Plasma-regulated N-doped carbon nanotube arrays for efficient electrosynthesis of syngas with a wide CO/H 2 ratio
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Published online 17 July 2020 | https://doi.org/10.1007/s40843-020-1396-7
Plasma-regulated N-doped carbon nanotube arrays for efficient electrosynthesis of syngas with a wide CO/H2 ratio 1
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Yan Ji , Yanmei Shi , Cuibo Liu and Bin Zhang Syngas, a mixture of CO and H2 with a specific ratio, is of great necessity for the industrial production of olefins, liquid fuels, polymers, and drugs [1–4]. Currently, syngas is mainly acquired under harsh conditions from the gasification of solid coal and petroleum coke, as well as the steam reforming of natural gas [5,6], which accelerate the energy crisis and aggravate CO2 emission. Electrochemical CO2 reduction reaction (CO2RR) is considered to be a promising strategy to solve these problems [7,8]. Although the conversion of CO2 to multicarbon products is still elusive, electrocatalysts towards CO are extensively studied [9–15]. By adjusting the reaction rates of CO2RR to CO and the competing hydrogen evolution reaction (HER), the syngas with a controllable ratio of CO/H2 can be obtained under mild conditions [16,17]. Carbon materials are among the well-established electrocatalysts for CO2RR, because of their excellent conductivity, chemical stability, and abundant active sites [18]. Though the intrinsic activity of carbon materials is poor, the introduction of heteroatoms (N, S, B, etc.) can effectively promote their electrochemical activity and selectivity [19–23]. Taking N-doped carbon materials as the examples, the doping N atoms exist in the forms of pyridinic N, pyrrolic N, graphitic N, and oxidized N in the carbon materials. With different N-doping forms, the corresponding electrochemical CO2RR performance may exhibit a huge difference [24,25]. For instance, recent studies showed that pyridinic N atoms were more likely to adsorb CO2 and serve as the favorable sites for CO2RR [26–28]. Accordingly, the CO2RR performances can be manipulated by regulating the component of the carbon materials. Plasma treatment has recently emerged as a promising
technology for surface modification and material synthesis in the field of electrocatalysis [29–31]. Plasma is the fourth state of matter composed of molecules, radicals, ions, and atoms with equal positive and negative charges [32]. Under sufficient energy (such as electric discharge), plasma is generated from argon, oxygen, etc. to produce charged particles bombarding the sample for cleaning, etching, or exfoliation [33]. Plasma treatment could be conducted at room temperature without producing chemical wastes and changing the main structure of the materials [34,35]. By optimizing the operating condition, plasma treatment will be an attractive strategy to regulate the component of carbon materials in a facile way. Here, we present the synthesis of syngas with a controllable ratio of CO/H2 by electrochemical CO2RR over Ar-plasma-treated N-doped carbon nanotube arrays (pCNTA, Fig. 1a). The component of the N-doped carbon nanotube arrays (CNTA) is regulated by Ar-plasma treatment. And the CO Faradaic efficiency (FE) of
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