Fuel Cells and Fuel Cells and Rechargeable BatteriesRechargeable Batteries

C5C5

C.5.1C.5.1

Describe how a hydrogen oxygen fuel cell works.Describe how a hydrogen oxygen fuel cell works.• Alkaline fuel cells usually use a mobilized or immobilized aqueous Alkaline fuel cells usually use a mobilized or immobilized aqueous

solution of potassium hydroxide as an electrolyte but sodium solution of potassium hydroxide as an electrolyte but sodium hydroxide is also acceptable. hydroxide is also acceptable.

• The electrochemical reactions inside the fuel cell are:The electrochemical reactions inside the fuel cell are:

2H2H44+4OH+4OHֿ→ֿ→ 4H4H22O+4eO+4eֿֿ anode reactionanode reaction

OO22+4e+4eֿֿ+2H+2H22O→4OHO→4OHֿֿ cathode reactioncathode reaction

2H2H22+O+O22→2H→2H22O overall reactionO overall reaction• Acid Fuel CellsAcid Fuel Cells

Porous carbon anode with catalyst in contact with HPorous carbon anode with catalyst in contact with H22(g)(g)

HH22(g)→2H(g)→2H++(aq)+2e(aq)+2eֿֿ

Cathode: porous carbon cathode with catalyst in contact with OCathode: porous carbon cathode with catalyst in contact with O22

OO22+4H+4H+++4e+4eֿֿ→→2H2H22OO

C.5.2C.5.2Describe the workings of rechargeable batteriesDescribe the workings of rechargeable batteriesA lead-acid battery is a electrical storage device that uses a reversible A lead-acid battery is a electrical storage device that uses a reversible

chemical reaction to store energy.chemical reaction to store energy.

Cathode: PbOCathode: PbO22 (s) + 2e- + 4 H+ ( (s) + 2e- + 4 H+ (aq aq ) + SO) + SO442- (2- (aq aq ) --> PbSO) --> PbSO44 (s) + 2 H (s) + 2 H22O O ((l l ))

Anode: Pb (s) + SOAnode: Pb (s) + SO442- (2- (aq aq ) --> PbSO) --> PbSO44 (s) + 2e- (s) + 2e- The The nickel-cadmium batterynickel-cadmium battery (commonly abbreviated (commonly abbreviated NiCdNiCd or or nicadnicad) is a ) is a

type of rechargeable battery using nickel oxide hydroxide and metallic type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.cadmium as electrodes.

This battery uses nickel oxide in its positive electrode (cathode), a This battery uses nickel oxide in its positive electrode (cathode), a cadmium compound in its negative electrode (anode), and potassium cadmium compound in its negative electrode (anode), and potassium hydroxide solution as its electrolyte. The Nickel Cadmium Battery is hydroxide solution as its electrolyte. The Nickel Cadmium Battery is rechargeable, so it can cycle repeatedly. A nickel cadmium battery rechargeable, so it can cycle repeatedly. A nickel cadmium battery converts chemical energy to electrical energy upon discharge and converts chemical energy to electrical energy upon discharge and converts electrical energy back to chemical energy upon recharge. converts electrical energy back to chemical energy upon recharge.

Continued.Continued.

Cd + 2HCd + 2H22O + 2NiOOH —> O + 2NiOOH —>

2Ni(OH)2Ni(OH)2 2 + Cd(OH)+ Cd(OH)22

A A Lithium-ion batteryLithium-ion battery (sometimes (sometimes Li-ion Li-ion batterybattery) is a type of rechargeable battery in ) is a type of rechargeable battery in which lithium ions move from the anode to which lithium ions move from the anode to cathode during discharge, and from the cathode during discharge, and from the cathode to the anode when charged. cathode to the anode when charged.

Similarities and differences between a Similarities and differences between a fuel cell and a rechargeable batteryfuel cell and a rechargeable battery

In principle, a fuel cell operates like a battery. In principle, a fuel cell operates like a battery.

Unlike a battery however, a fuel cell does not run down or require Unlike a battery however, a fuel cell does not run down or require recharging. It will produce electricity and heat as long as fuel and an recharging. It will produce electricity and heat as long as fuel and an oxidizer are supplied. It will produce electricity and heat as long as fuel and oxidizer are supplied. It will produce electricity and heat as long as fuel and an oxidizer are supplied. an oxidizer are supplied.

Both batteries and fuel cells are electrochemical devices.Both batteries and fuel cells are electrochemical devices. both have a positively charged anode, a negatively charged cathode and an both have a positively charged anode, a negatively charged cathode and an

ion-conducting material called an electrolyte.ion-conducting material called an electrolyte. Fuel cells are classified by their electrolyte material Fuel cells are classified by their electrolyte material

A A rechargeable battery rechargeable battery (also known as a (also known as a storage batterystorage battery) is a ) is a group of one or more group of one or more secondary cellssecondary cells

Rechargeable batteries use electrochemical reactions that are Rechargeable batteries use electrochemical reactions that are electrically reversible electrically reversible