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

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.