Energy Storage - Hydrogen Batteries Flashcards
Steam Reforming
This is used to produce H2 from hydrocarbons like methane and propane, with their reaction with steam over a catalyst produces H2 and CO2.
Electrolysis
This is the solvent flow resulting from application of an electric field across a solution next to a charged surface.
How can electrolysis be done?
In an Electrolytic Cell with two electrodes in a water/electrolyte solution, where battery/DC power supply connectes electrodes.
What two electrolytes are often used in steam reforming?
NaOH or KOH.
Process of Electroylsis?
Water at cathode reduced forming H2 and 2OH.
H2O oxidised to O2 and H+ at anode, with 4H+ +4e
What reactions are involved in first step in Electroyliss?
Elctron transfer from one molecule to another by catalyst, causing H2O ionisation, or water reduction by proton transfer between 2 H2O
Why does ionization in electrolysis occur?
Polar covalent bonds of water where O is more electronegative.
Why is hydrogen attractive?
High energy density.
Only H2O as byproduct.
Process of hydrogen battery mechanism?
H2 is oxidized at the anode, forming a proton and electrons creating electrical currents, H2 combining with O2 forming H2O.
Why does hydrogen have high energy density?
It is the smallest element, so a mass of hydrogen has many atoms.
Why is weak H2 important?
Easy to break with energy release.
What is the electronic structure of H2?
In ground state, electron in 1s orbital.
What happens when H2 orbitals overlap?
Bonding and Antibonding molecular orbitals form, with lower and higher energies relative to seperate protons.
Where are the electrons found in overlap?
Bonding orbital, being lower energy state than two seperate hydrogens.
Why is H2 bond weak?
Small energy difference between antibonding and bonding orbitals.
How do the molecular orbitals form?
Constructive and Destructive interfenreceo fhteir two individual wave functions.
Properties of bonding orbital?
Constructuve interference where electrons attracted to both nuclei with stabilizing effect.
Why does repulsion in antibonding orbital occur?
Opposite signs of the wave function in regions between two nuclei.
What causes electrons to move into antibonding orbitals?
Excitation by energy due to weakness of H2 bond
Structure of antibonding wavefunction?
Molevular orbital has electron density in antibonding between two nuclei.
What determines stability in between the nuclei?
Wavefunction is related to phase of electron waves(probability of finding an electron in a region of space)
Wavefunctions in bonding molecular orbital?
Same sign meaning probaiblity of finding electrons in the region between nuclei is increased, attracting both nuclei, being stable.
Wavefunctions in antibonding molecular orbital?
Opposite sign wavefunctions decrease finding electron chance.
Why does increasing probability of finding electrons resuit in lower energy?
More likelihood both electrons are attracted simultaneously by both protons.
