All about Fuel Cells

Heralded as the saviour to our global warming woes, just how do fuel cells work and do they measure up? Ashton Mills explores.

Fuel cells boast a wide range of implementations, but the most popular example you’ve probably heard of is the hydrogen/oxygen variety.

The reason you have heard so much about hydrogen/oxygen fuel cells is because they are in many ways the Holy Grail of energy production – hydrogen is the most abundant element in the universe, which obviously means that we have a plentiful supply, and the by-product of hydrogen/oxygen fuel cell reactants is water, which is about as clean as you can get.

Origin of the fuel cell
In recent issues we’ve covered many cutting-edge technologies that have their roots in the past, and fuel cells are no different. The first fuel cell was built by William Grove in 1843 – though he called it the gas voltaic battery – and while there was steady development over the next 100 years, they gained mainstream acceptance when NASA picked up the technology for its space program in the 1960s. Fuel cells are still used today for spacecraft where they produce both electricity and drinking water from the onboard supplies of hydrogen and oxygen.

Named after the Hindi word for magic, Jadoo is big in fuel cell development.

How they work
Fuel cells are an electrochemical energy conversion system that have a structure not too dissimilar to a normal battery – there’s an anode and a cathode as well as a fuel, oxidant, and an electrolyte. The key difference between a fuel cell and a battery is that a fuel cell consumes its reactants, and they need to be replaced. However assuming a continuous flow, and combined with the fact that fuel cells have no moving parts, they have the potential to produce continuous energy almost indefinitely.

Smaller than a Euro cent, but a whole lot more valuable.

Fuels can be hydrogen, methanol, diesel, and even zinc. Oxidants are usually oxygen, chlorine, or chlorine dioxide. The hydrogen/oxygen reaction is outlined in the diagram below.

Hydrogen/oxygen fuel cell. Source: Wikipedia.

This type of cell is typically called a PEMFC, or proton exchange membrane fuel cell, the most popular type of fuel cell in use. Hydrogen is fed into the cell where it reacts with the anode – a metal coated with a platinum catalyst – that causes the hydrogen to split into positively charged hydrogen ions and negatively-charged electrons. The polymer electrolyte membrane (PEM) allows the positively-charged ions to pass through it to the cathode side, where they combine with electrons from an external circuit and oxygen being fed into the cell along the cathode catalyst to produce water and heat. The negatively-charged electrons from the hydrogen reaction can’t pass through the PEM and are forced around the membrane to an external circuit – an electrical current.

Individually the cell doesn’t pump out a huge amount of current, so the cells are stacked and linked in series or parallel to form fuel cell stacks. Depending on the design, a PEMFC can produce between 100W and 500kW.