Modeling Analysis of the Impact of Platinum Oxides and Cerium Ion Migration on PEMFC Performance and Degradation Under a Realistic Driving Cycle
Authors: Verducci Francesco , Grimaldi Amedeo , Colombo Elena , Casalegno Andrea , Baricci Andrea 
Published: December 2024

The sluggish oxygen reduction reaction (ORR) kinetics represents the major source of efficiency loss in a Proton Exchange Membrane Fuel Cell (PEMFC) [1]. In the potential range where fuel cells operate, several platinum (Pt) oxide species form on the catalyst surface [2]. Their formation and reduction is a dynamic process which strongly influences ORR activity and the loss of electrocatalyst active surface area (ECSA) [3]. PEMFC performance and durability are also significantly affected by Cerium (Ce) ions which, under typical operating conditions, are known to migrate through the polymer electrolyte membrane (PEM) and the catalyst layers (CLs) driven by concentration and potential gradients [4]. Such mobility reduces scavenging efficacy, thus accelerating PEM degradation. Moreover, it affects cell performance since the progressive build-up, during normal fuel cell operation, of Ce ions into the cathode CL is found to decrease proton conductivity [5] and hinder oxygen diffusion through the ionomer film [4], as highlighted by the most recent literature. In this scenario, a 1+1D multiphase dynamic non isothermal PEMFC model of performance is developed [6]: the close relationship between ORR reaction and Pt oxide dynamics is investigated by modeling oxides formation/reduction with a four-step oxidation mechanism which involves three different types of oxide species. Furthermore, based on the work of [2], the effects of ionomer sulfonate groups adsorption onto platinum surface and of local relative humidity are also included in the ORR kinetics. As visible in Figure 1(a), the proposed ORR formulation allows to properly capture cell voltage dynamics under the operating conditions of the automotive ID-FAST cycle [7]. The PEMFC model of performance also accounts for Ce ions mobility, both in the along-the-channel and through-the-membrane directions: for this purpose, a Nernst-Planck equation is adopted, where the diffusivity and migration coefficients are properly calibrated and validated (Figure 1(b)) by reproducing the Ce ions migration profiles reported in the literature for different current density [5].
Lastly, the 1+1D multiphase dynamic non isothermal PEMFC model is coupled with a physical-based 0D model of platinum degradation [3]. The presented model framework is validated on experimental data gathered on a segmented hardware and representative of 600 cycles in the low power conditions of the automotive ID-FAST driving cycle load protocol [7]: as visible in Figure 1(c), the 67% of the initial ECSA is lost. Succeeding in the prediction, this modelling structure aspires to provide critical information for the development of proper mitigation strategies aimed at extending the lifetime of PEMFC stacks.
This work received support from the Italian government Progetto PERMANENT - BANDO MITE PNRR Missione 2 Investimento 3.5 A - RSH2A_0O0012.
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Figure 1