Zhongmiao Gong,Zhigang Chen,Hao Li,Guang Yang,Min Yuan,Zhiyun Li,Xueying Wan,Yi Cui
Surface-supported isolated atoms in single-atom catalysts (SACs) grant maximum utilization of metals in heterogeneous catalysis. Herein, we report a feasible pyrolysis strategy to synthesize Pd single atoms by thermally melting Pd nanoparticles on an oxygen-vacancy-rich tungsten-oxide matrix at reduction atmosphere. Near ambient pressure X-ray photoelectron spectroscopy was used to monitor the formation of zero-valence Pd single atoms and the increased metallic feature of WO 3− x substrate. Accordingly, the as-obtained zero-valence Pd single-atom catalyst exhibits a markedly boosted HER activity with a low overpotential ( η 10 = 70 mV) at the current density of 10 mA/cm 2 and a small Tafel slope ( b = 68 mV/dec), nearly 150 mV and a 3.0-fold enhancement than those of Pd nanoparticles ( η 10 = 220 mV, b = 133 mV/dec) under the same conditions. In addition, quasi in situ XPS results suggest the hydrogen spillover effect is more likely to occur on Pd single atoms during the electrochemical process. Our work may pave an interesting route for the rational design of highly-efficient single-atom catalyst, and the elucidation of corresponding enhanced reaction mechanisms by the utilization of advanced characterization techniques.
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.
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