Hydrothermal synthesis of palladium nitrides as robust multifunctional electrocatalysts for fuel cells

Abstract

Tremendous efforts have been devoted to exploring high-performance electrocatalysts for fuel cells, but the achievements in catalytic activity and durability are still far from satisfactory for commercialization. Filling metal nanoparticles with nonmetallic elements, such as nitrogen atoms, can greatly improve their catalytic performance; however, noble metal nitrides still suffer from the lack of efficient synthetic approaches. Herein, we report that PdN_x nanocrystals (x ≤ 0.5) with controllable stoichiometries can be prepared via hydrothermal synthesis. Theoretical studies reveal that delicately modifying the electronic structure of Pd by filling N atoms can optimize the d-band center of Pd sites, thereby improving the catalytic performance toward a wide range of reactions. Catalytic performance evaluation demonstrates that PdN_x nanocrystals exhibit superior catalytic properties for the cathodic oxygen reduction reaction and anodic formic acid and methanol oxidation reaction. Especially for the ORR in alkaline electrolytes, Pd₂N nanocrystals can deliver a mass activity as high as 0.83 A mg⁻¹, outperforming most of the Pd-based catalysts reported previously. Accelerated durability tests further demonstrate the excellent durability of Pd₂N nanocrystals toward the ORR, the activity of which decays by only ∼9% over 10 000 cycles, suggesting the huge impact of the N content on enhancing the stability of noble metal nanocatalysts.