Highly Durable and Active Pt/Sb-Doped SnO₂Oxygen Reduction Reaction Electrocatalysts Produced by Atomic Layer Deposition

Platinum supported on mixed-metal oxides (MMOs) are a class of active and durable cathode catalysts for proton exchange membrane fuel cell (PEMFC) due to a combination of the high oxidative stability of the supports and strong metal-support interactions (SMSI) that enable them to exceed the activity of Pt/C. Herein, we solve a significant remaining challenge with Pt/MMO systems, namely, the relatively low surface area and porosity. This is achieved by dispersing nearly uniform Pt clusters by using atomic layer deposition (ALD) on highly conductive (6.2 S/cm) and stable antimony-doped tin dioxide (ATO) support. ALD-Pt/ATO exhibited a significantly higher electrochemically active surface area (ECSA) (74 m2/g) and oxygen reduction reaction (ORR) catalytic activity (102 mA/mgPt at 0.9 V vs RHE) compared to Pt/ATO synthesized by using ethylene glycol (ECSA = 31 m2/gPt, mass activity = 52 mA/mgPt at 0.9 V vs RHE) and formic acid reduction methods (ECSA = 28 m2/gPt, mass activity = 46 mA/mgPt at 0.9 V vs RHE). Further characterization showed that wet chemical methods resulted in poorer Pt particle dispersion, poor control over Pt particle size distribution, and chemical degradation of the support (during Pt deposition). Given the near-ideal Pt particle size distribution of the ALD-Pt/ATO, particle size growth and loss of ECSA was found to be minimal over the course of rigorous potential cycling. Thus, after 10000 potential cycles between 1 and 1.5 V vs RHE, ALD-Pt/ATO and other Pt/ATOs were found to retain 100% of their initial ECSA compared to 57.6% retention for Pt/C. Upon testing in a H2/air PEMFC, following 1000 potential cycles, the change in ALD-Pt/ATO performance was negligible while Pt/C exhibited a 68.2% loss of initial peak power density. Thus, ALD-Pt/ATO is an active and highly durable ORR electrocatalyst in PEMFCs under start-up-shut-down conditions.