Cathodic deposition and characterization of tin oxide coatings on graphite for electrochemical supercapacitors

Amorphous tin oxide (SnOx) was cathodically deposited onto graphite electrode in a bath containing 0.1 M stannous chloride (SnCl2), 0.5 M sodium nitrate (NaNO3), and 0.4 M nitric acid (HNO3) in an aqueous solution of 50% (v/v) ethanol. The SnOx coatings grown on graphite were characterized as typical capacitive behaviors by cyclic voltammetry (CV), chronopotentiometric (CP) in 0.5 M KCl. Specific capacitance (in milli-farad per square centimeter, Ca) changes linearly with the deposition charge up to 4.5 C cm−2, and a maximum of as high as 355 mF cm−2 was obtained with the SnOx coating grown at around 5 C cm−2. For the SnOx coating deposited at 0.2 C cm−2, a maximum specific capacitance (in farad per gram, Cm) of 298 and 125 F g−1 was achieved from CVs at a scan rate of 10, and 200 mV s−1, respectively. The value of Cm significantly gets lower from 265 to around 95 F g−1 when the deposition charge increases from 0.2 to around 6.0 C cm−2. The long cycle-life and stability of the SnOx coatings on graphite via the presented cathodic deposition were also demonstrated.