“…Journal of The Electrochemical Society, 163 (13) F1317-F1329 (2016) of ice formation in the CL; 37 and to evaluate the effects of cell number, start-up current/voltage, external heating, and variable heat/load control 38 on cold-start performance. [39][40][41] The influence of operating parameters on fuel cell performance was shown through in situ total displacement and degree of deformation of the polymer membrane.…”
The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (−10 • C vs. −20 • C vs. −30 • C) and increasing current density (0.02 A cm −2 vs. 0.04 A cm −2 ). Ice formation monitored using in-situ highresolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈−20 • C) and high current densities (0.04 A cm −2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈−10 • C) and lower current densities (0.02 A cm −2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (−20 • C and −30 • C).
“…Journal of The Electrochemical Society, 163 (13) F1317-F1329 (2016) of ice formation in the CL; 37 and to evaluate the effects of cell number, start-up current/voltage, external heating, and variable heat/load control 38 on cold-start performance. [39][40][41] The influence of operating parameters on fuel cell performance was shown through in situ total displacement and degree of deformation of the polymer membrane.…”
The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (−10 • C vs. −20 • C vs. −30 • C) and increasing current density (0.02 A cm −2 vs. 0.04 A cm −2 ). Ice formation monitored using in-situ highresolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈−20 • C) and high current densities (0.04 A cm −2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈−10 • C) and lower current densities (0.02 A cm −2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (−20 • C and −30 • C).
“…With the assumption that excess liquid water is well and finely dispersed in electrode, the water content across the membrane was assumed at a constant level [73,74]. In these one-dimensional models [38,[72][73][74][75][76][77][78][79][80][81], the basic formulations are based on the assumption of continuity. These formulations have been widely used in many of the subsequent numerical studies.…”
“…Multi-dimensional and multiphase models are needed to study the basic theory. To study the cold start processes and performance optimization for PEMFC stacks, Zhou et al [78] developed a one dimensional model, in which the effects of cell number, start-up current/voltage, external heating and variable heating and load control (VHLC) were systematically investigated. Figure 5 shows the effect of stack cell numbers on the time durations and final volume averaged stack temperatures for the failed unassisted cold start processes from −20 °C at 0.1 A cm −2 .…”
“…It can be clearly seen that the startup process can last longer and the final temperature reached is higher with more cells in a cell stack. [78]. Reprinted/Reproduced with permission from [78].…”
“…The results indicated that it's better to increase the ionomer fraction in the cathode CL than to increase the size of the membrane in order to reduce ice formation. This model can also be used to evaluate the cold start performance with different design and operating parameters [78,79]. This numerical model was showed in Table 3 with these conservation equations.…”
Successful and rapid startup of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (also called cold start) is of great importance for their commercialization in automotive and portable devices. In order to maintain good proton conductivity, the water content in the membrane must be kept at a certain level to ensure that the membrane remains fully hydrated. However, the water in the pores of the catalyst layer (CL), gas diffusion layer (GDL) and the membrane may freeze once the cell temperature decreases below the freezing point (T f ). Thus, methods which could enable the fuel cell startup without or with slight performance degradation at subfreezing temperature need to be studied. This paper presents an extensive review on cold start of PEMFCs, including the state and phase changes of water in PEMFCs, impacts of water freezing on PEMFCs, numerical and experimental studies on PEMFCs, and cold start strategies. The impacts on each component of the fuel cell are discussed in detail. Related numerical and experimental work is also discussed. It should be mentioned that the cold start strategies, especially the enumerated patents, are of great reference value on the practical cold start process.
OPEN ACCESSEnergies 2014, 7 3180
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.