LAUSR

Abstract Effective utilization of waste biomass has been a fascinating topic for the development of sustainable energy. An effective alkaline hydrothermal/pyrolysis process was designed to prepare highly porous carbons noted as HK-PSC800 using waste Platanus acerifolia seeds as precursors. A symmetric supercapacitor (SSC) device based the same two HK-PSC800 electrodes owns the high specific energy density (30.9 Wh kg−1 at a low power density of 500 W kg−1) with excellent rate capability. To further optimize the energy density of the device, two types of asymmetric supercapacitors (ASC) with a working potential window of 1.5 V are designed and assembled by using HK-PSC800 and Co3O4 derived from zeolitic imidazolate framework-67 as electrode materials. The specific energy density of as-fabricated ASC (Co3O4//HK-PSC800) with pure Co3O4 materials as the positive electrode is nearly the same as the SSC (HK-PSC800//HK-PSC800). However, the specific energy density of the other ASC (Co3O4@HK-PSC800//HK-PSC800) can be improved by 18.8% when 28 wt% Co3O4 is in-situ grown in HK-PSC800 as the positive electrode. This research proves that the suitable composition of ASC electrode materials helps us to develop biomass based carbons materials for application in the high-voltage and high-energy devices.