KK6 + KK7 - Faraday's laws and Green chemistry

Law 1

The amount of charge carried by a galvanic/fuel cell is directly proportional to the mass of anode lost/fuel used.

Law 2

The number of moles of electrons produced by a galvanic or fuel cell is directly proportional to the coefficient of electrons in the balanced oxidation half-equation.

Why should chemistry be green?

Principles of 'green chemistry' were developed, which focus on:

• Designing processes to minimises raw materials required and waste produced

• Using renewable, safe, and environmentally harmless materials where possible

• Maximising energy efficiency of reaction

Green chemistry principles

Goal 2: Zero hunger

Goal 6: Clean water and sanitation

Goal 7: Affordable and clean energy

Goal 9: Industry, innovation and infrastructure

Goal 11: Sustainable cities and communities

Goal 12: Responsible consumption and production

Goal 13: Climate action

Goal 14: Life below water

Goal 15: Life on land.

Use of catalysts

• Catalysts speed up reactions in fuel cells, decreasing the amount of time for energy to escape the system and be lost to the atmosphere

  • Increasing energy efficiency

• Most effective catalysts used in many fuel cells are non-renewable (inc. Platinum) - also very expensive

Electrode porosity and nanomaterials

• The smaller and more numerous the pores are, the higher SA = greater ability of reactants to come into contact with catalyses = increasing efficiency

• Nanomaterial are used as electrodes in some fuels to maximise reaction efficiency

combined heat and power

• Heat is a by-product the fuel cell and is captured and used to heat cars or buildings

• Overall energy efficiently of the system is improved by making use of heat that would go to waste

  • Usefulness of heating setups is subject to the climate and season

hybrid systems

• One source of inefficiency in fuel cells is that they continually produce energy so long as fuel is supplied

  • Less energy may be needed, meaning that the energy is left unconsumed and probs. Wasted

• fuel cells can be combined with other energy conversion and storage technologies such as batteries

  • stores excess energy, minimising energy lost.

polymer membrane electrolytes

• Fuel cells use membrane electrolytes

• proton-conductive polymers used to maximise the speed of ion movement = increase current efficiency

• Use polymers = prevent leakage and potential cross-contamination between fuel and oxidising agent streams

• give the cell greater temperature resilience - many membranes can operate at almost all temperatures.

  • while aqueous electrolytes may freeze in cold temperatures or evaporate if too hot

• Can be expensive and derive form non-renewable crude oil

operating conditions

• higher temperatures and pressures increase the rate of fuel cell reactions = increased efficiency

• Maintaining high temps. Require a lot of energy, decreasing the net energy efficiency of the cell

• aim to use the heat produced by the fuel cell itself to heat the system, minimising the quantity of external energy required

durability

• The more frequently fuel cells need to be replaced, the more time they spend offline = the lower their long-term efficiency

• This also reduces waste: another key principle of green chemistry