Plant leaves contain things called chloroplasts that use sunlight to turn water and carbon dioxide into energy-rich carbohydrates. This process, photosynthesis, is one of the oldest chemical processes on Earth. It might also be the most important, because without it, higher forms of life might never have evolved. Photosynthesis happens in two stages. The first involves splitting water into oxygen and hydrogen, while the second produces new carbohydrates from carbon dioxide and hydrogen. Scientists working on artificial leaves hope to mimic the first step because hydrogen could be one of our main sources of energy in the future.
Interestingly, photosynthesis in nature is not all that efficient. Plants use just one percent or so of the solar energy to which they are exposed. There is a good reason for this, though: using more than that would put the plants at risk of producing chemical by-products that could harm them. This is not something that scientists involved in making artificial leaves have to consider. In fact, the technology could theoretically achieve efficiencies of as much as 40 percent.
Practically speaking, however, the challenges are numerous. In 2011, a group of American scientists announced that they had developed an artificial leaf that achieved ten percent efficiency. Unfortunately, the price was exorbitant. A team working at Helmholtz-Zentrum Berlin therefore recently attracted attention when they produced an inexpensive and comparatively simple system capable of turning five percent of the sunlight it absorbs into storable hydrogen.
This question was answered by Dr Antonia Rötger, a science writer responsible for science communication in the press office at Helmholtz-Zentrum Berlin für Materialien und Energie.