(FexNi1-x)9S8 electrocatalysts: Materials for hydrogen evolution and CO2 reduction reactions

Ulf-Peter Apfel, Ruhr-University Bochum / Fraunhofer UMSICHT, Bochum, Germany
Kai junge Puring, Ruhr-Universität Bochum; Fraunhofer UMSICHT, Bochum; Oberhausen, Germany
S. Piontek, Ruhr-Universität Bochum, Bochum, Deutschland
M. Smialkowski, Fraunhofer UMSICHT, Oberhausen, Deutschland

The efficient reduction of protons and CO2 under mild conditions is a current challenge for modern society. Nature utilizes enzymatic machineries that comprise iron- and nickel- containing active sites to perform these transformations.[1] Recently, we reported on the formidable HER activity of bulk Fe4.5Ni4.5S8 electrodes revealing similar structural and functional properties of the enzymes.[2,3,4] We herein set out to explore the influence of the Fe : Ni ratio on the performance of the electrocatalyst.[5] Using linear sweep voltammetry, we show that the increase in the Fe or Ni content, respectively, lowers the activity of the bulk electrocatalyst towards HER. Specific Fe-Ni interactions thus seem to be the key for the observed HER activity. In addition, we show that a temperature increase leads to a significant decrease of the overpotential. Furthermore, due to the resemblance of such sulfides with CO2 converting enzymes, we likewise investigated Fe4.5Ni4.5S8 electrodes to perform CO2 reduction. In non-aqueous conditions, this material is indeed a potential catalyst affording CO as main product with Faradaic yields of up to 80 %.

[1] F. Möller, S. Piontek, R. G. Miller, U.-P. Apfel, Chem. Eur. J. 2017, DOI: 10.1002/chem.201703451.
[2] B. Konkena, K. junge Puring, O. Khavryuchenko, I. Sinev, S. Piontek, M. Muhler, W. Schuhmann, U.-P. Apfel, Nature Commun. 2016, 7:12269, DOI: 10.1038/ncomms12269.
[3] K. junge Puring, S. Piontek, M. Smialkowski, J. Burfeind, S. Kaluza, C. Doetsch, U.-P. Apfel, J. vis. Exp. 2017, 124, DOI:10.3791/56087.
[4] I. Zegkinoglou, A. Zendegani, I. Sinev, S. Kunze, H. Mistry, J. Zhao, M. Y. Hu, E. E. Alp, S. Piontek, M. Smialkowski, U.-P. Apfel, T. Hickel, J. Neugebauer, B. Roldan Cuenya, J. Am. Chem. Soc. 2017, 139, 14360.
[5] S. Piontek, C. Andronescu, A. Zaichenko, B. Konkena, K. junge Puring, B. Marler, H. Antoni, I. Sinev, M. Muhler, D. Mollenhauer, B. Roldan Cuenya, W. Schuhmann, U.-P. Apfel, ACS Catalysis, 2018, 8, 987.

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