The conductivity of MgAl₂O₄ has been measured at 1273, 1473 and 1673 K as a function of the partial pressure of oxygen ranging from 10⁵ to 10⁻¹⁴ Pa. The MgAl₂O₄ pellet, sandwiched between two platinum electrodes, was equilibrated with a flowing stream of either Ar + O₂, CO + CO₂ or Ar + H₂ + H₂O mixture of known composition. The gas mixture established a known oxygen partial pressure. All measurements were made at a frequency of 1 kHz. These measurements indicate pressure independent ionic conductivity in the range 1 to 10⁻¹⁴ Pa at 1273 K, 10⁻¹ to 10⁻¹² Pa at 1473 K and 10⁻¹ to 10⁻⁴ Pa at 1673 K. The activation energy for ionic conduction is 1·48 eV, close to that for self-diffusion of Mg²⁺ ion in MgAl₂O₄ calculated from the theoretical relation of Glyde. Using the model, the energy for cation vacancy formation and activation energy for migration are estimated.

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.