Sustainable human development urgently calls for decreasing the cost of energy storage. Continuous massive consumption of dedicated carbon electrode materials with complex internal molecular architectures requires rethinking both the source of materials and the process of their production. Finding an efficient sustainable solution is focused on the reuse and development of waste processing into corresponding high‐value‐added carbon materials. The processing of solid wastes into solid value‐added carbon materials (“solid‐to‐solid”) is relatively well developed but can be a two‐stage process involving carbon architecture rearrangement and heteroatom doping. Processing liquid wastes into high‐value‐added solid material (“liquid‐to‐solid”) is typically much more challenging with the need for different production equipment. In the present study, a new approach is developed to bypass the difficulty in the “liquid‐to‐solid” conversion and simultaneously built in the ability for heteroatom doping within one production stage. Polycondensation of liquid humins waste with melamine (as a nitrogen‐containing cross‐linking component) results in solidification with preferential C and N atomic arrangements. For subsequent thermochemical conversion of the obtained solidified wastes, complicated equipment is no longer required, and under simple process conditions, carbon materials for energy storage with superior characteristics were obtained. A complete sequence is reported in the present study, including liquid waste processing, nitrogen incorporation, carbon material production, structural study of the obtained materials, detailed electrochemical evaluation and real supercapacitor device manufacture and testing.
Agriculture is the most massive material circulation activity of humans, with significant annual volumes of production as well as substantial amounts of waste. Transforming agricultural wastes into high‐value‐added products is the key to sustainable development with efficient usage of renewable resources. The present study demonstrates the fine‐tuning of the sugar beet pulp processing to access two types of materials for cutting edge applications—supercapacitors and fuel cells. Alkaline fine‐tuning results in N,O‐doped carbon material (CM) with an advantageous combination of surface area and morphology that allows to achieve high specific capacitance (308 F g−1), and excellent stability (>10 000 charge/discharge cycles). Not limited to the CM preparation and characterization, a real device is created in the present study to demonstrate the efficient usage of the carbon electrode in the form of the assembled coin cell. Acidic fine‐tuning, in contrast, yields a methodology for P,N,O‐doped material and optimizes to form active sites with electrocatalytic activity in the oxygen reduction reaction that is used for electricity production in proton‐exchange membrane fuel cells. The developed approach demonstrates the tuning of functional properties and morphology of CMs under experimentally simple conditions using conventional reagents (KOH and H3PO4) and opens up new directions in the circular biomass usage projects.
Nowadays, commercial electric double-layer supercapacitors mainly use porous activated carbons due to their high specific surface area, electrical conductivity, and chemical stability. A feature of carbon materials is the possibility of obtaining them from renewable plant biomass. In this study, fungi (Fomes fomentarius) were used as a bio-template for the preparation of carbon fibers via a combination of thermochemical conversion approaches, including a general hydrothermal pre-carbonization step, as well as subsequent carbonization, physical, or chemical activation. The relationships between the preparation conditions and the structural and electrochemical properties of the obtained carbon materials were determined using SEM, TEM, EDAX, XPS, cyclic voltammetry, galvanostatic measurements, and EIS. It was shown that hydrothermal pretreatment in the presence of phosphoric acid ensured the complete removal of inorganic impurities of raw fungus hyphae, but at the same time, saved some heteroatoms, such as O, N, and P. Chemical activation using H3PO4 increased the amount of phosphorus in the carbon material and saved the natural fungus’s structure. The combination of a hierarchical pore structure with O, N, and P heteroatom doping made it possible to achieve good electrochemical properties (specific capacitance values of 220 F/g) and excellent stability after 25,000 charge/discharge cycles in a three-electrode cell. The electrochemical performance in both three- and two-electrode cells exceeded or was comparable to other biomass-derived porous carbons, making it a prospective candidate as an electrode material in symmetrical supercapacitors.
Sugar production is accompanied by the formation of waste in the form of beet pulp. In this study, a procedure is described for turning sugar beet pulp waste into structured carbon materials for making electrodes in supercapacitors. The overall sustainable path is to produce sugar for human consumption and prepare high‐quality carbon material for energy storage. More details can be found in article number http://doi.wiley.com/10.1002/ente.202201145, Valentine P. Ananikov and co‐workers.
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