Week 2 - Investigating Carbon Expansion in Electrochemical Double Layer Capacitors

 

Investigating Carbon Expansion in Electrochemical Double Layer Capacitors 

Drexel iStar Summer Blog -  Week 2

Purpose

There are several applications for studying expansion due to carbon:

                  - Prevent long-term problems in EDLCs. Recent experiments have shown that the carbon electrodes within electrochemical double layer capacitors (EDLCs) expand, after successive charge/discharge cycles. These volume fluctuations could ultimately inhibit the long-term operation of the capacitors. In order to prevent this expansion, more has to be known about the nature of the expansion.

                  - High-Performance Actuators. An actuator is a type of motor designed for moving or controlling a mechanism. Often times, actuators are used in industrial factors for turning other devices on and off. Charge induced expansion in carbon electrodes could be used in a positive way, as extremely small actuators.

                  -Ultra-Sensitive Strain Sensors. Charge dependent carbon electrodes could also be used as ultraprecise sensors to monitor strain in a system.

  Bazant Equation: Governs Charge-Dependent Strain in Carbon Electrodes

(a)  ε = A ⋅ Q²_norm

        (b)   Q_norm =|Q|/(V⁻¹_ion ⋅S_BET ⋅m⋅d₅₀) 

A = 1.42 X 10⁴⁰    

Q_norm = Normalized Charge

V⁻¹_ion = Maximum Counterion Density

S_BET = Specific Surface Area (Determined via the BET Equation)

m = electrode carbon mass

d₅₀ = average pore size

Research Focus

My research will introduce various electrode and electrolyte combinations into a EDLC, to see how these factors effect the carbon electrode displacement, and if the Bazant equation accurately describes their performance.

Laboratory Hardware Training

This week I was trained on a number of scientific instruments, which I will used throughout the summer to analyze my carbon electrode samples. They are listed below, with a short description of what they will be used for. 

Scanning electron microscopy (SEM): This I will used to analyze the nature of my carbon electrodes (e.g. porosity). 

Roman inVia Raymond Spectrometer/Microscope: Again, this will be used to analyze the physical construction of the carbon electrodes fabricated in this experiment.  

Biologic VSP-300 Potentiostat/Galvanostat: This instrument is to test the EDLCs. Cycling Voltammetry (CV) and chronoamperometry are two types of measurements this device is used for.

Labmaster 130 Glove Box: The ionic liquid (IL) electrolytes used in this experiment are very sensitive to oxygen. Also, any water formation within the reaction would disassociate under high potentials, harming the experiment. 

Electrode Hot Roller: To create the thin-film carbon electrodes a roller is used.  

Electrochemical Dilatometer: This is used to test the EDLCs, while monitoring the carbon expasion in situ. 

Personal Notes

After a second week in Germany, I have concluded that Saarbrücken is a very relaxed, and normal little city. In fact, if everyone spoke English, Saarbrücken would seem like a typical little mid-western U.S. city. This weekend a “fair” of sorts was going on throughout the city. Carts selling food, clothes, and all sorts of trinkets, packed the city streets. Mini-stage areas were setup for local artists to perform. After enjoying some schwenker (a type of BQQ pork) from one of the food carts on Friday evening, I watched a drummer duo play. One of the artists was on a modern rock drum set, while the other artist had an array of bongos. Having dabbled in percussion instruments in the past (both modern drum sets, and some classical pieces), I was astonished by the quality of the performance; both were phenomenal. Everything else has been very nice this week, and I can't wait to see some German castles (and posting lots of pictures of them) in future weeks!