Artificial leaf mimics photosynthesis, converts solar into hydrogen

22 March 2016
By Jack Loughran
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The artificial leaf is composed of five layers: silicon (black), silicon oxide (gray), an 'intermediate' layer (yellow) and the protective layer (brown)

The artificial leaf is composed of five layers: silicon (black), silicon oxide (gray), an 'intermediate' layer (yellow) and the protective layer (brown)

An ‘artificial leaf’ that converts sunlight directly into hydrogen to be used for energy production has been developed by a German team.

The leaf consists of a solar cell that is combined with further functional layers that act as electrodes and are coated with catalysts.

If the complex system of materials is submerged in water and illuminated, it starts to break down water molecules into their constituent parts.

The process converts 12 per cent of the solar energy into hydrogen which is an effective way to store solar energy in chemical form.

However, the team from the energy research centre at the research institute, Helmholtz-Zentrum Berlin, say there are still a number of problems to overcome.

Sufficient light needs to reach the solar cell in order to create the voltage for water splitting which is partly hindered by the additional layers of material.

In addition, the semiconductor materials that the solar cells are generally made of are unable to withstand the typically acidic conditions of the process for long periods of time.

The artificial leaf therefore needs a stable protective layer that has to be simultaneously transparent and conductive.

The team worked with samples of silicon, a semiconductor material that acts as a simple solar cell to produce a voltage when illuminated.

Materials scientist Anahita Azarpira, who worked on the project, prepared these samples in such a way that carbon-hydrogen chains on the surface of the silicon were formed.

"As a next step, I deposited nanoparticles of ruthenium dioxide, a catalyst," she explained.

This resulted in the formation of a conductive and stable polymeric layer only three to four nanometres thick.

The ruthenium dioxide particles in this new method allowed for the simple development of an effective organic protective layer which is normally very complicated to produce.

This allows the catalyst to do its normal job of accelerating the partitioning of water into oxygen and hydrogen.

The silicon electrode protected with this layer achieves solar-to-hydrogen efficiency of about 12 per cent but the team has also considered using a graphene layer.

Chinese researchers recently demonstrated another type of artificial leaf that is capable of removing toxic pollutants from waste water while scientists in 2013 showed off a self-healing leaf that can produce energy.

In November, E&T Magazine looked at a new eco-friendly type of energy production that artificially emulates the photosynthesis processes.

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