Tin as “adhesive” in platinum nanoclusters boost power density and durability in PEM fuel cells

For actual working conditions of fuel cells, the local mixing potential of transient condition can be as high as 1.2 V or even 1.5 V due to the residual water vapor and air during start-up gas exchange, as well as reverse-current decay. Such high transient potential makes the fuel catalysts extremely susceptible to oxidation, resulting in severe performance degradation. In the past two decades, introducing a second metal element to form an alloy with Pt has been a common way to enhance the activity and stability of fuel cell cathode catalysts. However, elements such as Fe, Co and Ni suffer from dissolution under acidic conditions, which can seriously deactivate the catalysts at the cathode and poison the membrane. In this work, tin oxides-decorated Pt nanocatalysts (SnOx-Pt/C) are constructed by a two-step impregnation method and show much better stability owing to the chemical inertness of tin oxides in acidic media. The SnOx-Pt/C catalysts showed good performance in oxygen reduction reaction test, (specifically, < 30% loss in mass activity and < 20% in electrochemical activity area after 40,000 cycle scans from 0.6 to 1.2 V. On the one hand, the tin oxides on the Pt surface help to protect surface Pt atoms from oxidation and detachment; on the other hand, the tin oxides favor the adsorption of hydroxyl groups and, meanwhile, weaken the hydroxyl poison on Pt surface. More importantly, SnOx-Pt/C nanocatalysts achieve higher power density of fuel cells in comparison to Pt/C catalysts, and the Ostwald ripening of Pt nanoparticles is suppressed and the cycle life is significantly improved. The SnOx-Pt/C nanocatalysts show advantages including low cost and facile production, which provides a promising way for the development of stable catalysts for high power density fuel cells.