‘Fuel cells, which generate electricity by combining hydrogen and oxygen, are poised to become the leading energy sources of the 21st century, offering a clean and efficient solution to the problems of global warming, air pollution and energy shortages.’ So states a press release announcing a website ‘for the global fuel cell community . . . offering support for every single fuel cell organisation, application and technology’.
Maybe you share my surprise at how often the fuel cell is described as a hydrogen-oxidation or hydrogen-combustion device that benignly produces only electricity, heat and water. Even people who know better (such as the highly authoritative sponsors of that website) let their publicists indulge in this simplism.
I have a dictionary of energy technology, a volume brought out by a reputable scientific publisher, that defines a fuel cell as an electrochemical cell that ‘operates by using the energy of a spontaneous chemical reaction, eg the combustion of a carbonaceous, hydrogen or hydrocarbon fuel by oxygen from the air’. The words in quotation marks could equally be said of a heat engine, which is something that a fuel cell is not. The dictionary goes on to declare that the only product of the instanced fuel-cell combustion is water. Surely this could be true only for the hydrogen fuel; and water would equally be the sole combustion product of a heat engine fed pure hydrogen and oxygen (other things, too, would emerge from combustion with air).
McGraw-Hill’s Concise Encyclopaedia of Science and Technology, on the other hand, explains clearly that, ‘in principle, the nature of the reactants is not limited’, although ‘the fuel-cell reaction almost always involves the combination of hydrogen with oxygen’. The Encyclopaedia Britannica is likewise clear, pointing out that fuel cells differ from other electrochemical cells in that the chemicals for each cell’s two electrode processes are stored separately and supplied on demand. The reactants can be any materials that can combine with or remove oxygen molecules, concedes the encyclopaedia, but it adds that ‘the simplest fuel cell to describe, construct and understand is one that operates on hydrogen and oxygen’. From that relative simplicity temptation follows for pop science purveyors, and marketeers.
The temptation ought to be resisted. There is enough valid information about. To pluck one example from those I have immediately to hand: at the Seventh Grove Fuel Cell Symposium (London, September 2001), Professor Ray Gorte of Pennsylvania University discoursed on solid oxide fuel cells operating on synthetic diesel and other hydrocarbon liquid fuels that are directly and stoichiometrically oxidised to form carbon dioxide and water. To pluck another: according to a report from the IEA Clean Coal Centre, also in 2001, developers have been focusing initially on natural-gas-fuelled cells for stationary power-generating plant but (to spoil my thesis) future systems could be fed with hydrogen derived from coal, biomass and waste. Two or three years ago, I find with a third (and also spoiling) pluck, Toshiba of Japan were commercialising a fuel cell that ran on hydrogen derived from animal waste.
Plainly hydrogen is still a favourite, even if it comes from fossil fuels or other, relatively exotic, sources that are processed either by separate chemical ‘reforming’ plant or, as in vehicle fuel cells, by bolt-on ‘reformers’.
But the case for fuel cells against heat-engine-driven generators should not rest on the cell’s supposed preference for hydrogen. A taste for that fuel can be acquired by heat engines.
The most outlandish fuel cell I have come across is a US invention reported in a very respectable international business newspaper. Acronymed Oscar (ocean sediment carbon aerobic reactor), this cell is apparently fuelled with plankton (as the, mainly microscopic, little creatures that live in great numbers at various depths in the sea are collectively known). Plankton is, in the newspaper’s words, ‘connected to dissolved oxygen in the sea water by electrodes, allowing electrons to flow in the same way as in conventional cells’.
One of my editorial colleagues was much moved by this story and he politely sought details of Oscar from the US source cited by the newspaper – the Office of Naval Research, Arlington, Virginia – but alas he received no reply. So we are left to guess whether hydrogen is somehow extracted from the planktonic matter or whether the whole brineborne sedimentary lot is viable reactant.
It is well known that whales feed voraciously on plankton. Perhaps future subsea power stations will feed on it too.