Powering electrodes for high performance aqueous micro-supercapacitors: Diamond-coated silicon nanowires operating at a wide cell voltage of 3 V

In this study, we report originally the excellent electrochemical performance of a micro-supercapacitor based on diamond-coated silicon nanowire (SiNW) electrodes using an aqueous electrolyte (0.1 M LiClO4). The deposition of a nanometric boron-doped diamond coating on SiNWs allowed the enlargement of the electrochemical window up to 3 V maintaining an extraordinary capacitive electrochemical response due to its high overvoltage. Thereby, the device exhibited an areal capacitance of 0.4 mF cm-2, a high power density of 50 mW cm-2 as well as an outstanding cycling stability after 2·106 galvanostatic charge-discharge cycles at a high current density of 10 mA cm-2. In addition, an ultra-fast charge-discharge rate was determined to be 1.5 ms, demonstrating the supercapacitor's enormous ability to deliver high power values at very rapid pulse times (Pmax: 321 mW cm-2). These results also evidence the potential of diamond coating to overcome the main drawbacks of silicon (e.g. rapid silicon oxidation due to presence of water) to be employed in aqueous electrolyte supercapacitors. Consequently, the role of diamond paves the way to high performance SiNW-based micro-supercapacitor development at large electrochemical windows in aqueous electrolytes, which are at present limited to 1 V.