Transition Metal Oxides with Broaden Potential Window for High‐Performance Supercapacitors

The utilization of transition metal oxides (TMOs) as electrodes of supercapacitors (SCs) and energy storage devices has attained significant consideration. Various authors around the globe have reported the improvement in energy density of SCs by broadening the potential window (V), and here in this chapter, TMOs electrodes for SCs are debated to operate in expanded potential windows (~2.6 V) in aqueous electrolytes for asymmetric supercapacitors (ASCs). Initially, the grouping of nanoscale polyaniline (PANI) as an electrochemically active component and NiCo 2 O 4 as a conductive scaffold to form NiCo 2 O 4 @PANI nanorod arrays (NRAs) structure is discussed as an electrode for SCs. The fabricated electrode has operated in a broadened potential window (−0.2 to 0.8 V) and in 1 M H 2 SO 4 electrolyte has reported the better specific capacitance (901 F g −1 ) measured at 1 A g −1 . Moreover, the capacitance retention of ~91% after 3000 cycles at 10 A g −1 is also the highlight of the material. Afterward, a modified charge storage mechanism of potassium (K) ions intercalated α-MnO 2 has been debated for the first time, and it is reported that as the potential window for the material is expanded from 0 to 1.2 V for cyclic voltammetry (CV) measurements, development in specific capacitance occurs due to emergence of redox peaks. In the next section, the influence of high Na content in the Birnessite (Na 0.5 MnO 2 ) nanosheet assembled nanowall arrays (NWAs) is observed with an extended operating potential window (0-1.3 V) against Ag/AgCl electrode. Na 0.5 MnO 2 NWAs cathode has shown the specific capacitance 366 F g -1 . Notably, Na 0.5 MnO 2 //Fe 3 O 4 @C ASC is designed with a 2.6-V aqueous operating potential window reporting the improved energy density (81.7 Wh kg -1 ) and brilliant rate capability. Furthermore, Bi 2 O 3 -based electrode materials possessing broaden potential window (−1.2 to 0) are discussed as anode materials for SCs. This chapter will open new horizons for researchers and scientists to visualize the importance of broadening the operating potential window phenomenon to boost the energy density of the SCs.