Engineering model of a passive planar air breathing fuel cell cathode

Abstract

The behavior of an air breathing fuel cell (ABFC) operated on dry-hydrogen in dead-ended mode is studied using theoretical analysis. A one-dimensional, non-isothermal, combined heat and mass transport model is developed that captures the coupling between water generation, oxygen consumption, self-heating and natural convection at the air breathing cathode. The model is validated against planar ABFC experimental measurements over a range of ambient temperatures. The model confirms the strong effect of self-heating on the water balance within passive ABFCs. Model analysis provides several conclusions: (1) thermal runaway caused by inadequate heat rejection predominantly limits ABFC performance. (2) The natural convection boundary layer represents a significant barrier to cathode mass and heat transfer. (3) Because the mass and heat transport numbers associated with natural convection are small, even slight forced convection dramatically affects cell behavior. (4) Performance optimization requires maximizing heat rejection while minimizing flooding. Decoupling the latter two phenomena is challenging due to the exponential relationship between water vapor saturation and temperature.

The Hydro-electro-thermal Performance of Air-cooled, Open-cathode Polymer Electrolyte Fuel Cells: Combined Localised Current Density, Temperature and Water Mapping

“…This hydration / dehydration process has been experimentally reported for self-breathing, open-cathode fuel cells [46], and modelled [89]; but only now can the role of water be confirmed.…”

“…To acquire the 'map' data, a series of four air flow rates, 2.7, 3.9, 4.7 and 5.6 × 10 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 13 amount of water generated increases with increasing load, as described by Faraday's Law; while the low temperature (<40 °C) is in favour of water condensation [89]. A maximum hydration is reached between 35 and 45 °C, for a current density between 0.35 and 0.67 A cm -2 for low and high air flow rate, respectively.…”

A rollable ultra-light polymer electrolyte membrane fuel cell

“…These values are because the supply of air in the active RUFC is abundant because of forced convection, resulting in enhanced H 2 and O 2 diffusion into each GDL, which cannot be expected for the natural convection in the air-breathing RUFC, as observed previously. 34,35 Durability against repeated bending is one of the crucial factors in all flexible electronics. Therefore, we performed repeated bending tests to examine their fatigue durability.…”

“…22,23 The lower R ct of the active RUFC accounts for the better air supply by forced convection in the active RUFC than the natural convection of air in the air-breathing RUFC. 34,35 In addition, the lower RH in the air-breathing RUFC by directly exposing the GDL to ambient air could be another cause of the higher R ohm and R ct values. When comparing the values of R ohm and R ct before and after the bending test, the R ohm and R ct values of both RUFCs were found to change by only a small amount, in accordance with the performance changes discussed above (Figure 2e and f).…”

Fundamentals of Electrochemistry with Application to Direct Alcohol Fuel Cell Modeling

“…Passive fuel cells rely on natural mechanisms, such as capillary forces, diffusion, convection, and evaporation, to achieve cell feeding without extra power consumption. Among the passive systems used, one finds air-breathing systems for the anode electrode [12], pressurized cannisters [13], and capillary liquid systems [14]. There are also passive cells running on different fuels, such as hydrogen [12,15,16], methanol [17], and ethanol [18].…”