Phosphorus‐Doped Nanocrystalline Diamond for Supercapacitor Application

Abstract Heavily phosphorus‐doped nanocrystalline diamond (P‐NCD) has been grown by using a plasma‐enhanced chemical vapor deposition technique and further applied as an electrode for the construction of supercapacitors. This P‐NCD electrode shows a capacitance of 11.40 μF cm −2 in 1.0 M Na 2 SO 4 at a scan rate of 10 mV s −1 and behaves as a n‐type semiconductor electrode in redox‐active electrolyte of 0.05 M Fe(CN) 6 3−/4− +1.0 M Na 2 SO 4 . The post‐thermal treatment of as‐grown P‐NCD films in vacuum at high temperatures for several hours leads to the achievement of much higher capacitances. At the scan rates of 10 and 20 mV s −1 , the capacitances are up to 2.01 and 63.56 mF cm −2 for an electrical double layer capacitor and a pseudocapacitor, respectively. Such high capacitances originate from the improved electrical conductivity, varied surface state and surface functional groups, and changed content of non‐carbon diamond inside the P‐NCD films during the annealing treatment. Therefore, P‐NCD films are quite promising as an electrode material for supercapacitor applications.