Spectroelectrochemical investigation of MnO2 electro-generation and electro-reduction in acidic media

Agar Acts as Cathode Microskin to Extend the Cycling Life of Zn//α-MnO2 Batteries

The Zn/MnO₂ battery is a promising energy storage system, owing to its high energy density and low cost, but due to the dissolution of the cathode material, its cycle life is limited, which hinders its further development. Therefore, we introduced agar as a microskin for a MnO₂ electrode to improve its cycle life and optimize other electrochemical properties. The results showed that the agar-coating layer improved the wettability of the electrode material, thereby promoting the diffusion rate of Zn²⁺ and reducing the interface impedance of the MnO₂ electrode material. Therefore, the Zn/MnO₂ battery exhibited outstanding rate performance. In addition, the agar-coating layer promoted the reversibility of the MnO₂/Mn²⁺ reaction and acted as a colloidal physical barrier to prevent the dissolution of Mn²⁺, so that the Zn/MnO₂ battery had a high specific capacity and exhibited excellent cycle stability.

Extraction of moderate oxidation state technetium species between 30 % tri-n-butyl phosphate and H2SO4/HNO3

The extraction of technetium species at oxidation state lower than +7 has been examined in sulfuric and sulfuric/nitric acid solutions using UV–Vis spectroscopy and optically transparent thin layer cell (RVC-OTTLE). Soluble Tc(III), TcO²⁺ and [Tc₂O₂]³⁺ species with absorption bands at 420–450, 400, and 502 nm, respectively, were detected as products of pertechnetates electroreduction. The distribution ratios of ⁹⁹Tc with lower than +VII oxidation state ionic species between 4 M H₂SO₄ and 30 % TBP/kerosene were found and are significantly lower than for TcO₄⁻ in the same solution.

Thin layer spectroelectrochemical (RVC-OTTLE) studies of pertechnetate reduction in acidic media

The electroreduction of the pertechnetate ions has been examined in sulfuric acid solutions (0.5–4 M) using optically transparent thin layer spectroelectrochemical (RVC-OTTLE) cell. Soluble Tc(III), TcO²⁺ and [Tc(μ-O)₂Tc]^3+/4+ species with absorption bands at 420–450, 400, and 502 nm, respectively, were found to be formed during the reduction of TcO₄⁻ ions. The strongly acidic medium was found to stabilize technetium ionic forms with lower oxidation states. Spectroelectrochemical measurements performed in 4 M H₂SO₄ show different stability of dimeric structure of Tc(III, IV) and simple TcO²⁺ ions. The monooxotechnetium(IV) ions can be electrooxidized at potentials lower than 0.6 V versus Ag,AgCl_(sat.) while dimeric structures of Tc, [Tc(μ-O)₂Tc]^3+/4+, are electrooxidized to pertechnetate ions at potentials higher than 0.8 V versus Ag,AgCl_(sat.)