Modeling the Effect of Low Pt Loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells. Part II: Parametric Analysis

Abstract

A parametric analysis is presented using a previously validated 1D model for a cathode catalyst layer (CL). The results show that maximum power density at low Pt loading can be maximized with relatively thin CLs (${\rm thickness}\sim 2\;\mu \rm m$) featuring a high carbon volume fraction (low ionomer-to-carbon weight ratio, I/C) compared to high Pt loading CLs. The shift of the optimal carbon volume fraction (I/C ratio) is caused by the dominant role of the local oxygen transport resistance at low Pt loading, which is lowered by a reduction of the average ionomer film thickness (better ionomer distribution among carbon particles). In contrast, at high Pt loading, higher porosity and pore radius (lower carbon volume fraction) is beneficial due to an increase of bulk effective diffusivity despite thickening of ionomer films. Moreover, the results show that performance at low Pt loading is significantly improved with increasing mass-specific activity. The effect of average saturation and ionomer permeability on performance at low Pt loading is lower compared to dry CL composition and mass-specific activity.

Optimized mass transfer in a Pt-based cathode catalyst layer for PEM fuel cells

“…Similarly, several studies have reported that an ultra-thin water layer on the surface of Pt generates local O 2 transport resistance under high current density, which contributes to R total significantly. 30,50,51 Thus, it is evidenced that CCL confronts several challenges, which significantly influence the cell performance. These challenges encompass multifaceted issues such as the heightened resistance encountered in the local O 2 transport, limited mass transfer at the ionomer/Pt interface, and CCL flooding due to the accumulation of H 2 O by-products.…”

“…Similarly, several studies have reported that an ultra-thin water layer on the surface of Pt generates local O 2 transport resistance under high current density, which contributes to R total significantly. 30,50,51…”

Local oxygen transport resistance in polymer electrolyte fuel cells: origin, dependencies and mitigation

“…The local oxygen resistance per unit of active catalyst surface area, R i O2 , and the local oxygen resistance per unit of geometric area, R local O2 , are related by the roughness factor (Sánchez-Ramos et al, 2021;Sánchez-Ramos et al, 2022)…”

A Numerical Assessment of Mitigation Strategies to Reduce Local Oxygen and Proton Transport Resistances in Polymer Electrolyte Fuel Cells

“…), while ∆φ p was directly taken as the prescribed potential drop (∆φ p = 1). According to Equations (4a) and (4b), the local resistance per unit of the geometric area is inversely proportional to the roughness factor (R local ∝ r −1 f ), dramatically increasing at low Pt loading when A Pt → 0 [13,14,44]. Pt was assumed to be well dispersed over Pt surface, so no explicit description of the Pt nano-particle shape was made (A c A Pt ).…”