Study on the Dynamic Behaviors of PEMFCs with the Effect of the Interfacial Transfer Process

Abstract

The dynamic response of proton exchange membrane fuel cells (PEMFCs) to power demand remarkably influences the energy management system (EMS) for hybrid hydrogen vehicle applications. This study established a one-dimensional PEMFC model considering the interfacial gas transport behaviors to investigate the most fundamental dynamic process—step loading. The model provided rigorous analytic equations to describe the transient response of output voltage, and a dimensionless variable, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mo>=</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:mi>L</mml:mi> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mi>δ</mml:mi> <mml:mo>/</mml:mo> <mml:msub> <mml:mrow> <mml:mi>τ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mfrac> </mml:mstyle> <mml:mo>=</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mfrac> </mml:mstyle> <mml:mo>,</mml:mo> </mml:math> was found to link the appearance of undershooting quantitatively with the structural characteristics of components and operating processes. The analytic equations showed that the main reason for undershooting was the weaker capacity of remaining oxygen in the catalyst layer (CL) than the diffusion capacity of gas diffusion media (GDM). Deductions from analytic equations were confirmed by experimental results further and indicated that the degree of undershooting ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) was linear to the loading step ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>I</mml:mi> </mml:mrow> <mml:mo stretchy="true">˜</mml:mo> </mml:mover> </mml:math> ), which expressed as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>O</mml:mi> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:mi>b</mml:mi> <mml:mo>⋅</mml:mo> <mml:mi>ε</mml:mi> <mml:mrow> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> <mml:mi>F</mml:mi> <mml:mi>D</mml:mi> <mml:mi>c</mml:mi> <mml:mo>/</mml:mo> <mml:mi>L</mml:mi> <mml:mo>−</mml:mo> <mml:msub> <mml:mrow> <mml:mi>I</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:mfrac> </mml:mstyle> <mml:mo>⋅</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>I</mml:mi> </mml:math> to some extent. The quantitative expressions based on the fundamental theories were achieved in this study and provide new perspectives and methods on the studies of dynamic controlling of the PEMFCs power system.

Topics & Concepts