Kjelstrup Signe, Røsjorde Audun
Department of Chemistry, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
J Phys Chem B. 2005 May 12;109(18):9020-33. doi: 10.1021/jp040608k.
We show how to determine the local entropy production rate in the various parts of a polymer electrolyte fuel cell producing liquid water from air and hydrogen. We present and solve five sets of transport equations for the heterogeneous, one-dimensional cell at stationary state, equations that are compatible with the second law of thermodynamics. The simultaneous solution of concentration, temperature, and potential profiles gave information about the local entropy production and the heat and water fluxes out of the system. Results for the entropy production can be used to explain the polarization curve, and we find that diffusion in the backing is less important for the potential than charge transport in the membrane. We demonstrate that all coupling effects as defined in nonequilibrium thermodynamics theory are essential for a correct description of the dissipation of energy and also for the small temperature gradients that were calculated here. The heat flux out of the anode was smaller than the heat flux out of the cathode. The cathode surface temperature increased as the current density increased but was smaller than the anode surface temperature for small current densities. This type of modeling may be important for design of cooling systems for fuel cells. The method is general, however, and can be used to analyze batteries and other fuel cells in a similar manner.
我们展示了如何确定从空气和氢气产生液态水的聚合物电解质燃料电池各个部分的局部熵产生率。我们针对稳态下的非均相一维电池给出并求解了五组输运方程，这些方程符合热力学第二定律。浓度、温度和电势分布的联立解给出了关于局部熵产生以及系统输出的热通量和水通量的信息。熵产生的结果可用于解释极化曲线，并且我们发现对于电势而言，背衬中的扩散不如膜中的电荷输运重要。我们证明，非平衡热力学理论中定义的所有耦合效应对于正确描述能量耗散以及此处计算的小温度梯度都是必不可少的。从阳极输出的热通量小于从阴极输出的热通量。阴极表面温度随着电流密度的增加而升高，但在小电流密度下低于阳极表面温度。这种类型的建模对于燃料电池冷却系统的设计可能很重要。然而，该方法具有通用性，并且可以以类似的方式用于分析电池和其他燃料电池。
