The influence of graphitization on the thermal conductivity of catalyst layers and temperature gradients in proton exchange membrane fuel cells

Abstract

As the proton exchange membrane fuel cell (PEMFC) has improved its performance and power density, the efficiency has remained unchanged. With around half the reaction enthalpy released as heat, thermal gradients grow. To improve the understanding of such gradients, PEMFC component thermal conductivity has been increasingly investigated over the last ten years, and the catalyst layer (CL) is one of the components where thermal conductivity values are still scarce. CLs in PEMFC are where the electrochemical reactions occur and most of the heat is released. The thermal conductivity in this region affects the heat distribution significantly within a PEMFC. Thermal conductivities for a graphitized and a non-graphitized CL were measured for compaction pressures in the range of 3 and 23 bar. The graphitized CL has a thermal conductivity of 0.12 ± 0.05 WK −1 m −1 , whilst the non-graphitized CL conductivity is 0.061 ± 0.006 WK −1 m −1 , both at 10 bar compaction pressure. These results suggest that the graphitization of the catalyst material causes a doubling of the thermal conductivity of the CL. This important finding bridges the very few existing studies. Additionally, a 2D thermal model was constructed to represent the impact of the results on the temperature distribution inside a fuel cell.

Structure, Property, and Performance of Catalyst Layers in Proton Exchange Membrane Fuel Cells

“…Most of them are designed for the GDLs, and only the methods applied for CLs are reviewed in this section. Bock et al [221] measured the effective thermal conductivity of CLs using a custom-built apparatus as shown in Fig. 21a.…”

“…21c. In the GHF method, the test specimen is sandwiched between two flux meters and compressed by two plates with different temperatures, while in the TPS method, a circular double nickel spiral, serving as a heating [221]. Reprinted with permission from Ref.…”

“…Bock et al [ 221 ] measured the effective thermal conductivity of CLs using a custom-built apparatus as shown in Fig. 21 a.…”

“…21 Schematic of various experimental setups for effective thermal conductivity of catalyst layers in different studies. a Bock et al [ 221 ]. Reprinted with permission from Ref.…”

Modeling the Effect of Low Pt loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells: Part I. Model Formulation and Validation

“…In this context, an increasing number of works have been presented in the last years analyzing the properties, performance and durability of CLs. These contributions have provided relevant information on the main effective transport properties of CLs (effective diffusivity, [20][21][22][23][24] permeability, 25 and effective thermal, [26][27][28] electrical [29][30][31] and ionic [32][33][34][35] conductivities), as well as electrochemical properties, such as electrochemical surface area (ECSA) and exchange current density. [36][37][38][39][40][41][42][43][44][45][46][47][48] Nevertheless, further effort is still necessary to deconvolute the coupled phenomena that take place in CLs and optimize this key component.…”