Natural photosynthesis is the inspiration but solar fuels will not be produced by imitating it in detail. Natural photosynthesis has two stages: water splitting – producing hydrogen and oxygen – and carbon dioxide reduction to yield hydrocarbons and hence the panoply of organics. For now the emphasis is on water splitting: “fuel from air and water” is already a commercial operation where cheap electricity from hydrothermal sources is used for water splitting and carbon dioxide is then reduced to organics by the hydrogen. But to be able to produce hydrogen from sunlight would be a game changer for the whole world.
Now Michael Grätzel’s team at Lausanne (of fuel-cell fame) have coupled a perovksite solar cell to a cheap water-splitting catalyst to produce solar hydrogen with a 12.3% solar energy:hydrogen efficiency (natural photosynthesis is less than 1% efficient).
Tantalisingly, the new system so far meets only three of the requirements for a commercial process: efficient, cost-effective, scalable, and stable through many cycles. The perovskite solar cells fall at the last hurdle and urgent work is now being done to address this.
Science, 26 September 2014, pp. 1566-7; 1593-6.