Unit 6.11 - Hydrogen Fuel Cell

Question 1

Hydrogen Fuel Cell Basics

Answer 1

• Use hydrogen as a renewable, alternative fuel source to fossil fuels
  - H2 gas and O2are the inputs used to generate electricity; H2O is given off as a waste product
• H2gas enerts fuel cell where its split into Protons (H+) and electrons (e-) by an electrolyte membrane that only lets protons pass through
  - electrons take an alternative route (circuit) aound the membrane, which generats an eectric current
  - O2molecules enter fuel cell break apart into individual O atoms and combine with two hydrogens (H+) to form H2O as a by product (only emissions from fossil fuel cells)
• Most common application is vehicles
  - replaces gasoline (non-renewable,GHGreleasing, and air pollutiong) with H fueld (no air popllutants released and only H2O vapor)

Question 2

Creating H2 Gas

Answer 2

• Key challenge to hydrogen fuel cells is obtaining pure hydrogen gas (because it doesnt exist by itself as a gas naturally)
  - seperating Hh2 gas from othe rmolecules like H2O or CH4 is very energy intensive
  - two main processesa re steam reforming (95% of all H production) and electrolysis (less common but more sustainable)

Question 3

Steam Reforming

Answer 3

• Burning natural gas (CH4) and using steam o separate the H gas from the methane (CH4)
  - Emits CO2 and requires NG (fossil fuels) input

Question 4

Electrolysis

Answer 4

• Electrical current is applies to waer breaking it into O2 and H2
  - no CO2 emission, but does rewuire electricity

Question 5

Pros of Hydrogen as an energy carrier

Answer 5

• because H2 gas can be stored in pressurized tanks, it caan be transported for use creating elecricity later in a different location
  - unlike solar, hydro, and wind where te electricity must be used as soon as it’s generated and relatively closely to the location of generation
• can also be used as a fuel for vehicles (replacing gasoline) or to create ammonia for fertilizer, or in the chemical industry
  - As a gasoline replacement, it emits noa ir pollutants (NOx, PM, CO) and only H2O (technically GHG) no CO2
  - Manufacture of many different industrial chemicals requires H2 gas
  - Can be stores as liquid or gas, making it easy to transport
  - H fuel cells are about 80% efficient in converting chemical energy inH2 and O2 into electricity (coal power plants = 35% efficient)

Question 6

Cons of Hydrogen Fuel Cells

Answer 6

• Since 95% of H2 production requires methane (CH4), H fuel cells are based on a non-renewable and CO2 releasing energy source
  - if electrolysis is used to produce H2 its only as sustainable as the electricity source
  - widespread H fuel cell use would require building widespread H distrubiting network (similar to current system for gasoline)
  - H fuel stored in gas form in vehicles would reqire much larer taks than current gasoline tanks