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[Display omitted] • A new method for preparation of HA-K by alkali quenching of sludge was proposed. • Chlorination roasting and quenching can control the pore structure of carbon. • The specific capacitance of the prepared N, O porous carbon is 395F g−1. • This study provides a new idea for the harmless and resource utilization of sludge. Municipal sludge (MS) pyrolysis is often used to produce carbon materials for supercapacitors, however, the conventional heating process limits the improvement of its performance. In this paper, a facile method for the preparation of potassium humate (HA-K) by co-pyrolysis of MS and alkali was proposed for the first time, and then it was mixed with sodium chloride for roasting and quenching to obtain high performance HA-K carbon materials for supercapacitors. Compared with the electrode without chlorination roast quenching, the sample of HA-K-650-M−Q (the sample calcined at 650°C and quenched at 200°C) exhibited higher specific capacitance (395F g−1 at 1 A g−1) and enhanced energy density (32.28 Wh kg−1 at a power density of 2805 W kg−1). After 10,000 cycles at 10 A g−1, the capacitance retention rate reached 87%. This remarkable performance is due to its proper N- and O- self-doping and hierarchical porous geometry, which fundamentally promotes mass and charge transfer in the reaction. Therefore, this study provides a feasible method to solve the problem of sludge value-added and design suitable for the practical application of carbon materials. [ABSTRACT FROM AUTHOR]