Artificial Leaves Generate Hydrogen

Hydrogen has long been regarded as the ultimate green fuel by alternative energy gurus as it is rich in energy and fully carbon neutral. One of the biggest obstacles to hydrogen energy is the amount of electricity required to split hydrogen atoms away from oxygen in water. The electrolyzers currently available are intended for strictly industrial uses, require a very specific environment, and are very expensive. To confront these challenges, Chinese scientists have taken an entirely innovative approach in designing an artificial, fully inorganic leaf which mimics photosynthesis to split water and generate hydrogen.

Researchers at Shanghai Jiao Tong University have managed to create a miniature hydrogen factory by duplicating the photocatalytic hydrogen producing processes which exist within green leaves by utilizing their intricate micro-architecture to form a biotemplate. This artificial scaffold is able to carry out the organic leaf's tasks of light harvesting, separation of a photoinduced charge, and catalysis.

The process calls for various leaves to be used as a form of template. The leaves are treated with diluted hydrochloric acid and titanium trichloride which has the surprising effect of replacing the magnesium atoms in the porphyrin ring of chlorophyll (which are a critical component of photosynthesis) with titanium atoms. The leaves are then dried and heated to 934°F (500°C) to cremate any remaining organic material leaving only a skeletal framework of crystallized titanium dioxide.

Interestingly enough, titanium dioxide is a common element in solar photovoltaic cells to increase their efficiency, and in this crystalline scaffold which was once a leaf, it acts as a catalyst in splitting water molecules.

The basic structure retains the features critical to photosynthetic processes such as the surface cells that resemble lenses in order to capture light from all angles, and the vein structures which direct light deep into the leaf itself.

The precision of the process in preserving microscopic features is truly remarkable. The titanium framework even has the original thykaloids which are structures that add surface area to aid photosynthesis and are barely 10 nanometers in thickness.

Once the leaf is thoroughly morphed into a titanium crystal form, it is immersed in a 20 percent methanol solution and exposed to visible light at a spectrum close to the ultraviolet. The methanol acts as a catalyst for the photosynthesis-like process and pure hydrogen is released.

This artificial photosynthetic leaf is far more efficient than current means of generating hydrogen: it absorbs over 100% more light and produces more than 200% more hydrogen as a common commercial method utilizing titanium dioxide P25.

The researchers indicate that this titanium micro-scaffold process could represent a critical first step towards the creation of innovative solar energy transduction artificial structures which are based on entirely biological concepts.

It seems to make sense that we should harness the mechanisms which have been capturing light efficiently for billions of years on this planet, and it seems that the deeper we look into the micro-structures of leaves, the closer we arrive at a time when photosynthetic processes will be able to fuel the energy needs of not just our bodies, but our society as well.

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