Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC

Abstract

This study examines the effect of ink composition on the ionomer distribution in the catalyst layer of membrane electrode assemblies (MEA) prepared by decal transfer. We combine both structural and electrochemical characterization techniques to investigate the influence of the ionomer distribution on MEA performance determined by 50 cm 2 active area single-cell proton exchange membrane (PEM) fuel cell measurements. Cathodic catalyst layers were prepared from inks with different alcohols (1-propanol or 2-propanol) and varying water content (16-65 wt% H 2 O). The H 2 /air performance of cathode catalyst layers prepared from the different inks with 700 EW ionomer differed drastically, particularly under wet operating conditions, whereby the best performance was obtained for an ink based on 16 wt% H 2 O in 1-propanol. This was successfully correlated with the observation of ionomer patches at the cathode electrode surface (i.e., the surface facing the diffusion medium) determined by scanning electron microscopy (SEM), with N 2 adsorption analysis of the electrodes using a QSDFT model, and with dynamic light scattering data of ionomer/solvent mixtures. No correlation could be obtained between H 2 /air performance and the proton conductivity of the cathodes obtained by electrochemical impedance spectroscopy, and a model to rationalize this behavior will be proposed.

Effects of PEMFC Operational History under Dry/Wet Conditions on Additional Voltage Losses due to Ionomer Migration

“…Membrane electrode assembly preparation.-All membrane electrode assemblies (MEAs) used in this study were prepared by the decal transfer method. 36 All electrodes used were manufactured in-house according to Orfanidi et al 37 Catalyst inks were prepared by mixing first the catalyst powder with water, followed by solvent 1-propanol and last the ionomer dispersion containing water-solvent (725 EW 3 M dry powder dispersed in 40% H 2 O / 60% 1-propanol, resulting in a 18 wt% ionomer solution) in a 15 ml HDPE capped bottle containing 26.5 g of 5 mm ZrO 2 beads. In order to obtain an appropriate viscosity for the coating process, the solids content of the ink was set to 0.03 g ml ink −1 and the water content was adjusted to 16 wt%.…”

Effect of Dispersion Solvents in Catalyst Inks on the Performance and Durability of Catalyst Layers in Proton Exchange Membrane Fuel Cells

“…Optimization of porous electrodes has been achieved by controlling relative amounts of the ionomer and/or electrocatalyst if the polymer electrolyte membranes are fixed [7][8][9][10]. It has been reported that the distribution of ionomer within the carbon supported electrocatalyst (e.g., Pt/C) plays an important role in the design of high-performance porous electrode catalyst layers (CLs), as the transport of species such as oxygen and protons is controlled by the thickness of the ionomer on the catalyst surface and the continuity of the ionomer and gas networks in the CL, with the transport of electrons being related to the continuity of the carbon particle network [11][12][13][14][15][16]. The structural change of CLs significantly influences Pt utilization by the attachment of ionomers onto the carbon support of the Pt electrocatalyst [17].…”

Self-supported Pt–CoO networks combining high specific activity with high surface area for oxygen reduction

“…In addition, it was recently demonstrated that, in carbon-supported catalysts, not only oxygen diffusion can be rate limiting, but also proton transport 15 . Using new catalyst layer engineering methods, oxygen-related mass transport resistances can be to some extent overcome 16,17 . A disruptive change of the catalyst layer concept towards self-supported catalyst layers would allow new operation regimes for PEMFCs with regard to temperature and humidification.…”