Hydrogen Fuel Cells

What is a hydrogen fuel cell? A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent Hydrogen fuel cells (HFCs) are a type of electrochemical cell. HFCs generate electricity by reduction and oxidation reactions within the cell. They use three main components, a fuel, an oxidant and an electrolyte. HFCs operate like batteries, although they require external fuel. HFCs are a thermodynamically open system. HFCs use hydrogen as a fuel, oxygen as an oxidant, a proton exchange membrane as an electrolyte, and emit only water as waste.

FUEL CELLS MAJOR TYPES OF FUEL CELLS ARE PEM Alkaline PHOSPORIC ACID Molten carbonate Solid oxide Regenerative fuel cell

PEM FUEL CELL Proton Exchange Membrane (PEM) This is the leading cell type for passenger car application Uses a polymer membrane as the electrolyte Operates at a relatively low temperature, about 175 degrees Has a high power density, can vary its output quickly and is suited for applications where quick startup is required making it popular for automobiles Sensitive to fuel impurities

Alkaline Fuel Cell Used mainly by military and space programs Can reach 70% power generating efficiency, but considered to costly for transportation applications Used on the Apollo spacecraft to provide electricity and drinking water Uses a solution of potassium hydroxide in water as the electrolyte and operates at 75 -160 degrees Requires pure hydrogen and oxygen because it is very susceptible to carbon contamination Purification process of the hydrogen and oxygen is costly Susceptibility to poisoning affects cell’s lifetime which also affects the cost

PAFC FUEL CELL Phosphoric Acid This is the most commercially developed fuel cell It generates electricity at more than 40% efficiency Nearly 85% of the steam produced can be used for cogeneration Uses liquid phosphoric acid as the electrolyte and operates at about 450 degrees F One main advantage is that it can use impure hydrogen as fuel

How do they work? Fuel (H2) is first transported to the anode of the cell Fuel undergoes the anode reaction Anode reaction splits the fuel into H+ (a proton) and e- Protons pass through the electrolyte to the cathode Electrons can not pass through the electrolyte, and must travel through an external circuit which creates a usable electric current Protons and electrons reach the cathode, and undergo the cathode reaction

Chemistry behind the technology Oxidation At the anode of the cell, a catalyst (platinum powder) is used to separate the proton from the electron in the hydrogen fuel. Anode half-reaction: 2H2  4H+ + 4e- Eo = 0.00V Reduction At the cathode of the cell, a second catalyst (nickel) is used to recombine the protons, electrons, and oxygen atoms to form water. Cathode half- reaction: 4H+ + O2 + 4e-  2H2O Eo = 0.68V In electrochemistry, the Eocell value (energy) of a fuel cell is equal to the Eo of the cathode half-reaction minus the Eo of the anode half-reaction. For a hydrogen fuel cell, the two half reactions are shown above. So to calculate the energy of one fuel cell, we need to subtract the anode energy from the cathode energy. For a HFC, the Eocell = 0.68V – 0.00V which equals 0.68V

Benefits of Hydrogen fuel cell Physical Security Reliability Efficiency Environmental Benefits Battery Replacement /Alternative Military Applications

Problems regarding hydrogen fuel cells Lack of hydrogen infrastructure Need for refueling stations Lack of consumer distribution system Cost of hydrogen fuel cells 2013 Department of Energy estimated $30/kw Hyundai i35x costs around $50000 and price of this is going to be reduced for the promotion Carbon cost of producing hydrogen is high Problems with HFC cars Short range (~365miles) Warm up time (~5 minutes) Hydrogen occupies more volume than gasoline so less range

Uses of hydrogen fuel cells There are many different uses of fuel cells being utilized right now. Some of these uses are… Power sources for vehicles such as cars, trucks, buses and even boats and submarines Power sources for spacecraft, remote weather stations and military technology Batteries for electronics such as laptops and smart phones Sources for uninterruptable power supplies.

Conclusion Promising technology Most viable for niche market use in the near future The car’s would be in the market by 2015

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