Recently, scientists from the Swiss research institute EMPA, along with colleagues from the University of Basel and the Argonne National Laboratory in Illinois took a cue from photosynthesis and discovered that by coupling a light-harvesting plant protein with their specially designed electrode, they could substantially boost the efficiency of photo-electrochemical cells used to split water and produce hydrogen - a huge step forward in the search for clean, truly green power.
Until the discovery of deep sea life forms that thrive in lightless hyrothermal vents, photosynthesis was considered the engine that drives all life on Earth. For those of us not dwelling in the chilly depths, that's still pretty much true - plants use solar energy to combine carbon dioxide and water to build sugars for energy storage (food for us) and structure (wood for heat and shelter) - the ultimate in green. Somewhere in that cascade of reactions, water is quickly and efficiently split into hydrogen and oxygen - a property understandably of great interest to proponents of clean energy.
If you're not a plant, one way to break water into its components is through the process many of us learned about in high school science class - electrolysis, the energy for which can be cleanly supplied by photovoltaic cells or hydroelectric power. Another technique, the focus of the Swiss/US collaborators, uses photo-electrochemical cells (PEC), which employ light energy to directly cleave water electrochemically - a process that skips the step of converting the light to electricity first.
The material of choice for PEC electrodes (site of the actual water splitting) has centered on metal oxides because some are photocatalytic (activated by light). Recently, titanium dioxide was in the news after it was shown to disperse organic air and water pollutants when activated by UV light. Hematite, a form of iron oxide (otherwise known as rust) proved even more promising because it responds to visible wavelengths and is cheap and abundant.
While working on his doctoral thesis at EMPA, scientist Debajeet Bora hit upon the idea of cross-coupling molecules of a light-harvesting plant protein with nanoparticles of hematite.
"I was inspired by the natural photosynthetic machinery of cyanobacteria where phycocyanin acts as a major light-harvesting component. I wanted to make artificial photosynthesis using ceramics and proteins," Bora said. "The concept of hematite surface functionalization with proteins was completely novel in PEC research."
The phycocyanin molecule
It turns out phycocyanin, a protein found in blue-green algae (cyanobacteria), when bound to the electrode surface, doubled the amount of photocurrent compared to that generated by the hematite-only electrode. In an area of science where even small incremental increases in efficiency are considered noteworthy, this new plant-assisted boost to hydrogen generation is big news indeed and bodes well for the on-going quest to supply affordable earth-friendly energy for all of us.
