12 March 2015

Artificial Leaf

Written by Published in Technology

Once again, nature provides inspiration and a simple solution in a complex crisis

We are all aware of the risk of climate change induced from ever-increasing man-made carbon dioxide emissions, arising from our reliance on fossil fuels. Clearly we need to move to a low-carbon society, but how can we do this, and what would such a society be like? We
must remember that the planet cares only about the total carbon emitted to the environment. Therefore delays in reducing our emissions today will only require us to reduce our emissions more significantly in the future. Action today is imperative to buy us time to develop solutions for the future.

There are significant and important efforts being made to lower our carbon emissions. The first step is to reduce our energy demand. Here, greater use of Smart Building Technologies, which better control the demand for heat and electricity in our homes, is important. For example, fridges which moderate their energy use to respond to demand on the electrical grid would greatly reduce the peak loads experienced by the electrical network, and therefore help us implement more renewable technologies such as wind and solar. Fuel cell-powered combined heat and power units are being developed to replace conventional central-heating boilers, which generate both heat and electricity for the home. These will reduce the carbon emissions from a UK home by around 20%.

The second step is to remove carbon completely from our electricity network. This can be achieved by a combination of measures: increasing our use of renewable-electricity generators such as wind and solar; adding nuclear capacity; and ensuring that carbon is captured and stored from coal- and gas-fired power plants–so-called carbon capture and storage, or CCS. Once this is achieved then we should encourage the use of electricity to replace other carbon-rich energy sources wherever possible. An important example would be to use electric vehicles for the urban travel that dominates the number of journeys we make. For longer trips we will be increasingly reliant on biofuels, but not biofuels produced from food. Rather we will use energy crops that can be grown in conditions not suited to food production, or recycle waste into fuel. There are processes being developed which can convert the waste paper produced in London into sufficient fuel to power all of London’s buses.

The third step is to reduce the carbon used to heat our homes. Here the best options are to burn biomass–often as part of district heating schemes by which many homes and buildings are heated from a central source – and to encourage the increased uptake of ground-source heat pumps, especially those powered by low-carbon electricity.

Finally, the last outstanding challenge is to harness solar energy to convert carbon dioxide itself back into useful fuels. Scientists and
engineers are already making rapid progress in using solar energy to split water directly to produce renewable hydrogen – hydrogen that can then be used to produce electricity in a fuel cell. But even more radical is the prospect of using solar energy to combine hydrogen with carbon dioxide to produce sugars and other fuels – so-called solar fuels. Professor Jim Barber at Imperial College London has termed this vision ‘the artificial leaf’, a process which mimics photosynthesis to convert our problem, carbon dioxide, into something we want, namely fuel. The Grand Scientific Challenge before us, the Holy Grail of chemistry, biology and engineering, not only offers a golden opportunity for riches and a Nobel Prize for whoever solves it but also, for the planet, a truly sustainable future.

Energy Futures Lab at Imperial College London

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