Influence of Ink Composition and Drying Technique on the Performance and Stability of Fe-N-C-Based High-Temperature Proton Exchange Membrane Fuel Cells.

Abstract

Fe-N-C catalysts have emerged as a potentially cost-effective alternative to Pt-based catalysts in high-temperature polymer electrolyte membrane fuel cell cathodes. However, the optimal design and deposition method of the Pt-free catalyst layer remain unclear. Herein, the effect of conventional oven drying compared with freeze-drying on the performance of commercial Fe-N-C catalyst layers is investigated. The gas diffusion electrodes are fabricated by doctor blade coating. Freezing the wet catalyst layer at -26 °C and subsequent sublimation of the solvents leads to a 45 % increase in mass-normalized peak power density compared to the conventional oven drying. This is attributed to a templating mechanism of the solvents, resulting in a thicker catalyst layer and improved acid retention, which enables optimal reactant transport. In contrast, freeze-drying with liquid nitrogen negatively impacts the catalyst morphology, leading to reduced porosity and performance. During 100 h of operation, the performance decreases by a similar magnitude, regardless of the fabrication method used. Operando electrochemical impedance spectroscopy with the distribution of relaxation times shows no catalyst deactivation through the fabrication methods. The results highlight the importance of optimizing catalyst layer fabrication methods for Fe-N-C catalysts to achieve improved performance in fuel cell applications.