Exploring the impact of ionomer content and distribution on inkjet printed cathodes for anion exchange membrane fuel cells

Abstract

Electrode composition optimization is critical to achieving high and stable anion exchange membrane fuel cell (AEMFC) performance. In this article, inkjet printing is pioneered as a method to fabricate AEMFC electrodes with varying and graded cathode ionomer loading in order to assess its impact on electrode electrochemical properties, cell performance and stability. Inkjet printed catalyst layers (CLs) exhibited decreasing porosity with increasing ionomer content, maintaining a constant active area at 50 $°C$ under fully humidified conditions. The increase in active area and ionic conductivity with increasing ionomer content was detectable only at higher temperatures. At 60 $°C$ with 90% relative humidity inlet gases, the AEMFCs with cathode electrodes with optimal 20 wt% uniform ionomer content achieved a highly repeatable and stable performance of 0.53 $\text{W}/{\text{cm}}^2$ with a total loading of 0.3 ${\text{mg}}_{\text{Pt}}/{\text{cm}}_{\text{CL}}^2$. Grading the cathode ionomer content, with higher concentration near the membrane and lower near the gas diffusion layer (GDL), does not improve cell performance, indicating neither cathode conductivity nor mass transport limits performance. When tested at 80 $°C$, AEMFCs with a graded cathode ionomer structure (30 wt% near the membrane and 20 wt% near the GDL) demonstrated improved stability compared to those with a uniform 20 wt% ionomer content. This stability improvement is attributed to better water retention with more cathode ionomer content, as evidenced by the cell’s ability to maintain low resistance.