Effect of dispersant on catalyst ink properties and catalyst layer structure for high performance polymer electrolyte membrane fuel cells

Abstract

Here, catalyst ink is prepared using a dispersant with the hydrophile-lipophile balance (HLB) value of 17. The effects of the ionomer-catalyst agglomerate size on the ink rheological properties, and subsequent catalyst layer (CL) microstructure and electrochemical performance are investigated to elucidate the relationship between ink properties and cell performance. Results shows that the smallest agglomerate size (2.7 μm) and polydispersity index (PDI, 0.068) are obtained with 1 wt% dispersant content; the low PDI indicate that the ink is well dispersed. Steady-state and thixotropy tests also show that the ink has shear-thinning and gel-like behavior (Recovery ratio: 30.4%). It is proposed that this occurs because the agglomerates are smaller and the interaction forces between them increase. Thus, the ink structure is maintained until the dried CL is formed, and as a result, the pore volume of CL with 1 wt% dispersant is increased compared to those with 0 and 9 wt%. In addition, the 1 wt% CL-based MEA shows the highest performance (1224.4 mA cm⁻² at 100% RH) owing the increase in the number of channels (1190 mA cm⁻² in four-channel) and back pressure (1240 mA cm⁻² at 1.5 bar_ca).