Hydrogen Fuel Cells

A good mate of mine Angus, a rev head, recently pointed me to Top Gear's test drive of the new hydrogen fuel cell -powered Honda FCX Clarity.

Someone has helpfully posted the segment on YouTube. The rather hysterical YouTube-esque commentary makes some ridiculous, and some legitimate, criticisms of the Clarity, as well as of hydrogen powered vehicles in general.

With water the only waste product, Hydrogen seems at first glance to be the perfect fuel. In addition, it is often pointed out that "hydrogen is the most abundant element in the universe".

Though true, this statement is deliberately misleading when made by proponents of hydrogen power. It is equally true and equally misleading to say that oil grows on trees! (Or rather as trees, so to speak.) To be a useful fuel, hydrogen is required in its elemental gaseous form, H2, which this does not exist naturally on Earth. It must be extracted, at considerable energy cost, from some hydrogen-containing material (such as water, coal or oil).

This point is very important. Naturally-occurring hydrogen is everywhere, but is not an energy source. Energy must be expended to extract this universal hydrogen and convert it to H2. In this form, the energy is stored for later release - but thanks to the laws of thermodynamics, we can never get it all back again.

Thus in effect, the basics are no better than for a regular battery. We simply burn fossil fuels to make the hydrogen, instead of to run the car – and losing something in the process! These losses are manifested in the "well-to-wheel" efficiency of the fuel cell vehicle, as pointed out in this battery-electric car plug posted here on Change2.

Even if charged using coal-fired electricity, an electric car has lower carbon emissions than petrol-driven ones. The reason for this is that both regular car engines and coal-fired power plants are examples of thermal engines, whose efficiencies are limited by the temperature at which they operate. Higher temperatures give better efficiencies, and a coal plant operates at about 500 °C; a car at 90 °C.

Electrochemical (including battery and fuel cell) vehicles are not limited in this way. Therefore the higher energy efficiencies of both the power plant (assuming reasonably modern technology) and the electric vehicle, translate to a net reduction of emissions.

Unfortunately however, the H2 cars pay twice: First in making the power to make the hydrogen, then in using the hydrogen to power the vehicle, meaning much more coal needs to be burnt to power an H2 vehicle than a battery one.

In spite of this, there are some very good reasons why cars based on hydrogen fuel cells make good sense, and why we should not begrudge Honda their poetic license in calling the FCX "green".

Grid power won’t always be primarily fossil fuel-based (we hope!). If we use a carbon-free electricity source, from an emissions point of view we don’t care how much we need to make the H2. There are also very promising developments suggesting that H2 could be produced, from water, in a carbon-free manner and far more efficiently than is currently possible.

Meanwhile, changing to grid-powered cars (regardless of how that power is delivered) is a crucial component of the transition to a low-carbon economy. For these to be adopted by the mass market, a product is required that delivers performance and convenience approaching people's current expectations.

Apart from the clear superiority in performance of the fuel cell vehicle, the big bonus is the "fill it up" capability. The electric car needs to be charged – a process needing hours – at the end of its maximum range of around 200km. In the fuel cell, the charging is replaced by "filling up" with H2, delivered to the vehicle at about the same rate as petrol would be.

There is also an important additional point. Criticism of fuel cells on the basis of problems with hydrogen ignore that whilst H2 is potentially the cleanest fuel, the fuel cells can be easily made to operate on liquid fuels such as methanol – which is much more easily produced, stored and distributed than H2. A methanol fuel-cell car will still emit far less CO2 than a petrol engine – leaving an 'out' if the H2 infrastructure fails to materialize soon enough.

Honda has thrown down the performance and convenience gauntlets with their FCX, against the high efficiency of battery-electric vehicles. Ultimately the question, “which kind of electric car” will be answered by the market. The only important factor from an environmental perspective is how many people will drive them, and the more competition the better.

Change 2 contributor Dr Miles Page is an Australian scientist who has been working at the international coalface of the emerging Energy Revolution. After receiving his PhD from Sydney University, Dr Page held senior research positions with the Atomic Energy Commission in Paris and the Max Planck Institute in Potsdam. He has spent the past 3 years in Israel researching Thin Film Solar Cells at the Weizmann Institute of Science and developing alternative Fuel Cells.