Juan Zhang,Juncheng Wu,Taotao Guan,Guoli Zhang,Shengqin Guan,Jie Han,Jianlong Wang,Kaixi Li,Zhichang Liu
Advances in high-performance transition-metal–nitrogen–carbon catalysts (M–N–Cs) for the oxygen reduction reactions (ORR) are high-profile efforts to realize the large-scale implementations of rechargeable zinc–air batteries. However, it is extremely desirable but challenging to achieve stable active sites and excellent electron transport capability for M–N–C catalysts. Herein, spherical porous M–N–Cs (denoted as NPCS-Fc) with tailoring of the sp2-C/sp3-C ratio in carbon shell were prepared from low-cost coal tar pitch (CTP) via an acid-treatment-introduced defect-assisted one-step pyrolysis strategy. Due to the tradeoff among activity, conductivity, and stability, NPCS-Fc exhibits excellent ORR performance with a half-wave potential (E1/2) of 0.863 V, a low Tafel slope of 59 mV dec–1, and long-cycle durability in alkaline media. As the air cathode, the assembled rechargeable zinc–air battery delivers a high OCV of 1.538 V and a specific capacity of 870 mAh gzn–1. The enriched sp2-C atom strategy to give M–N–C materials opens up a facile way for developing high-performance catalysts in flexible, rechargeable zinc–air batteries.
The current challenge in the development of high-performance lithium–sulfur (Li–S) batteries is to facilitate the redox kinetics of sulfur species as well as to suppress the shuttle effect of polysulfides, especially at high current rates. Herein, aiming the application of Li–S at high current rates, we coupled a sp2 carbon configuration consisting of 3D carbon nanotubes/graphene prepared by ultrahigh temperature treatment (2850 °C) with S (2850CNTs–Gra–S) for application in Li–S batteries. The 2850CNTs–Gra as the host material exhibits a nearly perfect sp2 hybridized structure because ultrahigh temperature treatment not only repairs the raw defects in CNTs and graphene, but it also forms new sp2 C–C bonds between them. The 3D sp2 carbon network ensures ultrafast ion/electron transfer and efficient heat dissipation to protect the integrity of the separator when the Li–S battery is running at an ultrahigh rate. Based on these unique advantages, the 2850CNTs–Gra–S cathode shows a high current rate performance. Critically, it still delivers a considerable specific capacity after 1500 cycles even at a current rate of 15C and exhibits an extremely low capacity degradation rate of 0.0087% per cycle.
Phenol is a refractory organic pollutant that is difficult to degrade in wastewater treatment, and efficiently and stably degrading phenol presents a significant challenge. In this study, iron-doped humic acid-based nitrogen–carbon materials were prepared to activate peroxymonosulfate (PMS) for the degradation of phenol. The Fe-N-C/PMS system achieved a phenol degradation rate of 99.71%, which follows a first-order kinetic model, with the reaction rate constant of 0.1419 min−1. The phenol degradation rate remained above 92% in inorganic anions (Cl−, SO42−, HCO3−) and humic acid and the system maintained a 100% phenol removal rate over a wide pH range (3–9). The iron in the catalyst predominantly exists in the forms of Fe0and Fe3C, and Fe0, Fe2+/Fe3+are the main active sites that promote PMS activation during the reaction. Additionally, Fe-N-C has a large specific surface area (1041.36 m2/g). Quenching experiments and electron spin resonance (ESR) spectroscopy detected the active free radicals in the Fe-N-C/PMS system: SO4•−, •OH, O2•−, and1O2. The mechanism for phenol degradation was discussed, involving radical pathways (SO4•−, •OH, O2•−) and the non-radical pathway (1O2), in the Fe-N-C/PMS system activated by Fe0, Fe2+/Fe3+, sp2hybridized carbon, C-O/C-N, C=O, and graphitic nitrogen active sites. This study provides new insights into the synthesis of efficient carbon-based catalysts for phenol degradation and water remediation.
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