Electrocatalysts are required for clean energy technologies (for example, water‐splitting and metal‐air batteries). The development of a multifunctional electrocatalyst composed of nitrogen, phosphorus, and fluorine tri‐doped graphene is reported, which was obtained by thermal activation of a mixture of polyaniline‐coated graphene oxide and ammonium hexafluorophosphate (AHF). It was found that thermal decomposition of AHF provides nitrogen, phosphorus, and fluorine sources for tri‐doping with N, P, and F, and simultaneously facilitates template‐free formation of porous structures as a result of thermal gas evolution. The resultant N, P, and F tri‐doped graphene exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The trifunctional metal‐free catalyst was further used as an OER–HER bifunctional catalyst for oxygen and hydrogen gas production in an electrochemical water‐splitting unit, which was powered by an integrated Zn–air battery based on an air electrode made from the same electrocatalyst for ORR. The integrated unit, fabricated from the newly developed N, P, and F tri‐doped graphene multifunctional metal‐free catalyst, can operate in ambient air with a high gas production rate of 0.496 and 0.254 μL s−1for hydrogen and oxygen gas, respectively, showing great potential for practical applications.
Selectfluor, [1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo‐[2.2.2]octane bis(tetrafluoroborate)], is not only an important electrophilic fluorinating agent but also a facile and efficient “fluorine‐free” functional reagent in other organic reactions. In this Minireview, we will present a brief history of Selectfluor as a transition metal oxidant, fluorine cation and radical initiator in “fluorine‐free” functionalizations over the last five years.
more » « less- NSF-PAR ID:
- 10137332
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – An Asian Journal
- Volume:
- 15
- Issue:
- 6
- ISSN:
- 1861-4728
- Page Range / eLocation ID:
- p. 729-741
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract MXenes are a rapidly growing family of 2D transition metal carbides and nitrides that are promising for various applications, including energy storage and conversion, electronics, and healthcare. Hydrofluoric‐acid‐based etchants are typically used for large‐scale and high‐throughput synthesis of MXenes, which also leads to a mixture of surface terminations that impede MXene properties. Herein, a computational thermodynamic model with experimental validation is presented to explore the feasibility of fluorine‐free synthesis of MXenes with uniform surface terminations by dry selective extraction (DSE) from precursor MAX phases using iodine vapors. A range of MXenes and respective precursor compositions are systematically screened using first‐principles calculations to find candidates with high phase stability and low etching energy. A thermodynamic model based on the “CALculation of PHAse Diagrams” (CALPHAD) approach is further demonstrated, using Ti3C2I2as an example, to assess the Gibbs free energy of the DSE reaction and the state of the byproducts as a function of temperature and pressure. Based on the assessment, the optimal synthesis temperature and vapor pressure are predicted and further verified by experiments. This work opens an avenue for scalable, fluorine‐free dry synthesis of MXenes with compositions and surface chemistries that are not accessible using wet chemical etching.
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Abstract An intramolecular SNAr displacement of one
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