Strong Interaction Between Redox Mediators and Defect-Rich Carbons Enabling Simultaneously Boosted Voltage Windows and Capacitance for Aqueous Supercapacitors

Energy density,the Achilles’heel of aqueous supercapacitors,is simultaneously determined by the voltage window and specific capacitance of the carbon materials,but the strategy of synchronously boosting them has rarely been reported.Herein,we demonstrate that the rational utilization of the interaction between redox mediators(RMs)and carbon electrode materials,especially those with rich intrinsic defects,contributes to extended potential windows and more stored charges concurrently.Using 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl(4OH-TEMPO)and intrinsic defect-rich carbons as the RMs and electrode materials,respectively,the potential window and capacitance are increased by 67%and sixfold in a neutral electrolyte.Moreover,this strategy could also be applied to alkaline and acid electrolytes.The first-principle calculation and experimental results demonstrate that the strong interaction between 4OH-TEMPO and defectrich carbons plays a key role as preferential adsorbed RMs may largely prohibit the contact of free water molecules with the electrode materials to terminate the water splitting at elevated potentials.For the RMs offering weaker interaction with the electrode materials,the water splitting still proceeds with a thus sole increase of the stored charges.The results discovered in this work could provide an alternative solution to address the low energy density of aqueous supercapacitors.

Three-dimensional printing of high-mass loading electrodes for energy storage applications

Nanostructured materials afford a promising potential for many energy storage applications because of their extraordinary electrochemical properties.However,the remarkable electrochemical energy storage performance could only be harvested at a relatively low mass-loading via the traditional electrode fabrication process,and the scale of these materials into commercial-level mass-loading remains a daunting challenge because the ion diffusion kinetics deteriorates rapidly along with the increased thickness of the electrodes.Very recently,three-dimensional(3D)printing,a promising additive manufacturing technology,has been considered as an emerging method to address the aforementioned issues where the 3D printed electrodes could possess elaborately regulated architectures and rationally organized porosity.As a result,the outstanding electrochemical performance has been widely observed in energy storage devices made of 3D printed electrodes of high-mass loading.In this review,we systemically introduce the basic working principles of various 3D printing technologies and their practical applications to manufacture highmass loading electrodes for energy storage devices.Challenges and perspectives in 3D printing technologies for the construction of electrodes at the current stage are also outlined,aiming to offer some useful opinions for further development for this prosperous field.