One of effective solar-hydrogen conversion approaches is indirect usage of solar energy in electrocatalytic water electrolysis reactions. Highly purified hydrogen can be produced from water electrolysis, but the biggest disadvantage is high-energy consumption of this method [1]. In order to reduce the production costs by lowering the overpotential of hydrogen evolution reaction (HER), various electrocatalytic materials have been frequently tested as the best solutions. Due to the versatile properties, 2-D graphene based functional hybrid nanomaterials have been used for many fields such as, sensors, transparent conductors, purification, and dye-sensitized solar cells. Now a days, graphene oxide (GO) and based materials have been tested as active photocatalysts and photoelectrocatalyst for water splitting reactions [2]. Although GO and reduced azido graphene oxide (RGO) were used as active photocatalysts and photoelectrocatalyst for HER and active electrocatalyst for oxygen reduction reactions [3], there is no a study on the usage of GO and RGO for the electrocatalytic HER from water electrolysis. Therefore in this study we have investigated electrocatalytic activity of GO and RGO based modified electrodes for the electrocatalytic HER.

The complexes having metal-based reduction processes observed before HER processes generally showed good electrocatalytic activity. It was stated in our previous studies that MPcs having metal-based reduction processes showed higher activities for HER [4]. Therefore in order to increase electrocatalytic activity of the modified electrodes, GO and RGO were decorated with an active electrocatalyst, terminally alkyne substituted cobalt(II)phthalocyanine (TA-CoPc). For this purpose GO and RGO were functionalized with azide groups. Then TA-CoPc molecules were bonded to the azide groups of GO and RGO with click electrochemistry (CEC) technique and finally CoPc decorated GO and RGO based modified glassy carbon electrodes (GCE/GO-N₃/TACoPc and GCE/RGO-N₃/TACoPc) were developed.

The modified GCE/RGO-N₃/TA-CoPc and GCE/GO-N₃/TA-CoPc electrodes were characterized with square wave voltammetry and electrochemical impedance spectroscopy (EIS), and then tested as heterogeneous electrocatalysts for HER. Characterizations illustrated that GCE/GO-N₃/TA-CoPc and GCE/RGO-N₃/TA-CoPc electrodes have redox activities at small potentials and sufficient conductivities, which are the basic requirements for the electrocatalytic application of a modified electrode. GCE/RGO-N₃/TA-CoPc electrode illustrates well electrocatalytic activity by decreasing the over-potential of the bare electrode and increasing the current density of the electrode significantly with absolutely high stability and reproducibility. Analyses of Tafel responses of the electrodes show the proceeding of a Volmer–Heyrovsky mechanism during HER.

 Acknowledgement: This work is supported by the research fund of TUBİTAK (Project no: 113M991) and Marmara University (Project no: FEN-C-YLP-080415-0118).

 

References

1. Momirlan M, Veziroglu TN (2005) Int J Hydrogen Energ 30: 795-802.

2. Wang D, Li X, Chen J, Tao X (2012) Chemical Engineering Journal 198: 547-554.

3. Li Y, Li Y, Zhu E, McLouth T, Chiu C-Y, Huang X, Huang Y (2012) Journal of the American Chemical Society 134: 12326-12329.

4. Koca A, Kalkan A, Bayır ZA (2011) Electrochimica Acta 56: 5513-5525.