Electrochemically grown Polymer-graphene Quantum dot composites for Oxygen Reduction Reaction
Mrinmoy Kumar Chini1, Navneet Kumar2*
1Department of Applied Sciences (Chemistry), Galgotias College of Engineering and Technology,
Greater Noida - 201306, Uttar Pradesh, India.
2Department of Chemistry, Faculty of Engineering, Teerthanker Mahaveer University,
Moradabad - 244001, Uttar Pradesh, India.
*Corresponding Author E-mail: navkchem@gmail.com
ABSTRACT:
The work presents a facile method for the preparation of oxygen reduction reaction (ORR) catalysts through the electrochemical polymerisation of small molecule containing pyridinic and imine-type nitrogen atoms with lone-pair electrons to perform more effective ORR investigated in alkaline KOH medium. The PEDOT modified gold electrode showed a lower activity towards the ORR than the PEPE modified one owing to the presence of N containing pyridine units in the polymeric backbone structure. On further note, PEPE-CGQDs modified electrodes did not show any improvement in ORR activity compared to PEPE alone due to the ineffectiveness of CGQDs towards the development of a superior ORR catalyst.
Activity enhancement of oxygen reduction reaction (ORR) has long been a holy grail for electrochemical technologies and processes, especially polymer electrolyte fuel cells and metal-air batteries, because ORR is the rate-determining reaction (Markovic 2001, Gewirth 2010, Bruce 2012). Efficient and low-cost electrocatalysts for ORR have attracted great attention in scientific research and industrial application, since they determine the efficiency and cost of energy-conversion devices, such as fuel cells and metal–air batteries. To date, noble-metal (e.g., platinum) catalysts have been used as active catalysts for ORR, while the cost and scarcity of Pt is the major obstacle for this class of catalysts to be utilized in large-scale applications (Borup 2007, Stamenkovic 2007). Besides, Pt catalysts suffer from their susceptibility to time-dependent drifts, crossover effects of organic compounds and CO toxicity, which deteriorate their ORR activities under working conditions of fuel cells (Zhang 2009).
Therefore, to explore new strategies to overcome these limitations is inevitable. Much effort has so far been made to synthesize various kinds of efficient catalyst for ORR (Uhm 2011, Olson 2010). Among them, doping carbon nanomaterials with heteroatoms have been reported in the literature to tune their electronic, chemical and surface properties (Li 2012). Though, the direct N-incorporation in these structures introduces a large number of defect sites resulting in a less stable structure. Recently, remarkable advancement has been achieved in the synthesis of graphene quantum dots (GQDs) having excellent properties in terms of quantum confinement and edge effects on both the experimental and theoretical aspects (He 2013). On further note, chemical functionalization gives the rare opportunity to rationalize the structure-activity relationship of these metal-free catalysts systematically, through a fine-tuning of the electronic properties of the N-containing heterocyclic involved as “active site” in the catalytic process. High contents of these nitrogen species are therefore essential to obtain active catalysts. Conductive polymers are considered to be desirable for backbones in terms of their physical stabilities and electrical conductivities. They are known for for various electrical applications such solar cells (Sudhakar 2020), field effect transistors (Chini 2016, Dharmapurikar 2017), etc. Organic compounds containing pyridinic and –C=N atoms may be used without pyrolysis as catalysts, as part of our interest in the development of metal-free ORR catalysts (Ohtsubo 2023). Thus, the development of a new type of metal-free ORR catalysts under mild conditions is still extremely desirable and can be considered to be one of the highest priorities in the development of fuel cells and metal-air batteries.
Herein, we have synthesized GQDs with oxygen-rich functional groups via hydrothermal method (Chini 2017) in order to prepare the N-containing polymeric composites for the oxygen reduction reaction (ORR) in an alkaline medium. We expected that the plausible π-π interactions between the lone pair of electrons on the nitrogen containing functionality and oxygen atoms in the GQDs may contribute towards the overall activity and stability of the GQDs-polymer composites. As far as we are aware, however, only few attempts have been made to synthesize N-containing polymeric composites with carbon nano materials as ORR catalysts.
EXPERIMENTAL SECTION:
General methods and materials
All chemicals were reagent grade, used without further purification. The monomer EPE has been synthesized and EDOT has been obtained from Aldrich. The cyclic voltammogram (CV) and chronoamperometric scans were carried out in a conventional three-electrode arrangement using a computer controlled CHI900B Electrochemistry Workstation (CH Instrument, Inc. USA). The gold wire served as the working electrode, Ag/AgCl electrode as a reference electrode, and a Pt foil as a counter electrode.
Preparation of carboxylated GQDs (CGQDs)
Graphene oxide (GO) had been dissolved in DMF with the concentration of 25mg/10ml. The GO-DMF solutions were subjected to ultrasonication for 1 h. The GO-DMF solutions were transferred to a PTFE (25mL) and heated at 180℃ for 10h. Then, the reactors were allowed to cool at room temperature. The product was black precipitates and the black precipitates were filtered out through 0.02-micron PTFE membrane. The filtered was collected and the solvent of the brown suspension was removed with the aid of a rotary evaporator. The yield was about 2%. The GQDs have excellent dispersibility in many polar organic solvents or water.
RESULTS AND DISCUSSION:
The UV-vis spectrum of the carboxylated GQDs (CGQDs) in chloroform showed absorption peak at 270 nm indicating CGQDs formation and the characteristics blue colour of CGQDs under UV light (365nm) (Figure 1a) and Transmission Electron Microscopy (TEM) images show that the size of the CGQDS is approximately below 5nm (Figure 1b). Then to prepare PEPE and PEDOT, the solution of 0.01M PEPE/PEDOT and 0.1M TBAP in chloroform solution was freshly prepared prior to electropolymerisation. On further note, to prepare PEPE-CGQDs composite materials, the solution of 0.01M PEPE and CGQDs (1mg/mL) had been prepared, sonicated for 30 minutes and kept standing for another 30mintutes prior to the addition of supporting electrolyte for better binding of carboxylated GQDs with pyridine moieties of EPE trimer. The chronoamperometric scanning has been done using 0.01M EPE and CGQDs chloroform solution containing 0.1 M TBAP applying potential 0.8 V for 60s. The monomer oxidation started at 0.6 V. The chronoamperometric scanning shows the deposition of the polymers on working electrode. The polymerisation process will increase the content of pyridinic and imine-type nitrogen atoms which will favour the activity of our synthesized ORR electrocatalyst. The deposited polymers had been washed with electrolyte free solvent and collected for UV-vis spectroscopy studies. The UV-vis spectrum of chloroform solution of PEPE and PEPE-CGQDs materials had been shown in Figure 1c and 1d.
Figure 1 (a) UV-vis spectra and (b) TEM images of CGQDs. (c) and (d) represents UV-vis spectra of PEPE and PEPE-CGQDs, respectively
To evaluate the electrocatalytic activities for ORR, we have synthesized PEDOT and N-containing polymer PEPE by chronoamperometrically. The solution of 0.01 M EPE/EDOT and 0.1 M TBAP in chloroform solution was freshly prepared prior to electropolymerisation by applying potential 0.8 V and 1.1 V for 60s, respectively. The chronoamperometric scanning shows the deposition of the polymers on working electrode. Finally, the polymers had been washed with supporting electrolyte free organic solvents, electrochemically reduced by applying potential 1.0 V for 30 seconds and ready for further experiments. Figure 2a showed chronoamperometric scanning of electrochemical synthesis PEPE polymer. The cyclic voltammograms (CVs) of the deposited PEPE at different scan rates (30 to 100mV/s) was performed in order to see the electro active nature of the deposited polymer. Cyclic voltammetric (CV) measurements were carried out for newly synthesized polymers PEPE (Figure 2b), PEDOT and PEPE-CGQDs (Figure 3b) by means of electrochemical reduction of oxygen in 0.1 M KOH solution saturated with both Ar and O2 atm. implying polymer materials modified gold electrodes as working electrode whereas Pt foil and Ag/AgCl (0.1M) as counter and reference electrode, respectively. All three samples showed well defined reduction (cathodic) peaks towards ORR in aqueous solution of KOH (0.1M) saturated with O2 not in Ar within the potential range of 0.4 V to -0.4 V. The PEPE showed cathodic peak for ORR at -0.1 V at 50 mV s-1 (Figure 2a), which is more positive potential compared to PEDOT which showed the same at –0.14 V (Figure 2d). PEPE modified electrode indicates better effectiveness of towards the ORR than PEDOT. This phenomenon can be attributed to the presence of N-containing heterocycles in the conjugated polymeric backbone which increases the number of active sites for ORR which is absent in PEDOT backbone.
Figure 2 (a) Chronoamperometric curve of the polymerization of PEPE on gold electrode and (b) cyclic voltammograms (CVs) of the chronoamperometrically deposited PEPE at different scan rates (30 mV/s to 100 mV/s), (c) and (d) comparative ORR studies of PEPE and PEDOT in O2 saturated solution
Finally, the electrochemical reduction of oxygen in 0.1 M KOH solution implying PEPE-CGQDs modified electrodes both in Ar and O2 atm (Figure 3c). Figure 3d depicts typical cyclic voltammetric graphs obtained for the electrochemical reduction of oxygen in 0.1 M KOH solution implying both PEPE and PEPE-CGQDs modified electrodes both in O2 atm. The electrodes show cathodic peaks at -0.1 V at 50 mV s-1, which is comparable with the PEPE modified one indicating ineffectiveness of CGQDs towards the further improvement of ORR than PEPE. This can be further explained by the fact that the performance of the electrocatalyst towards ORR activity might be highly dependent on the presence of active sites.
Figure 3 (a) Chronoamperometric deposition of PEPE-GQDs, (b) CVs of the chronoamperometrically deposited PEPE-GQDs at different scan rates, (c) Oxygen reduction studies using PEPE-GQDs and (d) comparative ORR studies of PEPE and PEPE-GQDs in O2 saturated solution
CONCLUSION:
PEPE, PEPE-CGQDs composite, and PEDOT modified gold electrode had been prepared by electrochemical polymerization, and then the electrochemical oxygen reduction reaction behaviour was investigated in alkaline KOH medium. The PEDOT modified gold electrode show cathodic peak at -0.14 V at 50 mV s-1, which was at higher potential (-0.1 V) than the PEPE modified one indicating a lower activity towards the ORR. This can be contributed to the presence of N containing pyridine units in the polymeric backbone structure. Hence N containing molecules will be effective in further more effective ORR studies. On further note, PEPE-CGQDs modified electrodes did not show any improvement in ORR activity compared to PEPE alone due to the ineffectiveness of CGQDs towards the development of a superior ORR catalyst. These fundamental studies regarding ORR will be helpful in basic fuel cell research.
ACKNOWLEDGEMENT:
MK Chini acknowledges Dr. Kothandam Krishnamoorthy for providing his laboratory resources.
REFERENCES:
1. Markovic, N. M.; Schmidt, T. J.; Stamenkovic, V.; and Ross, P. N. (2001). Oxygen Reduction Reaction on Pt and Pt Bimetallic Surfaces: A Selective Review. Fuel Cells, 1, 105−116.
2. Gewirth, A. A.; and Thorum, M. S. (2010). Electroreduction of Dioxygen for Fuel-Cell Applications: Materials and Challenges. Inorg. Chem., 49, 3557−3566.
3. Bruce, P. G.; Freunberger, S. A.; and Hardwick, L. J. Li−O2 and Li−S batteries with high energy storage. (2012). Nat. Mater., 11, 19−29.
4. Borup, R.; Meyers, J.; Pivovar, B.; Kim, Y. S.; Mukundan, R.; Garland, N.; Myers, D.; Wilson, M.; Garzon, F.; Wood, D.; Zelenay, P.; More, K.; Stroh, K. Zawodzinski, T.; Boncella, J.; McGrath, J. E.; Inaba, M.; Miyatake, K.; Hori, M.; Ota, K.; Ogumi, Z.; Miyata, S.; Nishikata, A.; Siroma, Z.; Uchimoto, Y.; Yasuda, K.; Kimijima, K. I.; and Iwashita, N. (2007). Scientific Aspects of Polymer Electrolyte Fuel Cell Durability and Degradation. Chem. Rev., 107, 3904.
5. Stamenkovic, V. R.; Mun, B. S.; Arenz, M.; Mayrhofer, K. J. J.; Lucas, C. A.; Wang, G.; Ross, P. N.; and Markovic, N. M. (2007). Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. Nat. Mater., 6, 241.
6. Zhang, S.; Yuan, X.; Wang, H.; Mérida, W.; Zhu, H.; Shen, J.; Wu, S.; and Zhang, J. (2009). Int. J. Hydrogen Energy, 34, 388.
7. Uhm, S.; Jeong, B.; and Lee, J. (2011). A facile route for preparation of non-noble CNF cathode catalysts in alkaline ethanol fuel cells. Electrochim. Acta, 56, 9186.
8. Olson, T. S.; Pylypenko, S.; Atanassov, P.; Asazawa, K.; Yamada, K.; and Tanaka, H. (2010). Anion-Exchange Membrane Fuel Cells: Dual-Site Mechanism of Oxygen Reduction Reaction in Alkaline Media on Cobalt−Polypyrrole Electrocatalysts. J. Phys. Chem. C, 114, 5049.
9. Li, Y.; Zhao, Y.; Cheng, H.; Hu, Y.; Shi, G.; Dai, l.; and Qu, L. (2012) Nitrogen-Doped Graphene Quantum Dots with Oxygen-rich Functional Groups. J. Am. Chem. Soc., 134, 15−18.
10. He, G.; Song, Y.; Liu, K.; Walter, A.; Chen, S.; and Chen, S. (2013). Oxygen Reduction Catalyzed by Platinum Nanoparticles Supported on Graphene Quantum Dots. ACS Catal. 3, 831−838.
11. Sudhakar, V.; Singh, A. K.; and Chini, M. K. (2020). Nano porous reduced graphene oxide and polymer composites as efficient counter electrodes in dye sensitized solar cells. ACS Applied Electronic Materials, 2, 626.
12. Chini, M. K.; Das, C.; and Chatterjee, S. (2016). F and CF3 substituted solution processable oligo paraphenylenevinylene for ambipolar and hole-transporting organic field effect transistors. Chemical Physics Letters, 657, 26–32.
13. Dharmapurikar, S. S.; Arulkashmir, A.; Mahale, R. Y.; and Chini, M. K. (2017). Synthesis of amphiphilic isoindigo copolymers for organic field effect transistors: A comparative study. J. Appl. Polym. Sci., 134, 45461
14. Ohtsubo, N.; Gohda, S.; Gotoh, K.; Sato, S.; and Yamada, Y. (2023). Bottom-up synthesis of pyridinic nitrogen-containing carbon materials with C–H groups next to pyridinic nitrogen from two-ring aromatics. Carbon, 207, 270-291.
15. Chini, M. K.; and Chatterjee, S. (2017). Hydrothermally reduced nano porous graphene-polyaniline nanofiber composites for supercapacitor. FlatChem, 1, 1-5.
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Received on 08.03.2025 Revised on 22.03.2025 Accepted on 02.04.2025 Published on 14.04.2025 Available online from April 18, 2025 Asian J. Research Chem.2025; 18(2):87-91. DOI: 10.52711/0974-4150.2025.00014 ©A and V Publications All Right Reserved
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