Natural graphite powder

GO was prepared using natural graphite powder (Sinopharm Chemical Reagent Co., Ltd) according to the modified Hummer’s method. Prior to the synthesis of PtM/rG-O nanocomposites, the as-prepared GO was dispersed in deionized water by ultrasonication (KQ2200E system, Kunshan Ultrasonic Instruments Co., Ltd, 40 KHz, 80 W) for 3 h. PtM/rG-O nanocomposites were synthesized by the solvothermal method using ethylene glycol (EG)-water as the solvent. In a typical synthesis, Pt(acac)₂ (0.25 mmol, 0.0985 g) was dissolved in EG (30 mL) under magnetic stirring with a short heating (90–100 °C, 5 min). Co(NO₃)₂⋅6H₂O (0.25 mmol, 0.0728 g) or NiSO₄⋅6H₂O (0.25 mmol, 0.0657 g) was subsequently dissolved in the solution containing Pt(acac)₂. In the presence of the additional reductant, 1,2-hexadecanediol (HAD, 0.5 mmol, 0.129 g) was dissolved in EG (10 mL) and then added dropwise in the EG solution containing the metal salts (20 mL). Then, 10 mL of GO aqueous solution (2 mg/mL) was added dropwise into the EG solution. After 30 min of stirring, the mixture was transferred to, and sealed in, a 50-mL Teflon-lined stainless steel autoclave and heated to 180 °C for 8 h and then cooled to room temperature. The precipitate was collected and washed alternately with ethanol and deionized water by centrifugation (10,000 rpm, 5 min) and then dried at 60 °C in vacuum.

Natural graphite powder, agarose, EB, and other chemicals were purchased from Sinopharm Chemical Reagent Corp. and used without further purification. Deionized water (16 MΩ cm) was obtained from a Nanopure Water Systems UV (Thomas Scientific, Swedesboro, NJ).