Basic magnesium carbonate template assisted co-carbonization of potassium citrate toward hierarchical porous carbon for supercapacitors

Abstract

Hierarchical porous carbon (HPC) as the ideal host material for supercapacitors has received extensive attention. However, traditional methods of fabricating HPC often rely on organic macromolecules and complex procedures. Herein, a simple and straightforward approach is developed for the synthesis of HPC through basic magnesium carbonate template assisted co-carbonization of potassium citrate. Potassium citrate can be effectively embedded and encapsulated with basic magnesium carbonate due to the large bulk density difference between them. In the pyrolysis process, the carbon-containing small molecules produced by the pyrolysis of potassium citrate are deposited on the surface of MgO surface obtained from the decomposition of basic magnesium carbonate, and the etching reaction of potassium salt, CO2 and primary carbon structure occurs. The competitive rate of carbon deposition reaction and etching reaction can be easily controlled by changing the ratio of potassium citrate and basic magnesium carbonate. The obtained carbon materials show the morphology changes of nanoparticle accumulations, discontinuous carbon frames and carbon planar blocks, and the hierarchical porous structure of carbon materials can also be controlled in a wide range. HPC-2 exhibits the morphology of nanoparticle accumulation and generates abundant meso-macropores, which accelerates the rapid transport of electrolytic ions. The micropores inside the nanoparticles provide an accessible room for ionic adsorption. Benefited from this unique microstructural framework, HPC-2 shares a high capacitance of 305.5 F g−1 at 0.5 A g−1 and 173.1 F g−1 at 50 A g−1. Furthermore, the assembled symmetric supercapacitors exhibit a high energy density and power density than YP-50 F throughout the test range. The versatility of this synthetic strategy provides an insight into directional tailoring fine pore structure and micro-morphology of carbon materials based on small molecule deposition.