Refilling nitrogen into carbon sponge for enhanced performance of compressible supercapacitor

Direct carbonization and activation of nitrogen-contained three-dimensional precursors can obtain carbon electrodes for supercapacitors due to the nitrogen doping effect. However, during the carbonization and activation processes, a large amount of nitrogen is found to be lost. Herein, we report a strategy of nitrogen refilling to prepare carbon sponges with high nitrogen content using a commercial nitrogen-contained melamine sponge (MS). A carbon sponge with a nitrogen content of 8.01 atomic percent (at.%) has been obtained through the carbonization process of MS. However, the nitrogen content is reduced to 6.91 at.% after the activation of carbon sponge (ACS) by potassium hydroxide (KOH). Thus, the nitrogen lost by activation at high temperature is replenished through a hydrothermal reaction using urea and a high nitrogen-doped carbon sponge (NCS) with a nitrogen content of 9.83 at.% has been acquired. At a current density of 0.5 A g−1, a specific capacitance of 253 F g−1 by NCS is gained, while the ACS only exhibits a specific capacitance of 167.55 F g−1. Our study not only demonstrates the importance of refilling nitrogen for enhancing the energy storage performance, but also shows that NCS can be considered a candidate for high-performance energy storage materials.