PtPb ordered intermetallic nanoparticles (NPs) was deposited on titanium oxide (TiO₂)/cup-stacked carbon nanotube (CSCNT) for improvement of the activity of the electrochemical oxygen reduction reaction (ORR). Employment of CSCNT as a support material caused high loading of PtPb NPs/TiO₂. The PtPb NPs/TiO₂/CSCNT which was prepared by the step-by-step preparation method; annealing under inert gas atmosphere with Ti-alkoxide for TiO₂, photodeposition for Pt NPs and microwave synthesis to prepare ordered intermetallic PtPb NPs on TiO₂ via the reaction of Pb²⁺ with Pt/TiO₂, exhibited the enhancement of ORR electrocatalytic activity. Scheme 1 shows a schematic depiction of the step-by-step preparation method of PtPb NPs/TiO₂/CSCNT by annealing under inert gas atmosphere with Ti-alkoxide for TiO₂, photodeposition for Pt NPs and microwave synthesis to prepare ordered intermetallic PtPb NPs on TiO₂ via the reaction of Pb²⁺ with Pt/TiO₂. A commercially available CSCNT (100 nmf, Sankei Giken Kogyo Co., Ltd., Japan) was treated with an acidic mixture solution of H₂SO₄ (6 M) and HNO₃ (6 M) at 90 °C for 6 h to introduce a carboxylic acid functional group on the surfaces and then washed with water, followed by drying overnight at 110 °C. A Ti precursor solution was prepared by dissolving Titanium (IV) isopropoxide (TTIP, 0.2 g) in iso-propanol (100 mL). Functionalized carbon was added to the solution under vigorous stirring. De-ionized water (1.0 mL) was used to accelerate the reaction of TTIP. After further stirring for 6h, the resulting mixture was collected and dried overnight under vacuum condition, followed by heat-treatment at 450 °C for 1 h under Ar atmosphere to yield CSCNT-supported TiO₂ (TiO₂/CSCNT). Pt NPs were photochemically deposited on TiO₂/CSCNT to prepared Pt NPs/TiO₂/CSCNT. The Pt NPs/TiO₂/CSCNT (0.030 g) and Pb(CH₃COO)₂ ¥3H₂O (0.022 mmol) were dissolved in 50 mL of ethylene glycol. The mixture was then sonicated in a bath-type ultrasonicator and treated in the flask with a reflux set for 1 min under 300-W microwave radiation. The mixture in the flask was cooled to room temperature with water. The mixture was again treated under microwave (focused microwave instrument, CEM) radiation of 300 W for 9 min. After the mixture cooled, the PtPb NPs/TiO₂/CSCNT was collected via centrifugation, washed sequentially with methanol and dried under vacuum. Figure 1 shows linear-sweep ORR voltammograms for (a) PtPb NPs/TiO₂/CSCNT and (b) Pt NPs/CB in O₂-saturated 0.1 M HClO₄ solution. Here, CB-supported Pt NPs (b) was used as a control. The ORR curve (a) obtained with PtPb NPs/TiO₂/CSCNT shifts to the positive direction, owing to the interaction between PtPb NPs and TiO₂when compared with one of Pt/CB (b).

Scheme 1. Schematic representation of the step-by-step methode to prepare ordered intermetallic PtPb NPs/TiO2/CSCNT

Figure 1. Linear sweep voltammograms (LSV) for ORR on (a) PtPb/TiO₂/CSCNT and (b) Pt/CB in O₂-saturated 0.1 M HClO₄ aqueous solution at 10 mVs^-1. Inset: a TEM image of PtPb/TiO₂/CSCNT used to obtain the LSV.