N-doped carbon shell encapsulated PtZn intermetallic nanoparticles as highly efficient catalysts for fuel cells

The high cost and poor durability of Pt nanoparticles (NPs) have always been great challenges to the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-based intermetallic NPs with a highly ordered structure are considered as promising catalysts for PEMFCs due to their high catalytic activity and stability. Here, we reported a facile method to synthesize N-doped carbon encapsulated PtZn intermetallic (PtZn@NC) NPs via the pyrolysis of Pt@Zn-based zeolitic imidazolate framework-8 (Pt@ZIF-8) composites. The catalyst obtained at 800 ℃ (10%-PtZn@NC-800) was found to exhibit a half-wave potential (E_1/2) up to 0.912 V versus reversible hydrogen electrode (RHE) for the cathodic oxygen reduction reaction in an acidic medium, which shifted by 26 mV positively compared to the benchmark Pt/C catalyst. Besides, the mass activity and specific activity of 10%-PtZn@NC-800 at 0.9 V versus RHE were nearly 3 and 5 times as great as that of commercial Pt/C, respectively. It is worth noting that the PtZn@NC showed excellent stability in oxygen reduction reaction (ORR) with just 1 mV of the E_1/2 loss after 5, 000 cycles, which is superior to that of most reported PtM catalysts (especially those disordered solid solutions). Furthermore, such N-doped carbon shell encapsulated PtZn intermetallic NPs showed significantly enhanced performances towards the anodic oxidation reaction of organic small molecules (such as methanol and formic acid). The synergistic effects of the N doped carbon encapsulation structure and intermetallic NPs are responsible for outstanding performances of the catalysts. This work provides us a new engineering strategy to acquire highly active and stable multifunctional catalysts for PEMFCs.