Aging iridium oxide catalyst inks: a formulation strategy to enhance ink processability for polymer electrolyte membrane water electrolyzers.

Iridium oxide (IrO) is recognized as a state-of-art catalyst for anodes of low-temperature polymer-electrolyte membrane water electrolyzers (PEMWE), one of the promising clean energy technologies to produce hydrogen, a critical energy carrier for decarbonization. However, typical IrO ink formulations are challenging to process in liquid-film coating processes because of their poor stability against gravitational settling and low viscosities. Here we report on time evolution of the microstructure of concentrated IrO inks in a water-rich dispersion medium, probed using a combination of rheology and X-ray scattering for up to four days.

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe-N-C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells.

We present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe-N-C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1-propanol (PA). The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (HO %) in the DM on the ink microstructure were studied. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks.

Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application.

In situ electrochemical diagnostics designed to probe ionomer interactions with platinum and carbon were applied to relate ionomer coverage and conformation, gleaned from anion adsorption data, with O transport resistance for low-loaded (0.05 mg cm) platinum-supported Vulcan carbon (Pt/Vu)-based electrodes in a polymer electrolyte fuel cell. Coupling the in situ diagnostic data with ex situ characterization of catalyst inks and electrode structures, the effect of ink composition is explained by both ink-level interactions that dictate the electrode microstructure during fabrication and the resulting local ionomer distribution near catalyst sites.

Investigation of the Microstructure and Rheology of Iridium Oxide Catalyst Inks for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers.

We present an investigation of the structure and rheological behavior of catalyst inks for low-temperature polymer electrolyte membrane water electrolyzers. The ink consists of iridium oxide (IrO) catalyst particles and a Nafion ionomer dispersed in a mixture of 1-propanol and water. The effects of ionomer concentration and catalyst concentration on the microstructure of the catalyst ink were studied.

Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks.

We present a rheological investigation of fuel cell catalyst inks. The effects of ink parameters, which include carbon black-support structure, Pt presence on carbon support (Pt-carbon), and ionomer (Nafion) concentration, on the ink microstructure of catalyst inks were studied using rheometry in combination with ultrasmall-angle X-ray scattering (USAXS) and dynamic light scattering (DLS). Dispersions of a high-surface-area carbon (HSC), or Ketjen black type, demonstrated a higher viscosity than Vulcan XC-72 carbon due to both a higher internal porosity and a more agglomerated structure that increased the effective particle volume fraction of the inks.