Axis ultra xps system

G and GO nanosheets were obtained from the Nanjing XFNANO Materials Tech Co., Ltd., China. The single layer G was prepared by thermal exfoliation reduction and hydrogen reduction. GO was synthesized using Hummer's method. The physicochemical properties of G and GO are provided in Figures 1, 2 and S1–3. G 0.02 g was suspended in 200 ml pure water (18.2 Ω/cm) by ultrasonic apparatus running for 40 min at 400 W. Next, suspended G was placed in a light incubator maintaining 3000 Lx irradiation, 24°C temperature, and 80% humidity. The hydration was conducted for 120 days. During the hydration, pure water was complemented to keep the volume at 150–200 ml. Finally, water was evaporated and then lyophilized to collect HGR. XPS measurements were conducted using an Axis Ultra XPS system (Kratos) with a monochromatic Al Kα X-ray source (1486.6 eV). The spectra were analyzed using Casa-XPS V2.3.13 software. The peak deconvolutions were performed using Gaussian components after a Shirley background subtraction. AFM and TEM were performed on Veeco Nanoscope 4 and JEM-2010 FEF, respectively.

A Zennium Zahner electrochemistry workstation with a QCM was used for electrochemical deposition and analysis. The Pt deposition was done using a constant voltage mode. For the Pt monolayer deposition, a pulse duration of 5 s was set for each deposition cycle, whereas on the basis of the J-t curve (Fig. 2), the effective deposition lasted for ~0.2 s. The cyclic voltammetry (CV) and Tafel analysis were conducted in a nitrogen-purged H₂SO₄ solution with a scan rate of 50 mV s⁻¹. The catalysts were cycled many times by CV until a stable CV curve developed. Chronopotentiometry was carried out at a constant current density of 10 mA cm⁻² for Pt monolayer/Au NF/Ni foam. A Pt sheet was used as the counter electrode, and a calomel electrode was used as the reference (sweep rate, 50 mV s⁻¹). A Kratos Axis Ultra XPS system was used with a monochromatic Al-Kα source.