Electrolytes, And Their Corrosion Potential on Magnesium-Copper

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?