Preparation of zero valence Pd nanoparticles with ultra-efficient electrocatalytic activity for ORR

Zero valence palladium (Pd(0)) nanoparticles have been reported to be more favorable to the oxygen reduction reaction (ORR) than palladium oxide (PdO). However, PdO is normally concomitant in Pd(0) nanoparticles. Herein, we developed an inventive method to prepare pure Pd(0) nanoparticles supported with hydrogen-substituted graphyne (Pd/HsGY) and its nitrogen-doped sample (Pd/N-HsGY). Pd(0) nanoparticles were obtained by reducing the atomically dispersed bivalent Pd, which is easy to be anchored on HsGY. The unique sp-hybridized carbon atoms in HsGY exhibited obvious extrinsic charge compensation to maintain the supported Pd nanoparticles to zero valence state. The as-prepared samples, especially Pd/N-HsGY, displayed excellent activity for ORR, higher than that of commercial Pd/C and Pt/C. In an alkaline medium, the mass activity of Pd/N-HsGY at 0.8 V (vs.RHE) was 2.1 times higher than that of Pd/C, and 1.7 times higher than that of Pt/C. While in an acidic medium, the mass activity of Pd/N-HsGY was 17.7 and 1.6 times Pd/C and Pt/C, respectively. Pd/N-HsGY based Zn-air battery exhibited higher power density than Pt/C-based battery and superior stability for more than 300 hours. Density functional theory calculations confirmed that Pd(0) nanoparticles, Pd/HsGY and Pd/N-HsGY were favorable to ORR. This method brings new perspectives for designing zero valence metal nanoparticles for electrocatalytic applications.