Silicon-based supercapacitors are highly essential for the utilization of supercapacitor technology in consumer electronics, owing to their on-chip integration with the well-established complementary metal–oxide–semiconductor-related fabrication technology. In this study, silicon nanowalls were carved on commercially available silicon wafers by using a facile, low-cost and complementary metal–oxide–semiconductor compatible method of metal (silver)-assisted chemical etching. The electron microscopic studies of the carved out silicon nanowalls reveal that they are smooth, single crystalline and vertically aligned to their base silicon wafer. Raman and ATR-FTIR spectroscopy confirmthat the surface of the silicon nanowalls has Si–O–Si bonded structures. Cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) studies were carried out in the organic electrolyte tetraethylammonium tetrafluroborate(NEt$_4$BF$_4$) in propylene carbonate (PC). It is evident from both the CV and GCD studies that the silicon nanowalls exhibit redox peaks arising from the silver-related deep-level trap state in silicon in contact with adsorbed water and also from the oxidation of silicon and its hydrides by the water present in the electrolyte. The presence of silver in silicon nanowalls and water in the electrolyte are considered to be due to the minute amount of silver left over during its removal by HNO$_3$, owing to the bunching of nanowalls and the highly moisture sensitive nature of the electrolyte, respectively. The influenceof such redox peaks on capacitance and cycle life are discussed.

ZnO-flaky-like nanoflowers with enhanced photocatalytic activity were synthesized by a new hydrothermal technique. The material was characterized and the photocatalytic studies were conducted under solar light irradiation for a model azo dye, Orange G. The material was compared with ZnO nanosphere and nanorod. The results showed the particle size of the nanostructures as a nanorod is 62–81 nm, as a nanosphere is 40–70 nm and as flaky nanoflowers is 20–30 nm (thickness of the flake). The photocatalytic activity showed an enhanced 2-fold increase in the activity for nanoflowers when compared to nanorods and spheres. The Brauner–Emmett–Teller results showed that the nanoflowers (14.197 m$^2$ g$^{-1}$) had a higher surface area nearly 3.5 times when compared to the nanospheres (4.06 m$^2$ g$^{-1}$) and seven times with nanorods (2.1 m$^2$ g$^{-1}$) which is the possibility of such high photocatalytic activity. The smaller particle size and the arrangement of nanoflowers play an important role in enhanced photocatalytic activity.