Strategies and insights towards the intrinsic capacitive properties of MnO2 for supercapacitors: Challenges and perspectives

Highlights: • The electrolyte-dependent faradic reaction process for MnO₂-based supercapacitors was discussed. • Recent advances on activating intrinsic capacitance of MnO₂ were summarized. • The electrochemical performance comparisons for different strategies were displayed. • The remained challenges for MnO₂-based energy storage devices were highlighted. -- Abstract: Supercapacitors have been widely viewed as one promising candidate of next-generation energy storage devices. To configure a supercapacitor with high-charge storage for practical applications, it is one of urgent issues to take up effective/universal strategies to well tailor electrode materials for desired properties and functions. As one of representative materials with intrinsic pseudocapacitive behaviors, MnO₂ is attractive because of high theoretical capacitance value and large potential window. Nevertheless, a wide gap between the practical and theoretical capacitance value greatly hinders its further applications and remains a major challenge. Herein, we systematically reviewed recent advances on activating intrinsic capacitive properties of MnO₂ to shorten this distance, which was classified into five branches including conductive species coupling, single/few-layers constructing, heterojunction configuring, defects engineering and metal doping. In addition, an outlook on the practical applications of MnO₂ and involved potential challenges in energy storage field was discussed and highlighted. It is believed that this article can function as a momentum calling for more endeavors into development of advanced electrode materials with fasinating capacitive performance.