Hierarchical porous carbon from hazardous waste oily sludge for all-solid-state flexible supercapacitor

[Display omitted] •We first utilize oily sludge to fabricate three-dimensional hierarchical porous carbon (HPC) material.•The as-fabricated HPC exhibits super-high surface area and rational pore size distribution.•Outstanding performance of the HPC is demonstrated in all-solid-state flexible supercapacitor.•The cost of oily sludge-based HPC material is negligible. Rationally packed porous carbon with high ion-accessible surface area and low ion-transport resistance is proved to be an excellent candidate as electrode materials in high performance supercapacitors. However, its cost-effective fabrication still remains a significant challenge. Here, we report on a novel three-dimensional hierarchical porous carbon (HPC) synthesized via a facile and low-cost approach from hazardous waste oily sludge for the first time. Both the smart “self-template” effect and appropriate activation effect are crucial for the rational hierarchical porous structure. The “self-template” procedure is the key point for creating the skeleton of carbon, and the KOH activation process is able to regulate pore size distribution and increase specific surface area. The as-fabricated HPC possesses favorable features for supercapacitor, such as outstanding specific surface area (2561m2g−1), large pore volume (2.25cm3g−1), tunable and large range of pore size distribution. The HPC-based electrode can deliver an admirable capacitance of 348.1Fg−1 at 0.5Ag−1 and 94.3% capacitance retention at 5Ag−1 after 10,000 cycles in aqueous electrolyte. Remarkably, the all-solid-state HPC//HPC symmetric supercapacitor displays outstanding capacitance of 81.3Fg−1 at 0.5Ag−1 with high energy density of 7.22W h kg−1. It is demonstrated that the strategy developed here would provide cost-effective production of HPC electrode material for high performance supercapacitors and offer a promising avenue of large-scale fabrication of HPC from other hazardous industrial waste.