A step forward into hierarchically nanostructured materials for high performance micro-supercapacitors: Diamond-coated SiNW electrodes in protic ionic liquid electrolyte

•Development and performance of a symmetric micro-supercapacitor made of diamond-coated SiNWs using a protic ionic liquid•The device delivers a specific capacitance of 1.5 mF cm− 2 and a power density of 25 mW cm− 2 at a large cell voltage of 4 V.•The lifetime of the device exhibits remarkable electrochemical stability after 1 · 106 cycles.

Silicon nanowires (SiNWs) were successfully coated by uniform, adherent and homogenous ultra-thin crystalline diamond films through microwave enhanced chemical vapor deposition (MWCVD). The as-grown functionalized nanowires were employed as electrodes in a symmetric micro-supercapacitor (MSC) using a protic ionic liquid electrolyte [triethylammonium bis(trifluoromethylsulfonyl)imide; Et3NH TFSI]. The electrochemical performance of the device delivered a specific capacitance of 1.5 mF cm− 2 and a power density of 25 mW cm− 2 using an enlarged cell voltage of 4 V. Furthermore, a remarkable cycling stability was evaluated after 1 · 106 galvanostatic cycles at a high current density of 10 mA cm− 2 with an excellent capacitive behavior. These results confirm that diamond-coated SiNW micro-supercapacitors exhibit very promising performances dealing with MSCs based on CVD-grown SiNWs.

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