Dye Sensitized NiO Photocathodes for Solar Fuel Generation

The arguments for converting sunlight and H2O to H2 to provide cleaner fuels and chemicals are very powerful. However, there is still no efficient means of direct solar energy conversion to H2 on a large scale, despite a large research effort worldwide.  Our project seeks to develop a direct photocatalytic device, which offers a low-cost and sustainable alternative to the existing technology.

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Porous NiO is printed on conductive glass and stained with dyes to drive the reduction of water to hydrogen using sunlight.

There is enormous pressure to deliver a low cost, emission-free, highly efficient and sustainable alternative to H2 production from steam reforming. Each year, 475 billion cubic metres of H2 are consumed. Most of this is used to refine petrochemicals, with the rest used for producing ammonia, refining metals and food. The demand for sustainable and clean power is one of the greatest challenges facing humanity and many believe H2 will play a major part in our energy portfolio in the future. With increasing fuel prices, political tension surrounding supply and regulations on CO2 emissions there is a huge economic, political and environmental drive for alternative, sustainable production of hydrogen.

The most abundant source of hydrogen is water, but we lack at present a practical and cheap way of reducing water to hydrogen on a large scale. We could employ electrolysis, using hydroelectricity and offshore wind, but this would be expensive and there is insufficient power available from these technologies to satisfy the demand.  And while the electrical power from solar cells can be used to drive a conventional electrolyser, the reduction of water with platinum or semiconductors is slow, so better catalysts must be found.

A direct photocatalytic alternative would avoid the fabrication and systems costs required with existing technology, and this is what our project seeks to achieve. Building on our work to develop dye-sensitized solar cells that convert sunlight to electricity, we are modifying our porous NiO-based electrodes to use light to convert water to hydrogen.

At the heart of our device is a porphyrin dye, similar to pigments used by nature in photosynthesis. The dye absorbs the energy in sunlight and uses it to drive the extraction of charges from a NiO semiconductor, which are then consumed in the reduction reaction producing H2.

Using chemistry to convert sunlight into fuel in a cheap, sustainable way will have enormous global impact on society. In particular, it will allow the decentralisation of energy distribution so that the needs of the developing world can be met quickly without requiring heavy infrastructure.

Dr Elizabeth Gibson
University of Nottingham

Dr Gibson was awarded a Leverhulme Trust Research Project Grant in March 2013.