Preparation Of Electrode Materials Based On Typical Industrial Sludge And Their Performance Of Supercapacitors

Rising concerns over the environmental pollution and the increasing use of alternative energy sources is urgently calling for the development of green and sustainable electrochemical energy storage devices.Supercapacitors,as a novel type of energy storage device,are considered to be an important complement to traditional batteries because of their higher power-density,long cycle life and reliable safety performance.At present,the electrode materials of commercial supercapacitors are usually metal-based functional materials such as metal@carbon composites or metal compounds.However,the manufacturing cost of metal-based electrode materials with high capacitance performance is often high,limiting their commerical application.Therefore,the exploration of low-cost metal-based precursors and simple synthesis methods are important research directions in the field of supercapacitors.In this paper,the industrial sludge rich in heteroatoms such as O,N,P and S and inorganic metal elements such as Fe,Al and Ni were recycled to prepare high-performance electrode materials for supercapacitors.The formation process and energy storage performance of the metal-based electrode materials were also studied.Important research contents and innovations are as follows:（1）Porous Fe-N-C material（FCN-500）was successfully prepared chlorination calcination method using oily sludge containing calcium feldspar and pyridine as raw material.The formation mechanism of FCN-500 was also proposed,i.e.the iron ions(Fe³⁺)in the inorganic iron-containing minerals（calcium feldspar）in the oil sludge were rapidly dissociated with the assistance of Na Cl.Then the dissociated Fe³⁺coordinated with the main organic matter（pyridine nitrogen）in the oil sludge to form pyridine nitrogen-iron（（C₅H₆N）_n-Fe）complexes,and then the complexes were further carbonated to form FCN-500.Comparing to other electrode materials obtained without Fe-N-C active sites,FNC-500 has a higher specific capacitance(286.3 F·g^-1 at a current density of 0.5 A·g^-1),energy density(33.50 Wh·kg^-1 at an energy density of 606.10 W·kg^-1)and stability（over 80.1%capacitance retention after 10,000cycles）.（2）By using a self-templating method,the Aluminium-oxygen-doped porous carbon（AOPC）was successfully synthesized from organic waste salts.Detailed physicochemical characterization of the composites was carried out by combining various characterization techniques.The electrochemical properties of the AOPC materials were also investigated in depth.It was found that the AOPC-600 symmetric aqueous supercapacitor exhibited excellent double layer capacitance performance with a capacitance of 416.35 F·g^-1 at a current density of0.5 A·g^-1;When the power density is 1300 W·kg^-1,the energy density of AOPC-600 is 43.33Wh·kg^-1.The reasons for the better performance of AOPC-600 in supercapacitors are as follows:（i）larger surface area,which can absorb more electrolyte ions;（ii）the graded porous channels,which are beneficial to accelerating the transmission rate of electrolyte ions at the electrode/solution interface;（iii）more rich micropores,which can make the ion center closer to the surface of the electrode,thereby enhancing the capacitance;（iiii）The higher content of Al/O doping,providing more active sites.（3）Double-layer metal hydroxides（LDHs）were successfully prepared by a facile hydrothermal method by dissolving electroplating sludge containing Ni,Fe and Al elements with hydrochloric acid and adding urea precipitant.Furthermore,we found that the structure of the prepared LDH has various active Ni bridged by nitrogen atoms in coordination.These active Ni greatly facilitate the electron transfer at the electrolyte-electrode material interface,thus the LDH exhibits excellent pseudocapacitive performance(1652.20 F·g^-1specific capacitance at0.5 A·g^-1).