SEAL Manual - The Solar Army
Contents
1. DO 24 O FUEL The Solar Energy Activity Lab SEAL User s Guide Last Revised 29 July 2015 Table of Contents R go 2 02 0 eran ere arr ere cree een ee ee ee eee ee eee eee 3 Pah rs po 2124 NIMON Cerne nec Pm nen eee ere eee eee ee eee eee 4 CUM UCo eco sy O aaan E et E A a eT 5 3 1 Motivation Global Energy Demand and the Need for Solar POWED sssrinin 5 RAMBO Un gk CL 12 68 A 0 0 gale 6 deerme srmerenererenerer tre rere rate Urrrare Daterers eretmtennr arent er sen car cee een e tree cs mnt err ee ence 6 3 3 A More Detailed Look into the Photoelectrochemical Cell for Splitting Water uu 7 34 HOW Cie SEAL Experiments WOlK sisisi iniinis a aani awian aiaee 8 Bs HOw Semiconductors Wor skisis ae aa a ai aa 9 DUE a A A AT A A E A A EAA E A E 11 ee eg 2 P DA O aE E E 12 341 Decision of Metals toS pOlousnsissn a a N a anes nemesis 12 z2 o UggesU ons JOr SpOt NG sisisi iaeaea eaaa aaaea eiea 13 6 Assembly of the Instrument sseinnennnie naia aaeoa naca ea Aad araa aE Aia ai aAa aiaa 14 AV a O a E ee ee 16 B Savm and Uploading Dat Aisscscsnesei n a E N 17 Ds REL ONC GS ceca EEA E E E A E E ne estes heise ances aeie reve auekts es 19 For assistance setting up the SEAL kit or help troubleshooting any problems that may arise please contact Michelle DeBoever at mchansen caltech edu or 626 395 2829 1 Preface The Solar Energy Activity Lab SEAL enables users in collaboration with university sci2. Au Just about all of the other elements are fair game but you are encouraged to attempt experiments with different materials than those already studied To see what mixtures have already been studied you can access the Solar Materials Discovery database at http www bilrc caltech edu solmatdisc Remember to consult a Materials Safety Data Sheet MSDS before you handle any chemical with which you are not familiar Safety first 12 5 2 Suggestions for spotting When spotting to survey mixtures of elements it is considered efficient to test gradients of your mixtures In these patterns the spots are mixtures of the same elements in slightly different proportions usually arranged such that the concentration of an element steadily increases or decreases as you move down a column or across a row If you decide to use a gradient it may be easiest to follow the pattern shown below in Figure 6 This pattern is built into the software such that you can inform the program of the elemental composition of each spot in relatively few keystokes data entry while important can be monotonous Stet fe te sas ose ans sn one ane one om Doosan exe pes aee nee nee ene nee een pereje e ee e e exe eeslene nae nee eee oo 0 40 50 10 30 50 40 0 50 Eo cs ES Ka 60 30 0 60 20 10 60 10 20 60 0 30 a cs 70 20 0 70 10 10 70 0 20 T 80 10 0 10 uL Fe Figure 6 Gradient spotting pattern If you are running expe
3. crosscutting concepts and science and engineering practices NGSS STANDARD DESCRITPION Alignment with SEAL HS PS1 6 HS PS3 3 HS ESS3 2 HS ESS3 4 Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium Design build and refine a device that works within given constraints to convert one form of energy into another form of energy Evaluate competing design solutions for developing managing and utilizing energy and mineral resources based on cost benefit ratios Evaluate or refine a technological solution that reduces impacts of human activities on natural systems In the clarification statement it says Examples of designs could include different ways to increase product formation including adding reactants or removing products Different combinations of metal oxides are attempted by the students to find the best material Students must balance the cost of the material relative abundance and overall activity In the clarification statement it says Examples of devices could include Rube Goldberg devices wind turbines solar cells solar ovens and generators Examples of constraints could include use of renewable energy forms and efficiency Students being by creating different model systems of mixed metal oxide semiconductors These systems are constrained by factors such as abundance activity cost ligh
4. Hydroxide 0 1 M aqueous solution e Isopropanol or acetone e Micropipette 5 25 uL range and disposable tips Cheap version with 25 uL range http www flinnsci com store Scripts prodView asp idproduct 18990 e Jewelry kiln Good cheap version Paragon SC2 http www clay king com kilns paragon_kilns paragon_sc2 html e Scotch tape 11 5 Plate Preparation 1 2 3 4 5 6 Clean your glass slide both sides with water and isopropanol or acetone Next dry the slide Test for the conductive side of the glass using your multimeter on the 2000 Q setting The side with a measurable resistance is conductive will measure in the 20 100 Q range Place the glass plate conductive side up on top of the plate spotting template These circles will be the area in which to deposit the solutions Using a micropipette deposit between 5 10 uL total of solution per spot If using more than one solution be sure to calculate ratios of metal salts based on both their molarities and volumes deposited When the spotting is complete the solutions need to evaporate It is optional to warm the glass plate on a hotplate set at 80 100 C typically setting 2 3 for several minutes until spots evaporate This method is faster and will help avoid the coffee ring effect which often occurs from air drying but is not absolutely necessary Once the spots are evaporated fire the plate at 500 C for approximately 3 hours A smal
5. alibration problem Exit the program and try again Click on the button Check Dark Current also referred to as rest current This will generate a plot of volts vs time on the screen and should stabilize to a low value lt 0 5 The y scale is volts because there is a current to voltage conversion within the equipment itself Please remember that the units of current are typically microamps Continue to periodically click on this button until the points stabilize around a common value Ideally the points will be low on the plot lt 0 5 This process can take a little waiting 1 10 minutes but you can periodically recheck the dark current as many times as you like over this period If the rest current is large try reducing the applied voltage to 0 05 0 10 V High rest currents decrease the signal to noise ratio during the light driven experiment that forms the basis of the results obtained from the kit so the lower the Dark Current the better your results will be Make sure the glass plate i e the working electrode has its spots aligned properly over the LED array and in the proper orientation relative to the row column pattern you have used for spot composition Improper orientation of the plate will result in mismatch errors when the data are reported for the semiconductor materials Note the cone of light emitted from any one LED may overlap with an adjacent spot if the spots are not well defined and sharp This can lead to som
6. and edit experimental information or the file chosen if necessary To manually load chemical and pattern information follow the sequence of menus presented First enter how many total elements were used on the plate Select each element using the crosshairs on the periodic table Be sure to note the order the elements were chosen Then enter which metal salt was used for each element as well as the concentration of that solution On the next menu click manually load pattern information or go back and edit experiment information or chemical information if desired Pick a preexisting pattern or customize a blank template using the cross hair tool Be sure to not click outside of the window while editing or the program may crash Finally either save data to a file or go back and edit experiment chemical or pattern information Data will be saved locally as smd files that can be uploaded to the Caltech Solar Materials Discovery online database http www bilrc caltech edu solmatdisc index php as fig files that can be opened from a graphics window in the data collection program as bmp bitmap images and as xls excel spreadsheet The spreadsheet is especially useful since it contains the data as numerical values for easy manipulation later Click on Go to Solar Materials Discovery website in the main menu to log on to the website and 17 upload data The website also has downloads of the user guide templates sof
7. ar Energy Activity Lab SEAL and is the system you will use to search for catalysts to split water 3 3 A More Detailed Look into the Photoelectrochemical Cell for Splitting Water Building the photoelectrochemical cell shown in Figures 1 and 2 is the overarching goal of the NSF CCI Solar Center headquartered at Caltech We believe it holds promise as the solution to the world s energy needs but before we can build it we must research what materials and methods we can use to produce each component Figure 2 identifies these components and their functions short wavelength photon long wavelength photon high energy light will be absorbed low energy light will be absorbed by the photoanode to drive the by the photocathode to drive the oxygen evolving reaction S hydrogen evolving reaction oxygen evolving catalyst the brown spheres represent catalysts appended to the anode for the purpose of speeding the Ns reactions where electrons are removed from water and oxygen 2H 0 _ 4e gas is produced gt photoanode the red towers conduct electrons serve as supports for catalyst and absorb light to drive the oxidation of water or hydroxide to generate O O 4H photocathode the blue towers conduct electrons serve as supports for catalyst and absorb light to drive the reduction of protons to generate H gas membrane separates the compartments and the O and H gases produced but allows the passa
8. aterials Discovery shortcut Select yes to override any warnings that pop up The program takes several seconds to start up as various drivers are loaded Eventually you will see a prompt in the open window asking for the reading on the voltmeter This step is intended to calibrate the applied voltage and set the equipment to a zero position before beginning any experimental work You should enter the voltmeter reading in units of volts e g 0 035 V corresponds to 35 mV After entering the value the voltmeter should read 0 000 V or within a few mV ofthis value If it does not read close to zero you may have incorrectly entered the voltage reading Exit the program and try again Now connect the leads to the electrodes connect the counter electrode the graphite rod to the black alligator clip connect the working electrode the conducting glass sample plate to the red alligator clip You will notice the LEDs turn on and off This is an initialization sequence wait for it to complete A menu will open when the process is complete 15 7 Scanning a Plate 1 Click on the button Apply Voltage to set the bias potential in volts For general scanning for 2 3 4 water oxidation enter 0 100 to set the bias potential to 100 millivolts Wait afew moments and note that the voltmeter now reads 0 100 V within 0 02 V If the voltmeter does not read close to the value that you entered there may be a c
9. ce band and conduction band of a semiconductor respectively The electrons are naturally more stable in the lower energy valence band but while they are here they are not very mobile This lack of mobility presents a problem to us because we want to catalyze reduction oxidation reactions that require the exchange of electrons Energy is required to promote electrons into the conduction band where they are more mobile 10 4 Materials List Items included with the kit e USB Flash Drive with National Instruments hardware drivers standalone SMD software excel templates and User s Guide e LED Array Unit black box e Current Integrator aluminum box with electrode leads e Digital Voltmeter Multimeter small red box e CAT 5 ethernet cable connects LED to integrator e USB Cable connects integrator to PC e BNC Cable connects integrator to voltmeter e 5 FTO coated glass slides 3 x 3 square Hartford Glass TEC 15 765 348 1282 e Pre spotted iron oxide sample e Copper Tape with Conducting Adhesive McMaster Carr 76555A712 1 2 wide e 5 min Epoxy Devcon 20845 5 min epoxy e Insulated Wire McMaster Carr 8054T22 stranded wire e 2 Graphite Rods Wale Apparatus 12 1201 1 8 x 12 e Spotting Template e User s Guide Required items not included with the kit e Computer running Windows XP or 7 operating system NOT Windows 8 or Mac e Pyrex glass crystallization dish 125 mm x 65 mm or larger e Sodium
10. e cross talk With experience you will be sufficiently adept at pipetting to form the individual spots that this will not be a major problem Click Perform a Scan Enter the number of cycles that will be averaged for this scan e g 3 Each cycle takes 1 2 minutes If you were to input 3 then each spot will be scanned three times and the responses for each spot will then be averaged by the software to give a single final value Note that the LEDs will blink and the progress of the scans is reported in real time on the monitor in 3D The menu will re open when the scanning is complete Note you can rotate the chart in 3D by clicking the rotation option on the toolbar looks like a curvy arrow 16 8 Saving and Uploading Data 1 2 3 4 5 6 7 8 On the menu click Save Data to a File and then on experiment information in the next pop up window Enter the appropriate information as prompted by entries from top to bottom LED color will be white The next pop up will allow you to edit the experiment information again or load chemical and pattern information from excel or manually load chemical and pattern information To load from a file simply select the Microsoft Excel template that has been filled out with the chemical and pattern information previously and then verify the pattern is correct Finally either save data to a file or go back
11. ed to generate electricity when needed by a standard hydrogen fuel cell 1 2HO0 gt 2H O AG 4 92 eV 474 4kJ mol of O 2 4Ht 4e gt 2H AE 0 00V vs NHE 3 2HO m s gt O 4Ht 4e AE 1 23V vs NHE Equation 1 Water Splitting Equation 2 Proton reduction Equation 3 Water oxidation Equation 1 is the balanced chemical reaction for splitting Q water This overall reaction is the sum of two electrochemical C half reactions the reduction of protons to form hydrogen 2 RA and the oxidation of water to form molecular oxygen and protons 3 Figure 1 depicts a model photoelectrochemical cell for the 2H 0 photolysis of water It consumes water and sunlight to generate aati H2 and Oz The cell shown below is only a model in the sense that we know what generic components we ll need and the tasks we want them to perform but not what specific materials can be used to build these components That is the point of our research we are still working to determine the best materials to build this system With your SEAL experiments you will contribute to this research effort The model cell has two main compartments one for hydrogen evolution by the reduction of protons at the Figure 1 A model photoelectrochemical cathode and one for oxygen evolution by the oxidation of cell for splitting water into hydrogen and water at the anode The compartments are separated by a oxygen with sunlight m
12. embrane that keeps each half reaction contained but Image credit Elizabeth Santori allows protons generated at the anode to pass to the cathode where they react to form hydrogen The membrane also keeps the H2 and Oz gases that are produced from mixing Section 3 3 discusses the components of the electrochemical cell in greater detail Catalysts are substances that speed chemical reactions In the construction of the model cell in Figure 1 the electrodes need to serve two key purposes i to absorb photons capable of providing 6 the energy to split water and ii to catalyze the half reactions at the surface of the electrodes Metal oxides are the class of materials we will study in our experiments These materials can serve both purposes in our system Our experiments entail screening metal oxides for the photoelectrolysis of water This effort builds on the pioneering work of Bruce Parkinson and coworkers at the University of Wyoming 2 Their team constructed a system to screen combinations of metal oxide semiconductors and then simplified the system such that it could be distributed as a kit the Solar Hydrogen Activity Research Kit SHArK to be assembled locally for use in high schools and colleges Winkler and Winkler developed a second generation system the Solar Materials Discovery SMD kit that cut the screening time down from hours to minutes and introduced a multitude of other improvements This system was renamed the Sol
13. entists to conduct research directed at solving the greatest technological problem of our time using sunlight to meet the world s growing demand for consumable energy This user manual is not simply a set of instructions it is a comprehensive guidebook We outline the motivation of this specific line of research the function of the kit the experimental design and the scientific principles at play A second motivation for this guide is the establishment of a common protocol for these experiments A standard protocol will help maximize the productivity of participants and facilitate the analysis of data In any scientific effort it is important to be rigorous in maintaining a standard procedure that limits unintentional variation from experiment to experiment Such an approach allows the direct comparison of data collected by researchers using many different SEAL units This guide has been written to be accessible to anyone who has taken a high school class in chemistry For curious and advanced readers we suggest additional reading materials that discuss concepts in more depth than is practical here 2 NGSS Alignment As the SEAL kit is often used in the high school classroom or as an after school project for advancing STEM learning we have decided to include a list of NGSS standards that the SEAL project addresses We hope that the SEAL kit will be a valuable resource for high school teachers as they implement new curriculum that includes
14. fectively inexhaustible e Expensive at present e High capacity e Limited infrastructure e No output at night or when cloudy Table 1 Summary of some of the main advantages and disadvantages of various sources of consumable energy The values for capacity very rough estimates for the maximum global output of each technology have been taken from Lewis and Nocera Capacity estimates are given in units of remaining energy for non renewable sources and power for renewable sources It appears that solar technology is the only option that can meet the world s growing demand for energy estimated at 27 TW by the year 2050 without disastrous environmental consequences For solar energy to become a practical alternative to fossil fuels we must find efficient and economical methods for using sunlight to produce fuels that can be stored and transported easily The storage of solar energy in chemical fuels is of critical importance because people want to be able to power their vehicles and other mobile devices wirelessly as well as to use electricity at night when the Sun does not shine 3 2 Our General Approach There are many approaches to harvesting the energy in sunlight At CCI Solar we are especially interested in using sunlight to split water H20 into hydrogen H2 and oxygen 02 The idea is that the oxygen gas can be vented it already constitutes 21 of our atmosphere while the hydrogen gas that is produced can be stored and us
15. ge of protons hydrogen evolving catalyst the gray spheres represent catalysts appended to the cathode for the purpose of speeding the reactions where electrons are transferred to protons to produce hydrogen gas Figure 2 A diagram of the photoelectrochemical cell we wish to construct to split water into hydrogen and oxygen gases Each component is labeled with its function in the system The system depicted in Figure 2 probably does not look like the electrochemical cells you ve studied in chemistry textbooks Figure 3 is the equivalent cell drawn as a common H cell a depiction that may seem more familiar to you vg X A y A flow of electrons 2 HD 4 H O Figure 3 A diagram of the photoelectrochemical cell for splitting water drawn as a common H cell While this depiction is a useful learning tool since it is similar to the electrochemical cells most commonly encountered in general chemistry textbooks it is not practical for the mass production of consumer devices 3 4 How the SEAL Experiments Work While final target system for our collective research appears in Figure 2 we will focus on one piece of the puzzle investigating metal oxide semiconductors as materials that can both absorb light and catalyze the production of H2 or O2 gas from water In our work metal oxides will serve the combined roles of the towers and balls on the electrodes in Figure 2 Since we are focusing on this single aspect of
16. h temperature for several hours converts the evaporated solution of salt to a metal oxide Any counter ions in the metal salt are vaporized and all that is left behind is the desired metal oxide mixture adhered to the glass electrode that we will test for catalytic activity The glass electrode plate is fit with a wire and connected to the SEAL kit current integrator The plate is submerged in the electrolyte solution along with the graphite counter electrode The SEAL software then guides the user to start an electrochemical experiment that will measure the current generated from photocatalyzed water splitting at each individual metal oxide spot on the glass electrode 3 5 How Semiconductors Work A major aspect of electrochemistry and photochemistry is keeping track of the position and energy of electrons in various materials You may remember from introductory chemistry that electrons in single atoms are distributed into atomic orbitals and when multiple atoms bond to form molecules the atomic orbitals blend into molecular orbitals that hold the electrons in the system If we expand this concept further to bulk materials we see that orbitals mix together to constitute a low energy valence band while a grouping of higher energy orbitals form a conduction band 9 Anti Bonding Orbitals Conduction Band Molecules Semiconductor Valence Band Bonding Orbitals Figure 5 Bonding and anti bonding orbitals combining to form the valen
17. ial i e voltage across an electrochemical cell We will apply a small bias potential to our system to help push the reactions along e Choice of Electrolyte The equation relates the concentration of reagents involved in an electrochemical reaction with the observed potential for the reaction When higher concentrations of the reactants are present the potential becomes more favorable This is why when we are screening catalysts for the oxidation of water 3 we do so in aqueous base where the concentration of hydroxide is relatively high and the concentration of protons is relatively low RT Ox Econ E 2 In d L nF Red Equation 4 Nernst Equation In our experiments we are going to build a modified version of the electrochemical cell shown in Figure 3 in a fashion that is designed to study the specific reactions in which we are interested The SEAL electrochemical cell is drawn in Figure 4 you will notice that our physical system looks very different from the target system in Figure 1 4 e Current integrator o 4H Oz 9 2H20 a a 2 FTO Plate Pe Multimeter Figure 4 Cartoon of the SEAL setup and electrochemical cell The way we run experiments is as follows First you choose the material you want to study either a single metal oxide or a mixture of metal oxides Next we will mix solutions of salts of those metals and spot the mixtures on FTO glass electrodes Heating the plates at a very hig
18. l jewelry kiln works very well for this Cuta 5 piece of wire and strip 0 5 of insulation off of each end Once the plate is fired and cooled back to room temperature attach one end of the wire to the top left 1 1 corner of the plate using the copper tape Be sure to splay the wire strand onto the plate to make as much contact as possible Then cover all of the copper tape and exposed wire with 5 min epoxy If any copper or wire is exposed the circuit will short and the plate will not work 5 1 Decision of Metals to Spot You might think that any element on the Periodic Table is fair game for us to use in our research While many of these elements are of interest to us practicality forces us to exclude the following elements Non Metals We will focus on the study of metals elements that typically lose electrons and form stable oxides Most non metallic elements do not form oxides useful as catalysts for splitting water Radioactive elements We do not wish to use highly radioactive isotopes of elements because i they emit harmful radiation and ii radioactive elements decay to other elements over time Some elements that we will not use include U Pu and Th Precious metals We want to identify catalysts made from inexpensive earth abundant materials such that the construction of the final photoelectrochemical cell is economical Elements that are probably too rare for our purposes include Ru Pd Rh Te Ir Os Re Pt and
19. nd for consumable energy First the supply of fossil fuels is not limitless and in the future hydrocarbon reserves will be more difficult to access unless we develop new methods for doing so Second the extraction and combustion of fossil fuels harms the environment Carbon dioxide is an unavoidable byproduct of burning hydrocarbons and CO2 is a greenhouse gas that contributes to global warming We need to find alternative means for powering our planet that rely on sources of energy that are inexhaustible and don t pollute the environment The main alternatives to fossil fuels are nuclear wind hydroelectric hydrothermal biomass and solar technologies Each of these methods brings its own advantages and disadvantages which are briefly summarized in Table 1 Technology Capacity Advantages Disadvantages Fossil fuels gt 5000 Existing technology e Produces CO2 TW yr e Existing infrastructure e Not renewable e Inexpensive Nuclear 100 TW yr e Existing technology e Generates hazardous e Produces no CO waste e Ltd supply of radioactive ore Biomass 7 TW e Renewable e Uses agricultural land e Inefficient Hydroelectric 1 6 TW e Effectively inexhaustible e Very limited capacity e No pollution e Floods land affects wildlife Hydrothermal 11 TW e Effectively inexhaustible e Limited capacity e No pollution e Low energy density e Limited infrastructure Wind 4 TW Effectively inexhaustible e Limited capacity e No pollution Solar 600 TW e Ef
20. riments under non standard conditions you will want to spot one or more 0 05M Fe NO3 3 samples on every plate as a standard 90 0 0 Note that a small amount of light from one LED can spillover into the adjacent spots on the slide It is often is a good idea to leave a blank space between spots forming a checkerboard like pattern 13 6 Assembly of the Instrument Figure 7 Schematic diagram showing the connectivity of the SMD instrument SAFETY Always wear eye goggles and gloves when working with chemicals The electrolyte solution 0 1 M NaOH will burn skin and eyes Flush eyes or skin with water for 15 min in case of accidental contact Avoid skin and eye contact with epoxy resin Can cause irritation and bonding of skin to itself or other materials 1 2 Connect the components of the instrument as shown in Figure 7 Do not yet connect the leads to the electrodes the sample plate and the graphite rod counter electrode Itis generally good practice to plug the silver Current Integrator electronics box the box that connects to the voltmeter and the LED array black plastic box into different outlets The LED array may light up depending on the order the devices are connected This is perfectly fine The ground lead black of the BNC cable connects to the COM port of the voltmeter and the other lead red into the VQmA port Reversing the leads will makes all the voltages read the same numerical value bu
21. t absorbing capability ease of use and Stability The students will be able to compare their current materials to ones in the database or the internal standard while evaluating the usage of different metal precursors based off of their earth abundance Additionally the method of water splitting can be compared to other methods such as PV technology The projects goals to produce oxygen and hydrogen from sunlight using an inexpensive earth abundant material providing another option for renewable energy The students will be able justify their choices of precursors vs earth abundance and compare the current results to the results within the projects Also students will able to hypothesize ways to make the projects work on a large scale then compare their idea to the current technologies and how those technologies can impact natural systems 3 Introduction 3 1 Motivation Global Energy Demand and the Need for Solar Power The world is facing an energy crisis Our society s demand for consumable energy is increasing under the stresses of a growing population and escalating industrial development At present the vast majority of the world s energy needs are satisfied by the combustion of fossil fuels Common examples of this technology include powering vehicles with gasoline and generating electricity by burning coal There are two principal reasons why the present system is unsustainable in terms of meeting the world s growing dema
22. t with opposite sign Use tape to secure the graphite rod counter electrode to the side of the crystallization dish The rod should be vertical on the side of the dish with the bottom of the rod touching the bottom of the dish Be sure the tape is at least an inch above the bottom of the electrode so that the electrode makes contact with the sodium hydroxide solution next step in the dish Place the plate in the bottom of the dish with the metal oxide spots with epoxied wire facing upwards 14 3 4 5 6 7 8 9 Fill the glass dish with electrolyte e g 0 1 M NaOH so that the plate is completely immersed and that some part of the graphite rod is submerged A large quantity of electrolyte beyond this minimum is not required The level of electrolyte should NOT be so high that the alligator clips will come in contact with electrolyte the clips should only attach to the dry parts of the electrodes Make sure that the alligator clips have still not been attached yet then activate the power toggle switch on the current integrator box The LEDs might activate and blink at this step Note Having the alligator clips attached and the circuit completed when powering on the current integrator may cause too high of a voltage to pass through the system and fry the electronics Activate the voltmeter Set the voltage switch to 20 DCV range Start the Solar Materials Discovery program by clicking on the Solar M
23. the system we need not construct the complete electrochemical cells drawn in the figures above Instead we can introduce shortcuts and simplifications to speed our experiments e Examine one half reaction ata time To keep things simple we will only study catalysts for one half reaction at a time either equation 2 or 3 The electrode corresponding to this reaction either the anode or the cathode will be the working electrode The other electrode will be replaced by a simple graphite rod that serves as a counterelectrode to provide a source or sink for electrons that avoids the accumulation of charge By making this simplification we need only construct a cell with one compartment a simple glass dish e Usea glass plate as a substrate for the working electrode Whereas you might normally associate an electrode as a piece of wire or metal foil we will use 3 x 3 glass plates witha conductive fluorine tin oxide FTO coating on one side The fact that glass and FTO are transparent allows us to irradiate the spots with light through the electrode such that the photons are absorbed where the samples come in contact with the conductive plate The large surface area of the electrode will allow us to study multiple samples on one plate which will help to speed the process of screening them for activity e Potentiostat Perhaps the most important component of the SEAL kit is a potentiostat a device that can apply a constant potent
24. tware and other resources available A temporary guest log on is Username smdvisitor Password SolarPhoton case sensitive If you do not yet have your own password please contact Michelle DeBoever by email at mchansen caltech edu to request one 18 9 References 1 Lewis N S Nocera D G Proceedings of the National Academy of Sciences 2006 103 15729 15735 2 Woodhouse M Herman G S Parkinson B A Chem Mater 2005 17 4318 4324 3 Winkler G R Winkler J R Rev Sci Instrum 2011 82 114101 19
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