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ABSTRACT
The gas flow channels inside unitized regenerative fuel cells display obvious effects on relevant parameter changing behaviors such as species concentration, electrical signal and thermal signal during mode switching. In previous study, detailed transportation behaviors inside a cell constructed with streamlined channels have not been investigated. In our present study, a two-dimensional, transient model coupling non-isothermal characteristics is employed to study the changing characteristics of the cell with typical streamlined channel and comparatively analyze the channel structure impacts on the working states inside the operating cell regions. The simulated results indicate that when turning the mode from electrolyzer to fuel cells, the changing response occupied time of each parameter is required more, compared with the stabilizing procedure after entering the electrolytic cell procedure. For different oxygen-side channels, when reducing the channel depth, the current density output is raised, and the needed time-span for the stabilizing the working state is reduced. The present simulation results facilitate better understanding mass transportation behaviors inside unitized regenerative fuel cells when the mode switches from an electrolytic cell to fuel cell.
Nomenclatures
| = | specific heat capacity, J kg−1 k−1 | |
| = | molar concentration, mol m−3 | |
| = | diffusion coefficient, m2 s−1 | |
| Eeq | = | equilibrium potential, V |
| F | = | Faraday constant, C mol−1 |
| H | = | latent heat, J kg−1 |
| I | = | local current density, A m−3 |
| i | = | current density, A m−2 |
| k | = | thermal conductivity, W m−1 K−1 |
| kc | = | condensation coefficient |
| ke | = | evaporation coefficient |
| N | = | surface tension, N m−1 |
| n | = | number of electrons in the reaction |
| p | = | pressure, Pa |
| R | = | gas constant, J mol−1 K−1 |
| = | potential source term, A m−3 | |
| Si | = | species source term, mol m−3 s−1 |
| Sl | = | phase change source term, kg m−3 s−1 |
| Sm | = | mass source term, kg m−3 s−1 |
| ST | = | temperature source term, W m−3 |
| s | = | saturation |
| T | = | temperature, K |
| u | = | velocity vector, m s−1 |
| x | = | molar fraction |
| Greek letters | = | |
| = | potential, V | |
| = | conductivity, S m−1 | |
| = | contact angle,° | |
| = | transfer coefficient | |
| = | over potential, V | |
| = | porosity | |
| = | electrolyte volume fraction | |
| = | density, kg m−3 | |
| = | viscosity, Pa s | |
| = | permeability, m2 | |
| Subscripts and superscripts | = | |
| 0 | = | natural or standard state |
| g | = | gas phase |
| H | = | hydrogen side |
| i | = | gas species |
| m | = | membrane phase |
| O | = | oxygen side |
| r | = | relative |
| ref | = | reference |
| rp | = | round-trip |
| s | = | solid phase |
| sat | = | saturation |
| w | = | vapor water |
| l | = | liquid water |
| eff | = | effective |
| Abbreviate | = | |
| CL | = | catalyst layer |
| EC | = | electrolytic cell |
| FC | = | fuel cell |
| GDL | = | gas diffusion layer |
| PEM | = | proton exchange membrane |
| OCL | = | oxygen-side catalyst layer |
| HCL | = | hydrogen-side catalyst layer |
| OGDL | = | oxygen-side gas diffusion layer |
| HGDL | = | hydrogen-side gas diffusion layer |
| OGC | = | oxygen-side gas channel |
| HGC | = | hydrogen-side gas channel |
Acknowledgements
The present work is financially supported by National Natural Science Foundation of China (Grant No. 51976004) and to Ms. Yi Tong LI for typesetting.
Disclosure statement
No potential conflict of interest was reported by the author(s).