Batteries Self contained electrochemical cell Dry Cell (Flashlight Battery)! Primary batteries (not rechargeable)! Secondary batteries (rechargeable) Anode: Zn(s)! Research Needed to Improve Batteries: Zn(s)! Zn 2+ (aq) + 2e - Cathode: NH 4 Cl + MnO 2 + graphite paste 2NH 4+ (aq) + 2MnO 2 (s) + 2e -! Mn 2 O 3 (s) + 2NH 3 (aq) + H 2 O CHEM112 LRSVDS Batteries and Corrosion 1 CHEM112 LRSVDS Batteries and Corrosion 2
Battery Connection in Series Dry Cell Battery: Alkaline Version ALKALINE CELL BATTERY: NH 4 Cl is replaced by KOH. Provides up to 50% more energy. Zn is used as a powder mixed with the electrolyte. Total emf is the sum of the individual emfs Anode: Zn(s) + 2OH -! Zn(OH) 2 (aq) + 2e - Cathode: 2H 2 O (s) + 2MnO 2 (s) + 2e -! 2MnO(OH)(s) + 2OH - (aq) CHEM112 LRSVDS Batteries and Corrosion 3 CHEM112 LRSVDS Batteries and Corrosion 4
Lead/Acid Batteries DURING DISCHARGE: 12 V Automotive Lead-Acid Battery Anode: Pb(s) + SO 4 2- (aq)! PbSO 4 (s) + 2e - Cathode: PbO 2 (s) + SO 4 2- (aq) + 4H + + 2e -! PbSO 4 (s) + 2H 2 O Overall: Pb(s) + PbO 2 (s) + 2H 2 SO 4! 2PbSO 4 (s) + 2H 2 O CHEM112 LRSVDS Batteries and Corrosion 5 CHEM112 LRSVDS Batteries and Corrosion 6
Anode: Cd metal Cd(s) + 2OH - (aq)! Cd(OH) 2 (s) + 2e - Cathode: NiO 2 (s) NiO 2 (s) + 2H 2 O + 2e - Overall: Rechargeable Nickel- Cadmium Batteries Cd(s) + NiO 2 (s) + 2H 2 O! Ni(OH) 2 (s) + 2OH - (aq)! Cd(OH) 2 (s) + Ni(OH) 2 (s) NiMH: Nickel Metal hydride During Discharge: Cathode: NiO(OH)(s) Batteries Rechargeable NiO(OH)(s) + 2H 2 O + 2e -! Ni(OH) 2 (s) + 2OH - Anode: NiMH MH + OH -!H 2 O +M + e - NiMH= Nickel +metal alloy with dissolved H atoms: M = ZrNi 2 or LaNi 5 (intermetallic compounds) E 0 cell = 1.2 V Advantages: Light weight Last longer Uses: Batteries in hybrid cars CHEM112 LRSVDS Batteries and Corrosion 7 CHEM112 LRSVDS Batteries and Corrosion 8
Batteries Rechargeable H 2 -O 2 Fuel Cell Li-ion battery During Discharge Anode: solid (graphite) Li(s)! Li + + e - Cathode : Li + + CoO 2 + e -! LiCoO 2 Overall Li(s) + CoO 2! LiCoO 2 E 0 cell = 3.7 V Advantages: light weight, high energy density Uses: Cell phones, laptops CHEM112 LRSVDS Batteries and Corrosion 9 Anode: 2H 2 (g) + 4OH - (aq)! 4H 2 O(l) + 4e - Cathode: O 2 (g) + 2H 2 O(l) + 4e -! 4OH - (aq) Overall: 2H 2 (g) + O 2 (g)! 2H 2 O(l) E 0 cell = 1.23 V CHEM112 LRSVDS Batteries and Corrosion 10
Sample Problem: What is E cell for a fuel cell running in air (P O2 = 0.2 atm), at ph = 2, with P H2 = 1 atm? O 2 (g) + 4 H + (aq) + 4e -! 2 H 2 O(l) E o = +1.229 V 2 H + (aq) + 2e -! H 2 (g) E o = 0 Methanol fuel cells Methanol can be made from CO 2 +H 2. Use of CO 2 sequester from power plants Carbon neutral fuel Anode: CH 3 OH (g) + H 2 O(g)! CO 2 (g)+ 6H + + 6e - Cathode: 3/2 O 2 (g) + 6H + + 6e -! 3H 2 O(g) Overall: CH 3 OH (g) + 3/2 O 2 (g)! CO 2 (g)+ 2H 2 O(l) Expensive Pt catalyst needed. CHEM112 LRSVDS Batteries and Corrosion 11 CHEM112 LRSVDS Batteries and Corrosion 12
Corrosion Corrosion Spontaneous electrochemical process! What is needed for corrosion to occur?!!!!!!!!! How do we prevent corrosion?!!!! CHEM112 LRSVDS Batteries and Corrosion 13 CHEM112 LRSVDS Batteries and Corrosion 14
Corrosion CATHODIC PROTECTION OF IRON CHEM112 LRSVDS Batteries and Corrosion 15 CHEM112 LRSVDS Batteries and Corrosion 16
Corrosion CATHODIC PROTECTION OF IRON Definition: ELECTROLYSIS An electrolytic cell consists of two electrodes in: Electrolysis forces the reaction to run in the reverse: The anode is still where oxidation occurs. Anions migrate to the anode and lose electrons. CHEM112 LRSVDS Batteries and Corrosion 17 The cathode is still where reduction occurs. Cations migrate to the cathode and gain electrons. CHEM112 LRSVDS Batteries and Corrosion 18
COMMERCIAL APPLICATIONS OF ELECTROLYSIS ELECTROLYSIS OF MOLTEN NaCl; Commercial Method for Production of Na(s) and Cl 2 (g) Production of metals Na Al Purification of Metals Cu What are the reactions at the electrodes? Electroplating Ag Au Cathode: Anode: Overall: CHEM112 LRSVDS Batteries and Corrosion 19 CHEM112 LRSVDS Batteries and Corrosion 20
ELECTROLYSIS OF AQUEOUS NaCl What species are present in the system? Which will be the CATHODE? ELECTROLYSIS OF AQUEOUS Na 2 SO 4 Does this process produce Na(s)? What species are present in the system? Which will be the CATHODE? Which will be the ANODE? Which will be the ANODE? What are the reactions at the electrodes? Cathode: Anode: Overall: What is left behind? What are the reactions at the electrodes? Cathode: Anode: Overall: What is left behind? CHEM112 LRSVDS Batteries and Corrosion 21 CHEM112 LRSVDS Batteries and Corrosion 22
Electrometallurgy of Aluminum Electrorefining of Copper Hall Process Electrolysis Cell is used to produce aluminum. Problem: Al 2 O 3 melts at 2000 C. Why a problem? Solution: molten cryolite, Na 3 AlF 6 What happens to a MP when impurities are added? Anode: C(s) + 2O 2- (l)! CO 2 (g) + 4e - Cathode: 3e - + Al 3+ (l)! Al(l) What happens to the graphite rods during the reaction? What are the reactions at the electrodes? Anode: impure Cu; mixture of dissolved metal ions To produce 1000 kg of Al, we need:!!!! kg of bauxite, kg of cryolite, kg of C anodes of energy. Cathode: thin sheet of pure Cu As the reaction proceeds, what happens to Cu? CHEM112 LRSVDS Batteries and Corrosion 23 CHEM112 LRSVDS Batteries and Corrosion 24
ELECTROLYSIS CALCULATIONS 1 mole of e - = charge of 1 Faraday = 96,485 Coulombs = charge on 1 mole of e - 1 Ampere = 1 coulomb/second 1 coulomb = 1 Amp-sec Electromotive Force (EMF) = Cell potential force that causes electrons to flow (voltage) ELECTROLYSIS CALCULATION Electrolysis gives 1.00 g of Cu from CuSO 4 Reaction is: Cu 2+ + 2e -! Cu How many Faradays (F) of charge are required? 1 Watt = 1 Amp-Volt 1 Joule = 1 coul-volt = 1 Amp-sec-Volt = 1 Watt-sec 1 kw-hour = (1000 Watt)(3600 sec) = 3.6 x 10 6 Watt-sec = 3.6 x 10 6 Joules! How many Coulombs is this? CHEM112 LRSVDS Batteries and Corrosion 25 CHEM112 LRSVDS Batteries and Corrosion 26
ELECTROLYSIS CALCULATION If 1.00g of Cu is obtained in 1 hour, how many amps are required? If 2 amps were used, how long would it take to produce 1g? CHEM112 LRSVDS Batteries and Corrosion 27