ELECTROLYTES AND THEIR CORROSION POTENTIAL ON MAGNESIUM-COPPER CELLSPrepared by: Kevin Miranda
WHAT MAKES A GOOD BATTERY?• Battery life
• High Cell Voltage + Low Weight High Specific Energy
• Power output• No Side Reactions High
Coulombic Efficiency (>99.0%)
• Cost• Low cost materials High
Adaptation
WHAT MAKES A GOOD ELECTROLYTE?• Coulombic Efficiency
• Electrolytes must be chosen so as to minimize side reactions and prevent corrosion
• Conductivity• Capacity of electrolyte to create
potential without decomposing
• Creation of Solid Electrolyte Interphase (SEI)
• Form SEI without overexpansion• SEI increases surface resistance
• Also extends electrode life by preventing further corrosion of electrodes
APPLICATONS Stationary Energy Storage
Requirement: Low Cost Utility-scale grid stabilization,
Uninterrupted Power Supply (e.g. hospitals, schools, social facilities), and home use (e.g. wind farm, solar cells)
Partially Hybrid Electric Vehicles (PHEV) Requirement: High Power
Energy should be provided quickly
Energy is stored in gas tank Electric Vehicles
Requirement: High Capacity Battery is only available
location for energy storage Minimize number of charges
SUMMARY OF RESEARCH CONDUCTED
PROCEDURE
1. Prepare electrolyte solution (1M, solubility)
2. Polish copper and magnesium electrodes using 240 & 320 grit sandpaper
3. Wet separator (cotton or paper) in electrolyte
4. Build cell by placing separator between electrodes
5. Attach cell(s) to GAMRY cell and collect Ecorr vs. Time data
INITIAL EXPERIMENTATION
Magnesium Sulfate (MgSO4) Alum Potash (AlK(SO4)2) Acetic Acid (CH3CO2H) Distilled Water Ethylene Glycol (Antifreeze) used
as corrosion inhibitor
“Chlorides, sulfates, and foreign materials […] can promote corrosion and pitting […]”
“[…] magnesium oxide is converted to magnesium hydroxide […] and is stable in the presence of most bases, but rapidly breaks down in the presence of acids.”
3-CELL CORROSION POTENTIAL
Antifreeze inhibitor causes voltage to reach asymptoteLack of inhibitor results in continued voltage drop
SINGLE CELL POTENTIAL AS A FUNCTION OF ELECTROLYTE
Average Potential per cell: 1.86V (sans H2O)Average Potential per cell: 1.84V (sans H2O)
DATA GATHERED FOR SINGLE CELLS
Units (V) H2O H2O +AF Acetic Acetic +AF Alum Alum +AF MgSO4 MgSO4+AF
Average 1.47 1.50 1.71 1.87 1.98 1.87 1.83 1.85 Run #1 1.54 1.34 1.66 1.88 1.99 1.84 1.87 1.83 Run #2 1.40 1.65 1.76 1.86 1.97 1.90 1.78 1.86
Corrosion with Acetic Acid Original 3-cell stack Corrosion with Distilled Water
CHOOSING A NEW ELECTROLYTE
Potassium Hydroxide (KOH) High pH (12.7) Inexpensive High electronegativity of
potassium High diffusion/solubility Possibly passive (high internal
resistance/impedance)
Pourbaix chart for Magnesium at STP
POTASSIUM HYDROXIDE Data collected for 3600s Similar performance at 1800
seconds (30 minutes) with voltage approaching ~2.4V
Only Acetic Acid and Alum, both highly corrosive, remained significantly above
No asymptote is approached
No inhibitor used Passivation shown by lack of
corrosion
RUN 1• Initial Voltage: 2.87V• Final Voltage @ 2750s: 2.01V
• Final Voltage @3600s of selected linear data (est.): 1.21V
• Final Voltage @3600s of all data (est.): 1.68V
• Average corrosion rate: ΔV/time= -0.00038V/s
• ΔV/time of selected data: -0.00046V/s• ΔV/time of all data: -0.00031V/s
• % Error: 20.0%
RUN 2• Initial Voltage: 3.13 V• Final Voltage: 1.250V
• Using linear regression on entire data: 1.30V
• Linear regression on selected linear data: 1.58V
• Average corrosion rate: ΔV/time= -0.00049V/s
• ΔV/time of selected data:-0.00046V/s
• ΔV/time of all data: -0.00051V/s
• % Error= 4.49%
RUN 3• Initial voltage: 2.84V• Final Voltage: 1.03V
• Using linear regression on entire data: 0.94V
• Linear regression on selected linear data: 0.92V
• Average corrosion rate: ΔV/time= -0.00035V/s
• ΔV/time of selected data=-0.00033V/s
• ΔV/time of all data: -0.00036V/s
• % Error: 5.16%
INDIVIDUAL CELL POTENTIAL Average voltage per cell
decreased 0.75V Visible corrosion was greatly
reduced
VISIBLE CORROSION ON COPPER
CORROSION MAGNIFIED (COPPER)
VISIBLE CORROSION ON MAGNESIUM
CORROSION MAGNIFIED (MAGNESIUM)
CONCLUSION AND FURTHER WORK
Electrolyte: High pH reduces corrosion at cost of lower
overall single cell potential Low pH (acids) and sulfates increase single
cell potential but raise rate of corrision KOH (1.1V) offers less potential and corrosion
than water (1.5v), but can it increase power? Antifreeze (inhibitor) helps stabilize corrosion
Materials: Magnesium is highly susceptible to corrosion
Can we obtain Pourbaix immunity zone? Battery application is decided by its strengths
Suggested future work: Test other high pH electrolytes Obtain electrolyte yielding 2.8V per cell Is Copper-Magnesium a good battery?
Make use of inhibitors to find asymptote Find Voc voltage
Calculate internal resistance of battery Power (Coulombic efficiency)
Current density Is Copper-Magnesium cell rechargeable?
Calculate capacity (Energy density) Estimate Cost
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THANK YOU
DR. BAVARIAN & PROFESSOR REINER
QUESTIONS?