(Invited) Nanofibrous Doped Tin Oxide As Electrocatalyst Support for PEM Fuel Cells and Electrolysers

Abstract

In the way towards the reduction of noble metal loading in electrodes for proton exchange membrane fuel cells (PEMFC) and electrolysers (PEMWE), the use of metal oxides as support materials offers electronic electrocatalyst-support interactions beneficial for their activity and durability [1]. The morphology of the supports also plays a crucial role. Nanofibrous webs prepared by electrospinning provide a way to achieve increased performance when used in electrodes by the control of nanostructure and porosity [2]. Tin oxide loose-tubes doped with a range of elements (niobium, antimony and tantalum) were prepared by single-needle electrospinning and subsequent calcination leading to a fibre-in-tube morphology [3]. The doping allowed to increase the electrical conductivity of tin oxide, typical of a semiconducting material. In particular, Sb-SnO2 presented a conductivity similar to that of carbon (1 S cm-1 at 20 °C) [4]. The hollow morphology of doped SnO2 allowed the access of electrocatalyst as well as ionomer and gas, improving the triple phase boundary. The electrochemical stability of the different supports was evaluated in acidic medium at low and high potentials coupling electrochemistry and spectroscopic methods to investigate the specific degradation mechanism occurring. Pt and IrO2 nanoparticles synthesized by a microwave-assisted polyol method were deposited onto the SnO2-based loose-tubes. The resulting materials were characterised for their morphology and structure. Their electrochemical activity towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as their durability upon accelerated stress tests were evaluated by electrochemical analysis. X-ray photoelectron spectroscopy was a useful tool to demonstrate the strong metal-support interaction leading to improved electroactivity towards ORR and OER [5]. The obtained electrocatalysts were used to prepare PEMFC cathodes and PEMWE anodes and assembled with commercial electrodes and membranes and characterised in membrane-electrode assemblies. Their performance and stability were investigated in different operating conditions and will be discussed.