Ever-increasing global energy consumption has increased aggregate demand on electrochemical energy storage devices with high energy density. Over the past few decades, manganese oxides have attracted wide attention due to their abundant reserves, low cost, environmental friendliness, and high theoretical capacity. However, most reported manganese-based materials have exhibited capacity far below the theoretical capacity, which was only on the basis of Mn3+/Mn4+ couple. The rich chemistry of manganese enables it to exist in various valence states, such as Mn0, Mn2+, Mn3+, Mn4+, and Mn7+, providing great opportunity for discovering new manganese-based electrode systems. Herein, we formed a Mn2+/Mn4+ couple from a manganese-based colloidal system with rare earth (RE) modification, which was formed in-situ on nickel (Ni) foam in KOH electrolyte under an electric field assistance. The Mn-based colloidal electrode, with Mn:Ce mass ratio of 1:0.5, achieved a high specific capacitance of 2985 F g–1 at 3 A g–1, which was higher than the theoretical capacity of 2193 F g–1 on the basis of the Mn3+/Mn4+ couple. After the addition of Ce3+, the prepared sample exhibited improved rate capability performance. Our manganese-based colloidal electrode with RE modification delivered a high specific capacitance of 1223 F g–1 at 20 A g–1, with 54.5% retention of 2243 F g–1 at 3 A g–1 at Mn:Ce mass ratio of 1:0.05. Colloidal electrode systems involving Mn-based colloids are a novel way to engineer the electrochemical performance of inorganic materials.
Multifunctional and ultrathin tin oxide (SnO 2 ) compact layer is modified by europium ion doped ytterbium fluoride (YbF 3 :Eu 3+ ), which is first designed and fabricated by a facile spin-coating method for the dye-sensitized solar cell (DSSC). The device with SnO 2 /YbF 3 :Eu 3+ compact layer exhibits enhanced long-term stability and photoelectric conversion efficiency (PCE) compared to those of the device without compact layer. The enhanced long-term stability is due to the SnO 2 /YbF 3 :Eu 3+ compact layer can transform ultraviolet (UV) light into visible light to mitigate dye degradation . The enhanced PCE is associated with the reduced recombination rate of electrons, the enhanced short-wavelength light response, and the high transparency of the compact layer. Moreover, the novel strategy of preparation SnO 2 /YbF 3 :Eu 3+ compact layer is an universal method to adjust rare-earth species to achieve up- or down-conversion functions, and the multifunctional compact layer can be widely applied in the photovoltaic device .
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