Every cloud has a silver lining: wet weather could soon be harnessed as a power source, if a team of chemists in Brazil is to be believed.
In 1840, workers in Newcastle upon Tyne, UK, reported painful electric shocks when they came into close contact with steam leaking from factory boilers. Both Michael Faraday and Alessandro Volta puzzled over the mysterious phenomenon, dubbed steam electricity, but it was ultimately forgotten without being fully understood.
Fernando Galembeck at the University of Campinas in São Paulo, Brazil, is one of a small number of researchers who thinks there is a simple explanation, but it involves accepting that water can store charge – a controversial idea that violates the principle of electroneutrality. This principle – which states that the negatively and positively charged particles in an electrolyte cancel each other out – is widely accepted by chemists, including the International Union of Pure and Applied Chemistry (IUPAC).
"I don't dispute the IUPAC statement for the principle of electroneutrality," says Galembeck. "But it is seldom applicable to real substances," he says, because they frequently show ion imbalances, which produce a measurable charge.
His team electrically isolated chrome-plated brass tubes and then increased the humidity of the surrounding atmosphere. Once the relative humidity reached 90 per cent, the uncharged tube gained a small but detectable negative charge of 300 microcoulombs per square metre – equating to a capacity millions of times smaller than that of an AA battery.
The Victorian workers would have had to have been particularly sensitive souls to complain of such a shock, but Galembeck thinks his study shows steam electricity may be a credible phenomenon.
He thinks the charge builds up because of a reaction between the chrome oxide layer that forms on the surface of the tube and the water in the atmosphere. As the relative humidity rises, more water condenses onto the tube's surface. Hydrogen ions in the water react with the chrome oxide, leading to an ion imbalance that imparts excess charge onto the isolated metal.
The work finds favour with Gerald Pollack at the University of Washington in Seattle. Last year he suggested that pure water could store charge and behave much like a battery, after finding that passing a current between two submerged electrodes created a pH gradient in the water that persisted for an hour once the current had been switched off. He says this is evidence that the water stores areas of positive and negative charge, but the experiment led to a lively debate in the pages of the journal Langmuir (see links below) over whether the results really violated the principle of electroneutrality or whether there were salt impurities in the water that led it to behave like a conventional electrochemical cell.
Pollack calls the Campinas team's work "interesting". "It opens the door to many new possibilities," he says.
Power from air
Galembeck thinks those possibilities include harnessing atmospheric humidity as a renewable power source, as light is converted to electricity in solar panels. "My work is currently targeted to verify this possibility and to explore it," he says. However, he acknowledges that most researchers remain to be convinced that what he calls "hygroelectricity" will ever get off the ground.
Allen Bard at the University of Texas falls within that majority. "In general I think that it is true that our understanding of electrostatic phenomena and charging at solid/gas interfaces is incomplete," he says. "I am, however, very sceptical about these phenomena being harnessed as a power source. The amounts of charge and power involved are very small."
References: Galembeck presents his work at a national meeting of the American Chemical Society in Boston this week; it was previously published in Langmuir, DOI: 10.1021/la102494k. Pollack's work was published in Langmuir, DOI: 10.1021/la802430k; the resulting debate in the journal can be followed here, here and here.
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