Incorporation of PEDOT:PSS to Reduce Iridium Loading at Anode Catalyst Layer for Proton Exchange Membrane Water Electrolysis

Abstract

Proton exchange membrane water electrolysis (PEMWE) is one of the most promising technologies to produce green hydrogen with high efficiency. However, its commercialization is hindered by the large usage of expensive iridium as anode electrocatalyst [1-3] . Incorporation of cheap conductive materials into the catalyst ink, e.g., titanium powder [4], is a straightforward and efficient method to reduce noble metal loading of membrane electrode assembly (MEA). In this study, we aimed to use a conductive polymer PEDOT:PSS to build the low Ir loading catalyst layer for PEMWE.The MEAs at 0.3 mgIr cm-2 loading were fabricated with different PEDOT:PSS contents. In practice, the dispersion of IrO2 particles is difficult in catalyst ink, leading to the formation of big IrO2 agglomerates. We found that the zeta potential of the anode catalyst ink gained obvious enhancement after the addition of PEDOT:PSS. This indicated that PEDOT:PSS as dispersant could increase the stability of the catalyst ink. The morphology of anode catalyst layers was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface and cross-sectional images of morphology exhibited small IrO2 particles and porous structure in the catalyst layer with the addition of PEDOT:PSS, which would contribute to the water/gas movement in triple-phase boundaries. Electrochemical measurements such as polarization curves, electrochemical impedance spectroscopy (EIS), cyclic voltammogram (CV) and durability tests were conducted in a PEMWE single cell. The MEA using PEDOT:PSS as binder displayed better electrochemical performance (3.4 A cm-2@2.0 V) than other references with Nafion only (2.4 A cm-2@2.0 V). Moreover, the addition of PEDOT:PSS improved the high-frequency resistance due to its excellent electronic conductivity. In consideration of the conductive binder and dispersant effect of PEDOT:PSS, future research will focus on reducing Ir loading below 0.1 mg cm-2 through designing novel structure of anode catalyst layer with PEDOT:PSS. Keywords:PEM water electrolysis, low iridium loading, PEDOT:PSS