Mechanistic Study of Water Oxidation - Revision history

Scroslow at 16:56, 8 August 2019

2019-08-08T16:56:44Z

Scroslow at 16:53, 8 August 2019

2019-08-08T16:53:36Z

Scroslow at 16:53, 8 August 2019

2019-08-08T16:53:24Z

Scroslow: /* Troubleshooting */

2019-08-08T16:51:59Z

Troubleshooting

Scroslow at 16:51, 8 August 2019

2019-08-08T16:51:13Z

Scroslow: /* Electrochemistry */

2019-08-08T16:50:08Z

Electrochemistry

Scroslow: /* Additional Information= */

2019-08-08T16:49:50Z

Additional Information=

Scroslow: /* Configurations */

2019-08-08T16:48:44Z

Configurations

Scroslow at 16:48, 8 August 2019

2019-08-08T16:48:18Z

Scroslow: /* Electrochemical Quartz Crystal Microbalance */

2019-08-08T16:46:33Z

Electrochemical Quartz Crystal Microbalance

@@ Line 2: / Line 2: @@
 Note: the data on this page is intellectual property owned by Boston College
 =Personal Information=
 *'''Student''': Seth Croslow

@@ Line 1: / Line 1: @@
 This page was created to summarize Seth Croslow's REU experience at Boston College for the 2019 Summer
 Note: the data on this page is intellectual property owned by Boston College
 =Personal Information=

@@ Line 1: / Line 1: @@
 This page was created to summarize Seth Croslow's REU experience at Boston College for the 2019 Summer
 =Personal Information=
 *'''Student''': Seth Croslow

@@ Line 116: / Line 116: @@
 During data acquisition using the EQCM, we would nearly always get the following error:
-"''The quartz crystal microbalance can not work after the cell is connected''"
+:"''The quartz crystal microbalance can not work after the cell is connected''"
 After playing with it and trying to fix the error, with no luck, I contacted the manufacturer, CH Instruments. They suggested that it may be a software issue and sent the newest software for the computer as well as the instrument. I flashed new software to the EQCM and update the application on the computer and we still got the same error.

@@ Line 36: / Line 36: @@
 =Fourier-Transform Infrared Spectroscopy=
-==Configurations==
+===Configurations===
 For FTIR experiments, we began using a custom Otto Configuration that consisted of a ZnSe ATR crystal onto which we placed an FTO coated glass electrode with our cobalt catalyst face down. This, however, had large background noise and prevented evolved oxygen from escaping. We then switched to the Kretschmann Configuration which utilized a silicon ATR crystal plated with a gold film onto which our catalyst was then deposited. This configuration reduced some of the background noise and allowed oxygen to escape into the electrolyte solution.
@@ Line 45: / Line 45: @@
 </gallery>
-==Electrochemical Methods==
+===Electrochemical Methods===
 During our FTIR data collection, we also ran various electrochemical methods to test the potential-dependance of our intermediates. One of the methods we used is shown below.
@@ Line 52: / Line 52: @@
 For this method, we start at a potential of 1.8 (or 1.6) which is where we notice an oxidation wave form on the CV. We hold this potential for 2.5-5 minutes to achieve a steady state. We then decrease the potential at a rate of 20 mV/s by 100 mV and hold; we follow this method until we get down to 1.0 V and then increase the potential in 200 mV increments until back up to the initial voltage. We collect FTIR data continuously throughout these trials at a rate of 1 scan every 4.611 seconds.
-==Isotopic Studies for Peak Detection==
+===Isotopic Studies for Peak Detection===
 From previous literature (''Nat. Chem.'', '''2014''', 6, 362-367) we know the expected frequency, or range, where our two main intermediates should be located: 1,013 cm<sup>-1</sup> for the superoxide intermediate (Co-O-O-Co) and 740-920 cm<sup>-1</sup> for the peroxide intermediate (Co-O-OH). The graphs shown below show FTIR data at each potential mentioned above (''Electrochemical Methods'' Section). For these graphs, the x-axis shows the wavenumber, or frequency of IR light and the y-axis shows delta mOD, or absorbance. It should be noted that for these graph, the delta mOD is calculated by taking -1000 log(A/A<sub>i</sub>) where A is the absorbance of each spectrum and A<sub>i</sub> is the absorbance at the potential of 1.0V which we use as a reference.
@@ Line 80: / Line 80: @@
 </gallery>
-==Water-in-Salt Experiment==
+===Water-in-Salt Experiment===
 We then wanted to see if we could recreate the electrochemical water-in-salt experiment within the FTIR, so we used a 0M (1.00 water activity) and 7M (0.83 water activity) D<sub>2</sub>O electrolyte solution for the experiment. The following two spectra are normalized to the same maximum peak absorbance in order to compare the two separate trials. In the first spectra, we can see that at the 1,014 cm<sub>-1</sub> peak, the 1.00 water activity (blue line) has a slight shoulder with a higher absorbance compared to the 0.83 water activity (red line). This could indicate that the reduced activity is decreasing presence of the intermediate causing this peak. However, the second spectrum shows the second cycle of the FTIR at the high potential and shows almost difference between the two trials which indicate that the water isn't changing this peak. Due to these results, we are not sure if this peak is affected by the water activity or not and further studies will need to be done to make any conclusions.
@@ Line 91: / Line 91: @@
 As another way to try to validate the potential-dependent mechanism switch, we decided to try to use electrochemical quartz crystal microbalance (EQCM). We hypothesized that at the higher potential where the water hydrogen atom abstraction mechanism is favored (according to our hypothesis) there should be a large change in the mass of the catalyst due to adhesion of water onto the surface of the catalyst.
-==Background==
+===Background===
 EQCM utilizes an intrinsic property of a quartz crystal, the piezoelectric effect, to very precisely determine the mass change on the surface of the crystal. The inverse piezoelectric effect states that upon application of a potential difference to a crystal, acoustic sound waves will be produced. By changing the mass on the surface of the crystal, the fundamental frequency of the sound will change by a quantifiable amount which can allow for the extrapolation of the mass change on the surface of the crystal following the Sauerbrey equation:
@@ Line 102: / Line 102: @@
 [[File:eqcm_setup.PNG|500px|center]]
-==Initial Data==
+===Initial Data===
 The following data was collected using our cobalt catalyst in 0.1 M potassium phosphate electrolyte solution and was collected using linear sweep voltammetry.
@@ Line 113: / Line 113: @@
 It is very noticeable how variable the EQCM data is as it is very noisy and changes frequency from negative to positive very quickly. We ended up ignoring all of this data due to the fact that the instrument was not working.
-==Troubleshooting==
+===Troubleshooting===
 During data acquisition using the EQCM, we would nearly always get the following error:

@@ Line 28: / Line 28: @@
 The following graph shows four water activity levels (1.00, 0.94, 0.89, 0.83) and plots them with current density on the x-axis and potential on the y-axis. The method for data collection for these trials is as follows. The catalyst was deposited onto an electrode and a CV was recorded in water activity 0. A three electrode setup was utilized including a Pt wire counter electrode, a SCE reference electrode, and the cobalt electrode as the working electrode. A linear staircase sweep voltammetry was ran which held a specific potential for 5 minutes and then increased the potential by 20 mV. The electrode was then used in the 0.94, 0.89, and 0.83 water activity solution with the same method as before. A CV was then ran again in the 1.00 water activity solution and compared to the initial CV to test the stability of the film and insure that no film degradation occurred during the trials.
-<gallery mode="packed-hover" heights='250'>
+<gallery mode="packed-hover" heights='300'>
 File:water activity tafel.PNG|Tafel Plot of Water Activity for our Cobalt Catalyst
 </gallery>

@@ Line 8: / Line 8: @@
 *'''Project Title''': ''Mechanistic Study of Intermediates in the Water Oxidation Pathway''
-=Additional Information==
+=Additional Information=
 *'''Final Presentation''': [[:Media:Research Powerpoint FInal.pptx|Mechanistic Study of Intermediates in the Water Oxidation Pathway]]
 *'''Material and Methods''': [[:Media:Materials and Methods Summary (1).pdf|Materials and Methods Summary]]

@@ Line 40: / Line 40: @@
 For FTIR experiments, we began using a custom Otto Configuration that consisted of a ZnSe ATR crystal onto which we placed an FTO coated glass electrode with our cobalt catalyst face down. This, however, had large background noise and prevented evolved oxygen from escaping. We then switched to the Kretschmann Configuration which utilized a silicon ATR crystal plated with a gold film onto which our catalyst was then deposited. This configuration reduced some of the background noise and allowed oxygen to escape into the electrolyte solution.
-<gallery mode="packed-overlay" heights='300'>
+<gallery mode="packed-overlay" heights='250'>
 File:Otto configuration.PNG|Otto Configuration
 File:kretchmann configuration.PNG|Kretchmann Configuration

← Older revision		Revision as of 16:46, 8 August 2019
Line 85:		Line 85:

	=Electrochemical Quartz Crystal Microbalance=		=Electrochemical Quartz Crystal Microbalance=
		+	As another way to try to validate the potential-dependent mechanism switch, we decided to try to use electrochemical quartz crystal microbalance (EQCM). We hypothesized that at the higher potential where the water hydrogen atom abstraction mechanism is favored (according to our hypothesis) there should be a large change in the mass of the catalyst due to adhesion of water onto the surface of the catalyst.
		+
		+	==Background==
		+	EQCM utilizes an intrinsic property of a quartz crystal, the piezoelectric effect, to very precisely determine the mass change on the surface of the crystal. The inverse piezoelectric effect states that upon application of a potential difference to a crystal, acoustic sound waves will be produced. By changing the mass on the surface of the crystal, the fundamental frequency of the sound will change by a quantifiable amount which can allow for the extrapolation of the mass change on the surface of the crystal following the Sauerbrey equation:
		+
		+	[[File:eqcm_s_equation.gif\|600px\|center]]
		+
		+	The crystal we use has a fundamental frequency of 8 MHz which means that a change in frequency of 1 Hz equates to a mass change of 1.34 ng.
		+
		+	EQCM utilizes these properties and uses a AT-cut quartz crystal with a gold deposited film to act as a surface onto which chemical depositions can occur. This allows us to monitor the mass change of our catalyst during deposition to quantify the exact amount of catalyst deposited as well as quantify mass change at different potential. The setup for EQCM is shown below and allows us to run EQCM and electrochemical data collection simultaneously.
		+
		+	[[File:eqcm_setup.PNG\|500px\|center]]
		+
		+	==Initial Data==
		+	The following data was collected using our cobalt catalyst in 0.1 M potassium phosphate electrolyte solution and was collected using linear sweep voltammetry.
		+
		+	<gallery mode="packed-hover" heights='250'>
		+	File:eqcm_lsv.PNG\|LSV with EQCM Data Trial 1
		+	File:eqcm_lsv_2.PNG\|LSV with EQCM Data Trial 2
		+	File:eqcm_lsv_3.PNG\|LSV with EQCM Data Trial 3
		+	</gallery>
		+
		+	It is very noticeable how variable the EQCM data is as it is very noisy and changes frequency from negative to positive very quickly. We ended up ignoring all of this data due to the fact that the instrument was not working.
		+
		+	==Troubleshooting==
		+	During data acquisition using the EQCM, we would nearly always get the following error:
		+
		+	"''The quartz crystal microbalance can not work after the cell is connected''"
		+
		+	After playing with it and trying to fix the error, with no luck, I contacted the manufacturer, CH Instruments. They suggested that it may be a software issue and sent the newest software for the computer as well as the instrument. I flashed new software to the EQCM and update the application on the computer and we still got the same error.
		+
		+	The manufacturer then suggested to perform a trial in air to see if the error would still happen; no error was present. I then decided to test if maybe the reference or counter electrode were bad and replaced those and the error still arose. I then tested the setup with and without each electrode, and found out that the error only persist when the counter electrode is placed within the solution indicating that there some kind of problem when current flows between the working and counter electrodes.
		+
		+	With all of this in mind, we decided there was something most likely wrong with the crystal oscillator since the potentiostat worked when the EQCM option was not selected.
		+
		+	We then decided to ship the crystal oscillator and the cell back to the manufacturer for service.

	=Useful Articles=		=Useful Articles=