2D Fractal Arrays of Ultrathin Silicon Nanowires as Cost‐Effective and High‐Performance Substrate for Supercapacitors

Silicon is the most diffused material in the industry; thus, considering its high capacity for energy storage, silicon-based materials are well studied as battery anodes and supercapacitors. Si nanowires (NWs) emerge due to the high surface to volume ratio, its compatibility with a wafer processing typical of microelectronics, and are studied as anodes for lithium batteries as well as coupled with other materials for supercapacitor application. In this article, the synthesis and application are reported as a lithium anode of 2D fractal arrays of ultrathin Si NWs obtained by a thin-film metal-assisted chemical etching (MACE). These Si NWs exhibit a density of about 1012 NWs cm-2, maximizing the surface to volume ratio compared to silver-salts MACE and other NW fabrication approaches. By using 2.7 mu m long NWs, a pseudo-capacitor behavior with a specific capacitance of about 274.2 mu F cm-2 at a scan rate of 50 mV s-1 is obtained. This specific capacitance is two orders of magnitude higher than the one obtained in the same condition by using NWs synthesized by silver-salt MACE. In this result, the route is opened toward the application of these fractal arrays of ultrathin Si NWs as substrate for supercapacitors with improved efficiency.A 2Dfractal array of ultrathin Si nanowires (NWs) was studied for supercapacitors, achieving a specific capacitance of 274.2 mu F/cm2; at a 50mV/s scan rate with 2.7 mu m long NWs. This is two orders of magnitude higher than typical NWs, showcasing thematerial's potential for enhancing Si-based supercapacitors.image (c) 2024 WILEY-VCH GmbH