Hierarchical porous carbon materials from nanosized metal-organic complex for high-performance symmetrical supercapacitor

The accessible surface area, conductivity, and pore size determine the capacitive properties of carbon-based materials. In this work, hierarchical nanoporous carbon (NPC) materials with a large specific surface area, high conductivity, and suitable pore size are prepared from nanoscaled Al-based metal-organic complex (Al-MOC) by annealing. The annealing temperature has a profound influence on the morphology of the NPC materials which in turn impact the electrochemical performance. Compared to annealing at a low temperature, an interconnected structure is formed at an annealing temperature exceeding 950 °C to produce a larger accessible surface area. Owing to the interconnected structure and high conductivity, sample NPC-950 with the two-electrode configuration has the highest specific capacitance and the best stability. The specific capacitances are 298 Fg^-1 at a scanning rate of 1 mVs^-1 in symmetrical supercapacitor device. These values are the largest values reported from ultrapure carbon-based EDLCs in an aqueous electrolyte so far. Furthermore, 96.73% of the capacity is retained after 5000 cycles in 1 M H₂SO₄ electrolyte. In an organic electrolyte, the supercapacitor cells composed of NPC produce an energy density of 43 Wh kg⁻¹. The NPC materials with large specific capacity and excellent stability produced by the simple and cost effective technique have large potential in supercapacitors.