In Situ Construction of the Coral-like Polyaniline on the Aligned Silicon Nanowire Arrays for Silicon Substrate On-chip Supercapacitors

Silicon substrate on-chip (SSOC) supercapacitors have recently attracted considerable attention in electronic devices because of their compatibility with the current silicon-based micro- and nanofabrication processes. However, the low-energy density of the silicon substrate supercapacitors largely restricts their practical applications. Herein, in situ polymerization of coral-like polyaniline (PANI) was performed over the surfaces of aligned silicon nanowires (SiNWs) prepared by the metal-assisted chemical etching process. Especially, the coral-like morphology of the PANI over the aligned SiNWs (PANI@SiNWs) is regulatable with the control of the concentration of the aniline monomer. After systematical structural characterization of PANI@SiNWs by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and Raman spectroscopy, it is confirmed that the coral-like morphology provides higher specific surface area and more effective charge transport channels, which essentially benefits the exchange of the aqueous electrolytes on the surface of the electrode to improve the electrochemical performances of the material. Therefore, compared to individual PANI and SiNWs, the prepared PANI@SiNW-based supercapacitor electrode exhibited a much higher areal capacitance of ∼95 mF/cm2 at a scan rate of 10 mV/s. The obtained PANI@SiNW electrode exhibited reliable stable cyclability with a capacitance retention of 71.8% of the initial value compared with pure PANI. The presented work demonstrates a feasible approach to improve the areal capacitance value of SSOC supercapacitors.