The document discusses the synthesis of molecular electronic components for use as rectifiers. It explores substituting electron-rich and electron-poor rings separated by single bonds, as was theorized could act as rectifiers. It details optimizing the synthesis of dibromohemiquinone (Br2-HBQ) through varying reaction conditions, achieving a maximum 66% yield. Proof-of-concept substitutions were performed and frontier orbital energies were calculated to determine the best molecules for bonding to gold electrodes.
The Brønsted catalysis relationship is a Linear Free Energy Relationship (LFER) that relates ionization of an acid or base which catalyzes a reaction and the rate of the reaction.
Contributed by: Quincy Davis, Jonathan Greenhalgh, Joshua Visser (Undergraduates), University of Utah, 2016
The Brønsted catalysis relationship is a Linear Free Energy Relationship (LFER) that relates ionization of an acid or base which catalyzes a reaction and the rate of the reaction.
Contributed by: Quincy Davis, Jonathan Greenhalgh, Joshua Visser (Undergraduates), University of Utah, 2016
Determination of the hydrogen coefficient diffusion DH in the MmNi3.55Mn0.4Al...AI Publications
The hydrogen storage alloys MmNi3.55Mn0.4Al0.3Co0.75-xFex (0 ≤ x ≤0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. The discharge capacity reaches its maximum in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 270, 266, 260, 210 and 200 mAh/g after 12 charge-discharge cycles. The diffusion behaviour of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 5.86 10-10, 1.95 10-9, 3.44 10-9, 2.96 10-9 and 4.98 10-10 cm2 s-1. However, the values of the charge transfer coefficients are respectively equal to 0.35, 0.6, 0.5, 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.
Biochemical Redox Reactions
By Khair Ullah, Jr. Research.Fellow
International Center for Chemical and Biological Sciences (ICCBS) University of Karachi
Determination of the hydrogen coefficient diffusion DH in the MmNi3.55Mn0.4Al...AI Publications
The hydrogen storage alloys MmNi3.55Mn0.4Al0.3Co0.75-xFex (0 ≤ x ≤0.75) were used as negative electrodes in the Ni-MH accumulators. The chronopotentiommetry and the cyclic voltammetry were applied to characterize the electrochemical properties of these alloys. The obtained results showed that the substitution of the cobalt atoms by iron atoms has a good effect on the life cycle of the electrode. The discharge capacity reaches its maximum in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 270, 266, 260, 210 and 200 mAh/g after 12 charge-discharge cycles. The diffusion behaviour of hydrogen in the negative electrodes made from these alloys was characterized by cyclic voltammetry after few activation cycles. The values of the hydrogen coefficient in MmNi3.55Mn0.4Al0.3Co0.75-x Fex ( x = 0, 0.15, 0.35, 0.55 and 0.75) are, respectively, equal to 5.86 10-10, 1.95 10-9, 3.44 10-9, 2.96 10-9 and 4.98 10-10 cm2 s-1. However, the values of the charge transfer coefficients are respectively equal to 0.35, 0.6, 0.5, 0.33 and 0.3. These results showed that the substitution of cobalt by iron decreases the reversibility and the kinetic of the electrochemical reaction in these alloys.
Biochemical Redox Reactions
By Khair Ullah, Jr. Research.Fellow
International Center for Chemical and Biological Sciences (ICCBS) University of Karachi
Experiment 4: Electropolymerized Conducting Polymers.
Introduction:
Conductive polymers (CP) exhibit very useful properties such as flexibility, solubility [1], electrical conductivity, low energy optical transitions, low ionization potential, and high electron affinity.[2] These characterizations make them such effective candidates for many applications such as antistatic and antimagnetic shielding devices[3], microwave attenuation[4], light emitting devices, optical sensors, enzymatic biosensors[5], electronic circuits, and detectors of odors and flavors. The most widely known conducting polymers are polypyrole, polyanaline, and polythiophene. By applying an electrical potential (reversible reaction), these polymers can be reduced. The role of these polymers when they are used as active templates in biosensor applications is the immobilization of dynamic species on the electrode. This will contribute to enhancing the sensitivity and the accuracy of analyte detection. CPs have been used for stabilizing numerous biological species such as enzymes, antibodies, haptens, DNA, and more interestingly the whole cells. [1]
Aim:
The aim of performing this experiment is to create a conducting polypyrrole film which consists of a stabilized enzyme, identify the film and its characteristics, and utilize it as glucose biosensor.
Procedure:
“Refer to Manual for NANO 3101/8302, Electropolymerized Conducting Polymers, Flinders University, p.24-29.”
Results and Discussion:
In the biosensor uses, the deposition of the polymers on the electrode surface can be done by applying an oxidative potential. During this action, the enzymes can be stabilized, and by modifying the deposition time, the amounts of the deposited layer can be recreated. The sensitivity, selectivity, and the accuracy of detection of the biosensors are reliant on the architecture of the polymer, the biological activity of the enzymatic immobilization, and the electropolymerisation circumstances.
In this experiment, the glucose oxidase (enzyme) was immobilized in a conducting polypyrole film on an electrode to find out their appropriateness as a functioning electrode. The performance of the electrode was measured through a Cyclic Voltammogram (CV) of ferricyanide
The geometric area of the electrode was measured by a ruler, and it was found to be 3.14 mm ²which is identical to 0.00314 cm².
The Randles-Sevcik equation is used in the redox reactions
at 25 C °
Where is the peak current, A is the electrode area (cm²), n is the number of electrons involved, C is the concentration of the bulk (mol/ml) for active species, v is the scan rate (V/s), and D is the diffusion coefficient.
n = 1, therefore
, therefore = 0.002756809.
V = 20mV/s = 0.02 V/s, therefore
C = 10 mM = 0.01 mol/L = 0.00001 mol/mL.
can be determined from figure.1
Figure 1: Cyclic Voltammograms (CV) as a function of escalating the scan rate for Platinum Electrode in ferrricyanide solution.
This c ...
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Impedance Spectroscopy Analysis of a Liquid Tin Anode Fuel Cell in Voltage Re...AEIJjournal2
A concept of a liquid tin anode-indirect carbon air fuel cell (LTA-ICFC) are described. Experimental
setups for analysis of LTA-ICFC polarisations of an operational electrochemical reactor of the LTA-ICFC
are presented. Results from Electrochemical Impedance Spectroscopy (EIS) Analysis of the electrochemical
reactor of the LTA-ICFC are shown and analysed.The rate-determining step of the system is concluded.
The charge-transfer resistance did not show considerable differences at 700-800 °C. This can be implied
that the charge-transfer resistance is not the rate-limiting step of the transport processes of the fuel cell.
The increase of the Warburg impedance concurrently with the resistance to fit mass-transport loss (R3)
suggests that the rate-limiting step for the LTA-ICFC in voltage recovery mode is the diffusion of the oxide
ions through SnO2 layer. The increment of mass transport lost, R3, of the cell causes the slowly increase of
the cell’s voltage over the voltage from 0.7-0.8 V at 700, 750, and 800 °C.
Impedance Spectroscopy Analysis of a Liquid Tin Anode Fuel Cell in Voltage Re...
CBH Poster S14a (1)
1. The field of molecular electronics centers around the
synthesis of single-molecule electronic components. These
components have the potential to one day replace their
silicon-based counterparts, resulting in both smaller and
more efficient devices which can be assembled from the
ground up rather than with the inefficient top-down
approach taken today. As part of a project involving
molecular scale electronic devices, we are exploring the
synthesis of potential rectifiers. A rectifier functions to
convert alternating current (AC) to direct current (DC) by
allowing unidirectional electron flow. Our target molecules
contain electron-rich dimethoxybenzene donor rings and
electron-poor quinone acceptor rings separated by single
bonds.
Figure 1. Br2-HBQ
Here is shown the design of Dibromohemibiquinone (Br2-
HBQ), the precursor molecule which exhibits the acceptor
and donor features (orange and blue, respectively) as well as
bromine substitution sites (white). It was posited by Aviram
and Ratner in 1974 that such a molecule, if synthesized,
could rectify. Their hypothesis was that an electron-rich ring
and an electron-poor ring separated by a long enough
insulator would allow a molecule to conduct electricity. While
their theoretical molecule possessed a two-carbon bridge as
an example of such an insulator, our molecules of interest
possess only a single bond (here shown in green).
Our goals were to:
The proof-of-concept reaction suggests that our substitutions
may in fact be possible. By finding an optimized synthesis
reaction, we were able to improve yield, reduce waste, and
more efficiently synthesize materials for our further
experiments. In the future, we will attempt further
substitutions and test how well the derivatives bond to a gold
surface. Each of these derivatives’ HOMO/LUMO calculations
will be compared to spectral and electrochemical data
gathered by J. Meany. These calculations will be compiled in
order to find the optimum HOMO/LUMO levels for use with a
gold electrode (work function 5.1 eV).
Reaction Name Addition ACN/H2O Ratio Separate Dissolution % Yield
KSW 1-08 quick 1:1 (100 mL ACN/g) No 26%
KSW 1-09 slow 1:1 (50 mL ACN/g) No 21%
KSW 1-10 quick 2:1 (100 mL ACN/g) No 26%
KSW 1-12 slow 1:1 (50 mL ACN/g) No 37%
KSW 1-22 quick 1:3 (25 mL ACN/g) Yes 22%
KSW 1-24 quick 1:3 (50 mL ACN/g) Yes 31%
KSW 1-36* quick 1:3 (50 mL ACN/g) Yes 66%
KED 1-05 slow 1:1 (100 mL ACN/g) No 25%
KED 1-06 quick 1:1 (100 mL ACN/g) Yes 29%
KED 1-07 quick 1:2 (100 mL ACN/g) Yes 34%
KED 1-24 quick 2:9 (40 mL ACN/g) Yes 26%
KED 1-30 quick 1:3 (25 mL ACN/g) Yes 11%
KED 1-32 quick 1:3 (50 mL ACN/g) Yes 20%
KED 1-50* quick 1:3 (50 mL ACN/g) Yes 50%
*Replication of JEM 3-63, a confirmation of OCR 1-13
Figure 2. Alkylation using 1-bromohexane
For proof-of-concept, alkyl substitution was carried out
using 1-bromohexane. This showed the feasibility of future
substitutions for assemblage.
Figure 3. Substitution using cyanobenzoyl
Cyanobenzoyl presents a potential substituent capable of
bonding to a gold surface. The cyano-group nitrogen has a lone
pair which may serve this purpose. Characterization is ongoing.
Figure 4. Br2-HBQ HOMO Figure 5. Br2-HBQ LUMO
Figure 6. Cyanobenzoyl-
substituted HOMO
Figure 7. Cyanobenzoyl-
substituted LUMO
Compound
Br2-HBQ NH2,Br-HBQ Alkyl Sub Cyanobenzoyl Sub
HOMO (eV) -8.96 -8.85 -8.83 -8.92
LUMO (eV) -1.94 -1.55 -1.54 -1.83
• Optimize the synthesis of Br2-HBQ from 2,5-
dimethoxy-1-bromobenzene
• Perform proof-of-concept substitution reactions of
NH2,Br-HBQ
• Add a substituent capable of bonding to a gold
electrode surface
• Model highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital (LUMO)
characteristics
• Calculate HOMO and LUMO energies
Table 1. Optimization of Br2-HBQ synthesis
Table 2. PM3 calculations of HOMO and LUMO energies
This data is in reference to the optimization of reaction two of the synthesis scheme shown above. Prior to these attempts, yield
was between 20 and 30%. Multiple iterations were performed, varying the rate of addition, type of dissolution (2,5-dimethoxy-1-
bromobenzene separately from vs. together with cerium ammonium nitrate), and ratios of the solvents (acetonitrile and water)
each time. Highlighted reactions were the most successful – these were replications of a promising reaction attempted by O. Roe,
a lab colleague. The optimum addition method appears to be the quick addition of 2,5-dimethoxy-1-bromobenzene and cerium
ammonium nitrate, each separately dissolved in acetonitrile (overall 50 mL per gram of 2,5-dimethoxy-1-bromobenzene) and
water (overall 150 mL per gram of 2,5-dimethoxy-1-bromobenzene). While these yields include some minor impurities, they are
overall more efficient than the previous iterations.
• “Does molecular electronics compute?” Editorial. Nature
Nanotechnology. 8, 377 (2013).
• Aradhya, S. & Venkatamaran, L. Single-molecule junctions beyond
electronic transport. Nature Nanotechnology. 8, 399- 410 (2013).
• Aviram, A. & Ratner, M. A. Molecular Rectifiers. Chemical Physics
Letters. 29, 277-283 (1974).
• Ratner, M. A brief history of molecular electronics. Nature
Nanotechnology. 8, 378-381 (2013).
Special thanks to The University of Alabama, the College of Arts and
Sciences, the Department of Chemistry, and the Computer-Based
Honors Program.