Optimizing Catalyst Layer Structure with Carbon Nanofiber Additive for Better Performance of Proton Exchange Membrane Fuel Cell

Abstract

Increasing the power density of proton exchange membrane fuel cell (PEMFC) is essential for its commercialization. Cathode catalyst layer (CCL) carbon additive is an effective method that can improve membrane electrode assembly (MEA) performance under high current density. In this work, carbon nanofiber (CNF) is used as CCL additive and its mechanism is studied. The influence of CNF on the CCL structure is studied by scanning electron microscope (SEM), nitrogen adsorption method and contact angle experiment. Meanwhile, the mechanism is examined by using polarization decomposition and impedance analysis combined with the result in characterization experiments. The results show that: (1) the MEA used in this work has the best performance when adding 1 wt%. The voltage rises 74 mV (15.42%) at 2 A cm−2; (2) CNF varies the MEA performance mainly through changing the hydrophobicity of CCL, influencing the mass transport resistance and the concentration polarization. The mass transport resistance decreases 57.18% at 2 A cm−2; (3) activation polarization values have a negative linear correlation with the peak volume values of the primary pores at around 4 nm in diameter. This study provided a detailed understanding of the mechanism of CNF additive in CCL and will be helpful for improving PEMFC performance.