Pre-Oxidation-Tuned Oxygen and Nitrogen Species of Porous Carbon as an Advanced Electrocatalyst of the Oxygen Reduction Reaction for Flow Zn–Air Batteries

Abstract

The co-engineering of defects and N doping is highly important for the development of advanced metal-free carbon-based electrocatalysts for the oxygen reduction reaction (ORR). It remains a great challenge to efficiently tune the doped nitrogen species, and the role of oxygen species is often overlooked. Here, a facile strategy is developed for fabricating three-dimensional oxygen and nitrogen codoped porous carbon (ONPC) via air pre-oxidation, followed by carbonization. The optimal catalyst, i.e., ONPC-300, mainly contains pyridinic N and graphitic N species with oxygen-rich functional (ketone CO) groups and has an enhanced specific surface area, superhydrophilic surface structure, and abundant defect sites for ORR, which endows it with excellent ORR performance, as evidenced by a half-wave potential of 0.862 V and high long-term stability over 100 h in an alkaline medium. Density functional theory (DFT) calculations reveal that ketone CO groups can optimize the adsorption energy of intermediates and decrease the energy barrier for the rate-determining steps, thus promoting the ORR activity. A flow Zn–air battery using ONPC-300 as the cathode shows outstanding performance, including a remarkable peak power density of 258.5 mW cm–2, high discharge stability over 180 h, and an ultralong cycle life exceeding 800 h.

In-Situ Nanoarchitectonics of Fe/Co LDH over Cobalt-Enriched N-Doped Carbon Cookies as Facile Oxygen Redox Electrocatalysts for High-Rate Rechargeable Zinc–Air Batteries

“…The presence of pyridinic and graphitic nitrogen has been known to aid in shifting the onset potential toward more positive potential, thereby increasing the ORR activity. A substantial amount of pyridinic nitrogen signifies better closeness of the outermost plain, which fosters the transfer and sorption of the oxygen molecules, triggering the breakdown of the O–O bond, , whereas graphitic nitrogen limits the current density and enhances the mass transport by improving the diffusion process . According to Cao et al, a considerable amount of pyrrolic and pyridinic nitrogen aid by increasing the difference in electronegativity, leading to the carbon next to it having a greater affinity for oxygen, thus leading to an enhanced ORR activity .…”

In Situ Alloying with Hybrid Mesoporous Fe–N–C to Accelerate the Catalysis Efficiency of Pt for the Oxygen Reduction Reaction

“…The typical spectrum of TEM-EDX analysis of Meso-PDAC-5 and the corresponding elemental composition are shown in Figure S6, which demonstrate that the content of Fe is about 0.58 (wt %). In this work, the ratio of defects and the degree of graphitization for the synthesized carbon matrices were evaluated by Raman spectroscopy because the relative peak intensity ( I D / I G ) could be significantly affected by the amount of defects and microcrystalline graphite existing in the carbon matrices Figure i demonstrates that I D / I G of well-graphitized commercial carbon Vulcan XC-72R is about 0.93, while I D / I G is 0.97 for Meso-PDAC and 0.98 for both Meso-PDAC-1 and Meso-PDAC-3, suggesting abundant defect and mesopore formation in the as-synthesized carbon supports.…”

Self-Sacrificial Templated Nanoarchitectonics of Nitrogen-Doped Carbon Derived from Viologen-Based Covalent Triazine Polymer: An Oxygen Reduction Electrocatalyst in Zinc–Air Batteries

“…Generally, nitrogen-doped carbon is regarded as a superior oxygen reduction catalyst as it creates sufficient tunable micro- and mesopores, and with enhanced nitrogen doping a high degree of graphitization is obtained . It has been claimed that pyridinic nitrogen offers π electrons to the aromatic system, which in turn boosts the ability to donate electrons and as an outcome of which the ORR activity is enhanced. , Third, from the BET studies, it is evident for the presence of a higher specific surface area in both ACTP-1 and ACTP-2, but the former lacks the active site necessary for the mass transport of the ORR catalytic activity which is not the case with the latter, leading to enhanced activity . Finally, ACTP-2, though it showed slight tolerance toward the methanol crossover effect when compared to Pt/C, has high utility in zinc–air batteries.…”