Boron Element Nanowires Electrode for Supercapacitors

Abstract

attention as ideal energy storage devices owing to their excellent power density, high safety, quick charging/discharging, and good cycling stability. [7][8][9][10][11][12][13] A research frontier is to develop flexible supercapacitors with good electrochemical and mechanical performance, where the integration of flexibility in supercapacitors is of great importance for powering various flexible electronics and enabling applications in multifunctional flexible electronics. [11,[14][15][16][17] Notably, the electrode material is the most crucial component for a supercapacitor, which directly determines the performance of supercapacitors. Electrical double-layer capacitors (EDLCs) suffer from the low specific capacitance which constitutes a huge obstacle for increasing the energy density, whereas pseudocapacitors possess the higher specific capacitance but are confined by relatively poor cycling stability and long discharging time. [1,14,18] So far, intensive efforts are aimed at improving the performance of supercapacitor based on traditional active materials including carbon-based material, transitional metal-based material, and conducting polymers. [1][2][3][4]7,8,19] Although some novel materials, including sulfides, selenides, etc., have been proposed to be supercapacitive materials, the pursuit of new categories of active materials as electrodes of supercapacitors remains a great challenge. [20][21][22] Recently, Jiang and co-workers theoretically predicted the superior capacitive performance of 2D boron sheets, which exhibit specific capacitance on the order of 400 F g −1 owing to their metallicity and low weight, suggesting boron element might be a potential electrode material of supercapacitors. [23] Unfortunately, so far, the desired experimental work on any materials based on boron element for supercapacitor has not been reported.Herein, we report a new category of supercapacitor materials: boron element nanowires (BNWs). Single-crystal BNWs were synthesized through a cost-effective chemical vapor deposition (CVD) method. Surprisingly, the as-prepared BNWs demonstrate high stability and promising capacitance in all alkaline, neutral, and acid aqueous electrolytes. Especially, in an H 2 SO 4 electrolyte, the BNWs on a carbon fiber cloth (CFC) substrate achieved a capacitance up to 60.2 mF cm −2 . Moreover, to understand the mechanism of capacitance in BNWs-CFCs, we studied the electrochemically charge/discharge processes of BNWs-CFC electrodes in three different electrolytes, which reveals different The pursuit of new categories of active materials as electrodes of supercapacitors remains a great challenge. Herein, for the first time, elemental boron as a superior electrode material of supercapacitors is reported, which exhibits significantly high capacitances and excellent rate performance in all alkaline, neutral, and acidic electrolytes. Notably, boron nanowire-carbon fiber cloth (BNWs-CFC) electrodes achieve a capacitance up to 42.8 mF cm −2 at a scan rate of 5 mV s −1 and 60.2 mF cm −2 at a current d...

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