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Abstract
Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest. Herein, a simple template-free approach is devised to obtain porous and heteroatom-doped carbon, by using the most abundant human waste, “urine”. Removal of inherent mineral salts from the urine carbon (URC) makes it to possess large quantity of pores. Synergetic effect of the heteroatom doping and surface properties of the URC is exploited by carrying out energy storage application for the first time. Suitable heteroatom content and porous structure can enhance the pseudo-capacitance and electric double layer capacitance, eventually generating superior capacitance from the URC. The optimal carbon electrode obtained particularly at 900 °C (URC-900) possesses high BET surface area (1040.5 m2g−1), good conductivity, and efficient heteroatom doping of N, S, and P, illustrating high specific capacitance of 166 Fg−1 at 0.5 Ag−1 for three-electrode system in inorganic electrolyte. Moreover, the URC-900 delivers outstanding cycling stability with only 1.7% capacitance decay over 5,000 cycles at 5 Ag−1. Present work suggests an economical approach based on easily available raw waste material, which can be utilized for large-scale production of new age multi-functional carbon nanomaterials for various energy applications.
Highlights
Obtaining functionalized carbonaceous materials, with well-developed pores and doped heteroatoms, from waste precursors using environmentally friendly processes has always been of great interest
Contingent on mechanism of charge storage, the capacitance value of supercapacitors is determined mainly by two storage principles[28,29,30]. This can be categorized in electrochemical double layer capacitance (EDLC) arising from the non-faradaic charge separation at an electrode/electrolyte interface and pseudo-capacitance originating from fast sequence reversible faradaic redox reactions of electroactive species
The obtained yellowish-brown urine deposit was carbonized at different temperatures 800, 900, and 1000 °C followed by acid washing of as-prepared carbon materials at the third step to obtain the final product urine carbon (URC)-X, where X signs carbonization temperature
Summary
Based on the observation drawn from the above results, the enhanced performance of URC-900 can be addressed in terms of large surface area, and appropriate distribution of micro-/mesopores, which enable increased formation of charge double layer, along with good conductivity, high heteroatom content, and high amount of active heteroatom species, which facilitate electron and charge transfer and contribute to surface faradaic pseudo-capacitance. Highly micro-/meso porous and heteroatom-doped carbon materials with good conductivity were prepared for high performance supercapacitor by a unique, simple template-free procedure comprising of urine pyrolysis at different temperatures followed by acid-treatment for removal of inherent mineral salts. When tested as supercapacitor electrodes, URC-900 due to the synergistic effect of the high surface area (1040.5 m2g−1) with a proper micro-/mesopore distribution, good conductivity, and efficient heteroatom doping along with high amount of active heteroatom species doped at graphitic edges, illustrates high specific capacitance of 166 F.g−1 at 0.5 Ag−1 for three-electrode system in inorganic electrolyte among all other URC materials. Considering the convenient and innovative template-free procedure without using any external heteroatom precursor and activation agent, and easy-availability of raw material, the current urine-based synthesis can be adjusted for scale-up industrial approach and definitely open up new dimensions in preparing new age electrodes for the application in energy fields
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