Effect of pH on PtRu electrocatalysts prepared via a polyol process on carbon nanotubes

Nanofabrication of uniform and stabilizer-free self-assembled platinum monolayers as counter electrodes for dye-sensitized solar cells

“…This observation might indicate that the reaction reverted to the Pt IV species, as proposed by Herricks et al 30 We therefore hypothesize that the formation of hydroxo-chloro Pt IV complexes, Pt(OH) n Cl 6-n 2 À , might be involved during the initial stage of the polyol reduction in the presence of NaOH. This mechanism is consistent with that proposed by Ren and Xing, 28 who indicated the formation of hydroxo-chloro Pt II complexes, Pt(OH) n Cl 4-n 2 À , during the hydrolysis of a Pt II precursor at a high pH. In our case, the hydrolysis to form Pt(OH) n Cl 6-n 2 À competed with the reduction of Pt IV to Pt 0 via a Pt II intermediate PtCl 4 2 À ; further reduction of the Pt(OH) n Cl 6-n 2 À complexes would become a rate-determining step to significantly slow the reduction at higher pH.…”

“…Rather than adding a capping agent to protect the reduced Pt NPs from further aggregation, we added various proportions of NaOH to the polyol solutions to control the rate of reduction to form Pt NPs under various pH conditions. 23,28,29 The SH-modified TCO substrate was then immersed in the Pt NP solution prepared at 295 K for 12 h to complete the formation of SAM-Pt on a clean surface of TCO. The bottom right panel of Scheme 1 shows an energy dispersive X-ray spectrometer mapping image of a SAM-Pt on a fluorine-doped tin oxide (FTO) glass substrate (also shown in Supplementary Figure S1), demonstrating the uniform morphology of the SAM-Pt NP synthesized under conditions free of stabilizer and with a controlled pH.…”

“…[26][27][28] Ethylene glycol (EG) was used in the polyol approach to serve not only as a solvent to dissolve the H 2 PtCl 6 precursor but also as a gentle reducing agent to produce the required Pt NPs with a uniform size. Xia et al 26,27 demonstrated that a shapecontrolled synthesis of Pt nanocrystals is achievable during the polyol reduction of a Pt precursor in the presence of a capping agent and a Fe III species in a trace amount under oxygen-free conditions.…”

Effect of pH Value on Performance of PtRu/C Catalyst Prepared by Microwave‐Assisted Polyol Process for Methanol Electrooxidation

“…In addition, while in the solution with lower pH value (pH < 2), the higher concentrations of proton and chlorine ions in the solution can hinder the reduction reaction. And the glycolate is nearly non-existing and replaced by glycolic acid which is a poor stabiliser [23] for the Pt colloids, that is, glycolic acid can not effectively inhibit growth of metallic nanoparticles [29,30], and can easily lead to the agglomeration of catalyst particles. Because the intermediate Pt and Ru hydroxide phases produced [23] at the higher pH value in polyol medium [17] may limit the reduction rate of metals and the difference of reduction rate between Pt 4+ and Ru 3+ with the pH value variation may also influence the synthesis of PtRu particles, the pH value variation can result in the formation of nonuniform PtRu catalyst.…”

“…Nowadays, microwaveassisted polyol process has been widely used in preparing metal particles [17][18][19][20][21][22]. Ren and Xing [23] synthesised the PtRu/CNTs via polyol process with the smaller size and the higher electrocatalytic activity for methanol electrooxidation. Nanosised PtRu catalyst with average particle size of 2.6 nm and distributed homogeneously on carbon support was prepared via the polyol process by Lee et al [24], and its performance is comparable with that of the commercial catalyst.…”