Electrochemistry, Rechargeable Batteries, Fuel Cells, Photovoltaic Cells and Dye-Sensitized Solar Cells (HL Option C.6 & C.8) Flashcards
What is a redox reaction?
Reaction where electrons are transferred from the species being oxidized to the species being reduced
What is a battery?
A series of electrochemical cells
What is a primary electrochemical cell?
cell where the the materials are consumed and the reaction is not reversable
Why can’t primary electrochemical cells not be used anymore?
Anode is oxidized and cannot be used, solution becomes polarized which increases build up of hydrogen bubbles on the anode which increases the internal resistance of the cell
What is the main limitation of primary electrochemical cells?
They do not operate well under high current demand
What is a secondary cell / rechargeable cell?
cell where chemical reactions generate electricity and reactions can be reversed by applying a current
What is the main limitation of secondary electrochemical cells / rechargeable cells?
they have a higher rate of self - discharge
Why must cars batteries be toped up with distilled water occasionally?
if a cell runs too long it may have an over-voltage, which produced hydrogen and oxygen
What is a lithium ion battery?
Battery with a graphite anode with lithium atoms absorbed into the lattice, the cathode is a lithium cobalt
What is the benefit of using lithium in lithium ion batteries?
Lithium has the highest oxidation potential and is light weight
What is the electrolyte in lithium - ion cells? Why?
a gel polymer of H2SO4, otherwise the lithium is an active metal and would react with the water
What is occurring at the cathode while a lithium - ion cell is charging? (Remember anode/cathode reversed)
Li+ + e- -> Li
What is occurring at the anode while a lithium ion cell is charging? (Remember anode/cathode reversed)
LiCoO2 -> Li+ + e- + CoO2
What is occurring at the anode while a lithium - ion cell is charging?
Li -> Li+ +e-
What is occurring at the cathode while a lithium - ion cell is charging?
Li+ + e- + CoO2 -> LiCoO2
What are the advantages of lithium - ion batteries?
high charge specific density, can hold charge better than other batteries, can withstand many recharge cycles, contain no heavy metals so they are considered safe for the environment
What are the disadvantages of lithium - ion batteries?
sensitive to high temperatures, damaged if allowed to run completely flat, they last only a few years, could explode if overheated or punctured
What is a Nickel - Cadmium battery?
Cell with a nickel (III) oxide hydroxide cathode and a cadmium metal anode
What determines the wavelength of light which a conjugated system absorbs?
the length of the conjugated system, the longer the system the longer the wavelength of light
What is electron conjugation?
The pi - electron clouds of adjacent double bonds partly overlap with one another and form a large cloud of delocalized electrons
What is a semi-conductor?
materials with electrical conductivity half way between conductors and insulators
What influences the conductivity of a semi-conductor?
temperature (increases conductivity)
What is a photovoltaic cell?
cell made of semi-conductors that can absorb photons of light resulting in electrons being knocked free from atoms and creating a potential difference
What are elements that are semiconductors, used in photovoltaic cells?
usually group 14 (ie. silicon or germanium) , maybe groups 13 or 15 (gallium arsenide)
