Wide Electrochemical Window of Supercapacitors from Coffee Bean‐Derived Phosphorus‐Rich Carbons

Abstract

Phosphorus-rich carbons (PCs) were prepared by phosphoric acid activation of waste coffee grounds in different impregnation ratios. PCs were characterized by nitrogen and carbon dioxide adsorption and X-ray photoelectron spectroscopy. The results indicate that the activation step not only creates a porous structure, but also introduces various phosphorus and oxygen functional groups to the surface of carbons. As evidenced by cyclic voltammetry, galvanostatic charge/discharge, and wide potential window tests, a supercapacitor constructed from PC-2 (impregnation ratio of 2), with the highest phosphorus content, can operate very stably in 1 M H2 SO4 at 1.5 V with only 18 % degradation after 10 000 cycles at a current density of 5 A g(-1) . Due to the wide electrochemical window, a supercapacitor assembled with PC-2 has a high energy density of 15 Wh kg(-1) at a power density of 75 W kg(-1) . The possibility of widening the potential window above the theoretical potential for the decomposition of water is attributed to reversible electrochemical hydrogen storage in narrow micropores and the positive effect of phosphorus-rich functional groups, particularly the polyphosphates on the carbon surface.

Enhanced electro-oxidation resistance of carbon electrodes induced by phosphorus surface groups

“…Moreover, they assigned the enhanced oxidation resistance to the physical blockage of active sites by phosphate groups [33], thus, using arguments employed in the thermal-oxidative gasification of carbons [35][36][37][38][39][40]. On the other hand, instead of an effect on the oxidation resistance, Huang et al have recently objected that the P-groups, especially polyphosphates, play a critical role in stabilizing the surface of carbons during the reversible electrochemical hydrogen storage at low potentials [34].…”

“…Thus, whereas the presence of oxygen groups has been commonly found to be detrimental to the electrochemical stability [30], a beneficial influence of certain surface functionalities of nitrogen [31,32] or phosphorus [33,34] has been claimed. In spite of the promising perspectives for various applications, to the knowledge of the authors, there are few works proposing an enhanced electrochemical stability induced by Pfunctionalities and, in all cases, applied for widening the stability potential window of carbon-based supercapacitors [33,34].…”

“…In spite of the promising perspectives for various applications, to the knowledge of the authors, there are few works proposing an enhanced electrochemical stability induced by Pfunctionalities and, in all cases, applied for widening the stability potential window of carbon-based supercapacitors [33,34]. Nevertheless, apart from the significance of the results, neither the electro-oxidation behavior nor the enhanced stability effect were M A N U S C R I P T…”

Biomass-derived carbon materials with structural diversities and their applications in energy storage

“…It has been reported that P-doped biomass-derived carbon can also widen the electrochemical window of supercapacitors [132,180]. For example, Huang et al [180] prepared phosphorus-rich carbons (PCs) through phosphoric acid activation of waste coffee grounds.…”

“…All the characteristics strongly suggest that biomass-derived carbon could be qualified for the electrode of supercapacitors. To date, various biomass-derived carbon materials with high SSA, abundant pore structure and modified functional groups have been prepared, such as the stems [87,102,157,[177][178][179], leaves [34,90,101,103,126], seeds [48,77,79,154], fructus [180][181][182], pericarp [88,89] of plants, nut shells [94,143,[183][184][185], fungi [53,109,[186][187][188], abandoned food [96,131,189], shellfish [49,72,133], animal tissue [112,115,124], polysaccharide [44,85,147,155,190], protein [137].…”