A comparative experimental and density functional study of glucose adsorption and electrooxidation on the Au-graphene and Pt-graphene electrodes

https://doi.org/10.1016/j.ijhydene.2019.10.163Get rights and content

Highlights

  • Few layer graphene produced by the CVD method is succesfully coated on ITO.

  • Pt and Au are succesfully electrodeposited on few layer graphene/ITO electrode.

  • Pt-graphene/ITO indicates the best C6H12O6 electrochemical activity and stability.

  • C6H12O6 adsorption is examined via DFT over Au and Pt doped graphene surfaces.

  • The interaction between C6H12O6 and OH adsorbed Pt-doped surface is robust.

Abstract

At present, the graphene is covered on Cu foil with the 5 sccm hexane (C6H14) flow rate, 50 sccm hydrogen (H2) flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil is then covered onto few-layer ITO electrode. Furthermore, the Pt and Au metals are electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes are characterized by Raman spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-Ray analysis (SEM-EDX). The graphene structure is approved via Raman analysis. Au, Pt, and graphene network are openly visible from SEM results. In addition, glucose (C6H12O6) electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. As a result, Pt-graphene/ITO indicates the best C6H12O6 electrooxidation activity with 9.21 mA cm−2 specific activity (highly above the values reported in the literature). In all electrochemical measurements, Pt-graphene/ITO exhibits best electrocatalytic activity, stability, and resistance compared to the other electrodes. The adsorption of the C6H12O6 molecule is examined theoretically over metal atom (gold and platinum)-doped graphene surfaces using the density functional theory (DFT) method. The interaction between C6H12O6 molecule and OH adsorbed Pt-doped surface is stronger than that of OH adsorbed Au-doped graphene surface thermodynamically according to the reaction energy values.

Introduction

Energy needs are very important for humanity throughout history [1]. The world energy need accommodated with fossil fuels as oil, coal, and natural gas but these fossil fuels cause environmental hazards [2]. The energy need has increased due to the growing industry and the increasing population [[3], [4], [5]]. Fuel cells (FCs) are practical power systems used in many fields such as spaceship locations and meteorology stations by converting chemical energy into electrical energy [6,7]. Various liquid fuels have been employed in directly liquid-feed fuel cells (DLFCs) such as ethanol [8], methanol [9], formic acid [10], and C6H12O6 [[11], [12], [13]]. C6H12O6 is a monosaccharide abundant in nature and is used directly as fuel for directly glucose fuel cells (DGFCs) [14]. C6H12O6 is categorized into two types mechanism as (i) enzymatic glucose, (ii) non-enzymatic glucose for glucose oxidation reaction (GOR) [15,16]. The enzymatic glucose has disadvantages due to low chemical stability and complex synthesis. Thus, it was examined to improve non-enzymatic C6H12O6 electrooxidation to forestall deficiencies originating from enzymatic glucose in literature [17]. C6H12O6 electrooxidation has been the subject of hot research in electrochemistry due to the interest in implantable glucose fuel cells for artificial hearts and heart beat, as well as the importance of reliable and rapid in vivo or in vitro blood glucose monitoring for the treatment and control of diabetes in electrochemistry with an electrochemical glucose sensor [18]. DGFCs produce 24 electrons through complete electrooxidation to CO2 when C6H12O6 is fed directly to the anode [19]. When C6H12O6 is fed to the alkaline fuel cells, it displays better activity than proton conducting membrane fuel cells [20,21]. In most studies, researchers have attempted to advance efficient and stable electrocatalysts for C6H12O6 electrooxidation. For C6H12O6 electrooxidation reaction, specific activity values compiled from the literature were given in Table 1. These studies investigated the effect of different support material, monometallic, bimetallic, and trimetallic catalysts for C6H12O6 electrooxidation. Furthermore, literature studies such as Pd [22], PdAu [18], PdBi [23], NiCo [24], and NiCrCo [25] have examined to evaluate electrocatalytic activity towards C6H12O6 electrooxidation.

Graphene structure has many superior properties such as a hexagonal, single-atom, and two-dimensional (2D) hexagonal cage with sp2-hybrid carbon atom layer allocated from 3D structured graphite [32,33]. Graphene synthesis has been performed by different methods such as reduction of graphene oxide [34], mechanical exfoliation [35], epitaxial growth on SiC [36], and CVD [[37], [38], [39]]. CVD is known as the leading growth method that is inherently scalable for large area film generation. The graphene synthesis with CVD method has ability to solve metal to transfer the graphene to another substrate in several aspects with its capability for large-area, high-quality synthesis as well as layer controllability according to other methods [40]. In the CVD processes, copper (Cu) and nickel (Ni) foils are widely employed as a growth template for covering the graphene by utilizing carbon sources such as acetylene, methane, and ethylene for graphene synthesis [41,42].

Herein, the graphene was covered on Cu foil with the 5 sccm C6H14 flow rate, 50 sccm H2 flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil was then covered onto few-layer the ITO electrode. Furthermore, the Pt and Au metals were electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes were characterized via SEM-EDX and Raman Spectroscopy measurements. The C6H12O6 electrooxidation activity, stability, and resistance of these electrodes were investigated by using CV, CA, and EIS. The interaction of the molecules in the reaction medium with Pt-doped graphene and Au-doped graphene surface were also examined with density functional method (DFT).

Section snippets

The synthesis and transfer of graphene

The graphene layers were coated onto Cu foil via MCM-CVD process. The Cu foil was first placed in CVD system after cleaning with isopropyl alcohol and acetone. In order to increase the grain size of Cu foil, it was annealed at temperatures of about 900–1000 °C under Argon/Hydrogen atmosphere in CVD device. H2 was then fed into the system. The reactor was set at 950 °C at a rate of 50 °C/min without interrupting the hydrogen flow. When the temperature reached the set value, initially, Cu foil

Characterization

Raman analysis of graphene was realized to detect impact of defects and layers number of graphene. Three typical band of graphene were obtained for graphene which are the D band at 1347 cm−1, G band at 1581 cm−1, and Gı band at 2694.8 cm−1 due to defects in the structure, C–C stretching pulsation and second-order two phonon process, respectively (Fig. 1). The intensity of G-band for graphene at 1581 cm−1 was 8.2 times higher than that of its D-band indicated that the interaction of C atoms were

Conclusion

At present, the graphene modified ITO electrodes were synthesized by CVD method and Au and Pt metals were electrodeposited on graphene/ITO. These electrodes were defined via Raman spectroscopy and SEM. The graphene network was approved via Raman analysis. Au, Pt, and graphene structure was openly visible from SEM results. Among obtained the electrodes, Pt-graphene/ITO electrode was obtained the best electrocatalytic activity toward the oxidation of C6H12O6. The specific activity toward C6H12O6

Acknowledgements

Hilal Kivrak would like to thank for the financial support for The Scientific and Technological Research Council of Turkey TUBITAK project (project no:116M004). The numerical calculations reported in this paper were fully performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources). Visit http://www.truba.gov.tr/for more information.

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