Improvement of Catalytic Activity by Nanofibrous ... - ACS Publications

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Improvement of catalytic activity by nanofibrous CuInS2 for electrochemical CO2 reduction Abdalaziz Aljabour, Dogukan Hazar Apaydin, Halime Coskun, Faruk Ozel, Mustafa Ersoz, Philipp Stadler, Niyazi Serdar Sariciftci, and Mahmut Kus ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b11151 • Publication Date (Web): 01 Nov 2016 Downloaded from http://pubs.acs.org on November 2, 2016

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ACS Applied Materials & Interfaces

Improvement of catalytic activity by nanofibrous CuInS2 for electrochemical CO2 reduction Abdalaziz Aljabour,*,‡,¥,§ Dogukan Hazar Apaydin,§ Halime Coskun,§ Faruk Ozel,Փ Mustafa Ersoz,¥ Philipp Stadler,§ Niyazi Serdar Sariciftci,§ and Mahmut Kus*,‡,¥ ‡

Selcuk University, Department of Chemical Engineering, 42075, Konya, Turkey

¥

Selcuk University, Advanced Technology Research and Application Center 42075, Konya,

Turkey §

Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes Kepler University

Linz, Altenbergerstrasse 69, A-4040 Linz, Austria Փ

Karamanoglu Mehmetbey University, Department of Metallurgical and Materials Engineering,

Faculty of Engineering, 70100, Karaman, Turkey KEYWORDS (Carbon dioxide, CuInS2, Electrochemical reduction, Nanofiber, Electrolysis)

ACS Paragon Plus Environment

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ABSTRACT The current study reports the application of chalcopyrite semiconductor CuInS2 (CIS) nanofibers for the reduction of CO2 to CO with a remarkable faradaic efficiency of 77±4%. Initially the synthesis of CuInS2 nanofibers was carried by adaptable electrospinning technique. In order to reduce the imperfection in the crystalline fiber Polyacrylonitrile (PAN) was selected as template polymer. Afterwards the desired chemical structure of nanofibers was achieved through sulfurization process. Making continuous CuInS2 nanofibers on the cathode surface by electrospinning method brings the advantages of being economical, environmentally safe and versatile. The obtained nanofibers of well investigated size and diameter according to the SEM (Scanning Electron Microscope) were used in electrochemical studies. An improvement of faradaic efficiency was achieved with the catalytic active CuInS2 in nanofibrous structure as compared to the solution processed CuInS2. Thus underlines the important effect of the electrode fabrication on the catalytic performance. Due to being less contaminated as compared to solution processing, having a well-defined composition and increased catalytically active area, the CuInS2 nanofiber electrodes prepared by the electrospinning technique, show four times higher faradaic efficiency. Furthermore, in this study attention was paid to the stability of the CuInS2 nanofiber electrodes. The electrochemical reduction of CO2 to CO by using CIS nanofibers coated onto FTO electrodes was carried out for 10 hours in total. The observed current density of 0.22 mA cm-2 and the stability of CIS nanofiber electrodes are found to be competitive with other heterogenous electrocatalysts. Hence we believe that the fabrication and application of nanofibrous materials through electrospinning technique might be of interest for electrocatalytic studies in CO2 reduction.


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1. Introduction The emission of carbon dioxide (CO2) into the atmosphere is expected to deteriorate the ecosystem adversely due to global warming. To cope with this issue, two solutions are suggested: a.) Carbon capture and sequestration (CCS) which is based on storage of CO2 underground, and b.) Carbon capture and utilization (CCU), by use of renewable sources like solar, wind, and water. Recycling of CO2 by CCU for creation of useful chemical products and synthetic fuels might also be an alternative for the problem of large scale storage of renewable energies.1 Both heterogeneous and homogeneous catalysis can be employed for the CO2 reduction using photocatalysis, photoelectrocatalysis and electrocatalysis.2-4 It should be noted that the required electrical energy for this process has to be provided by renewable sources to eliminate the further environmental pollution. The electrochemical cell for the reduction of CO2 principally works like a fuel cell in reverse. In aqueous electrolyte the reduction of CO2 is accomplished on the cathode while oxygen evolution reactions are processed at the anode. Thus the performance of cathode is therefore of outmost value for the reduction of CO2. Efforts are being devoted to improve the kinetics of cathode reaction by designing active and efficient catalysts. An ideal catalyst should be product selective to avoid the unwanted side reactions. Furthermore, the active sites of the catalyst should not be blocked easily (catalyst poisoning) for effective recycling and usage.5


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The electrocatalysis appears as one of the most convenient ways to reduce and therefore transform CO2 by utilizing various kinds of materials as catalysts. Thus, electrochemically driven reactions can be conducted on bulk metallic electrodes, in which overpotentials are varying. Interested readers on metallic electrode cases are highly suggested to refer to the work of Hori Y.6 It is necessary to find a marvelous compromise between the selectivity, stability and low overpotentials in electrocatalysts for CO2 reduction.7-10 In this work we represent the competitive catalytic behavior of nanofibrous CuInS2 in the field of electrocatalytic CO2 reduction with a moderate overpotential and excellent product selectivity and electrode stability. In table 1 literature about selected catalysts CO production is summarized. Table 1: Literature values of faradaic efficiencies for heterogeneous electrocatalysts for CO production.

Material

Method of catalyst deposition

solution process (4,4-BisphenylEthynyl-2,2 Bipyridyl)Re(CO)3Cl solution deposition CuInS2 by spin coating Alkynyl-Substituted Rhenium(I) Complex Ag nanoparticle

F.E. [%]

Ref.

12.7

(11)

20

(12)

electropolymerization 33

(13)

layer-by-layer deposition

94

(2)

~25

(8)

98

(14)

-

(9)

solution process Cu-Pt alloy nanocube Heteroatomiccarbon electrospinning nanofiber MnP immobilized on drop-casting TiO2


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nanoflake by chemical vapour -

24

(15)

81.5

(10)

-

57.9

(10)

Metallic Zn

-

39.6

(10)

Metallic Cd

-

14.4

(10)

WSe2 Au (99.95%) electrode Pd metal

Different techniques and material classes were applied in order to reduce CO2 to CO. The catalytic activity of CuInS2 was reported earlier in the literature, however depending on the fabrication method different yields of desired products were observed. Having in mind to obtain a high yield in CO2 reduction to CO in our paper the CuInS2 nanofibers were used. The nanofiber technology is one of the most important fields in the society gaining interest. Especially in the medical science nanofibers were applied in capturing individual cancer cells, penetrating in diseased cells and in drug delivery.16 Furthermore, carbon nanofibers were used in lithium ion batteries in order to store higher capacity of current, in the sensor technology and recently as catalysts in the reduction of CO2.17-20 Among all these applications our motivation was to use the economical, environmentally safe and versatile CuInS2 nanofibers in CO2 reduction due to the material’s suitable band gap (1.3eV), stability, facile synthesis route and remarkable catalytic efficiency.12,21-24 In particular the latter can be improved by the combination of the catalytic active material CuInS2 with the adaptable electrospinning method in order to obtain nanofibers. The outstanding performance of the CIS nanofibers is attributed to the increased number of the catalytically active sites introduced by the fiber character. The nanocrystalline shaping of the CuInS2 to a nanofiber network offers the possibility to expand the catalytically active surface to volume ratio, which is imperative to obtain high yields in faradaic efficiency. Thus the increased


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activity from the structural nanofibrous structure gave a competitive faradaic efficiency in comparison to organic heteroatomic carbon nanofibers. Thus our work demonstrates that the faradaic efficiency of the CuInS2 can be improved four times by changing the electrode fabrication technique. 2. Materials and Methods 2.1. Materials The chemicals used in the present study include copper (II) chloride dihydrate (CuCl2.2H2O, 99%, Merck), indium (III) chloride anhydrous (InCl3, 99.99%, Alfa Aesar), 1-dodechanethiol (%98, ABCR), dimethylformamide (DMF, 99%, Sigma-Aldrich) and polyacrylontrile (PAN, Mw

=

150,000,

Sigma-Aldrich),

Acetonitrile

(CH3CN

99.9%,

Roth,

anhydrous,

Improvement of Catalytic Activity by Nanofibrous ... - ACS Publications

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