(Invited) Assessing Corrosion Resistance of Antimony-, Niobium- and Tantalum-Doped Tin Oxide Aerogels As Oxygen Evolution Reaction Catalyst Supports in Acidic Media

Abstract

Despite the fact that iridium (Ir) is among the rarest elements on Earth [1], it remains the state-of-the-art anode electrocatalyst in Proton Exchange Membrane Water Electrolyzers (PEMWE). Indeed, Ir dioxide (IrO2) presents the best compromise between activity toward the Oxygen Evolution Reaction (OER) and stability under the harsh operating conditions of the anode: E > 1.5 V vs. the reversible hydrogen electrode (RHE), 60 < T < 80 °C, presence of oxygen and highly acidic environment [2].In this context, research efforts have been dedicated to minimize Ir loading without compromising OER activity and stability. One possible approach is to stabilize the metal nanoparticles (NPs) on a high surface area support. The classical carbon black supports, widely used in fuel cells, are easily oxidized in OER conditions: carbon corrosion leads to particle aggregation and eventually detachment from the support surface [3]. As an alternative to carbon, metal oxides such as tin dioxide (SnO2) [4] or titanium dioxide (TiO2) [5] feature a good corrosion resistance in PEMWE operating conditions and may strongly interact with the catalyst (strong metal–support interaction (SMSI) effect [6]).In this presentation, we shine a spotlight on iridium oxide (IrOx) NPs supported on SnO2 aerogels doped with, niobium (Nb), tantalum (Ta) or antimony (Sb). The aerogels, synthesized via a sol-gel process, feature a rutile structure after calcination, a specific surface area about 80 m2 g-1 and an electronic conductivity spanning from 5 mS cm-1 to 1 S cm-1 depending on the dopant [7-8]. A highly reproducible colloidal polyol route was used to deposit the IrOx NPs onto the aerogels, ensuring a straightforward comparison of their catalytic performance towards the OER and their resistance to corrosion. We used a home-made flow cell coupled to an inductively-coupled plasma mass spectrometer (ICP-MS) to assess metal dissolution under various potential conditions. As expected, carbon support proved to be unstable in OER conditions (Figure 1.a). In contrast, SnO2 aerogels clearly improved catalyst stability at high potential (Figures 1.b and 1.c). Especially, Ta-doped SnO2 (TaTO) aerogels showed an outstanding corrosion resistance with a negligible loss of dopant when compared to Sb-doped SnO2 (ATO). Based on our experimental observations, we demonstrate that a judicious doping of SnO2 aerogels could help developing highly active and robust OER electrocatalysts in acidic media.Figure 1. Metal concentration under staircase potential profiles from 0.9 V vs. RHE to 1.6 V vs. RHE in 100 mV steps with 300 seconds hold time at each potential for IrOx NPs deposed onto (a) Vulcan© XC-72, (b) ATO (10 at.% of Sb) and (c) TaTO (5 at.% of Ta) . The experiments were performed at room temperature by coupling a home-made flow cell to a PerkinElmer Nexion2000 ICP-MS instrument. A 0.05 M H2SO4 solution deaerated with argon was used as electrolyte. The catalyst ink was deposited on the surface of the glassy carbon electrode (4 mm in diameter) resulting in a loading of 20 μgIr cmgeo -2.