sustainability Article
Design of an Extended Experiment with Electrical Double Layer Capacitors: Electrochemical Energy Storage Devices in Green Chemistry Yannan Lin 1 , Hongxia Zhao 2 , Feng Yu 1, * 1 2
*
and Jinfeng Yang 1, *
Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, School of Chemistry and Chemical Engineering, Shihezi University, Shihezi 832003, China;
[email protected] Department of Education, Normal College, Shihezi University, Shihezi 832003, China;
[email protected] Correspondence:
[email protected] (F.Y.);
[email protected] (J.Y.)
Received: 30 August 2018; Accepted: 8 October 2018; Published: 11 October 2018
Abstract: An extended undergraduate experiment involving electrochemical energy storage devices and green energy is described herein. This experiment allows for curriculum design of specific training modules in the field of green chemistry. Through the study of electrical double layer capacitors, students learned to assemble an electrical double layer capacitor and perform electrochemical measurements (cyclic voltammetry and galvanostatic charge-discharge) to evaluate the effect of various electrolytes. In addition, students powered a diode with the electrical double layer capacitors. We use the laboratory module to successfully connect electrochemistry with green chemistry through the study of a real-world application. In addition, a green chemistry case study was introduced to the laboratory curriculum. During the experiment, students acquired fundamental experience in electrochemistry and gained analysis skills, critical thinking, and scientific literacy. The results of this work can be used as a case study on green chemical education that considers the students’ awareness of renewable and clean energy fields. Keywords: curriculum; undergraduate green chemistry; electrochemistry
research;
laboratory
equipment/apparatus;
1. Introduction The development of environmentally benign, sustainable, and renewable energy sources, as well as new technologies for energy conversion and storage, is economically and ecologically critical. The depletion of fossil fuels and increasing environmental pollution necessitate advances in the fields of green chemistry and renewable energy [1,2]. Up to now, sustainable and renewable energy sources, including solar power, ocean waves, and wind, have been widely utilized in the world. Electrochemical energy storage devices (e.g., supercapacitors, secondary batteries, etc.) are well positioned to store regional and seasonal energy [3,4]. For training future scientists to create these tools, Shihezi University has developed green energy (green chemistry) courses for undergraduate students. These courses respond to the increasing energy needs of modern society and emerging ecological concerns. Green chemistry is an essential part of modern chemical education [5,6] and is critical for future innovation and industrial applications to meet society’s growing demand for sustainable products and processes. Chemical educators should continue to refine laboratory curricula to reflect these principles. Increasing evidence suggests that laboratory courses improve students’ knowledge of scientific methods, and engagement with chemistry [7,8]. These courses enhance the ability to think scientifically and critically, as well as to communicate effectively. The green energy curriculum established at our institution involves both the theory and practice of green chemistry. It gives students
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scientifically and critically, as well as to communicate effectively. The green energy curriculum established at our institution involves both the theory and practice of green chemistry. It gives the tools to design manufacture next-generation chemicals and chemicals products without harmingwithout human students the toolsand to design and manufacture next-generation and products health or the natural environment [9,10]. harming human health or the natural environment [9,10]. The basis of the lecture component of these green chemistry courses is instruction in alternative Students are are also also exposed exposed to to green green energy energy storage storage devices; devices; energy sources (i.e., wave, tide, and solar). Students this article focuses on electrical double layer capacitors (EDLCs). EDLCs EDLCs are novel energy storage components between and electrostatic capacitors [11,12]. As the energy storage components betweenbatteries batteries and electrostatic capacitors [11,12]. Asfirst thereversible first reversible energy devices, EDLCs have attracted significant attention due to their high power density, long lifecycle, storage devices, EDLCs have attracted significant attention due to their high power density, long and ability to ability bridge to thebridge energythe gap between dielectric dielectric capacitorscapacitors and batteries. A typical lifecycle, and energy gaptraditional between traditional and batteries. EDLC consists two electrodes, a separator, and an electrolyte that can bethat classified two types: A typical EDLCofconsists of two electrodes, a separator, and an electrolyte can beinto classified into aqueous and organic. However, purely classroom-based instruction in electrochemistry has significant two types: aqueous and organic. However, purely classroom-based instruction in electrochemistry limitations. Therefore, we describe herein protocol that is suitable for students, and teaches has significant limitations. Therefore, wea laboratory describe herein a laboratory protocol that is suitable for the essential about laboratory will help to create a new generation of students, anddetails teaches the EDLCs. essentialThis details about component EDLCs. This laboratory component will help to green-minded researchers. create a new generation of green-minded researchers. 2. Methods Methods 2.
Students were were involved involved in in this this experiment experiment as as aa three-stage project in Students three-stage project in aa first-semester first-semester undergraduate electrochemistry electrochemistry laboratory. laboratory. The The first stage (pre-class) included discussions of undergraduate first stage (pre-class) included discussions of the the principles of green chemistry, how the EDLC worked and was assembled, and how to principles of green chemistry, how the EDLC worked and was assembled, and how to generate cyclic generate cyclic voltammetry and galvanostatic charge-discharge curves with the electrochemical voltammetry and galvanostatic charge-discharge curves with the electrochemical workstation. The workstation. second stage (in-class) students to assemble an EDLC and test second stage The (in-class) allowed students allowed to assemble an EDLC and practically test thepractically product. The the product. The third stage (after-class) involved analyzing the test results and finishing lab reports. third stage (after-class) involved analyzing the test results and finishing lab reports. The process of The process of “teaching” and “learning” in the three-stages was designed involveexperimentation, experimentation, “teaching” and “learning” in the three-stages was designed to to involve implementation, and Supplementary Materials. Figures 1 and 2 express the implementation, andreflection, reflection,asasshown shownininthe the Supplementary Materials. Figures 1 and 2 express teaching idea, purpose, and the time arrangements of the experimental curriculum. the teaching idea, purpose, and the time arrangements of the experimental curriculum.
Figure 1. Experimental Experimental design design and and concept concept of green chemistry. Figure
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Figure 2. The time arrangements of the experimental curriculum.
2.1. Preparatory Phase:Figure Obtaining and Forming Practicecurriculum. Groups 2. TheKnowledge time arrangements of theGreen experimental This phasePhase: contained three main parts: laboratory assistant preparation, students obtaining 2.1. Preparatory Obtaining Knowledge and Forming Forming Green 2.1. Preparatory Phase: Obtaining Knowledge and Green Practice Practice Groups Groups knowledge, and forming green practice groups. The latter two sections were based on a network This contained education platform. This phase phase contained three three main main parts: parts: laboratory laboratory assistant assistant preparation, preparation, students students obtaining obtaining knowledge, and forming green practice groups. The latter two sections were based on a network The laboratory assistant materials and apparatus ahead time. on Thea materials knowledge, and forming greenprepared practice the groups. The latter two sections wereofbased network education platform. included activated education platform. carbon, CR2032 coin cell case, spacer disk, wave washer, Celgard separator, The assistant the and of The tweezer, pipette, electric wire,prepared clip connector, light emitting diode, 6.0 ahead mol/L (50 mL), 1.0 mol/L The laboratory laboratory assistant prepared the materials materials and apparatus apparatus ahead KOH of time. time. The materials materials included activated carbon, CR2032 coin cell case, spacer disk, wave washer, Celgard separator, tweezer, Li2SO4 (50activated mL), andcarbon, 1.0 mol/L LiPF6coin (50 mL). The apparatus included punching machine, sealing included CR2032 cell case, spacer disk, wave washer, Celgard separator, pipette, electric wire, clip connector, light emitting diode, 6.0 mol/L KOH (50 mL), 1.0 mol/L 2 SO4 machine,pipette, glove box, andwire, electrochemical workstation. tweezer, electric clip connector, light emitting diode, 6.0 mol/L KOH (50 mL), 1.0Limol/L (50 mL), and 1.0 and mol/L mL). The apparatus included punching machine,the sealing machine, 6 (50 The assigned tasks on6 a(50 network education platform. Thereafter, students were Li2SO 4 (50teacher mL), 1.0LiPF mol/L LiPF mL). The apparatus included punching machine, sealing glove box, and electrochemical workstation. divided into self-selected groups of three students each to evaluate the voltage window of three machine, glove box, and electrochemical workstation. The assigned onLiPF a network the students were divided electrolytes (KOH, Li2SOtasks 4, tasks and and education study theplatform. effects ofThereafter, these electrolytes the chemical The teacher teacher assigned on a6)network education platform. Thereafter, theonstudents were into self-selected groups of three students each to evaluate the voltage window of three electrolytes performance of the EDLC.groups of three students each to evaluate the voltage window of three divided into self-selected (KOH, Li2 SO(KOH, effects of these electrolytes on electrolytes the chemicalon performance of 4 , and LiPF 6 )4,and electrolytes Li2SO andstudy LiPF6the ) and study the effects of these the chemical the 2.2.EDLC. Operation:ofTraining Practical Green Chemistry Ability and Fostering the Spirit of Cooperation performance the EDLC. This module tookPractical approximately 4 h, during students completed EDLC assembly, 2.2. Operation: Training Green Chemistry Ability which and Fostering the Spirit of Cooperation 2.2. Operation: Training Practical Green Chemistry Ability and Fostering the Spirit of Cooperation performed testing, and powered the diode. Figure 3 shows the EDLC assembly sequence. The This first module took approximately 4 h, during which students completed EDLC assembly, students added theapproximately electrolyte to the between the students separator and gasket.EDLC The edge of the This module took 4 h,gap during which completed assembly, performed powered the itdiode. Figure 3 shows the EDLC assembly sequence. Thetostudents spacer wastesting, prone and toand roll up when the electrolyte, were required smooth performed testing, powered thecontacted diode. Figure 3 shows so thetweezers EDLC assembly sequence. The first added the The electrolyte to the gap between the separator and gasket. The edge of theand spacer was the separator. battery center of the twogap electrodes closedand with tweezers carefully students first added the electrolyte to the betweenwas thethen separator gasket. The edge of the prone to rolltoupprevent when it contacted the from electrolyte, so tweezers wereprocess. requiredThe to smooth the separator. controlled breaking during this samples spacer was prone to rollthe upseparator when it contacted the electrolyte, so tweezers were required underwent to smooth The battery center of the two electrodes was then closed with tweezers and carefully controlled to tableting withThe a tablet machine assembly, and the capacitor be placed in theand center of the the separator. battery centerafter of the two electrodes was then should closed with tweezers carefully prevent the separator from breaking during this process. The samples underwent tableting with a carrier tablet. controlled to prevent the separator from breaking during this process. The samples underwent tablet machine after assembly, and the capacitor should be placed in the center of the carrier tablet. tableting with a tablet machine after assembly, and the capacitor should be placed in the center of the carrier tablet.
Figure Figure 3. 3. (a) (a) EDLC EDLC operation operation schematic schematic and and (b) (b) EDLC EDLC installation installationsequence. sequence.
Figure 3. (a) EDLC operation schematic and (b) EDLC installation sequence.
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The electrochemical performance of the EDLC was determined by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests performed using a CHI600A electrochemical workstation. Cyclic voltammetry can rapidly provide a diverse range of data, including the reversibility and mechanism of electrode reactions and adsorption of the electrochemical material. Galvanostatic charge-discharge is another method used to study electrode materials via characterization of specific capacitance and cycle performance [13,14]. The students studied the change in potential as a function of time at a constant current. They then analyzed the capacitance via GCD curves and calculated the specific capacitance of the electrode material based on the continuous current discharge curve and Equation (1) [15,16]: 4It Cm = (1) m·∆V where m is the weight of the electrode material in the electrode layer (g), I is the constant current value (A), t is the discharge time (s), and is the average voltage drop of the discharge curve (V). Students used different electrolytes in the EDLC and observed the diode brightness as a function of time as the EDLC was charged and discharged. 2.3. Feedback and Summary: Calculation and Analysis of the Specific Capacitance Data and Finished Lab Reports In this stage, the students learned how to measure and draw CV and GCD curves using Origin software. They observed the voltage window from CV curves of the three electrolytes and calculated and analyzed the specific capacitance of the EDLC from the corresponding GCD curves. Finally, the students completed their lab reports and shared the results with each other. 3. Hazards Potassium hydroxide (KOH) is a strong base which is caustic. It is essential to wear gloves during the assembly of the EDLC to avoid damaging skin and clothing. If there are any spills, the area should be rinsed with ample amounts of water. The organic electrolyte should be used in the glove box. 4. Results and Discussion 4.1. Independent Study Students reached conclusions through reviewing literature information, finding that the capacitance of the electrode was a function of the potential-dependent accumulation of electrostatic charge at the interface. During charging, electrons accumulated on the supercapacitor electrodes and traveled from the negative to the positive electrode, as shown in Figure 4. Within the electrolyte, cations moved towards the negative electrode, while the anions moved to the positive electrode. This process formed the electric double layer at the solid-liquid interface. The reverse processes occurred during discharge and decreasing electrical potential between the two plate electrodes was observed. In this type of EDLC, no charge transfers across the wire or electrolyte interface occurred, and no net ion exchange between the electrode and electrolyte were observed. This indicates that the electrolyte concentration remained constant during charging and discharging. The energy was stored in the double-layer interface using this method. The students were self-divided into groups of three people. The students obtained information regarding the three electrolytes from reading the literature, as this was a critical component of the EDLC. The electrolyte provided ionic conductivity and facilitated charge compensation for each electrode in the cell. The electrolyte played a fundamental role in the EDLC and determined EDLC performance. This laboratory procedure evaluated both aqueous and organic electrolytes. With the aqueous electrolytes, including alkaline (KOH) and neutral (Li2 SO4 ), the potential window was approximately 1.0–1.6 V. These electrolytes are inexpensive and can easily be handled in the laboratory without special conditions, greatly simplifying the fabrication processes. Organic electrolytes (such as LiPF6 ) currently dominate the commercial market due to their extensive operation potential window
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electrolytes (such as LiPF6) currently dominate the commercial market due to their extensive electrolytes (such as LiPF6) currently dominate the commercial market due to their extensive operation potential window (approximately 2.5–4.5 V), and the the cycling CV experiment evaluated the cycling (approximately 2.5–4.5 V), and the CV experiment evaluated performance of thethe EDLC and operation potential window (approximately 2.5–4.5 V), and the CV experiment evaluated cycling performanceitsofvoltage. the EDLC and determined its voltage. determined performance of the EDLC and determined its voltage.
Figure 4. 4. Schematic illustration illustration of of charge/discharge charge/discharge process in EDLC. (a) The charging process, (b) Figure processin in EDLC. EDLC. (a) (a) The The charging charging process, process, (b) (b) Figure 4. Schematic Schematic illustration of charge/discharge process EDLC after charging, and (c) the discharging process. EDLC after after charging, EDLC charging, and and (c) (c) the the discharging discharging process. process.
4.2. Experimental Illustration of Green Energy 4.2. Experimental Illustration of Green Energy The experiment was performed a total of The CV and GCD curves shown in the of 11 11 times. times. The The experiment was performed a total of 11 times. The CV and GCD curves shown in the following parts are representative representative results results obtained obtained by by the the students. students. following parts are representative results obtained by the students. The CV results were used to evaluate evaluate the cycling cycling performance of the EDLC and determine its The CV results were used to evaluate the cycling performance of the EDLC and determine its voltage range. Figure 5 shows representative electrolytes. representative CV CV curves curves for for the the KOH, KOH, Li Li22SO4, and LiPF66 electrolytes. voltage range. Figure 5 shows representative CV curves for the KOH, Li2SO4, and LiPF6 electrolytes. KOH and and Li Li22SO SO4 4exhibited exhibited excellent current response, CV curves rectangular. anan excellent current response, andand theirtheir CV curves werewere rectangular. This KOH and Li2SO4 exhibited an excellent current response, and their CV curves were rectangular. This This approached an ideal thatperfectly was perfectly whereas CV curves LiPF6 approached an ideal EDLCEDLC curvecurve that was square,square, whereas the CVthe curves for LiPFfor 6 deviate approached an ideal EDLC curve that was perfectly square, whereas the CV curves for LiPF6 deviate deviate from this trend. The results indicated KOH better electrochemical electrochemical from this trend. The results indicated thatthat KOH andand thethe LiLi 2SO 4 exhibited 2 SO 4 exhibitedbetter from this trend. The results indicated that KOH and the Li2SO4 exhibited better electrochemical performance with the active active carbon carbon electrode electrode than than that that of of LiPF LiPF66. performance with the active carbon electrode than that of LiPF6.
Figure 5. Representative RepresentativeCV CVcurves curvesofof(a)(a) KOH, (c) LiPF at different KOH, (b)(b) Li2Li SO 4, and (c) LiPF 6 electrolytes at different scan 2 SO 4 , and 6 electrolytes Figure 5. Representative CV curves of (a) KOH, (b) Li2SO4, and (c) LiPF6 electrolytes at different scan scan rates using a two-electrode testing setup. (d) CV curves of the three samples at a sweep rate of rates using a two-electrode testing setup. (d) CV curves of the three samples at a sweep rate of 5 mV rates using a two-electrode testing setup. (d) CV curves of the three samples at a sweep rate of 5 mV − 1 −1 5s mV . s . s−1.
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As the scanning speed increased, the CV curves flattened (Figure 5a–c). Some students thought it As the scanning speed increased, the CV curves flattened (Figure 5a–c). Some students thought was because could speed not easily accessthe theCV electrode charging and 5a–c). discharging at a highthought scan rate. As theions scanning increased, curves for flattened (Figure Some students it was because ions could not easily access the electrode for charging and discharging at a high scan it was because ionsstored could on notthe easily access did the electrode for at charging and discharging at a high However, the charge electrode not increase a steady rate. This decreased thescan active rate. However, the charge stored on the electrode did not increase at a steady rate. This decreased the rate. However, the charge stored on the electrode did not5d increase at a steady rate. This decreased the material on the electrode and tilted the CV curve. Figure shows that the voltage windows were 0–1, active material on the electrode and tilted the CV curve. Figure 5d shows that the voltage windows active material on the electrode and tilted the CV curve. Figure 5d shows that the voltage windows 0–1.4, and 0–3.0 V for the KOH, Li SO , and LiPF electrolytes, respectively. 2 KOH, 4 were 0–1, 0–1.4, and 0–3.0 V for the Li2SO4,6 and LiPF6 electrolytes, respectively. were 0–1, 60–1.4, andthe 0–3.0 V for the KOH, Li2KOH, SO4, and LiPF respectively. when measured Figure shows GCD curves of the Li22SO SO4,46and , electrolytes, and LiPF 6 electrolytes Figure 6 shows the GCD curves of the KOH, Li LiPF 6 electrolytes when measured at Figure 6 shows the GCD curves of the KOH, Li 2SO4, and LiPF6 electrolytes when measured at at different using aa two-electrode testing system. system.The TheKOH KOHand andLiLi2SO samples 2 SO different current current densities densities using two-electrode testing 4 4 samples different current densities using a two-electrode testing system. The KOH and Li 2SO4 samples exhibited symmetrical shapes and resistance (IR) (IR)drop. drop.The Theslight slight curvature exhibited symmetrical shapes anda arelatively relativelysmall smallinternal internal resistance curvature exhibited symmetrical shapes and a relatively small internal resistance (IR) drop. Thesheet. slight curvature in the GCD curves corresponded active species species the addition, in the GCD curves correspondedtotothe theredox redoxreaction reaction of the active ininthe sheet. InIn addition, in the GCD curves corresponded to the redox reaction of the active species in the sheet. In addition, thethe GCD curves in the LiPF specimen remained constant at different current densities and showed no GCD curves in the LiPF 6 specimen remained constant at different current densities and showed 6 the GCD curves in the LiPF6 specimen remained constant at different current densities and showed no visible IR drops. visible IR drops. no visible IR drops.
Figure 6. GCD curves KOH,(b) (b)LiLi 2SO and (c) (c) LiPF LiPF66 electrolytes Figure 6. GCD curves of of (a)(a) KOH, electrolytesatatdifferent differentcurrent currentdensities densities 2 SO 44,,and Figure 6. GCD curves of (a) KOH, (b) Li2SO4, and (c) LiPF6 electrolytes at different current densities determined using a two-electrodetesting testingsetup. setup. (d) GCD GCD curves determined using a two-electrode curves of ofthe thethree threesamples samplesatata acurrent current determined using a two-electrode testing setup. (d) GCD curves of the three samples at a current −1. − 1 density of 5 A g density of 5 A g −1. density of 5 A g . −11at Figure exhibits specific capacitancewith withthe theKOH KOHelectrolyte electrolytewas was 231.4 231.4 FF gg− Figure 7a 7a exhibits thethe specific capacitance at0.5 0.5AAgg−1−1 Figure 7a exhibits the specific capacitance with the KOH electrolyte was 231.4 F g−1 at 0.5−1A g−1−1 based Equation(1). (1).This Thisvalue value was twice of of thethe Li2SO electrolyte (115.4(115.4 F g ) Fand based onon Equation twiceas asmuch muchasasthat that Li 4SO g ) 4 electrolyte based on Equation (1). This value was twice as much as that of the Li2SO24 electrolyte (115.4 F g−1) and −1 − 1 greater than the LiPF 6 electrolyte (55 F g ), as shown in Figure 7b,c. At a current density of andfour-fold four-fold greater than the LiPF electrolyte (55 F g ), as shown in Figure 7b,c. At a current 6 four-fold greater than the LiPF6 electrolyte (55 F g−1), as shown in Figure 7b,c. At a current density of −1, the specific −1 with a−1 −1 , the capacitance 1 A gof of the KOH electrolyte remainedremained as high as 205.3 F g205.3 density 1 A g specific capacitance of the KOH electrolyte as high as F 1 A g−1, the specific capacitance of the KOH electrolyte remained as high as 205.3 F g−1 with ga capacitance retention rate of 88.8%. The Li2SO4Li electrolyte reduced the performance by 25.4% or 86 F with a capacitance retention of 88.8%. the performance 25.4% 2 SO4 electrolyte capacitance retention rate ofrate 88.8%. The LiThe 2SO4 electrolyte reducedreduced the performance by 25.4% by or 86 F −1. The g LiPF 6 electrolyte exhibited a specific capacitance of 16.8 F g−1, a reduction of 69.4% under − 1 − 1 or 86 g LiPF . The6 LiPF exhibited a specific capacitance g , a reduction 69.4% −1, a F 6 electrolyte g−1.FThe electrolyte exhibited a specific capacitance of 16.8 Fofg16.8 reduction of 69.4% of under constant parameters. These data showed that the specific capacitance of the EDLC gradually under constant parameters. These showed specific capacitance EDLC gradually constant parameters. These datadata showed thatthat the the specific capacitance of of thethe EDLC gradually decreased as the current density gradually increased, and the KOH formed an excellent electrical decreased asas thethe current and the the KOH KOHformed formedan anexcellent excellentelectrical electrical decreased currentdensity densitygradually gradually increased, increased, and double layer, showing good electrode conductivity. double layer, showing good electrode conductivity. double layer, showing good electrode conductivity.
Figure 7. The specific capacitance of active carbon materials calculated by GCD curves using various Figure 7. The specific calculatedby byGCD GCDcurves curvesusing using various Figure 7. The specificcapacitance capacitanceofofactive activecarbon carbon materials materials calculated various electrolyte: (a) KOH, (b) Li2SO4, and (c) LiPF6. 2SO and (c) (c) LiPF66.. electrolyte: KOH, (b)LiLi electrolyte: (a)(a) KOH, (b) 2 SO 4 4,,and
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It can be seen that, the specific capacitance of active carbon was affected by various factors, It canfor be electrolytes. seen that, the specific capacitance of active carbon was affected by various factors, especially Generally, the capacitance of activated carbons is higher in aqueous especially for electrolytes. Generally, the capacitance of activated carbons is higher in aqueous electrolytes (ranging from 100 F g−1 to 300 F g−1) than that in inorganic electrolytes (less than 150 F electrolytes (ranging from 100 F g−1 to 300 F g−1 ) than that in inorganic electrolytes (less than 150 F g−1 ). F g−1) is similar to the results g−1). In this manuscript, the student’s experimental data (55–231 − 1 In this manuscript, the student’s experimental data (55–231 F g ) is similar to the results summarized summarized in Ref. [3]. in Ref. [3]. The students connected a diode to the EDLC after charging it on the electrochemical workstation. The students connected a diode to the EDLC after charging it on the electrochemical workstation. The intensity of the diode is shown in Figure 8. The diode was rated at 5 V, and its brightness The intensity of the diode is shown in Figure 8. The diode was rated at 5 V, and its brightness increased increased with applied voltage when the voltage was less than 5 V. The diode powered by an EDLC with applied voltage when the voltage was less than 5 V. The diode powered by an EDLC with LiPF6 with LiPF6 electrolyte was the brightest followed the diode powered by the Li2SO4 and KOH EDLCs. electrolyte was the brightest followed the diode powered by the Li2 SO4 and KOH EDLCs. These results These results were consistent with the CV and GCD data. were consistent with the CV and GCD data.
Figure Figure 8. 8. Diode Diode brightness brightness using using (a) (a) KOH, KOH, (b) (b) Li Li22SO SO44, ,and and(c) (c)LiPF LiPF6 6electrolytes electrolytesininEDLC. EDLC.
4.3.Green GreenChemistry ChemistryApplication Applicationand andConnecting ConnectingIdeas Ideas 4.3. Feedbackfrom fromstudents studentssuggested suggestedthat thatthe thedeveloped developedmethod methoddelivers deliverson onthe thedesired desiredlearning learning Feedback outcomes.This Thiswas wasconcluded concludedthrough throughthree threemajor majoraspects. aspects.First, First,this thisapproach approachstimulated stimulatedstudents’ students’ outcomes. interest in in aa topic topic typically typically seen seen as as abstract, abstract, as as EDLCs EDLCs are are rarely rarely featured featured in in undergraduate undergraduate lab lab interest experiments. It allowed the students to observe how electrolyte selection affected EDLC performance experiments. It allowed the students to observe how electrolyte selection affected EDLC performance andenabled enabledthem themto togain gainaabetter betterunderstanding understandingofofelectrochemistry, electrochemistry,increase increasefamiliarity familiaritywith withenergy energy and store device technology, provided valuable hands-on experience with electric chargescharges and circuits. store technology,and and provided valuable hands-on experience with electric and Second, these chemistry topics provided exciting opportunities, created green chemistry circuits. laboratory and encouraged students. We endeavored to improve the Second,activities, these chemistry topics discussion provided among excitingtheopportunities, created green chemistry students’ analytical critical-thinking skills, and understanding of endeavored energy science. All of these laboratory activities, ability, and encouraged discussion among the students. We to improve the goals were achieved, as evidenced by a post-course questionnaire. For the students students’ analytical ability, critical-thinking skills, and understanding ofinstance, energy science. All of began these to think about whichas electrolyte would be suitable for petroleum coke electrodethe material in EDLCs goals were achieved, evidenced by a post-course questionnaire. For instance, students began after experimental data analysis,would whichbe electrode was best forelectrode EDLCs, how to improve the to think about which electrolyte suitablematerial for petroleum coke material in EDLCs voltage window, how toanalysis, reduce hazardous waste, among other Novelhow ideas inspired, after experimental data which electrode material wassuggestions. best for EDLCs, towere improve the discoveries were made, memories createdwaste, by these electrochemical experiments and are worth voltage window, how toand reduce hazardous among other suggestions. Novel ideas were implementing in the laboratory component. inspired, discoveries were made,course and memories created by these electrochemical experiments and Third, this experiment shaped the student-centered teaching and study-based learning modules, are worth implementing in the laboratory course component. which did this not rely on implanting knowledge and skillsteaching to students, but inspiredlearning students to think Third, experiment shaped the student-centered and study-based modules, and focus learning. For example, students passionately participated in the which did on notparticipatory rely on implanting knowledge andthe skills to students, but inspired students to online think platform chose electrolytes of their own volition, which highlights the success of theinexperiment. and focus and on participatory learning. For example, the students passionately participated the online Furthermore, this experiment towards system-based thinking, the use of platform and chose electrolytesorients of theireducation own volition, which highlights the successincluding of the experiment. interdisciplinary, and inquiry-based methods. Furthermore, this experiential, experiment orients education towards system-based thinking, including the use of In general, experiential, green chemistry curricula willmethods. play a central role in establishing a course on interdisciplinary, and inquiry-based sustainability. experiment could attract students science role and allow them to think about on the In general,This green chemistry curricula will playinto a central in establishing a course proper relationship between natural and artificial environments using an integrated viewabout of social, sustainability. This experiment could attract students into science and allow them to think the political, ecological,between economic, and possibly cultural dimensions.using In addition, the students will gain proper relationship natural and artificial environments an integrated view of social, valuable ecological, experience economic, to pursue careers in green chemistry. political, and possibly cultural dimensions. In addition, the students will gain valuable experience to pursue careers in green chemistry.
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5. Conclusions To improve teaching and research, an experiment testing electrochemical performance was designed and integrated into the green chemistry curriculum. This 4 h module (EDLC) significantly progressed student understanding of electrochemistry and energy storage equipment. It also sustained and enhanced their intellectual enthusiasm and passion for both education and research. This laboratory module will unleash the potential of students and cultivate their responsibilities and obligations toward green chemistry via consultation of the scientific literature and participation in the experiment. Overall, the primary objective of this curriculum is to increase student knowledge of electrochemistry. However, they also develop important skills related to green chemistry, such as problem-solving, analytical skills, critical reasoning, and creative thinking. Therefore, more such experiments involving green chemistry should be integrated into the undergraduate chemistry curriculum. Supplementary Materials: Teaching plan and learning plan are available online at http://www.mdpi.com/20711050/10/10/3630/s1. Author Contributions: Conceptualization, H.Z., F.Y. and J.Y.; methodology, F.Y. and J.Y.; formal analysis Y.L.; data curation, Y.L.; writing—original draft preparation, Y.L.; writing—review and editing, H.Z., F.Y. and J.Y.; supervision, F.Y. and J.Y. Funding: This work was financially supported by the Research Center for Online Education of the Ministry of Education (No. 2017YB149) and Blending Learning for Teaching Reform of the Shihezi University (No. BL2016004). Conflicts of Interest: The authors declare no conflict of interest.
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