Electrochemical reduction of CO2 on Ni (OH)2 doped water dispersible graphene under different electrolyte conditions
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Association of the cathodic operation of Ni(OH)2 doped water dispersible graphene (WDG) nanocomposite with three different electrolytes (NaHCO3, KHCO3, and NaCO3) with the help of carbon dioxide (CO2) electrochemical reduction is presented in this research. Graphene in short time is effectively synthesized and Ni(OH)2 doped on WDG by electrochemical method, structure, morphology and characterization analysis by X-ray diffraction, scanning electron microscope, transmission electron microscope and Raman spectroscopy. CO2 is effectively reduced to carbon monoxide (CO) at enhanced situation. Fourier transform infrared spectroscopy, which is used to exanimate integrated Ni(OH)2–WDG nanocomposite surfaces so as to uncover the carbonate ions and CO during reduction at three different electrolytes. The electron charge resistance of the nanocomposite is investigated by using electrochemical impedance spectroscopy analysis. Analysis of the Ni(OH)2–WDG nano composite was performed to decouple electrochemical reduction processes of CO2 to CO at different electrolytes by cyclic voltammetry and linear sweep voltammetry.
KeywordsCO2 Reduction Carbon dioxide Electrochemical Cyclic voltammetry Linear sweep voltammetry
Although, CO2 plays a significant part in producing greenhouse effect, it is accountable for the warming of the Earth [1, 2, 3]. CO2 is emanated, while performing human activities such as deforestation, fossil fuels combustion, and industrial processes. One must follow most of the valuable methods for reducing CO2 emissions, i.e.to diminish the consumption of fossil fuels. In current times, the ratio of atmospheric mixing of CO2 is higher than what it was in the last 800,000 years [4, 5, 6, 7, 8, 9, 10].In the nineteenth century, a chemical scheme of converting CO2 and hydrogen (H2) to methane was developed and later the same was transformed to liquid fuels .For the production of gases like carbon monoxide (CO)/H2 and other supportive organic compounds like methanol, methane, ethylene, and formic acid, CO2 was utilized as the C1 feedstock. The organic compounds have been merged with numerous chemical, photochemical, biochemical, and electrochemical procedures [8, 9, 10].
Owing to several reasons, the conversion of using CO2 electrochemical catalysis methods enticed a great deal of attention among researchers. Let us take a look at these reasons: (1) by means of electrode potentials and reaction temperature, the method is controllable; (2) the supporting electrolytes can be totally reprocessed, so as to minimize the whole chemical utilization to simply water (or) waste water; (3) the electricity utilized to drive the method can be attained without producing any new CO2-sources; and (4) The electrochemical reaction systems are compressed, modular, on-demand, and simple to scale-up . In the past decades, the electrochemical CO2 reductions at metals (e.g. Hg, Cu, etc.) and related electrodes in addition to electrocatalytic CO2 reduction have been extensively examined in aqueous and non-aqueous Medias [12, 13, 14, 15, 16, 17, 18].
Carbon materials incorporates glassy carbon, graphite, boron-doped diamond (BDD), carbon black, carbon nano fiber, carbon tubes (CNTs), and these days graphene is extensively used as an electrode in the elementary innovations and application aspects of electrochemistry and electro analysis [19, 20]. Ni(OH)2/graphene composite has proven its application in energy storage applications like supercapacitor owing to its high specific capacitance of graphene, energy density, and good cyclic stability [21, 22].
In this paper, graphene is synthesised through electrochemical technique and then graphene is converted to WDG. In addition, Ni(OH)2 is doped on the surface on WDG with the help of electrochemical techniques. The cathodic performance of Ni(OH)2–WDG composite at three different electrolytes, namely, NaHCO3, KHCO3, and NaCO3 are investigated in detailed manner.
2.1 Preparation of graphene
The graphene was made with the help of electrochemical process. The graphite rods were treated both as an anode and cathode by distributing at a distance of 2 cm in 3 M intensity of H2SO4 mixture. This mixture was used as an electrolyte. The graphene was washed from the graphite rod by escalating a potential of more than 7 V through DC electrical power supply. The acquired graphene was blended with the electrolyte mixture. The pure graphene was separated from the solution by several exfoliating with the help of double distilled water.
2.2 Preparation of water dispersible graphene
Graphene powder (0.1 g) was dissolved in 100 mL purified water and sonicated. Furthermore, 0.5 M NaOH is added to the solution drop wise and pH was altered to above 8. Additionally, the mixture was dehydrated at 80 °C to attain powdered mixture .
2.3 Ni (OH)2 doped water dispersible graphene
Ni(OH)2 was effetely doped on WDG by using electrophoretic deposition (EPD). The conductive substrate such as stainless steel (SS) is used as negative electrode during the EPD procedure. The substrate was rinsed by ultrasonic vibrations caused in acetone, ethanol, and deionised water, correspondingly. The positive counter electrode was Pt with the same elements. Prior to EPD, the WDG and NiCl2 in 50 mL of deionised water were ultrasonically spread for 2 h. The electrodes were in the gap of 10 mm and immersed in the colloidal solution saturated with nitrogen gas. An applied potential of 2–10 V was used for 30–500 s to deposit. EPD was carried out on a current–voltage monitor and the current accuracy of 13 mA, when the applied voltage came to 10 V. After EPD, the nanocomposite film was dehydrated at 80 °C in an oven overnight.
2.4 Materials characterization
With the help of CuKα(λ = 1.5406Å) as a radiation source, the phase and crystalline nature of the synthesised samples were examined by X-ray diffractometer (XRD) (X’-Pert PRO, PANalytical, The Netherlands). The samples were examined over the 2θ range of 10–80 °C at room temperature (298 K). In relation to the reference diffraction data, the observed peak positions and the relative concentration of the powder pattern were indexed. The surface morphology of WDG and Ni(OH)2–WDG were decided by means of a scanning electron microscope coupled with energy dispersive X-ray analysis (SEM-EDAX) (JEOL JSM-6390LV, Japan) at 20 kV with a magnification of 10000× at 1 μm scale. Functional group information about powder surface was examined by means of FTIS (Spectrum 100; PerkinElmer, USA). The spectra were collected in the range of 4000–500 cm−1.
2.5 Electrodes preparation and characterization
The SS plate was sliced into small pieces (16 cm2) and later on buffed delicately with the help of a solvent (acetone). The synthesized Ni(OH)2–WDG nanocomposites powder was assorted with a polyvinylidene difluoride (PVDF) at a ratio of 85:15 in a small quantity of N-Methyl-2-pyrrolidone as a solvent to make a paste. The paste substance was covered over the separate SS plates by means of a doctor blade . The coating was done repetitively multiple times so as to attain a uniform thickness (10 mm) of electrodes on the SS plates. The Ni(OH)2–WDG nanocomposites electrodes were dehydrated at 85 °C in a hot-air oven for about 1 h and then used for further examination. The method of electrolysis was handled in the terylene diaphragm cell of 100-mL volume. The anode was an SS net (16 cm2) and cathode was an Ni(OH)2–WDG electrode (16 cm2). The gap between the anode and cathode was 2 cm. The electrical power was presented by a laboratory direct current power supply with a current–voltage monitor.
2.6 Electrochemical measurements
The CV and EIS behavior of Ni(OH)2–WDG nanocomposites electrode was investigated with the help of a three-electrode cell set-up. In this set-up, the Ni(OH)2–WDG was used as a working electrode, where as platinum (Pt) and saturated calomel were majorly used as the counter and reference electrodes, correspondingly, for the carbonate-based electrolytes. The CV analysis was done in Ni(OH)2–WDG at different electrolytes in fixed scan rate by means of Autolab equipment (PGSTAT302 N, Metrohm Autolab, and the Netherlands). The applied potential window for CV study was − 1–1 V at 10 mV/s scan rate. The present performance of cathode was determined from the extrapolated data of the CV test.
3 Results and discussion
3.1 Structural characterizations
3.2 FTIR of FeTiO3
3.3 Electrochemical impedance spectroscopy
3.4 Cyclic voltammetry
This anion radical, however should react rapidly with the intermediate at the desired product. Graph (a) indicates CV for Ni(OH)2–WDG in CO2 saturated at 1 M NaHCO3 electrolyte, graph (b) shows CV for Ni(OH)2–WDG in CO2 saturated at 1 M KHCO3 electrolyte and graph (c) depicts CV for Ni(OH)2–WDG in CO2 saturated at 1 M NaCO3 electrolyte. In CV reduction peaks, positive site shifted depending on electrolyte serial (NaHCO3, KHCO3 and NaCO3). Increasing the cathodic behavior of Ni(OH)2–WDG in CO2 saturates NaHCO3 than KHCO3 and NaCO3 electrolytes. These CV results indicate that electrolyte plays an important role in CO2 electrochemical reduction and HCO−3 ions also offers great help in the CO2 reduction process.
The K+ ions, increasing the cathodic behavior and increasing reaction intermediated for CO2 to CO , this CV results represents that the Na+ ions increases the cathodic behavior than K+ ions in electrolyte medium. The Na+ ions are well coordinated to the intermediate components of the CO2 electrochemical reduction.
3.5 Linear sweep voltammogram
The electrolysis researches were transmitted out in an undivided cell under mild conditions; prevent the adding up of toxic solvents and catalysts. The electrical power was provided by a laboratory direct current power supply with a current–voltage monitor. Ni(OH)2–WDG mixture could be functioned at low current density 8 (mA/cm2) attained with the help of electrode for CO2 reduction at three different electrolytes. XRD specifies good crystalline peaks that exist by effective fusion of WDG. When doped Ni(OH)2 on WDG, it has fully reduced the crystalline structure of WDG and it is well indicated in the XRD for Ni(OH)2–WDG. Raman, SEM, and TEM images signifies WDG had monolayer by effectively blended WDG, another SEM and AFM images epitomizes the white portion point to the Ni(OH)2 fine doped on WDG. FTIR indicates adsorbed carbonyl functional groups on Ni(OH)2–WDG at three different electrolytes (NaHCO3, KHCO3, and NaCO3) after CO2 reduction, increased concentration peaks appear NaHCO3 than KHCO3 and NaCO3 electrolytes on Ni(OH)2–WDG electrode surface. The results of CV and LSV specifies the good cathodic behavior of Ni(OH)2–WDG composite in CO2 reduction than Cd, Co, and Cu (− 0.75), this consequence epitomises Ni(OH)2–WDG has better CO2 reduction behavior (− 0.4 V) in NaHCO3 than the KHCO3 and NaCO3, Na+ and HCO−3 ions augments the CO2 reduction cathodic behavior of Ni(OH)2–WDG electrode.
Compliance with ethical standards
Conflict of interests
The authors declare that they have no conflict of interest.
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