The expense of commonly used electrocatalysts such as Platinum and Palladium, make many battery technologies and electrochemical reactions cost-prohibitive. A new group of promising low-cost catalysts is doped carbon complexes. These materials need further development to reach the same activity as traditional catalysts. But by examining the Oxidative Reduction Reactions (ORR) of various carbon complexes, desirable characteristics and geometries can be identified and enhanced. For this comparative analysis, a series of Carbon Nanotube (CNT) and Graphene Complexes were tested

Kaviani, Shayan

Mason, Andrew

Nejati, Siamak

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln UCARE Research Products UCARE: Undergraduate Creative Activities & Research Experiences 2018 Title: Investigation of Oxidative Reduction Reactions in Carbon-Based Electrocatalysts Presentation Andrew Mason University of Nebraska-Lincoln, andmason311@gmail.com Siamak Nejati University of Nebraska - Lincoln, snejati2@unl.edu Shayan Kaviani University of Nebraska - Lincoln, shayan.kaviani@huskers.unl.edu Follow this and additional works at: https://digitalcommons.unl.edu/ucareresearch  Part of the Catalysis and Reaction Engineering Commons Mason, Andrew; Nejati, Siamak; and Kaviani, Shayan, "Title: Investigation of Oxidative Reduction Reactions in Carbon-Based Electrocatalysts Presentation" (2018). UCARE Research Products. 262. https://digitalcommons.unl.edu/ucareresearch/262 This Poster is brought to you for free and open access by the UCARE: Undergraduate Creative Activities & Research Experiences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in UCARE Research Products by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Equipment and ORR TheorySUMMARYInvestigation of Oxidative Reduction Reactions in Carbon-Based ElectrocatalystsAndrew Mason, Shayan Kaviani, Siamak NejatiDepartment of Chemical and Biomolecular Engineering, University of Nebraska-LincolnThe premise for this research is the expense of current electrocatalysts such as Platinum and Palladium. By examining the Oxidative Reduction Reactions (ORR) of various Carbon Nanotube (CNT) and Graphene Complexes, this project was able to compare and analyze their relative electrocatalytic properties.For these tests, all of the samples were drop cast onto a Glassy Carbon Electrode and were analyzed for reactivity using Cyclic and Linear Sweep Voltammetry on an MSR Rotator. These testes showed the current induced with respect to changing voltage and from this the LevichEquation was used to find the number of electrons transferred in each half reaction of ORR for each sample. The samples were also tested with X-ray Photoelectron Spectroscopy (XPS) to identify their compositions in order to identify any correlation between their electrocatalytic and compositional properties.Cyclic and Linear Sweep VoltammetryLevichXPSCONCLUSIONREFERENCESThe results of the testing showed that carbon based electrocatalysts are viable options thatneed further exploration. The tests conducted favored both long MWCNTs and high impuritysamples. This gives credence to the theory that surface layers containing impurities are the sitesfor ORR and that internal structures facilitate the transfer of electrons as current.The results form XPS, CV, and LV suggest that carbon nanostructure with varying surfacechemistry heighten ORR activity given these impurities do not disturb the internal structure. Thedata also suggests that the surfactant, DDBS, used in the solutions also heightened the reactivityof the electrocatalysts. Sample 7 was approximately the average of the other samples in the LVand CV graphs, but as to why this phenomenon occurred is unknown. To eliminate the possibilityof errors, all future experiments will be run multiple times and compared to each trial. Moreover,Sample 4 and 1 had the highest impurity with sample 1 also having the greatest electron rate,but these samples differed in reactivity greatly suggesting that ORR is based upon a combinationof impurities and nanostructures.Future experiments will be aimed at exploring these phenomenon as well as altering thesample’s surface chemistry with oxidative Chemical Vapor Deposition and varying types ofpolymers, as an attempt to improve their ORR activity and longevity. The data presented in thisinvestigation suggests several options to explore as paths to improve the samples ORR and makethem better electrocatalysts. Overall, the continued exploration of carbon based electrocatalystsas a viable new option for battery applications is promising.[1] “MSR Rotator.” Pine Research Instrumentation Store, 23 Jan. 2018, www.pineresearch.com/shop/rotators/standard/msr/.[2] Rotating Electrode Theory. (2017, November 20). Retrieved March 19, 2018, fromhttps://www.pineresearch.com/shop/knowledgebase/rotating-electrode-theory/[3] Ozoemena, K. I. (2016). Nanostructured platinum-free electrocatalysts in alkaline direct alcohol fuel cells:Catalyst design, principles and applications. RSC Advances, 6(92), 89523-89550. doi:10.1039/c6ra15057h[4] Zhang, T., Tang, M., Zhang, S., Hu, Y., Li, H., Zhang, T., . . . Pu, Y. (2017). Systemic and immunotoxicity ofpristine and PEGylated multi-walled carbon nanotubes in an intravenous 28 days repeated dose toxicity study.International Journal of Nanomedicine, Volume 12, 1539-1554. doi:10.2147/ijn.s123345Figure 1. (Right) MSR Rotator from Pine Research Equipment used for CV and LV tests[1]. This was used in conjunction with the Gamry Instruments potentiostat Interface1000. (Left) Vessel used for ORR testing with 3D printed lid that holds the referenceelectrode (KOH tube, black), counter electrode (graphite rod, red), and workingsense electrode (Glassy Carbon with Sample, tan) in place while testing.In Linear Sweep Voltammetry, the rotation rate (RPM) is held constant as the electrode isswept from one potential to another. Current can be limited by the mass transport ions to theelectrode surface, which is directly related to the electrode RPM. Rotating the electrode at afaster rate increases the rate at which material arrives at the electrode surface [2]. Thus, thelimiting current decreases with increasing rotation rate. At higher RPM’s, the limiting currentresponses decreases and becomes less chaotic. This indicates that all of the electrocatalystsimprove in efficiently as limited mass transport is reduced but the best electrocatalystsseemed to be Samples 5 and 4 as they consistently produced the lowest current peaks.Figure 8. European Convention of Cathodic Sweep on SamplesSamplesSample EC OD (nm)Length (μm)Purity (wt%)Add Cont(wt%)Ash (wt%)Ratio(DDBS:EC:H20)1 SW/DWCNT 1-4 5-30 >60 <35 <1.5 10:1:100002 SW/DWCNT 1-4 5-30 >90 <1.5 10:1:100003 MWCNT <8 10-30 >95 <1.5 10:1:100004 MWCNT 8-15 10-50 >95 <1.5 10:1:100005 MWCNT >50 10-20 >95 <1.5 10:1:100006 GMWCNT 30-50 10-20 >99.9 <0.1 10:1:100007 DDBS 10:0:10000Figure 4. (Above) Table of sample solutions. (EC = Electro Catalyst, OD = Outer Diameter, SW/DWCNT = Single Wall/Double Wall Carbon Nanotubes, MWCNT = Multi Walled Carbon Nanotubes, GMWCNT = Graphitized Multi-Walled Carbon Nanotubes, Add Cont = Additional MWNT Content, DDBS = dodecylbenzene sulfonic acid)Sample Equation Regression Electrons Transferred1 y = 18042x R² = 0.8548 4.01E+002 y = 33597x R² = 0.9965 2.15E+003 y = 31555x R² = 0.9931 2.29E+004 y = 33468x R² = 0.9956 2.16E+005 y = 35512x R² = 0.9903 2.04E+006 y = 34151x R² = 0.9997 2.12E+007 y = 33762x R² = 0.9992 2.12E+00GC y = 38938x R² = 0.9986 2.01E+00The current signal recorded during these ORR tests can be easily influenced by the bulk flow of ions in solution [2]. In cyclic voltammetry (CV), a placid solution is used for short time scales to look at the activity in cyclic voltage changes. However, for longer time trials bulk flow is unavoidable and for consistent results it is necessary to control the solution flow as in linear sweep voltammetry (LV). Tests were conducted at variant RPMs (Revolutions Per Minute) because the spinning rotor produces a steady-state laminar flow adjacent to the RRDE ( Rotating Ring Disk Electrode), which assists in producing repeatable results that canbe accurately modeled for reaction kinetics. Figure 2. Reductive Half Reaction of KOH solution showing electron transfer [3]CV is where the electrode potential is swept back-and-forth between two extremes, in this case it is swept in the negative (cathodic) direction [2]. The current eventually reaches a maximum value (limiting current) once the applied potential is sufficiently negative relative to the standard electrode potential [2].Sample 5 and 4 were most reactive towards increasingly negative potentials as is evident in Figure 8. These samples were both longer MWCNT with some impurities. The preserved internal structure and surface impurities of these samples is suggest as to making them more conducive to transferring electric current. It is also of note that all the samples have higher reactivity than GC.Figure 13. Table of samples at their limiting currents with their electrons transferred in each half reaction A negative potential was applied to basic 2 M KOH solution, which reduced ions as shown in the reductive half reactions in figure 2. It is also of note that half reactions transfer either 2 or 4 electrons, which indicates the steps completed during ORR.Preparation of 10 mL increment solutions were in the following ratio (10 mg DDBS, 1 mg EC, 10000mg H20). These solutions where then vibrated for 5 minutes to create a homogeneous solution for proper drop casting onto the Glassy Carbon Electrode. -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0-1.4x10-4-1.2x10-4-1.0x10-4-8.0x10-5-6.0x10-5-4.0x10-5-2.0x10-50.02.0x10-5mAV 250 rpm 500 rpm 750 rpm 1000 rpm 1250 rpm 1500 rpm 1600 rpmy = 31629x1.00E+041.10E+041.20E+041.30E+041.40E+041.50E+041.60E+041.70E+040 0.05 0.1 0.15 0.2 0.25im^-(1)ω^-(1/2)-.3 V GC 1Levich EquationiL=(0.620)*n*F*A*D^(2/3)*ω^(1/2)*v^(-1/6)*C• iL, is the Levich current• n, is the number of electrons transferred in the half reaction• F, is the Faraday constant• A, is the electrode area• D, is the diffusion coefficient• ω, is the angular rotation rate• v, is the kinematic viscosity• C, is the analyte concentrationLevich Graphs are a series of voltammograms acquired over a range of different rotation rates. For a simple electrochemical system where the rate of the half reaction is governed by mass transport to the electrode surface. An intercept above zero, however, is an indication that the half-reaction is limited by sluggish kinetics rather than by mass transport. From figure 13, sample one was the only sample to produce 4 electrons in its half reaction. This sample also had the second highest impurity, which is the suspected cause of the greater electron transfer rates.-1000 -750 -500 -250 0 250-250-200-150-100-50050(A)E (mV vs. Ref) Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Glassy CarbonCV Samples-1000 -750 -500 -250 0 250-250-200-150-100-50050I (A)E (mV vs. Ref) Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Glassy CarbonLV 1600 RPMAlkaline MediumDirect Path:           O2 + 2H2O + 4e- 4OH- E0=1.230 VSeries Pathway:    O2 + H2O + 2e- H2O- + OH- E0= 0.695 VH02- + H2O + 2e- 3OH- E0= 1.230 VSample Oxygen Impurity (%)1 3.162 2.033 0.624 3.245 1.756 0Sample 4 and 1 showed the highest oxygen impurity. These impurities are ingrained in the surface chemistry of the samples and changes their electro-catalytic properties. The intense SP Carbon peak also confirms that we measured our Carbon Samples accurately. Figure 7. Table of Atomic Percentage of Oxygen ContentFigure 3. (Above Right) Scanning Electron Microscope image of Multi Walled Carbon Nanotubes [4]Figure 6. XPS survey spectra  of six samplesFigure 9. Linear Sweep at 1600 RPM on SamplesFigure 10. American Convention of Cathodic Sweep with varying RPM tests [3]Figure 11. Levich Equation with Constants DefinedFigure 12. Levich plot of varying currents at constant potentials across multiple RPMs Sample 1Figure 5. SP Carbon Peak of Sample 1 CNTs

Title: Investigation of Oxidative Reduction Reactions in Carbon-Based Electrocatalysts Presentation

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1286&context=ucareresearch

Title: Investigation of Oxidative Reduction Reactions in Carbon-Based Electrocatalysts Presentation

Abstract

Similar works

Full text

Available Versions

DigitalCommons@University of Nebraska