Carbon-coated Si/MnO2 nanoneedle composites with optimum carbon layer activation for supercapacitor applications

Carbon-coated Si/MnO2 ternary hybrid composites were fabricated. Initially, a carbon layer was formed directly on the Si surface by thermal vapor deposition. The resulting carbon layer was activated using phosphoric acid to control its surface area and porosity. The degree of activation of the carbon layer was optimized by measuring the specific capacitance of electrodes activated using different phosphoric acid concentrations. The carbon-coated Si electrode made by activation with 3 M phosphoric acid (Si@C(3)) exhibited the highest specific capacitance (117.2 F g−1 at 1 A g−1). Subsequently, MnO2 nanoneedles were formed on the carbon-coated Si surface with different feed ratios. The MnO2 nanoneedles were found to be homogeneously dispersed. The Si@C(3)/MnO2 composite formed with a MnO2/Si@C(3) feed ratio of 2:1 (Si@C(3)/MnO2(2)) showed the highest specific capacitance (240.1 F g−1 at 1 A g−1) of the Si@C(3)/MnO2 composite electrodes. The proposed ternary-hybrid composites can be used for the fabrication of high-performance electrodes.