N-doping induced tensile-strained Pt nanoparticles ensuring an excellent durability of the oxygen reduction reaction

The availability of highly active and durable Pt based catalysts at a high metal loading is a prerequisite for practical applications in proton exchange membrane fuel cells (PEMFCs). Herein, we for the first time report the simple surfactant- and polymer-free synthesis of nonmetallic N doped Pt nanoparticles as electrocatalysts with an enhanced activity and excellent durability for oxygen reduction reaction (ORR) and such a synthetic procedure has been extended in a large-scale (>100 g/batch) for practical production already. X-ray diffraction and aberration-corrected transmission electron microscopy results clearly confirm that the doping of N within Pt lattice leads to the tensile strain in Pt nanoparticles. The tensile-strained Pt nanoparticles exhibit a negligible ORR activity decay by only 3.7% after a 20,000-cycle accelerated durability test (ADT) between 0.6 and 1.1 V/RHE, which places it among the most durable Pt-based catalysts reported for the ORR. While eliminating the strain effect, the activity degradation of the ORR on the Pt nanoparticles increases to 18.1%, close to that of commercial Pt/C catalyst (27.9%). Importantly, the tensile strain of N doped Pt nanoparticles is still remained after the ADT, assessing the structural stability of N-doped Pt nanoparticles. Theoretical calculations reveal that the N-doped Pt nanoparticles are chemically more stable than pristine ones due to Pt-N bonding effect, thus explaining well its excellent durability during the ORR. PEMFC integrated with as-prepared catalyst delivers a cell voltage of 0.65 V at the current density of 1.4 A·cm⁻², satisfying the needs for vehicle use. The simple surfactant- and polymer-free approach presented here can be readily applied to other nonmetal doped Pt nanostructures and provides a promising potential for the practical applications in PEMFCs.
© 2019 Elsevier Inc.