The urgency to move from critical raw materials to highly available and renewable feedstock is currently driving the scientific and technical development. Within this context, the abundance of natural resources like chitosan paves the way to synthesize biomass-derived nitrogen-doped carbons. This work describes the synthesis of chitosan-derived N-doped mesoporous carbon in the absence (MC-C) and presence (N-MC-C) of 1,10-phenanthroline, which acted as both porogen agent and as second nitrogen source. The as-prepared MC-C and N-MC-C were thoroughly characterized and further employed as catalytic materials in gas-diffusion electrodes (GDEs), aiming to develop a sustainable alternative to conventional GDEs for H2O2 electrogeneration and the photoelectro-Fenton (PEF) treatment of a drug pollutant. N-MC-C presented a higher content of key surface N-functionalities like pyrrole group, as well as an increased graphitization degree and surface area (63 vs. 6 m 2 /g), being comparable to commercial carbon black. These properties entailed a superior activity of N-MC-C for the oxygen reduction reaction, as confirmed from its voltammetric behavior at a rotating ring-disk electrode. The GDE prepared with N-MC-C catalyst showed greater H2O2 accumulation, attaining values close to those obtained with a commercial GDE. N-MC-C-and MC-C-derived GDEs were employed to treat drug solutions at pH 3.0 by PEF process, which outperformed electro-oxidation (EO). The fastest drug removal was achieved using N-MC-C, needing only 16 min at 30 mA/cm 2 instead of 20 min required with MC-C. The replacement of the dimensionally stable anode by a boron-doped diamond (BDD) accelerated the degradation process, reaching an almost complete mineralization in 360 min. The main degradation products were identified, revealing the formation of six different aromatic intermediates, alongside five aliphatic compounds that comprised three nitrogenated structures.The initial N was preferentially converted into ammonium.
The development of platinum group metal-free (PGM-free) electrocatalysts derived from cheap and environmentally friendly biomasses for oxygen reduction reaction (ORR) is a topic of relevant interest, particularly from the point of view of sustainability. Fe-nitrogen-doped carbon materials (Fe-N-C) have attracted particular interest as alternative to Pt-based materials, due to the high activity and selectivity of Fe-Nx active sites, the high availability and good tolerance to poisoning. Recently, many studies focused on developing synthetic strategies, which could transform N-containing biomasses into N-doped carbons. In this paper, chitosan was employed as a suitable N-containing biomass for preparing Fe-N-C catalyst in virtue of its high N content (7.1%) and unique chemical structure. Moreover, the major application of chitosan is based on its ability to strongly coordinate metal ions, a precondition for the formation of Fe-Nx active sites. The synthesis of Fe-N-C consists in a double step thermochemical conversion of a dried chitosan hydrogel. In acidic aqueous solution, the preparation of physical cross-linked hydrogel allows to obtain sophisticated organization, which assure an optimal mesoporosity before and after the pyrolysis. After the second thermal treatment at 900 °C, a highly graphitized material was obtained, which has been fully characterized in terms of textural, morphological and chemical properties. RRDE technique was used for understanding the activity and the selectivity of the material versus the ORR in 0.5 M H2SO4 electrolyte. Special attention was put in the determination of the active site density according to nitrite electrochemical reduction measurements. It was clearly established that the catalytic activity expressed as half wave potential linearly scales with the number of Fe-Nx sites. It was also established that the addition of the iron precursor after the first pyrolysis step leads to an increased activity due to both an increased number of active sites and of a hierarchical structure, which improves the access to active sites. At the same time, the increased graphitization degree, and a reduced density of pyrrolic nitrogen groups are helpful to increase the selectivity toward the 4e- ORR pathway.
The development of platinum group metal-free (PGM-free) electrocatalysts derived from cheap and environmentally friendly biomasses for oxygen reduction reaction (ORR) is a topic of relevant interest, particularly from the point of view of sustainability. Fe-nitrogen-doped carbon materials (Fe-N-C) have attracted particular interest as alternative to Pt-based materials, due to the high activity and selectivity of Fe-Nx active sites, the high availability and good tolerance to poisoning. Recently, many studies focused on developing synthetic strategies, which could transform N-containing biomasses into N-doped carbons. In this paper chitosan was employed as a suitable N-containing biomass for preparing Fe-N-C catalyst in virtue of its high N content (7.1%) and unique chemical structure. Moreover, the major application of chitosan is based on its ability to strongly coordinate metal ions, a precondition for the formation of Fe-Nx active sites. The synthesis of Fe-N-C consists in a double step thermochemical conversion of a dried chitosan hydrogel. In acidic aqueous solution, the preparation of physical cross-linked hydrogel allows to obtain sophisticated organization, which assure an optimal mesoporosity before and after the pyrolysis. After the second thermal treatment at 900 °C, a highly graphitized material was obtained, which has been fully characterized in term of textural, morphological and chemical properties. RRDE technique was used for understanding the activity and the selectivity of the material versus the ORR in 0.5 M H2SO4 electrolyte. Special attention was put in the determination of the active site density according to nitrite electrochemical reduction measurements. It was clearly established that the catalytic activity expressed as half wave potential linearly scales with the number of Fe-Nx sites. It was also established that the addition of the iron precursor after the first pyrolysis step leads to an increased activity because of both an increased number of active sites and of a hierarchical structure, which improves the access to active sites. At the same time, the increased graphitization degree, and a reduced density of pyrrolic nitrogen groups are helpful to increase the selectivity toward the 4e- ORR pathway.
In the recent years, the global energy economy is experiencing a transition towards its production from more sustainable and “green” sources. The intrinsic characteristics of these methods, such as the intermittency and misalignment between disposability and demand, require the use of energy storage systems, such as secondary batteries. Despite the high performance of Li-ion batteries, the high cost, low abundance and toxicity of their components (e.g., the Co-based cathodes) request the development of new devices based on novel chemistries. In this regard, the holy grail is the production of battery systems based on abundant multivalent metals. It has been recently demonstrated that ionic liquids (ILs) are suitable solvents in order to obtain stable and high performing electrolytes able to conduct and deposit/strip multivalent metals [1-5]. The outstanding electrochemical properties of these materials are ensured by the presence of a high-reactive magnesium salt (i.e., the “delta” form of MgCl2) and of a suitable metal halide (e.g., AlCl3, TiCl4, etc.). In this project we have developed a family of IL-based electrolytes for the Mg2+ ion conduction doped with an alkyl tin halide compound. In this way, the hybrid chemico-physical properties of Sn-based species can be exploited to improve the coordination existing between the inorganic magnesium salt and the organic IL. An advanced study on the thermal and structural properties of the proposed material will be presented, with a particular focus on the interactions established between the different chemical species and complexes composing the materials. Insights on the conductivity mechanism occurring in a wide range of temperature will be gauged and thoroughly described by means of the broadband electrical spectroscopy studies. Acknowledgments The project “Interplay between structure, properties, relaxations and conductivity mechanism in new electrolytes for secondary Magnesium batteries” (Grant Agreement W911NF-21-1-0347-(78622-CH-INT)) of the U.S. Army Research Office. The project “ACHILLES” (prot. BIRD219831) of the University of Padua. The project “VIDICAT” (Grant Agreement 829145) of the FET-Open call of Horizion 2020. References [1] G. Pagot, K. Vezzù, S. Greenbaum and V. Di Noto, Journal of Power Sources 492 (2021) 229681. [2] R. Dominko, J. Bitenc, R. Berthelot, M. Gauthier, G. Pagot and V. Di Noto, Journal of Power Sources 478 (2020) 229027. [3] G. Pagot, F. Bertasi, K. Vezzù, F. Sepehr, X. Luo, G. Nawn, E. Negro, S.J. Paddison and V. Di Noto, Electrochimica Acta 246 (2017) 914-923. [4] F. Bertasi, F. Sepehr, G. Pagot, S.J. Paddison and V. Di Noto, Advanced Functional Materials 26 (2016) 4860-4865. [5] F. Bertasi, C. Hettige, F. Sepehr, X. Bogle, G. Pagot, K. Vezzù, E. Negro, S.J. Paddison, S.G. Greenbaum, M. Vittadello and V. Di Noto, ChemSusChem 8 (2015) 3069-3076.
In recent years, the lack of high-performing electrical energy storage systems is seriously bottlenecking the operation of appliances in several fields, that include portable electronics, electric automotive, and stationary devices [1]. Until now, lithium batteries (LiBs) are the highest-performing systems that could address satisfactorily all the requirements of such appliances [2]. Indeed, LiBs show a high specific capacity, a high efficiency, and a long lifespan [3]. However, improvements are still needed in the operating potential (that influences the specific energy and power of the LiBs) and in the rate capability properties of the cathodes. Indeed, electric vehicles need high power during acceleration, and a large amount of stored energy to achieve a sufficient mileage. Herein we describe the synthesis and the study of an innovative family of high-energy and high-rate cathodes for application in LiBs. The structure of a high-performing olivine material of the type LiMPO4 (M = Fe, Ni, and Co) [4] has been doped with high-valence transition metal ions (V(V), Nb(IV), or Ta(IV)). In a first step, the synthesis procedure has been optimized. Five different materials have been obtained, as follows: (i) LFNCVP is a vanadium-doped olivine obtained under oxidizing conditions; (ii) LFNCVP/C is a vanadium-doped olivine obtained under partially reducing conditions (graphite is added during the pyrolysis); (iii) LFNCVP/H is a vanadium-doped olivine obtained under reducing conditions (pyrolysis is carried out under a hydrogen atmosphere); (iv) LFNCNP is a niobium-doped olivine obtained under oxidizing conditions; and (v) LFNCTP is a tantalum-doped olivine obtained under oxidizing conditions. The effects of the different synthesis protocols and ion insertion on the structural, morphological, and electrochemical properties of the cathodes have been thoroughly investigated. The composition of the cathodes has been evaluated by means of Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), the morphology and size distribution have been gauged by Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM); the structure has been revealed through powder X-Ray Diffraction (XRD) and IR spectroscopy techniques. The electrochemical performance has been investigated by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and coin battery charge/discharge tests at different current rates. As expected (see Figure 1), the proposed materials reveal a high performance in terms of working potential (4.0÷5.0 V vs. Li/Li+), specific capacity (149 mAh∙g-1), and specific energy (656 mWh∙g-1). Moreover, the insertion of high-valence transition metals is able to boost the rate capability of the cathodes, allowing for fast charge and discharge processes without depleting the cathodes. References [1] B. Dunn, H. Kamath, J. M. Tarascon, Science 334 (2011) 928-935. [2] V. Di Noto, T. A. Zawodzinski, A. M. Herring, G. A. Giffin, E. Negro, S. Lavina, Int. J. Hydrogen Energy 37 (2012) 6120-6131. [3] B. Scrosati, J. Garche, J. Power Sources 195 (2010) 2419-2430. [4] G. Pagot, F. Bertasi, G. Nawn, E. Negro, G. Carraro, D. Barreca, C. Maccato, S. Polizzi, V. Di Noto, Adv. Funct. Mater. 25 (2015) 4032-4037. Figure 1
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