Effect of Nafion content and hydration level on the electrochemical area of Pt nanocatalyst in the triple-phase boundary

JIMÉNEZ-GARCÍA, JUAN C.; JIMENA A. OLMOS ASAR; ESTEBAN A FRANCESCHINI; MARISCAL, MARCELO M.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2021

1463-9076

Despite the great scientific effort, there are still some aspects of polymeric membrane-based fuel cells (PEMFC) operation that are difficult to access experimentally. This is the case of the so-called triple-phase boundary (TPB), where the ionomer (commonly Nafion) interacts with the supported nanocatalysts (commonly Pt), and is key in the catalytic activity of the system. In this work, we use Molecular Dynamics simulations and electrochemical experiments on a Nafion/Pt/C system. We perform a systematic analysis, at an atomistic level, to evaluate the effect of several fundamental factors and their intercorrelation on the electrochemically active area (ECSA) of the catalysts. Our results reveal that at high Nafion contents, the catalyst utilization is affected due to the strong interaction between the sulfonic groups of the ionomer and the surface of the Pt nanoparticles (NPs). On the other hand, when the hydration level of the membrane decreases, the sulfonic groups have a higher occupation on the NP surface, covering the active area with hydrophobic Nafion chains and therefore, increasing the inactive area. Voltammograms can corroborate our calculations. Overall, this investigation allows us to rationalize how the catalyst utilization is affected, which is an important step to establish the relationship between the environment and the effectiveness and durability of the PEMFC system.