capacity, water uptake, gas permeability, methanol permeability, durability, thermal stability and fuel cell performance test.
In situ and micro‐scale visualization of electrochemical reactions and multiphase transports on the interface of porous transport electrode (PTE) materials and solid polymer electrolyte (SPE) has ...been one of the greatest challenges for electrochemical energy conversion devices, such as proton exchange membrane electrolyzer cells (PEMECs), CO2 reduction electrolyzers, PEM fuel cells, etc. Here, an interface‐visible characterization cell (IV‐CC) is developed to in situ visualize micro‐scaled and rapid electrochemical reactions and transports in PTE/SPE interfaces. Taking the PEMEC of a green hydrogen generator as a study case, the unanticipated local gas blockage, micro water droplets, and their evolution processes are successfully visualized on PTE/PEM interfaces in a practical PEMEC device, indicating the existence of unconventional reactant supply pathways in PEMs. Further comprehensive results reveal that PEM water supplies to reaction interfaces are significantly impacted with current densities. These results provide critical insights about the reaction interface optimization and mass transport enhancement in various electrochemical energy conversion devices.
An interface‐visible characterization cell (IV‐CC) is developed to in situ visualize micro‐scaled and rapid electrochemical reactions and transports in porous transport electrode (PTE)/solid polymer electrolyte (SPE) interfaces. Taking the proton exchange membrane (PEM) water electrolyzer as a study case, the water supply pathways in PEM and the local gas blockage in PTE/SPE interfaces are discovered for the first time.
•A framework combing surrogate modeling and optimization algorithm is proposed.•The framework is used to optimize CL composition for improving maximum power density.•A 3D CFD full cell and CL ...agglomerate model is used for surrogate model development.•The validity of the framework is demonstrated in the paper.•The framework can guide the multi-variables optimization of complex systems.
Catalyst layer (CL) is the core electrochemical reaction region of proton exchange membrane fuel cells (PEMFCs). Its composition directly determines PEMFC output performance. Existing experimental or modeling methods are still insufficient on the deep optimization of CL composition. This work develops a novel artificial intelligence (AI) framework combining a data-driven surrogate model and a stochastic optimization algorithm to achieve multi-variables global optimization for improving the maximum power density of PEMFCs. Simulation results of a three-dimensional computational fluid dynamics (CFD) PEMFC model coupled with the CL agglomerate model constitutes the database, which is then used to train the data-driven surrogate model based on Support Vector Machine (SVM), a typical AI algorithm. Prediction performance shows that the squared correlation coefficient (R-square) and mean percentage error in the test set are 0.9908 and 3.3375%, respectively. The surrogate model has demonstrated comparable accuracy to the physical model, but with much greater computation-resource efficiency: the calculation of one polarization curve will be within one second by the surrogate model, while it may cost hundreds of processor-hours by the physical CFD model. The surrogate model is then fed into a Genetic Algorithm (GA) to obtain the optimal solution of CL composition. For verification, the optimal CL composition is returned to the physical model, and the percentage error between the surrogate model predicted and physical model simulated maximum power densities under the optimal CL composition is only 1.3950%. The results indicate that the proposed framework can guide the multi-variables optimization of complex systems.
Non-noble-metal catalysts based on Fe–N–C moieties have shown promising oxygen reduction reaction (ORR) activity in proton exchange membrane fuel cells (PEMFCs). In this study, we report a facile ...method to prepare a Fe–N–C catalyst based on modified graphene (Fe–N–rGO) from heat treatment of a mixture of Fe salt, graphitic carbon nitride (g-C3N4), and chemically reduced graphene (rGO). The Fe–N–rGO catalyst was found to have pyridinic N-dominant heterocyclic N (40% atomic concentration among all N components) on the surface and have an average Fe coordination of ∼3 N (Fe–N3,average) in bulk. Rotating disk electrode measurements revealed that Fe–N–rGO had high mass activity in acid and exhibited high stability at 0.5 V at 80 °C in acid over 70 h, which was correlated to low H2O2 production shown from rotating ring disk electrode measurements.
Schroeder's paradox discovered by Schroeder in 1905 refers to the phenomenon that polymers have different maximum water uptake in the liquid and saturated vapor phases. For more than a hundred years, ...people have often debated whether this phenomenon conforms to thermodynamics. As proton exchange membrane fuel cell (PEMFC) gradually becomes a promising renewable energy utilization device, its impact on the physical properties of the proton exchange membrane has been studied widely. This paper reviews the theory and experiments on Schroeder's paradox over more than 100 years, especially the exploration of perfluorosulfonic acid membranes and PEMFCs in recent decades. Since membrane water content determines the operational performance of the PEMFC, this paper discusses and analyzes the effect of Schroeder's paradox on the PEMFC performance, including mechanical properties, electrical conductivity, and water transport mechanism. The effect of this phenomenon on the non-equilibrium operation of PEMFC has been highlighted, such as cold start-up, because of the different properties of membranes in contact with liquid water and air. This review gives an introduction to critical aspects of Schroeder's paradox to serve governments and organizations to promote the application of PEMFC in different regions.
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•Schroeder's paradox in proton exchange membrane fuel cells is reviewed.•Mechanisms and experimental methods of Schroeder's paradox are critically analyzed.•Evaluated the effect of Schroeder's paradox on membrane performance.•The existence of Schroeder's paradox lower freezing point is discussed.•Future research directions of Schroeder's paradox are presented.
A honeycomb-like flow channel was proposed and investigated for the performance of proton exchange membrane fuel cells (PEMFCs). The effects of various thicknesses and porosities of the gas diffusion ...layer (GDL) on the honeycomb-like flow channel were studied. Compared with parallel and serpentine flow channels, the honeycomb-like flow channel exhibited the lowest oxygen non-uniformity value of 0.59 at 0.4 V, and the pressure drop was 6.9 times lower than that of the serpentine flow channel. The current density was 8034.9 A/m2, which was 14.0% and 10.4% higher than that of the parallel and serpentine flow channels. For a porosity of 0.4, the decrease in GDL thickness from 0.58 to 0.38 mm for the honeycomb-like flow channel facilitated oxygen diffusion, and the current density increased from 7717.2 to 8034.9 A/m2; the oxygen mass fraction gradually increased at the cathode channel but decreased at the center of the honeycomb-like structure. At a thickness of 0.38 mm, the porosity increased from 0.2 to 0.6, leading to a decrease in the oxygen non-uniformity value from 0.89 to 0.42. For a porosity of 0.6, the current density was 8787 A/m2, which was 60% and 9.4% greater when compared with the porosities of 0.2 and 0.4.
•The novel honeycomb-like flow channel design was proposed.•The performance improvement of PEMFCs with different flow channels was characterized.•The effect of GDL thickness and porosity for the novel flow channel were studied.
Replacing scarce and expensive platinum (Pt) with metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has largely been impeded by the low ...oxygen reduction reaction activity of M–N–C due to low active site density and site utilization. Herein, we overcome these limits by implementing chemical vapour deposition to synthesize Fe–N–C by flowing iron chloride vapour over a Zn–N–C substrate at 750 °C, leading to high-temperature trans-metalation of Zn–N4 sites into Fe–N4 sites. Characterization by multiple techniques shows that all Fe–N4 sites formed via this approach are gas-phase and electrochemically accessible. As a result, the Fe–N–C catalyst has an active site density of 1.92 × 1020 sites per gram with 100% site utilization. This catalyst delivers an unprecedented oxygen reduction reaction activity of 33 mA cm−2 at 0.90 V (iR-corrected; i, current; R, resistance) in a H2–O2 proton exchange membrane fuel cell at 1.0 bar and 80 °C.Replacing platinum with metal–nitrogen–carbon catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has been impeded by low activity. These limitations have now been overcome by the trans-metalation of Zn–N4 sites into Fe–N4 sites.
Poly(vinyl alcohol) (PVA) is a biodegradable, water-soluble membrane that has low methanol permeation and reactive chemical functionalities. Modification of these features makes PVA an attractive ...proton exchange membrane (PEM) alternative to Nafion
TM
. However, the pristine PVA membrane is a poorer proton conductor than the Nafion
TM
membrane due to the absence of negatively charged ions. Hence, modification of PVA matrixes whilst complying with the requirements of projected applications has been examined extensively. Generally, three modification methods of PVA membranes have been highlighted in previous reports, and these are (1) grafting copolymerization, (2) physical and chemical crosslinking, and (3) blending of polymers. The use of each modification method in different applications is reviewed in this study. Although the three modification methods can improve PVA membranes, the mixed method of modification provides another attractive approach. This review covers recent studies on PVA-based PEM in different fuel cell applications, including (1) proton-exchange membrane fuel cells and (2) direct-methanol fuel cells. The challenges involved in the use of PVA-based PEM are also presented, and several approaches are proposed for further study.
•Transient responses of fuel cell under various operation conditions are studied.•Fuel cell after activation can be loaded from 0 to 1.5 A cm−2 within 1 s.•Dehydration in membrane results in large ...discrepancies in dynamic performance.•Load strategies are suggested for fuel cell at start-up with a large step-current.
The capability of proton exchange membrane fuel cell to be loaded successfully in a short time is an important consideration for its evaluation as a reliable power source in different applications. In this study, the transient response of the proton exchange membrane fuel cell under various operation states is analysed. The output power is increased by applying a step current, and the response voltage, as an indicator of the dynamic performance, is recorded. The experimental results show that the fuel cell cannot be successfully loaded at start-up when the current step is increased from 0 A cm−2 to 0.8 A cm−2. It can be loaded successfully with a step current density of 1.5 A cm−2 after activation. The dehydration of the membrane can result in large discrepancies in the dynamic performance. A state-of-the-art proton exchange membrane fuel cell should show favourable response to a high step current when loaded smoothly to a high-power output within a short time. The study can provide guideline for the design and control of the dynamic loading in proton exchange membrane fuel cell.
•Implementation of several ML techniques to investigate performance of degraded FCV.•The Deep Neural Network algorithm has the most accurate prediction among the other.•Dynamic simulation of a fresh ...& degraded FCV considering environmental aspects.•The life cycle assessment for the fresh and degraded fuel cell vehicles.•Using real driving cycle for a better dynamic simulation.
Fuel cell degradation is one of the main challenges of hydrogen fuel cell vehicles, which can be solved by robust prediction techniques like machine learning. In this research, a specific Proton-exchange membrane fuel cell stack is considered, and the experimental data are imported to predict the future behavior of the stack. Besides, four different prediction neural network algorithms are considered, and Deep Neural Network is selected. Furthermore, Simcenter Amesim software is used with the ability of dynamic simulation to calculate real-time fuel consumption, fuel cell degradation, and engine performance. Finally, to better understand how fuel cell degradation affects fuel consumption and life cycle emission, lifecycle assessment as a potential tool is carried out using GREET software. The results show that a degraded Proton-exchange membrane fuel cell stack can result in an increase in fuel consumption by 14.32 % in the New European driving cycle and 13.9 % in the FTP-75 driving cycle. The Life Cycle Assessment analysis results show that fuel cell degradation has a significant effect on fuel consumption and total emission. The results show that a fuel cell with a predicted degradation will emit 26.4 % more CO2 emissions than a Proton-exchange membrane fuel cell without degradation.
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