Platinum (Pt)-based metals are the most used electrocatalysts, but the high cost and scarcity of Pt hinder its wide application. Alloying Pt with other transition metals or developing non-precious metal catalysts with comparable performance to Pt is promising to address the cost issue. Excellent oxygen reduction activity has been demonstrated on octahedral Pt-Ni nanoparticles with enriched {111} facets. In this study, Pt-Ni/C octahedra were synthesized and subjected to various heat treatment protocols. The impacts of thermal treatment temperature and atmosphere on structure, composition and in turn on electrocatalytic activities were systematically studied. Interestingly, an ultrathin carbon layer was formed on the catalyst surface after treatment in Ar at a temperature higher than 350˚...[ Read more ]

Platinum (Pt)-based metals are the most used electrocatalysts, but the high cost and scarcity of Pt hinder its wide application. Alloying Pt with other transition metals or developing non-precious metal catalysts with comparable performance to Pt is promising to address the cost issue. Excellent oxygen reduction activity has been demonstrated on octahedral Pt-Ni nanoparticles with enriched {111} facets. In this study, Pt-Ni/C octahedra were synthesized and subjected to various heat treatment protocols. The impacts of thermal treatment temperature and atmosphere on structure, composition and in turn on electrocatalytic activities were systematically studied. Interestingly, an ultrathin carbon layer was formed on the catalyst surface after treatment in Ar at a temperature higher than 350˚C, which significantly decreased the activity toward most of the electrochemical reactions. This carbon layer, however, was not observed during heat treatment in other atmospheres including N₂, air, O₂, vacuum, or H₂. Transmission electron microscopy (TEM) indicates that the Ni-enriched surface on Pt-Ni/C formed at high temperature might play a critical role in catalyzing the formation of carbon layer via carbon support. These results demonstrate the importance of the atmosphere in annealing nanoparticles with carbon support.

I also explored the approaches to developing carbon-based non-precious metal electrocatalyst co-doped with N and Fe (Fe-N-C). In this work, zeolitic imidazolate framework-8 (ZIF-8) was used as the self-template for a facile one-pot synthesis of Fe-N-C catalysts with atomically dispersed Fe atoms. The catalyst derived from the precursor (zinc and iron ratio: 0.95/0.05) pyrolyzed in Ar atmosphere showed the best ORR activities both in 0.1 M HClO₄ (E_onset= 0.95 V_RHE and E_1/2 =0.81 V_RHE) and 0.1 M KOH (E_onest > 1 V_RHE and E_1/2 =0.90 V_RHE) solutions. This material also showed excellent stability in the O₂-saturated 0.1 M HClO₄, with only 16 mV shift in the half-wave potential after 10000 cycles between 0.65 and 1.0 V. This single Fe atom material is a promising alternative to Pt due to its high activity and stability.