Recent progress in trimetallic/ternary-metal oxides nanostructures: Misinterpretation/misconception of electrochemical data and devices

Supercapacitors (SCs) have been widely explored as emerging, electrochemically clean, and green energy storage devices. Metal oxides have been focused as promising SC electrode materials due to their excellent electrochemical, chemical and physical properties. With rapid progress in this area, mixed bimetallic oxides as well as mixed trimetallic oxides have also been explored. In a comparison, trimetallic/ternary-metal oxide-based nanostructure materials are highly desired for overcoming the limitation of poor electronic conductivity of single and bimetallic oxides. Owing to the presence of multiple oxidation states and synergistic effect, such mixed metal oxides offer high specific capacitance/capacity, excellent cycle life, and high energy density. The current review article summarizes the structure, properties, and electrochemical performance of the trimetallic/ternary-metal oxides-based nanostructures for SC applications. For the electrochemical evaluation of these electrodes, many basic fundamental misinterpretation/misconception arises over the past few years. To clarify such misconceptions, the misinterpretation in thermal terminologies; charge storage mechanism in capacitive-, pseudocapacitive-, and battery-type electrode materials; symmetric, asymmetric, and hybrid devices; and the equations used for different calculations in energy storage devices have been clarified and discussed systematically in the second part of this review article. Finally, the future outlook of the SC applications of such trimetallic/ternary-metal oxides has been addressed.