Core-shell nanostructures have been widely investigated to improve the electrocatalytic perfor-mance of platinum. However, organic precursors, surfactants or high temperature are usually nec-essary during the preparation procedure. Unfortunately, these requirements limit the application of these methods on a large scale. Herein, a Pdcore@ Pt shell nanostructure was fabricated through the reduction of fcPtCU by dissociated hydrogen at room temperature without the assistance o f either a surfactant or a high-boiling point solvent. The shell thickness of this nanostructure was successfully controlled by varying the amount of fcPtCU; core-shell nanoparticles with a shell thickness of 0.45, 0.75 and 0.90 nm w ere obtained, as determined by TEM. The remarkable crystallinity and epitaxial growth of the Pdcore@ Pt shell nanostructure were revealed by HRTEM and EDS. According to ICP and XPS, surface segregation of Pt was established. The impressive ORR performance was attributed to the weak adsorption strength of the OHads species, which resulted from the electron transfer impact between the Pdcore and Ptshell. The facile and clean preparation method can be used to prepare other core-shell nanostructures under a mild atmosphere.
在无表面活性剂存在条件下,采用NaBH4还原CuCl_2得到Cu纳米颗粒,以此为助分散剂,进一步还原CuCl_2与K_2PtCl_4得到平均粒径为2.1 nm的PtCu合金纳米颗粒,并被担载到活性炭上.超小的单分散PtCu合金纳米颗粒表现出明显的晶格紧缩、一定程度的Pt表面偏析、较高比例的非氧化态Pt单质和较高的电子结合能,进而表现出较弱的Pt与含氧物种的吸附作用强度.半电池测试得到的0.9 V vs.RHE处氧还原催化(ORR)的面积比活性、质量比活性分别达到Pt/C(JM)的6.6倍和3.8倍,并且加速衰减测试后,ORR电催化活性优势仍很明显,表现出良好的稳定性.在全电池100 mA/cm^2测试条件下,超小的合金催化剂显示出优于Pt/C(JM)的电催化活性及稳定性.本文制备方法也可应用于得到担载型超小单分散PtCo、PtNi等合金纳米颗粒.
The development of a non-precious metal electrocatalyst （NPME） with a performance superior to commercial Pt/C for the oxygen reduction reaction （ORR） is important for the commercialization of fuel cells. We report the synthesis of a NPME by heat-treating Co-based metal organic frameworks （ZIF-67） with a small average size of 44 nm. The electrocatalyst pyrolyzed at 600 ~C showed the best performance and the performance was enhanced when it was supported on BP 2000. The resulting electrocatalyst was composed of 10 nm Co nanoparticles coated by 3-12 layers of N doped graphite layers which as a whole was embedded in a carbon matrix. The ORR performance of the electrocatalyst was tested by rotating disk electrode tests in O2-saturated 0.1 mol/L KOH under ambient conditions. The electrocatalyst （1.0 mg/cm~] showed an onset potential of 1.017 V （[vs. RHE] and a half-wave potential of 0.857 V （vs. RHE], which showed it was as good as the commer- cial Pt/C （20 BgPt/cm2）. Furthermore, the electrocatalyst possessed much better stability and re- sistance to methanol crossover than Pt/C.
