Biomass-based controllable morphology of carbon microspheres with multi-layer hollow structure for superior performance in supercapacitors.

The electrochemical properties of corn starch (CS)-based hydrothermal carbon microsphere (CMS) electrode materials for supercapacitor are closely related to their structures. Herein, cetyltrimethyl ammonium bromide (CTAB) was used as a soft template to form the corn starch (CS)-based carbon microspheres with radial hollow structure in the inner and middle layers by hydrothermal and sol-gel method. Due to the introduction of multi-layer hollow structure of carbon microsphere, more micropores were produced during CO2 activation, which increased the specific surface area and improved the capacitance performance. Compared to commercial activated carbon, the four different morphologies of corn starch CMS had better electrochemical performances. Consequently, the proposed CO2-(CTAB)-CS-CS exhibits a high discharge specific capacitance of 242.5F/g at 1 A/g in three-electrode system with 6 M KOH electrolyte, better than commercial activated carbon with 208.5F/g. Moreover, excellent stability is achieved for CO2-(CTAB)-CS-CS with approximately 97.14 % retention of the initial specific capacitance value after 10,000 cycles at a current density of 2 A/g, while the commercial activated carbon has 86.96 % retention. This implies that the corn starch-based multilayer hollow CMS could be a promising electrode material for high-performance supercapacitors.

High-Voltage Redox Mediator of an Organic Electrolyte for Supercapacitors by Lewis Base Electrocatalysis.

Redox electrolytes for supercapacitors (SCs) have recently sparked widespread interest. Due to the redox reactions within electrolytes, they can achieve high capacitance and long cycle stability. However, the energy density of SCs with redox electrolytes is limited by the narrow applied electrochemical window due to the irreversible side reaction of redox mediators at high potential. To overcome this issue, a redox mediator with a high redox potential, tetrachloridehydroquinone (TCHQ), is added to organic electrolytes to obtain a broad electrochemical window. TCHQ is designed to undergo a dehydrogenation reaction catalyzed by N-doped activated carbon to provide capacitance. The pyrrole N atoms have the highest electrocatalytic activity based on the theoretical calculation of reaction overpotential with predicted reaction pathways due to their Lewis basicity. Benefitting from that, TCHQ shows promising reversibility with a larger electrochemical window (up to 2.7 V). As a result, a higher energy density is obtained when compared to commercial SCs. This study proposes a strategy for designing redox mediators and interfaces of SCs with high energy density and a calculation method of dehydrogenation reaction electrocatalysis.