Supplementary Material (ESI) for Chemical Communications

Graphitized multiwalled CNTs (carbon nanotubes) were purchased from ECHO Chemical Co. Ltd. (Taiwan) with an external diameter of 2040 nm and a length of 0.5200 m. The raw CNT powder was etched in 15 M boiling nitric acid solution for 1h. The CNTs were then washed several times with de-ionized water until the pH value of the solution became neutral. Nickel hydroxide nanonets were grown on the bare stainless steel (SS) and SS-supported CNT film by a simple hydrothermal method. In a typical procedure, NiSO4·6H2O (0.09 g) and urea (0.09 g) were dissolved in deionized water (30 mL) under continuous magnetic stirring at room temperature for 30 min to form a homogenous solution. The mixture was then transferred into a Teflon-lined SS autoclave. SS sheets of type 304 (2 cm x 2 cm) were used as the electrode substrate. SS sheets were polished by emery paper with grain size of about 65 m, and cleaned by rinsing with acetone then rinsed with de-ionized water to remove any trace of contaminants from their surface. The SS-supported CNT film was prepared by EPD (electrophoretic deposition) in a suspension containing CNT powder (20 mg), 0.1 mM Ni(NO3)2, and isopropyl alcohol (50 mL). The nickel nitrate acted as a charging agent for facilitating the dispersion and EPD of CNTs. EPD was carried out by applying a potential difference of 60 V (Keithley, 2400 source meter) across the working (negative electrode, SS) and counter (positive electrode, Pt) electrodes at room temperature. The working electrode was placed in between two parallel Pt counter electrodes. After EPD, the electrode with attached CNT film was rinsed with de-ionized water and then dried at 300oC for 1 h. The mass loading of CNT film was measured to be 0.22 mg. Two sheets of SS or SS-supported CNT film were put into the