Solar Energy Conversion

Artificial photosynthesis is a process that mimics natural photosynthesis – the process plants use to convert sunlight, water, and carbon dioxide into carbohydrates and oxygen. The goal of artificial photosynthesis is to produce a sustainable source of clean energy, typically in the form of hydrogen or other fuels, or to sequester carbon dioxide.

Solar energy can reduce greenhouse gases and provide increased energy efficiency, says a scientist at Argonne National Laboratory. When fossil fuel is turned into useful energy through combustion, it often produces environmental pollutants that are harmful to human health and greenhouse gases that threaten the global climate. In contrast, solar resources have a benign effect on the environment and climate, making it an appealing alternative energy source. Argonne is creating next-generation nanostructured solar cells using sophisticated atomic layer deposition techniques that replace expensive silicon with inexpensive titanium dioxide and chemical dyes.

Its artificial photosynthesis program imitates nature using simple chemical components to convert sunlight, water and carbon dioxide directly into fuels like hydrogen, methane and ethanol. Its program on thermoelectric materials takes heat from the sun and converts it directly to electricity. In future, for electricity, important research developments lie in the development of new materials for solar cells, including organics, thin films, dyes, and shuttle ions, and in understanding the dynamics of charge transfer across nanostructured interfaces.

For fuel, solar photons can be converted into chemical fuel more resourcefully by breeding or genetically engineering designer plants, connecting natural photosynthetic pathways in novel configurations and using artificial bio-inspired nanoscale systems. For heat, controlling the size, density and distribution of nanodot inclusions during bulk synthesis could enhance thermoelectric performance and achieve more reliable electricity production from the sun's heat.

There are two main approaches to artificial photosynthesis:

1. Photocatalytic Water Splitting: This process mimics the natural photosynthesis' light reactions, where water molecules are split into hydrogen and oxygen using sunlight. The hydrogen can then be used as a clean fuel. Typically, this process uses a photocatalyst (often a type of semiconductor) that absorbs sunlight and facilitates the water-splitting reaction.
2. Carbon Dioxide Reduction: This process mimics the dark reactions of natural photosynthesis, where carbon dioxide is converted into carbohydrates. In the artificial version, the goal is to reduce carbon dioxide into a useful fuel, such as methane or methanol. This not only provides a potential renewable fuel source, but also could help reduce carbon dioxide levels in the atmosphere, assisting in climate change mitigation efforts.