Abstract
We report a photonic technique to instantaneously synthesize cobalt oxide reduced graphitic oxide (CoOx-rGO) supercapacitor electrodes. The electrode processing is achieved through rapidly heating the precursor material by irradiation of high-energy pulsed mostly visible light from a xenon lamp. Due to the short duration of the light pulse, we prepared the electrodes at room temperature instantaneously (ms), thus eliminating the several hours of processing times of the conventional techniques. The as-prepared electrodes exhibited a highly porous morphology, allowing for enhanced ionic transport during electrochemical interactions. The electrochemical properties of the CoOx-rGO electrodes were studied in 1 M KOH aqueous electrolyte. The non-rectangular cyclic voltammetry (CV) curves with characteristic redox peaks indicated the pseudocapacitive charge storage mechanism of the electrodes. From the discharge curves at 0.4 mA/cm2 and 1.6 A/g constant current densities, the electrode showed areal specific capacitance of 17 mF/cm2 and specific capacitance of 69 F/g, respectively. Cyclic stability was tested by performing 30,000 galvanostatic charge–discharge (GCD) cycles and the electrode exhibited 65% capacitance retention, showing its excellent electrochemical performance and ultra-long cycle life. The excellent electrochemical electrode properties are attributed to the unique processing technique, optimum processing parameters, improved conductivity due to the presence of rGO, and highly porous morphology which offers a high specific surface area. The novel photonic processing we report allows for high-temperature heating of the precursor films achieved via non-radiative recombination of photogenerated electron holes pairs during irradiation. Such extremely quick (ms) heating followed by instantaneous cooling results in the formation of a dense and robust bottom layer of the electrode, resulting in a long cycle life.
Highlights
Based on the charge storage mechanism, the supercapacitors can be further categorized as electric double-layer capacitors (EDLCs) with carbon-based electrodes, and pseudocapacitors with metal oxides and conducting polymer electrodes
In EDLCs, the charge storage on the electrode’s surface is achieved through physical adsorption, whereas, in pseudocapacitors, the charge storage is achieved via Faradaic redox reactions between electrolyte ions and the active materials at the electrodeelectrolyte interface [5,6,7]
Due to these fast and reversible redox reactions, metal oxides provide higher energy density than EDLCs based on carbonaceous materials [1,8,9]
Summary
Supercapacitors (SCs) have attracted significant interest as efficient energy storage devices because of their high-power density, fast charge–discharge ability, and long cycle life [1,2,3,4] Due to these attributes, supercapacitors have been used in portable electronics, electric vehicles, and smart toys, etc. In EDLCs, the charge storage on the electrode’s surface is achieved through physical adsorption, whereas, in pseudocapacitors, the charge storage is achieved via Faradaic redox reactions between electrolyte ions and the active materials at the electrodeelectrolyte interface [5,6,7] Due to these fast and reversible redox reactions, metal oxides provide higher energy density than EDLCs based on carbonaceous materials [1,8,9]
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