To understand the effects of cobalt precursor on electrochemical performance of the corresponding Syk inhibitor Co-PPy-TsOH/C catalysts, many physicochemical techniques have been employed in this work. Figure 4 presents XRD patterns of the Co-PPy-TsOH/C catalysts prepared from various precursors, the standard data for CoO and α-Co are also shown for comparison. Four apparent characteristic peaks can be clearly observed at 2θ of 24.5°, 44.2°,

51.5°, and 75.8° in all of the synthesized catalysts, which could be assigned to C(002), Co(111), Co(200), and Co(220) plane. This suggests that cobalt in the Co-PPy-TsOH/C catalysts exists mainly as metallic α-Co with face-centered cubic (fcc) structure. The Co(111) and Co(200) peaks become sharper and sharper with the order of cobalt acetate, cobalt nitrate, cobalt chloride and cobalt oxalate, implying a growth in the crystallite size of metallic cobalt. Generally, an average crystallite size, d, can be estimated with the Shcherrer equation [27, 28]: (4) where λ is the wavelength of incident X-ray, θ is the incident angle of X-ray for a

specific mirror, and B is the half-peak width. In order to avoid the interference of CoO on the Co(111) plane, the Co(200) plane was adopted in this study to calculate the crystallite size of metallic cobalt. The calculated specific values are listed in Table 1. It can be inferred that the relativity of the crystallite size of metallic cobalt in the catalysts is exactly opposite to the trend of ORR performance. ABT-888 in vitro In addition, Clomifene two weak diffraction peaks observed at 2θ of 36.5° and 42.2° indicate the co-existence of a very small amount of CoO (PDF 43–1004) in the catalysts. Therefore, it could be figured out that the crystallite size of metallic cobalt in the catalysts has essential influence on the catalytic performance towards ORR, the smaller the crystallite size, the better the performance. A small-amount co-existence of CoO in the catalysts does not have an adverse effect on the performance. But on the contrary, it is probably that the synergetic effect between metallic cobalt and the oxide may effectively enhance

the catalytic performance as presented by previous researches [29, 30]. Figure 4 XRD patterns of Co-PPy-TsOH/C catalysts prepared from various cobalt precursors. Table 1 Crystallite size of metallic cobalt in Co-PPy-TsOH/C catalysts prepared from various cobalt precursors Cobalt precursor Crystallite size of metallic co/nm Cobalt acetate 0.4253 Cobalt nitrate 0.4947 Cobalt oxalate 0.6432 Cobalt chloride 0.6099 Figure 5 GSK2118436 solubility dmso displays TEM images of the Co-PPy-TsOH/C catalysts prepared from various precursors. Small and uniformly distributed metallic cobalt particles can be clearly seen in the catalyst with cobalt acetate as precursor. Yet, when cobalt nitrate is used as the precursor, serious agglomeration of the catalyst particles can be found, the particle size even reaches as large as 50 nm.