Using Eggs to Harvest Clean Energy
What if the future of renewable energy lies in a good breakfast? While the thought of the most important meal of the day, or one of its components, powering anything other than a human body may be novel, the race for renewable energy has been going for decades. Though most everyday people can imagine a world filled with more solar panels or wind farms, perhaps fewer think of another contender: hydrogen power. Researchers led by Professor Yusuke Yamada at Osaka City University in Japan have found a new way to produce hydrogen using egg white protein and light—an innovation that could make hydrogen energy production emission free in the future.
Although hydrogen itself, when used for energy, only leaves water as a byproduct, its positive impact on the environment is diminished if it is produced from non-renewable sources. Currently, most hydrogen power is produced from fossil fuels, primarily natural gas, through a chemical process known as reforming. Researchers have overcome this problem by creating a process that avoids the need for fossil fuels entirely: a photocatalytic hydrogen evolution system. As the name suggests, the system uses light to catalyze, or speed up, a reaction that produces hydrogen. The transfer of electrons between molecules provides the energy needed for the hydrogen evolution to occur.
In the new process, lysozyme, the principal protein in egg white, provides a porous, cross-linked framework that immobilizes rose bengal molecules in very close proximity to platinum nanoparticles at the molecular level. Rose bengal, a red dye used to detect damage to eye tissue, is photosensitive and becomes negatively charged in the presence of light, and platinum nanoparticles are hydrogen production catalysts. When light hits a rose bengal molecule, it becomes highly reactive, gains an electron from a nearby electron-rich molecule, and passes that electron, along with the energy stored in it, to the platinum nanoparticles, which then use this energy to catalyze the creation of hydrogen molecules.
While photocatalytic systems like the one described above have been created before using other substrates, egg white provides unique advantages for such a system. “Lysozyme is a very well-known protein that can be [cheaply] produced in bulk,” said Hiroyasu Tabe, first author on the paper. “We can easily make lysozyme crystals and manipulate their structure.” What’s more, lysozyme is amenable to containing entire systems of molecules. “We can complex two or more compounds [within the cross-linked lysozyme framework] and visualize their chemical structure using crystal structure analysis,” said Tabe.
Naturally filled with large pores, cross-linked lysozyme crystals can house, within their solvent channels, charged molecules like rose bengal as well as metal nanoparticles within small molecular compartments. These combined structures were visualized using x-ray crystallography, a technique that uses the diffraction of x-rays to map the three-dimensional structure of crystals.
Anchoring molecules in a substrate framework is critical to the success of the photocatalytic system because the random movement of particles in solution impedes the precise accumulation of hydrogen for useful purposes. The researchers tested this scenario against systems where the rose bengal and platinum nanoparticles were immobilized in cross-linked lysozyme crystals, which were found to improve the efficiency of the reaction. Three times as much hydrogen was produced when the photocatalytic system was embedded within a crystal framework.
The experiments were completed at the two- and three-liter scale, but now that the method has been shown to have potential, industrial applications are possible in the future. Scaling up will be important to areas such as automotive fuel and residential electricity. Although fuel cell cars such as Hyundai’s Tucson already exist, one of the most important limits to their expanded adoption is the scarcity of hydrogen fueling stations in existing infrastructure. Increasing the supply of clean-produced hydrogen for such vehicles could have an important role in lessening our carbon footprint, as transportation accounts for about thirty percent of US greenhouse gas emissions.
The researchers are hopeful that their method will help to reverse this trend. The proof of concept—that a photocatalytic hydrogen evolution system is feasible, paves the way for further exploration of different substrates.
Although the lab’s current work deals with the production of hydrogen itself, future work will focus on the creation of hydrogen fuel cells, which convert stored hydrogen and oxygen into water, releasing electricity in the process. Ultimately, the researchers hope to expand the green production of energy through sunlight. In a world whose environmental future is increasingly uncertain, creative solutions like egg white will become key drivers of positive change.