Influence of Three-Dimensional Flow Field Structures Consisting of Expanded Metal Meshes on the Physicochemical Loss Processes in Pemfcs

Abstract

To further increase the performance of polymer electrolyte membrane fuel cells (PEMFCs) at high current densities, a reduction of mass transport losses by an enhanced evacuation of water from the cell and an improved supply of gases to the reactive sites are necessary.The application of three-dimensional flow field structures in PEMFCs is a promising measure to promote the evacuation of excess liquid water from the cell while boosting the transport of reactants from the gas channel in the direction of the cell. Expanded metal meshes offer a three-dimensional geometry, which predestines them to be used as flow field structures in PEMFCs. In the past, their application as flow fields has primarily been investigated for direct methanol fuel cells (DMFCs) [1, 2, 3] and electrolyzers [4, 5]. To gain a profound understanding of the impact of such three-dimensional flow field structures on the electrochemical properties of PEMFCs, the physicochemical loss processes of the cell have to be analyzed in detail.In this contribution, the results of an in-depth analysis of the influence of three-dimensional flow field structures consisting of expanded metal meshes on the physicochemical loss processes in PEMFCs and their effect on the cell performance is presented. To assess the impact of expanded metal meshes in comparison to a conventional channel rib flow field design, the physicochemical loss processes were examined for both flow field designs. The operating conditions (j, RH, T, pO2) of the incremental PEM fuel cells (1 cm2 active cell area) [6] were varied systematically and the cells were analyzed by means of polarization curves and electrochemical impedance spectroscopy (EIS). The physicochemical loss processes of the cells were identified by a subsequent impedance data analysis by the distribution of relaxation times (DRT) [7, 8].This investigation aims to determine the physicochemical loss process in PEMFCs with expanded metal meshes as flow field structures and compare them to the results of a conventional flow field design. Based on the physical interpretation of the results, consequences and conclusions for the further development of the expanded metal flow field geometries are discussed.