Dual storage mechanism of charge adsorption desorption and Faraday redox reaction enables aqueous symmetric supercapacitor with 1.4 V output voltage

Abstract

Preparation of heterostructure electrode materials with dual storage mechanisms of charge adsorption desorption (electric double-layer capacitance) and Faraday redox reaction (pseudo-capacitance) remains a great challenge for supercapacitors with wide operating voltage and high energy density. Herein, the heterostructure ZnO nanoparticles decorated NiFe/CNTs/rGO (ZnO-FeNi/CG) was rational designed and synthesized via a straightforward two-step hydrothermal process for supercapacitor application. The rational designed flower-like heterostructure ZnO-FeNi/CG reveals outstanding specific capacitance of 1265F/g at 1 A/g and 88.5 % capacitance retention after 10,000 cycles even at 30 A/g in three-electrode test. Benefiting from the designed unique heterostructure and the effective anti-catalytic strategy, the Faradaic redox reactions of ZnO-FeNi/CG electrode were well coordinated by HER and OER, so that water splitting process was greatly suppressed under high operating voltage in aqueous alkaline electrolytes. Thus, the fabricated symmetric supercapacitor based on the dual storage mechanisms of electric double-layer capacitance and pseudo-capacitance displays 1.4 V output voltage, ultrahigh capacitance of 227F/g (1 A/g), and exceptional energy density of 62 Wh kg−1 at power density of 1400 W kg−1 as well as extraordinary capacitance retention 84.7 % for 10,000 cycles, outperforming the previous spinel-type metal oxides/carbon-based supercapacitors in aqueous alkaline electrolytes. The dual storage mechanism of charge adsorption desorption and Faraday redox reaction can provide a pathway to design next-generation aqueous symmetric supercapacitors with wide output voltage and ultrahigh energy density for advanced energy storage systems.