batteries

Zinc- Carbon Dry Cell

• Anode: Zn (s) → Zn⁺² (aq) + 2 e^-

• Cathode: 2 MnO₂ (s) + 2 NH₄⁺ (aq) + + 2 e^- → Mn₂O₃ (s) + 2NH₃ (aq) +H₂O (l)

  • Graphite cathode (inactive electrode)

• Disadvantage: Ammonia leaks out slowly as a gas -> causes batteries to die and limits shelf-life, non rechargeable, low energy density 

• Advantages: Low cost, simple design, everywhere

• Uses: flashlights, remote controls, clocks

• Different sizes give off same voltage but can be run for longer periods of time/at higher currents b/c more reactants

  • If run too quickly battery dies but can rebound after sitting idle

Alkaline Dry cell

• Anode: Zn (s) + 2OH^- (aq) → Zn(OH)₂ (s) + 2 e^-

• Cathode: 2 MnO₂ (s) + 2 H₂O (l) + + 2 e^- → 2 MnO(OH) (s) + 2OH^- (aq)

• Advantages: No ammonium/ammonia -> longer shelf life, More current produced b/c greater surface area of powdered zinc which leads to a faster reaction

• Disadvantages: more expensive, not rechargeable

• Uses: toys, cameras, remote controls, portable electronics

• Zinc is powdered

• Paste is alkaline b/c potassium hydroxide

• Cathode is made of manganese (4) oxide

Silver Oxide Battery

• Anode: Zn (s) + 2OH^- (aq) → Zn(OH)₂ (s) + 2 e^-

• Cathode: 2 Ag₂O (s) + H₂O (l) + 2 e^- → 2 Ag (s) + 2OH^- (aq)

• Uses: wristwatches and hearing aids (If counter ion of the hydroxide is sodium b/c constant voltage at low current), photographic strobe flashes (if counter ion of hydroxide potassium b/c cells more consistent at higher currents)

• Advantages: small size, stable output voltage high energy density

Disadvantages: expensive (silver), limited availability in larger sizes, non rechargeable

Lead-Acid Storage Battery

• Anode: Pb (s) + HSO₄^- (aq) → PbSO₄ (s) + H⁺ (aq) + 2 e^-

• Cathode: PbO₂ (s) + 3 H⁺ (aq) +HSO₄^-  + 2 e^- → PbSO₄ + H₂O (l)

• Advantages: rechargeable, inexpensive for large capacities, high current output, provide large amount of energy, long shelf-life, reliable at low temperatures

• Disadvantages: heavy, contains toxic lead and corrosive acid, limited cycle life

• Uses: Starting engines

• Secondary battery

  • When charging reactions are reversed

NiCd Battery

• Anode: Cd (s) + 2OH^- (aq) → Cd(OH)₂ (s) + 2 e^-

• Cathode: NiO(OH) (s) + H₂O (l) +  e^- → Ni(OH)₂ (s) + OH^- (aq)

• Advantages: longer life, constant voltage for entire life (only drop when discharged), more difficult to damage

• Disadvantages: More expensive than lead-acid storage batteries (b/c size), contains toxic cadmium, lower energy density compared to newer batteries

• Uses: Rechargeable power tools, electric shavers, some electronic devices (ex. Cordless phones)

• Secondary cell

  • Reactions reversed when charging

Lithium Battery

• Advantages: Lighter, higher capacity, recently invented, last longest

• Disadvantages: expensive, can overheat or catch fire if damages, special circuitry for charging

• Uses: smartphones, laptops, electric vehicles, cameras

•  Primary or secondary cells 

• Voltage depends on cathode reaction

Fuel Cell

• Anode: 2H₂ (g) + 4OH^- (aq) → 4H₂O (l)  + 4 e^-

• Cathode: O₂ (g) + 2 H₂O (l) +  4e^- → 4OH^- (aq)

• Only net product is water

• Advantages:  reliable in controlled environments, immediate power delivery

• Disadvantages: corrode chemicals, heavy

Uses: space missions, early stationary power generation for buildings/hospitals

Modern Fuel Cells

• Anode: 2H₂ (g) → 4H⁺ (aq)  + 4 e^-

• Cathode: O₂ (g) + 4H⁺ (aq) +  4e^- → 2 H₂O (l)

• Advantages: Smaller, lighter, don’t require corrosive chemicals, never run down

  • Never run down b/c H⁺ and O₂ constantly pumped from external source

• Uses: Provide electricity to spacecrafts and produces water for drinking

Disadvantages:  high cost, lifetime, hydrogen storage issues