MoO₃–Carbon Nanotube Negative Electrode Designed for a Fully Hybrid Asymmetric Metal Oxide-Based Pseudocapacitor Operating in an Organic Electrolyte

Abstract

A carbon nanotube/molybdenum trioxide hybrid material has been developed in this contribution as a negative electrode for pseudocapacitors. Molybdenum oxide was obtained by cathodic electrodeposition directly on binder-free carbon nanotube mats, followed by annealing of the electrode at 350 °C under air. The resulting pseudocapacitive material has been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and electrochemistry. The effect of heat treatment on the crystallinity and oxidation state of molybdenum oxide as well as on electrochemical performances was investigated. By optimizing the synthesis conditions, a maximum capacitance of up to 274 F/g has been obtained at 2 mV/s in an organic electrolyte (LiTFSI/GBL 0.5 M) with high electroactive material loading and binder-free electrodes (1 mg/cm2 with up to 75% of MoO3). A fully asymmetric pseudocapacitor was then developed in association with a positive pseudocapacitive hybrid electrode material based on MnO2 mixed with rGO/CNT mats. This MoO3–CNT||MnO2–rGO–CNT hybrid system, fabricated using industrially suitable, nontoxic, and low-energy-consuming fabrication methods (dynamic spray-gun deposition of an alcohol suspension followed by electrodeposition in an aqueous electrolyte), showed a high energy density of 23 Wh/kg with a power density of up to 100 W/kg. This system was able to maintain energy densities higher than 10 Wh/kg for high power densities of up to 4 kW/kg, proving that optimization of pseudocapacitive materials through specific adaptations to organic electrolytes is viable. The controlled nanostructuration and crystallization of the electrode material and the complementary asymmetric configuration have important beneficial effects on the performances of the global system.

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