In:
ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 40 ( 2016-09-01), p. 3054-3054
Abstract:
A number of researchers in various chemical fields have investigated the conversion of N 2 to NH 3 under mild conditions. A transition metal complex has previously been found to promote electrochemical generation of NH 3 as the catalysts. For example, Pickett and co-worker reported the electrochemical synthesis of NH 3 through protonation of cis –[W(N 2 ) 2 (PMe 2 Ph) 4 ] under ambient conditions [1] , in which the reaction was carried out in THF–0.2 M [NBu 4 ][BF 4 ] using a toxic Hg–pool cathode as the working electrode at –2.6 V (vs. Fc/Fc + ). Furuya and co−workers demonstrated electrochemical reduction of N 2 to NH 3 using a gas diffusion electrode modified by Fe−phthalocyanine, but the current efficiency of NH 3 production was less than 0.1% after controlled−potential electrolysis for 10 min [2]. Becker and co−workers reported that titanocene dichloride, Cp 2 TiCl 2 , could reduce N 2 to NH 3 when the controlled−potential electrolysis (CPE) was carried out at −2.2 V (vs. Ag wire) in MeOH solution containing 0.3 M LiClO 4 and 0.25 M catechol [3]. This reaction was proceeded at room temperature under 1 atm using hydrogen atoms from catechol and/or MeOH, but the yield of NH 3 per Cp 2 TiCl 2 and the current efficiencies were both found to be quite low (1.45% and 0.28 %, respectively). In order to improve this reaction, we have decided to carry out CPE using a solid polymer electrolyte cell (SPE cell), which is composed of a working electrode (W.E.) and a counter electrode (C.E.) separated by a proton exchange membrane. Electrochemical synthesis of NH 3 in an SPE cell using a Ru cathode as W.E. was previously reported [4]. In this case, a proton was generated by oxidation of H 2 O at C.E., which was transferred to W.E. to react with N 2 . It is advantageous that the proton originated from H 2 O oxidation has been employed and the generated O 2 has been separated from W.E. by proton exchange membrane. Thus, it is possible to use H 2 O as the hydrogen source. Furthermore, in order to use Cp 2 TiCl 2 as the metal complex in the SPE cell, we investigated an ionic liquid as the supporting material. An ionic liquid, which is a salt in a liquid state under ambient conditions, has recently been employed in a number of different research fields, because it has several unique properties such as low volatility, large electrochemical window, high thermal and chemical stabilities, and high electric conductivity [5]. In particular, 1−butyl−1−methylpyrrolidinium tris(pentafluoroethyl)trifluoro−phosphate, [C 9 H 20 N] + [(C 2 F 5 ) 3 PF 3 ] – , is appropriate for use as a supporting material because of its high stability [6]. The W.E. is conveniently fabricated by coating the ionic liquid [C 9 H 20 N] + [(C 2 F 5 ) 3 PF 3 ] – supported with a transition−metal complex. We have reported the first example of the electrochemical reduction of N 2 to NH 3 using the W.E. coated with Cp 2 TiCl 2 –supported ionic liquid, [C 9 H 20 N] + [(C 2 F 5 ) 3 PF 3 ] – , under ambient conditions [7]. When the controlled potential electrolysis was carried out at -1.5 V (vs. Ag/AgCl), the yield of NH 3 per Cp 2 TiCl 2 and current efficiency were 27% and 0.2%, respectively, which are significantly higher in comparison with those reported previously [3, 7]. In this paper, we will report the controlled potential electrolysis by Cp 2 TiCl 2 -supported [C 9 H 20 N] + [(C 2 F 5 ) 3 PF 3 ] – in other experimental conditions. [1] C. J. Pickett et al. , Nature , 1985 , 317 , 652–653. [2] N. Furuya et al. , J. Electroanal. Chem., 1989 , 263, 171–174. [3] J. Y. Becker et al. , J. Electroanal. Chem., 1987 , 230, 143–153. [4] C. Lambrou et al ., Chem. Commun., 2000 , 1673–1674. [5] P. Hapiotet et al ., Chem. Rev., 2008 , 108 , 2238–2264. [6] N.V. Ignat’ev et al. , J. Fluor. Chem., 2005 , 126 , 1150–1159. [7] A. Katayama et al ., Electrochem. Commun. , 2016 , 67 , 6–10.
Type of Medium:
Online Resource
ISSN:
2151-2043
DOI:
10.1149/MA2016-02/40/3054
Language:
Unknown
Publisher:
The Electrochemical Society
Publication Date:
2016
detail.hit.zdb_id:
2438749-6
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