Anchoring ordered PtZn nanoparticles on MOF-derived carbon support for efficient oxygen reduction reaction in proton exchange membrane fuel cells

초록

Despite their superior catalytic activity for the oxygen reduction reaction (ORR), ordered platinum (Pt)-transition metal nanoparticles suffer from limitations that hinder their use in polymer electrolyte membrane fuel cells (PEMFCs), such as particle growth during the ordering transformation and insufficient durability over extended operation. In this study, a zeolitic imidazolate framework-8 (ZIF-8) is pyrolyzed into zinc and nitrogen-doped carbon (ZnNC). Pt nanoparticles are synthesized on the ZnNC and undergo heat treatment. Through this simple process, ordered PtZn nanoparticles are obtained with an average particle size of approximately 4.5 nm (OPtZn/ZnNC). In a half-cell, the O-PtZn/ZnNC achieves outstanding ORR mass activity (1.21 A mg Pt- 1 at 0.9 V) and durability (35 % loss of mass activity after 30 k cycles), significantly surpassing Pt/C (0.41 A mg Pt- 1 and 61 % loss). As a cathode catalyst of a PEMFC, the O-PtZn/ZnNC outperforms Pt/C in both performance and durability; O-PtZn/ZnNC and Pt/C cells exhibit current densities of 71 and 39 mA cm- 2 , respectively, at a cell voltage of 0.8 V. These values fall to 43 (-39 %) and 11 (-72 %) mA cm- 2 , respectively, after 30 k cycles. Density functional theory calculations illustrate that ZnNC has a strong binding energy with O-PtZn (-8.13 eV) and a small interfacial minimum distance of 2.03 & Aring;, resulting in exceptional retention of electrochemical active surface area retention for O-PtZn/ZnNC (-7%, from 57.9 to 53.8 m2 g Pt-1 , after 30 k cycles).

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