Research On Modeling Of Ionomer-free Pt Catalyst Layer For PEM Fuel Cell

The high cost of fuel cell is one of the challenges that prevent the large-scale commercialization of fuel cell vehicles.Reduction of Pt loading in catalyst layer has been viewed as the key to the overall cost reduction of fuel cell.Owing to its highly ordered structure as well as innovated ingredients,ionomer-free Pt catalyst layer exhibits prominent capability in terms of Pt loading reduction as well as durability enhancement,but operational robustness remains its Achille’s heel.Therefore,expanding the range of suitable operating conditions has become the focus of research on ionomer-free Pt catalyst layers.Starting from the structural unit of ionomer-free Pt catalyst layer,which is waterfilled Pt nanopore,the impedance spectroscopy model for a water-filled Pt nanopore has been developed.Based on the time domain model for a water-filled Pt nanopore,the time domain performance model for ionomer-free Pt catalyst layer membrane electrode assembly has been developed.Based on experimental measured performance data of ionomer-free Pt catalyst layer membrane electrode assembly,the time domain performance model has been used to propose an optimization route to expand the favorable operating conditions.The research content consists of three sections.The first section is the development of a theoretical impedance model for a water-filled Pt nanopore,which is based on the steady-state model for a water-filled Pt nanopore.The impedance characteristics of metal charging as well as chemisorption effects and corresponding experimental verification approaches are discussed.The imprint for finite chemisorption effect is the adsorption arc in Nyquist plot for the case without ORR,whose radius is inversely related to the adsorption rate.The imprint for metal surface charging effect is the potential dependence of the length of the 45-degree line in Nyquist plot for blocking electrode.Based on the relation between proton conductivity and the length of the 45-degree line,electrochemical impedance spectroscopy(EIS)data measured under H2/N2 could be used to extract the proton conductivity.The second section is the time domain performance model for an ionomer-free Pt catalyst layer membrane electrode assembly,which contains three submodels,namely the water transport sub-model,the oxygen transport sub-model and the oxygen reduction reaction sub-model.This model innovatively couples the effect of nonmonotonic charging behavior of metal surface on the proton conduction with the water transport and oxygen transport within the membrane electrode assembly and is parameterized and validated by experimental results in the literature.The third section is the optimization for the ionomer-free Pt catalyst layer membrane electrode assembly.With the sensitivity characteristics for operating conditions verified by experiments as well as numerical simulation results of the time domain performance model,optimization route for expanding suitable operating conditions has been put forward.In this paper,the impedance model for the structural unit of the ionomer-free Pt catalyst layer and the time domain performance model of its membrane electrode assembly are systematically developed,and an optimization scheme for extending the favorable operating conditions of the ionomer-free Pt catalyst layer is proposed.What is more,the results offer theoretical support for the impedance measurement of ionomerfree Pt catalyst layers and guide the future direction for the design of ionomer-free Pt catalyst layers.