Artificial Photosynthesis

Artificial photosynthesis is a chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term is commonly used to refer to any scheme for capturing and storing the energy from sunlight in the chemical bonds of a fuel (a solar fuel). Photocatalytic water splitting converts water into protons (and eventually hydrogen) and oxygen, and is a main research area in artificial photosynthesis. Light-driven carbon dioxide reduction is another studied process, replicating natural carbon fixation. 

The photosynthetic reaction can be divided into two half-reactions (oxidation and reduction) , both of which are essential to producing fuel. In plant photosynthesis, water molecules are photo-oxidized to release oxygen and protons. The second stage of plant photosynthesis is a light-independent reaction that converts carbon dioxide into glucose. Researchers of artificial photosynthesis are developing photocatalysts to perform both of these reactions separately.

Here's how the reaction works: 

 
First of all, the photo-electrode is filled with water and illuminated. The light is absorbed, and the water molecules react, producing electrons, oxygen molecules, and hydrogen ions. The electrons move through wires to a catalyst electrode, where they react with CO2 and hydrogen ions in presence of metal catalyst and light. This reduction reaction produces organic substances, mainly formic acid. In addition, by designing the material for the metal catalyst, it's possible to vary the type of organic substances produced, such as hydrocarbons or alcohol.

Furthermore, the hydrogen and oxygen resulting from water splitting can be store for production electricity and pure water through fuel cell.

Recent developments & Applications: 

1) Panasonic (Osaka, Japan) has developed an artificial photosynthesis system which converts carbon dioxide (CO2) to organic materials by illuminating with sunlight at a world's top efficiency of 0.2%. The efficiency is on a comparable level with real plants used for biomass energy. The key to the system is the application of a nitride semiconductor which makes the system simple and efficient. This development will be a foundation for the realization of a system for capturing and converting wasted carbon dioxide from incinerators, power plants or industrial activities. On this development, Panasonic holds 18 domestic patents and 11 overseas patents, including pending applications. From now on, Panasonic aims to achieve an efficiency similar to that of plants in ethanol production. As a future prospect, the company wants to operate artificial photosynthesis plants, which could absorb CO2 from factories and produce ethanol. 

2) Inspired by the photosynthesis performed by plants, researchers at MIT had developed an unprecedented process that will allow the sun's energy to be used to split water into hydrogen and oxygen gases. Later, the oxygen and hydrogen may be recombined inside a fuel cell, creating carbon-free electricity to power your house or your electric car, day or night.

The key component of this new process is a new catalyst that produces oxygen gas from water; another catalyst produces valuable hydrogen gas. The new catalyst consists of cobalt metal, phosphate and an electrode, placed in water. When electricity — whether from a photovoltaic cell, a wind turbine or any other source — runs through the electrode, the cobalt and phosphate form a thin film on the electrode,  oxygen gas is produced. Than those gases are store for use in fuel cell to produce electricity and pure water.

Potential global impact 

Being a renewable and carbon-neutral source of solar fuels, producing either hydrogen (which when burnt or use in fuel cell produces energy and fresh water) or carbohydrates, artificial photosynthesis is set apart from other popular renewable energy sources, specifically hydroelectric, solar photovoltaic, geothermal, and wind – which produce electricity directly and centrally with no easily stored and transportable fuel intermediate. As such, artificial photosynthesis may become a very important source of fuel for transportation; unlike biomass energy, it does not require arable land and, consequently, will not compete with the food supply. One vision for globalizing artificial photosynthesis involves large light capture facilities linked to coastal metropolitan industrial plants where sea water is split to produce hydrogen and oxygen; the other involves all human structures covering the earth's surface (i.e., roads, vehicles and buildings) doing photosynthesis more efficiently than plants