Effect of the physical adsorption of ionomer on Pt particles on the fluid characteristics of PEMFC catalyst ink

Abstract

The physical adsorption between ionomer and Pt particles affects the fluid properties of a catalyst ink, which in turn affects the surface morphology of ink coating. In this study, catalysts with varying Pt loadings were used to produce catalyst ink with the same solid content, and carbon ink with different solid content was prepared as a comparative test. The rheological test revealed that in carbon ink without Pt, the interaction between ionomer and carbon was more stable, and ink showed a behavior similar to that of a Newtonian fluid. The viscosity and storage modulus of carbon ink have a linear relationship with the apparent volume fraction of carbon. In the catalyst ink, Pt particles and ionomer's action make the ink a pseudoplastic fluid. With the increase of carbon content of the catalyst ink, the structural strength of the ink increases rapidly. In the catalyst ink with carbon apparent volume fractions of 41.42, 38.59, 35.37, and 31.68 vol%, the storage modulus of ink is 31.20, 15.50, 5.10, and 1.10 Pa, respectively, and the solid-state physical properties of ink gradually disappear. When the Pt loading exceeds 40 wt%, the ink has an optimal thixotropy and improves the integrity of the surface morphology of the catalytic layer. The electrochemical test results show that the output voltage of 50 wt% Pt/C catalyst ink-MEA can achieve 0.711 V at 1000 mA cm−2, and the output power is 1121.1 mW cm−2 at 2000 mA cm−2.