Artificial leaf device produces hydrogen in water using only sunlight

This technology, which has been named artificial photosynthesis, was inspired by photosynthesis which occurs naturally (a process in which plants use sunlight to transform organic material into organic compounds, freeing chemical energy stored in the bonds of the molecule adenosine triphosphate-ATP, and obtaining energetic compounds such as sugars or carbohydrates).

The efficient production of hydrogen using semiconductor materials and sunlight constitutes a crucial challenge to make a paradigm shift towards sustainable energy technology, using inexhaustible resources that are environmentally friendly. "Although the energy efficiency of the device is still not sufficient enough for us to consider marketing it, we are exploring various ways to improve its efficiency and to show that this technology represents a real alternative to meet the energy demands of the 21st century," comments Sixto Giménez, one of the researchers responsible for the investigation.

Hydrogen is an extremely abundant element on Earth's surface, but in combination with oxygen: water (H₂0). The hydrogen molecule (H₂) contains a great amount of energy that can be released when burned due to the reaction with atmospheric oxygen, creating water as the result of this combustion process. In order to convert water into fuel (H₂), the H₂O must be broken down into its separate components and so that the process can be carried out in a renewable way (without using subsoil fossil fuels), it is necessary to use a device which relies on solar power, and with no other assistance, to provoke the chemical reactions to break the water and form hydrogen in a way similar to leaves on plants. For this reason these devices are named artificial leaves.

The device is submerged in an aqueous solution which, when illuminated with a light source, forms hydrogen gas bubbles. Firstly, the research group used a solution with an oxidizing agent and studied the evolution of hydrogen produced by photons. "Now the biggest challenge," comments Iván Mora, member of the team developing the solution, "is to understand the physical-chemical process which is produced by the semiconductor material and its interface with the aqueous medium in order to streamline the device process."

The development of the artificial leaf is a great scientific challenge due to the difficulty posed by the selection of materials that will be used in the process, working continuously and not decomposing. Currently, the Photovoltaic and Optoelectronic Devices group from the Universitat Jaume I is one of the few research groups on an international level that has shown the viability of a device with these characteristics, together with the North American laboratories from MIT in Boston or NREL in Denver. The research group leader, Juan Bisquert, comments that "in comparison to other devices, that which has been developed by the UJI has the advantage of low production costs and a large collection of incident photons of light, used in the production of hydrogen photons in the infrared spectrum."

In experiments of this device, the following research group members have participated: Eva Maria Barea, Francisco Fabregat, Roberto Trevisan, Maria Victoria González, Pau Rodenas, Pablo P. Boix and Laura Badia.