p–n Heterojunction‐Enhanced Multifunctional Silicon Nanowires/MnO 2 Nanocomposites for High‐Performance Supercapacitors and Photocatalytic Applications

Silicon nanowires/manganese oxide (SiNWs/MnO 2 ) nanocomposites were developed to exploit the p–n heterojunction effect for simultaneously enhancing electrochemical energy storage and photocatalytic performance. Silicon (001) substrates were first nanostructured into one‐dimensional SiNWs by metal‐assisted chemical etching, followed by rapid electroless deposition of MnO 2 nanoparticles. The resulting nanocomposites were characterized by SEM, EDX, XRD, SIMS, and electrochemical methods (CV, EIS, Mott‐Schottky, and GCD). MnO 2 deposition promoted efficient charge transport through the p–n heterojunction while providing abundant electroactive sites. Consequently, the MnO 2 /SiNWs electrode delivered an areal specific capacitance of 123.97 mF/cm 2 and a specific energy of 12.44 mWh/cm 2 at 10 mV/s, significantly outperforming SiNWs. In addition, at a current of 2 mA, the electrode achieved 69 mF/cm 2 with excellent coulombic efficiency and retained 90.49% of its initial capacitance after 10,000 cycles. The MnO 2 /SiNWs nanocomposite also exhibited outstanding visible‐light photocatalytic activity, degrading 98.34% of Rhodamine B within 4 h, compared with only 11.45% for SiNWs, while maintaining 86.13% degradation efficiency after six reuse cycles. The enhanced performance is attributed to improved electron–hole separation at the SiNWs/MnO 2 p–n heterojunction. These results demonstrate that MnO 2 /SiNWs nanocomposites are promising multifunctional materials for high‐performance supercapacitors and efficient photocatalytic degradation of organic pollutants.