In order to further explore the influence of decoration on Pt surface, the as-prepared electrocatalysts were investigated in N
2-saturated 0.1 mol/L HClO
4 and 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution
via cyclic voltammogram (CV). It was reported that the range of 0.05–0.40 V was known as underpotential-deposited of hydrogen (H upd, H
+ + e
− ⇋ H
upd), the region between 0.40–0.80 V was the pseudocapacitance region, and in 0.80–1.05 V the oxidation of Pt took place, where a large amount of oxygen-containing species could be generated on the surface of Pt [
24,
25]. In
Fig. 2a, the H upd region of Mel-Pt/C and DCD-Pt/C are both smaller than that of Pt/C, demonstrating that two organic compounds are decorated on Pt surface successfully and the region of Mel-Pt/C is the smallest, indicating that the decoration amount of Mel is higher due to the stonger interaction strength with Pt [
26]. Also, the same conclusion can be obtained from
Fig. 2b, where the H upd of Mel-Pt/C is the smallest. In 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution, a couple of redox peaks in double electrode layer region (0.4–0.75 V) are regarded as the adsorption of phosphate ions [
14]. When these electrocatalysts are applied to 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution, the redox peaks of DCD-Pt/C (
Fig. 2c) and CA-Pt/C (
Fig. 2d) are relieved only modestly, whereas the redox peaks of Mel-Pt/C disappear almost completely relative to Pt/C, which indicates that Mel-Pt/C has the strongest resistance to PA because the decoration amount of Mel is the most. The decorated organic compounds can cause the third body effect, inhibiting the adsorption of PA on Pt surface [
23]. Next, CO stripping voltammetry was used to analyze Pt-OH
ad formation on Pt surface decorated with organic compounds because it has been reported that CO oxidation can be facilitated by neighboring Pt-OH
ad. From Figs. S7a and b (Supporting information), the peak potential for CO stripping of Mel-Pt/C is more positive than that of Pt/C, DCD-Pt/C and CA-Pt/C and the same results can be obtained in 0.1 mol/L HClO
4 and 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution (Figs. S8a and b in Supporting information). The result indicates that the decoration of Mel is capable of suppressing the formation of OH
ad on Pt surface to a greater extend and means that Mel-Pt/C may exhibit the highest ORR activity [
27]. After that, the effect of these organic compounds on Pt performance was investigated in O
2-saturated 0.1 mol/L HClO
4 and 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution
via linear sweep voltammetry (LSV). As shown in Figs. S9a and b (Supporting information), the half-wave potential (
E1/2) of Mel-Pt/C, DCD-Pt/C and CA-Pt/C is 0.900, 0.879 and 0.870 V (
versus RHE) that is superior to Pt/C (0.865 V), meaning that electrons transferring from organic compounds to Pt can enhance the electron density of Pt and thus improve ORR activity. Additionally, because of the strongest interaction between Mel and Pt, Mel-Pt/C has the largest increase of ORR activity (35 mV), surpassing DCD-Pt/C (14 mV) and CA-Pt/C (5 mV). When these electrocatalysts are analyzed in O
2-saturated 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution (
Figs. 2e and
f), the improvement of ORR activity is even more dramatic as a result of the decontamination of active sites. Likewise, Mel-Pt/C has the largest enhancement of ORR activity (71 mV), exceeding DCD-Pt/C (35 mV) and CA-Pt/C (24 mV). Deeper insights into their ORR activity could be obtained through comparing their MA and SA values at 0.9 V. The ECSA of these electrocatalysts was investigated by integrating CO stripping curves. The ECSA of Pt/C, Mel-Pt/C, DCD-Pt/C and CA-Pt/C were 82.5, 40.3, 45.8 and 60.6 m
2/g
Pt in 0.1 mol/L HClO
4 solution, respectively. As shown in Figs. S10a and b (Supporting information), Mel-Pt/C has the highest mass activity (MA) and specific activity (SA) in 0.1 mol/L HClO
4 solution and the MA and SA are 1.68 times and 3.45 times higher than that of Pt/C. In addition, DCD-Pt/C and CA-Pt/C also have pretty higher MA and SA. The former is 1.30 times and 2.37 times higher and the latter is 1.16 times and 1.53 times higher than that of Pt/C. Similarly, the enhancement of electrocatalysts decorated by organic compounds is larger in 0.1 mol/L HClO
4 + 0.1 mol/L H
3PO
4 solution due to the stronger tolerance to PA (Figs. S11a and b in Supporting information).