Oxygen and ion transporter co-polymer shell on silver oxygen reduction reaction catalyst in alkaline exchange membrane fuel cell

The intrinsic sluggishness of oxygen reduction reaction (ORR) limits the widespread adoption of low-temperature anion exchange membrane fuel cells (AEMFCs) technology, and effective ORR electrocatalysts and methods for ORR enhancement are needed. Herein, we investigate the mechanism behind the improvement of ORR activity of Ag electrocatalyst coated with a shell based on polydopamine (PDA) crosslinked with polyethylene imine (PEI) during AEMFC operation. We show a correlation between electrochemical and physical properties of the PDA/PEI Ag catalyst, with its performance within membrane-electrode assembly (MEA) in practical fuel cell operating environments. Higher current density observed in a catalytic region of polarization curve in AEMFC, matches the positive shift in the half-wave potential of ORR on Ag PDA/PEI as measured by rotating disc electrode (RDE) experiments. Additionally, lower cell resistance is recorded over durability test with Ag PDA/PEI catalyst, along with higher cell voltage. The PDA/PEI shell thickness and its weight ratio on the Ag catalyst was determined using transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA), respectively. Meanwhile, the chemical composition of PDA/PEI and its impact on the stability of the Ag catalyst are analyzed through X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The significant role of the PDA/PEI shell was identified in hydroxide transport at the catalyst surface and within cathode layer, in destabilizing catalyst-OH bond and removing the hydroxide from catalyst surface through H-bond network. To our understanding, this is the first time a non-Pt catalyst with an ion-conducting shell is successfully tested in AEMFC, and underlying enhancement mechanism was provided, offering promising foundation for the future development and commercialization of AEMFC technology.