Electrochemical cells are the workhorses of energy conversion. Galvanic cells, like batteries, turn chemical energy into electricity. Electrolytic cells do the opposite, using electricity to drive chemical reactions.
These cells have key components: electrodes for redox reactions, electrolytes for ion flow, and salt bridges for charge balance. Understanding their types and operations is crucial for harnessing electrochemical power in various applications.
Types of Electrochemical Cells
Galvanic vs electrolytic cells
- Galvanic cells convert chemical energy into electrical energy through spontaneous redox reactions (batteries, fuel cells)
- Electrons flow from the anode to the cathode through an external circuit generating usable electrical current
- Electrolytic cells convert electrical energy into chemical energy by driving non-spontaneous redox reactions (electroplating, electrolysis)
- An external power source forces electrons to flow from the cathode to the anode enabling desired chemical transformations
Components of galvanic cells
- Electrodes serve as sites for redox reactions
- Anode undergoes oxidation releasing electrons into the external circuit
- Cathode undergoes reduction accepting electrons from the external circuit
- Electrolytes are ion-containing solutions that enable electrical current flow
- Anolyte surrounds the anode while catholyte surrounds the cathode
- Salt bridge connects the two half-cells allowing ion flow to maintain charge balance without mixing the electrolytes
Operation of electrolytic cells
- External power source supplies electrical energy driving non-spontaneous redox reactions
- Reduction occurs at the cathode where electrons are supplied
- Oxidation occurs at the anode where electrons are removed
- Electroplating deposits a thin metal layer onto a conductive surface
- Object to be plated is placed at the cathode
- Metal ions in the electrolyte are reduced and deposited onto the object
- Electrolysis decomposes compounds using electrical energy
- Water electrolysis produces hydrogen gas (H2) at the cathode and oxygen gas (O2) at the anode
Fuel cells vs concentration cells
- Fuel cells generate electricity by oxidizing a continuously supplied fuel (H2, methanol)
- Produce water and heat as byproducts
- Used for power generation and transportation
- Concentration cells generate electricity from a concentration gradient between two half-cells
- No net chemical reaction occurs
- Measure species concentrations or study membrane permeability