**Cu-Doped Porous Carbon Derived from Heavy Metal-Contaminated Sewage Sludge for High-Performance Supercapacitor Electrode Materials**

**Zhouliang Tan 1, Feng Yu 1, Liu Liu 1, Xin Jia 1, Yin Lv 1, Long Chen 1, Yisheng Xu 1,2, Yulin Shi 1,\* and Xuhong Guo 1,2**


Received: 25 April 2019; Accepted: 11 June 2019; Published: 17 June 2019

**Abstract:** In this paper, we report a complete solution for enhanced sludge treatment involving the removal of toxic metal (Cu(II)) from waste waters, subsequent pyrolytic conversion of these sludge to Cu-doped porous carbon, and their application in energy storage systems. The morphology, composition, and pore structure of the resultant Cu-doped porous carbon could be readily modulated by varying the flocculation capacity of Cu(II). The results demonstrated that it exhibited outstanding performance for supercapacitor electrode applications. The Cu(II) removal e fficiency has been evaluated and compared to the possible energy benefits. The flocculant dosage up to 200 mg·L−<sup>1</sup> was an equilibrium point existing between environmental impact and energy, at which more than 99% Cu(II) removal e fficiency was achieved, while the resulting annealed product showed a high specific capacity (389.9·F·g<sup>−</sup><sup>1</sup> at <sup>1</sup>·A·g<sup>−</sup>1) and good cycling stability (4% loss after 2500 cycles) as an electrode material for supercapacitors.

**Keywords:** heavy metal; flocculation; Cu-doped carbon; supercapacitor
