Galvanic Cells

Electrochemical Cell

A cell that converts chemical energy to electrical energy (or vice versa)

Galvanic Cell

A cell which converts chemical energy into electrical energy (used in mobile phones and laptops)

Battery

Combination Of Cells

Used to describe cells as well in common day language

External Cicrcuit

Wire that flows outside of the circuit connecting the electrodes

Why The Electrolyte In The Salt Bridge Is Unreactive

If it were reactive, it could participate in chemical reactions, form precipitates, alter cell potential

As it is unreactive, it is only a spectator ion

Spontaneous Reaction

No need for external energy

The reaction happens naturally, and by itself

Primary Cells

Cells that are used once, and cannot be recharged

Alkaline Cells

Cells that are non-rechargeable, once the equilibrium has been reached

Equilibrium

When there is a large chemical potential difference (EMF) between the anode and cathode

anode (has a large driving force to donate electrons)(

cathode (has a large driving force to obtain electrons)

The force slowly depletes as the battery discharges, and charges balance out

Potential Difference/Electromotive Force

In reference to the disparity between anode and cathode

One has a higher tendency to attract electrons, whilst one has tendency to donate

The force is referenced as voltage

Standard Electrode Potential

A standard E value for each half cell - how good a substance is at being reduced

Higher E value = greater tendency to loose electrons

Lower E value = greater tendency to gain electrons

Standard Hydrogen Half Cell (SHE)

Is the hydrogen half cell

Has a value of 0

Is considered a baseline

EMF

Electrode of high potential - Electrode Of Lower Potential

Limitations On The Predictions Of Redox Equations

In different conditions other than SLC - order in electrochemical series may be different

Does not indicate rate of reaction (can be very quick, or barely anything)

Direct Redox Equations (Reactants mixed together)

Heat energy is released

Products are made almost instantaneously

Rule For Predicting Whether Redox Reaction Will Take Place

Top left to bottom right

e.g. bromine solution is added to a solution

containing chloride ions

Find reduction potential

Whatever’s higher is on top

Whatever’s lower is below

Then establish top left bottom right - if not then no reaction

Fuel Cells

Type of galvanic cell that produces electricity from chemical energy

Are very efficient - create electricity with the by-product of only heat and water

Electricity is made for as long as fuel is supplied

Hydrogen Economy

A society is where hydrogen is used as a primary source of fuel

Used as a major carrier source - perhaps replacing fossil fuels entirely

Fuel Cell

Electrolyte In The Middle

Depending on medium, can have H+ ions or OH- ions

Electrodes

Are porous (have little holes in them)

Greater porosity leads to maximising the reaction

The reaction occurs in the small holes in the electrode itself - where the reactants interact with the electrolyte

What happens at electrode

For oxidation, protons and electrons split - electrons go through external wire

protons travel through electrolyte to cathode

By products are heat and water

How It Works (Acidic)

At anode, oxdiation occurs (electrons and protons are split)

The protons go through the electrolyte to the cathode

The electrons go through the external circuit to the cathode (because there is a potential difference)

The hydrogen and oxygen react at the cathode, forming water - water is produced in Cathode

Fuel Cell Annotated

Alkaline Fuel Cells

Instead of H+ ions, OH- ions are used

They go from Anode to Cathode

Water is produced at Anode - cathode produces OH- and it travels through electrolyte to react with hydrogen gas - water moves through electrolyte back to cathode

Key Parts in Alkaline Cell

Water is both used and made - less total output of water

Water is made at anode

Water moves through the electrolyte (though OH- goes the other way), and then reacts with cathode

Electrolyte In Half Equations

Appear in half equations, but not full equations

Efficiency Of Fuel Cells

More efficient (40-60%) than thermal energy (30-40%), and combustion engines (20-25%)

Waste product of steam (water) can be used to push turbines - electricity (efficiency is raised to 85%)

List Of Fuel Cells

Electrode Surface Area

Surface Area Of Electrode = current that can be drawn

More surface area - more reaction sites - more oxidation can occur - more electrons - more current

Catalysts

Typically Platinum - increases oxidation and reduction

Speeds up reaction

Common Electrolytes

Applications Of Fuel Cells

Making hydrogen-cell fueled vehicles

Will play a key role in transitioning from fossil fuels to sustainable energy sources

Adv vs Disadv of fuel cells

Limitations of usage of biofuels

Biodiesel and bioethanol - require food sources to produce enough energy

Supplying 10% of energy required = sacrificing 30% of agricultural land for energy purposes

Biogas - Not enough energy content (low energy density)

Hydrogen Production

Can be renewable or non-renewable

Steam Reforming

95% of Hydrogen is made this way

Methane is reacted with very hot steam to produce Carbon moxoide and hydrogen

Is done again to produce H2 gas

Steam Forming Image

Steam Reforming Products

Hydrogen has lower energy content than normal hydrogen (some energy is lost as heat)

CO₂ emissions can be stored underground - geosequestration

Other Forms Of Hydrogen Production

Using electrical energy to sperate the Hydrogen from water

Using biomass from landfill - turning that into biogas and doing steam reforming (preferable to do sustainably)

Storing Hydrogen

Liquid Hydrogen, Compressed Hydrogen, Material Based Storage

Liquid Hydorgen

Hydrogen is liquefied and is used as a liquid fuel - vehicles need larger fuel tank for satisfactory usage

Is less energy dense

Material Based Storage

Hydrogen adsorbs onto a metal, and desorbs when required

Can release hydrogen when required

Can store hydrogen at lower pressure and smaller volumes

Compressed Hydrogen

Keeping hydrogen in its gas form

Must be large in size - as energy density is low

Designing Better Fuel Cells

Avoiding electrode materials posign environmental and humanitarian risks - e.g. not using nickel or cobalt (are being mined by those in extreme labour conditions)

Moving from linear economy - circular economy

Linear Economy - Circular Economy

Optimal use and reuse of resources (fuel cells are on-par with this idealogy)

Green Principles In Relation To Sustainable Fuel Production

design for energy efficiency

use of renewable feedstocks