APES 6.11 Hydrogen Fuel Cell

Enduring Understanding:

• Humans use energy from a variety of sources, resulting in positive and negative consequences.

Learning Objective:

• Describe the use of hydrogen fuel cells in power generation.
• Describe the effects of the use of hydrogen fuel cells in power generation on the environment.

Essential Knowledge:

• Hydrogen fuel cells are an alternate to nonrenewable fuel sources.  They use hydrogen as fuel, combining the hydrogen and oxygen in the air to form water and release energy (electricity) in the process.  Water is the product (emission) of a fuel cell.
• Hydrogen fuel cells have low environmental impact and produce no carbon dioxide when the hydrogen is produced from water.  However, the technology is expensive and energy is still needed to create the hydrogen gas used in the fuel cell.

Process

• Hydrogen fuel cells are an alternative to nonrenewable fuel

• Hydrogen fuel (H2) is added to the cell

  • This can be in liquid or gas form

• In the first reaction layer, hydrogen molecules are split into protons (H+) and electrons (-)

• Protons and electrons take different paths through the cell

  • Protons move across the membrane
  • The electrons are free to take an alternate route, creating a flow of electric current
  • After being used and having switched from negative to positive charge, they are returned to the cell for the next step

• In the second reaction layer, oxygen molecules (O2) are split and combine with the protons and electrons

  • This produces water vapor which is released
  • Water is the only byproduct of hydrogen fuel cells

Sourcing

• Hydrogen is usually found in compounds, like water and natural gas

• very rarely, hydrogen gas in the form we want is found in nature, so there are two methods that we most commonly source it from

• By a process known as electrolysis, where an electric current is used to split water into hydrogen and oxygen

• By splitting methane (CH4) from natural gas using heat

  • This does, however, result in CO2 pollution

• Since it requires energy or heat to create the hydrogen gas, the net energy from hydrogen as a fuel source is decreased

Battery-like

• The process is like a typical battery
• A chemical reaction occurs inside the cell to create an electrical current
  • In a typical battery, the chemicals are in a closed container and can only react so much
  • Once depleted, a regular battery must be recharged or discarded
• In a hydrogen fuel cell, the chemical reactants can be added continuously because the container is “open”
  • The fuel does not “go dead”

Fuel Cell Vehicles (FCV)

• This is the primary use for hydrogen fuel cells at the moment, especially for larger utility vehicles
  • Larger vehicles are not well suited to be electrically powered because of their size but hydrogen cells have an efficient enough output to sustain them

Consequences

Positive

• There are no CO2 emissions if produced from water
• The electricity produced from HFC is more efficient that internal combustion

Negative

• The technology is very expensive because it is new
  • Research and development costs are involved
  • Production costs will drop as more are manufactured, but they have yet to become very popular
  • Platinum and other rare earth minerals are used as catalysts, which increases the cost
• Producing hydrogen fuel for the cells, if sourced from fossil fuels, is not clean

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