Net Water Drag Coefficient during High Temperature Operation of Polymer Electrolyte Fuel Cells

Abstract

For polymer electrolyte fuel cell (PEFC) systems in vehicle applications, net water drag coefficient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) is an essential index and must be negative for system operation. The feasibility of PEFC operation at temperatures over 100 °C was examined here by measuring and comparing the current density ( j )— <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> characteristics using PEFCs with either an Aquivion or Nafion membrane. The effect of cell temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">cell</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> was evaluated at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">cell</mml:mi> </mml:mrow> </mml:msub> </mml:math> range from 80 °C to 120 °C. Results clearly demonstrated that, for both membrane types, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> significantly increased with increasing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">cell</mml:mi> </mml:mrow> </mml:msub> <mml:mo>.</mml:mo> </mml:math> Results also confirmed that, at a constant flow rate of H 2 at the anode, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> decreased with decreasing stoichiometric ratio of air ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">air</mml:mi> </mml:mrow> </mml:msub> </mml:math> ), although the effect of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">air</mml:mi> </mml:mrow> </mml:msub> </mml:math> on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> was relatively small. Finally, the effect of relative humidity (RH) balance of supplied gases in both sides (anode/cathode) on water transport at temperature up to 120 °C was examined for the Aquivion cell. Results revealed that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">NWD</mml:mi> </mml:mrow> </mml:msub> </mml:math> could be significantly decreased by decreasing the RH of hydrogen supplied to the anode (RH A ) and that the control of RH A is an effective method for lowering <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">

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