Base-Accelerated Degradation of Nanosized Platinum Electrocatalysts

In the pursuit of a hydrogen economy, extensive research has been directed at developing acidic and alkaline hydrogen fuel cells. Such fuel cells often utilize platinum-based catalysts. These materials have been studied extensively in acidic conditions but not in alkaline ones. This focus on acidic systems creates a marked knowledge gap, since recent studies indicate that carbon-supported platinum (Pt/C) electrocatalysts degrade more rapidly in bases than in acids. Addressing this gap, the present work investigates Pt/C degradation at pH 2 and pH 12 using electrochemistry, transmission electron microscopy (TEM), and in situ X-ray absorption spectroscopy (XAS). TEM and XAS reveal accelerated Pt/C degradation at high pH levels, which results in increased Ostwald ripening, Smoluchowski agglomeration, and nanoparticle detachment. These processes are driven by platinum-catalyzed carbon corrosion and the dissolution and redeposition of platinum nanoparticles. Although these processes take place at both low and high pH levels, basic conditions accelerate the degradation. Base-enhanced Pt dissolution and redeposition was assessed in further detail, revealing an oxidation onset reduction of 100 mV in the base; however, there were no significant differences between undissolved Pt oxidation in acid and in base. The results suggest that soluble Pt oxidation products are stabilized in the base instead. These conclusions are important for translating acidbased literature to alkaline conditions.