Sunny outlook for cheap hydrogen

A UK company plans to commercialise a process to use sunlight to produce hydrogen directly from water within the next six months.

The process uses a new type of photovoltaic device which is said to be cheaper to make than conventional solar cells. It combines the functions of generating electricity from sunlight, then using it to electrolyse water to split it into hydrogen and oxygen, into a single process.

The Hydrogen Solar Production Company or H2SPC, which holds the rights to the process, is being funded by venture capital firm E-Synergy for the first stage of commercialisation.

H2SPC chairman Julian Keable said the new process would be ‘cheaper, simpler and more affordable’ than using conventional solar cells made from silicon. He said the process would produce hydrogen on site on a sufficient scale to meet the needs of an individual car, avoiding transporting the gas.

‘Solar energy in the UK is not sufficiently concentrated to produce enough on a small filling station site to satisfy cars in any great numbers. But you could site the cells on something not hugely larger than a domestic garage to produce enough for an average car user’s needs,’ he said.

The new process depends on mesoscopic or nanocrystalline semiconductor materials whose molecular structure gives them an enormous internal surface area. They use oxides of titanium, zinc, tin or niobium which form crystalline arrays. The minute pores between the crystals are filled with a semiconducting or conducting medium.

This forms an extremely fine network and explains the substances’ conductivity. Dye may then be absorbed into the structure, to enhance the range of light wavelengths that can be ‘harvested’.

Two layers

H2SPC is concentrating on a ‘tandem cell’ approach, using two thin layers of different metal oxides for the two electrodes of the cell, again to enhance the range of wavelengths absorbed.

One electrode absorbs blue light and sets up a voltage, starting a current flowing and allowing water to be oxidised to oxygen and hydrogen ions. The second layer absorbs green and red light and makes electrons available to convert the hydrogen ions into hydrogen gas. The process has proved to be five to 10 per cent efficient in the lab.

Dr Andrew Stevenson, chairman of E-Synergy, said: ‘Our target is above 10 per cent.’ But he believed the process could be viable at between five to 10 percent efficiency because of the lower cost of the material, though cells would have to be larger in area. Manufacture of conventional silicon solar cells is more expensive and energy intensive.

The E-Synergy funding would allow scaling-up to an early-stage industrial process to demonstrate acceptable cost and reproducibility. ‘It will take us out of the lab to the real-world stage. It will take six months to be able to demonstrate the process on a commercial scale,’ said Keable. At that point, H2SPC expects to generate ‘more serious funding’.