Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors

In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO₂–Ta₂O₅ coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 °C preserves a large fraction of hydrous RuO₂·xH₂O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta₂O₅ incorporation can manipulate the RuO₂ crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO₂–Ta₂O₅ electrode, which can deliver an energy density of 4.8 Wh kg⁻¹ at a power density of 8720 W kg⁻¹ (or 8.3 Wh L⁻¹ at 15,000 W L⁻¹). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO₂–Ta₂O₅ thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.