Artificial Photosynthesis - History

History

In the late 60s, Akira Fujishima discovered the photocatalytic properties of titanium dioxide, the so-called Honda-Fujishima effect, which could be used for hydrolysis.

The Swedish Consortium for Artificial Photosynthesis, the first of its kind, was established in 1994 as collaboration between groups of three different universities, Lund, Uppsala and Stockholm, being presently active around Lund and the Ångström Laboratories in Uppsala The consortium was built with a multidisciplinary approach to focus on learning from natural photosynthesis and applying this knowledge in biomimetic systems. Research in artificial photosynthesis undergoes a boom in the beginning of the 21st century. In 2000, Commonwealth Scientific and Industrial Research Organisation (CSIRO) researchers publicize their intent to focus on carbon dioxide capture and conversion to hydrocarbons. In 2003, the Brookhaven National Laboratory announced the discovery of an important intermediate step in the reduction of CO₂ to CO (the simplest possible carbon dioxide reduction reaction), which could lead to better catalyst designing.

One of the drawbacks of artificial systems for water-splitting catalysts is their general reliance on scarce, expensive elements, such as ruthenium or rhenium. With the funding of the United States Air Force Office of Scientific Research, in 2008, MIT chemist and head of the Solar Revolution Project Daniel G. Nocera and postdoctoral fellow Matthew Kanan attempted to circumvent this issue by using a catalyst containing the cheaper and more abundant elements cobalt and phosphate. The catalyst was able to split water into oxygen and protons using sunlight, and could potentially be coupled to a hydrogen-producing catalyst such as platinum. Furthermore, while the catalyst broke down during catalysis, it could self-repair. This experimental catalyst design was considered a major breakthrough in the field by many researchers.

Whereas CO is the prime reduction product of CO₂, more complex carbon compounds are usually desired. In 2008, Princeton chemistry professor Andrew B. Bocarsly reported the direct conversion of carbon dioxide and water to methanol using solar energy in a highly efficient photochemical cell.

While Nocera and coworkers had accomplished water splitting to oxygen and protons, a light-driven process to produce hydrogen from protons still needed to be developed. In 2009, the Leibniz Institute for Catalysis reported inexpensive iron carbonyl complexes able to do just this. In the same year, researchers at the University of East Anglia use also iron carbonyl compounds to achieve photoelectrochemical hydrogen production with a 60% efficiency, this time using a gold electrode covered with layers of indium phosphide to which the iron complexes were linked. Both these processes used a molecular approach, where discrete nanoparticles are responsible for catalysis.

Hydrogen photoproduction in heterogeneous systems is also possible, even if not directly mimicking photosynthesis. Also in 2009, F. del Valle and K. Domen showed the impact of the thermal treatment in a closed atmosphere using Cd1-xZnxS photocatalysts. Cd1-xZnxS solid solution reports high activity in hydrogen production from water splitting under sunlight irradiation. A mixed heterogeneous/molecular approach by researchers at the University of California, Santa Cruz in 2010, using both nitrogen-doped and cadmium selenide quantum dots-sensitized titanium dioxide nanoparticles and nanowires, also yielded photoproduced hydrogen.

Artificial photosynthesis remained an academic field for many years. However, in the beginning of 2009, Mitsubishi Chemical Holdings was reported to be developing its own artificial photosynthesis research by using sunlight, water and carbon dioxide to "create the carbon building blocks from which resins, plastics and fibers can be synthesized." This was confirmed with the establishment of the KAITEKI Institute later that year, with carbon dioxide reduction through artificial photosynthesis as one of the main goals.

In 2010, the DOE established, as one of its Energy Innovation Hubs, the Joint Center for Artificial Photosynthesis. The mission of JCAP is to find a cost-effective method to produce fuels using only sunlight, water, and carbon-dioxide as inputs. JCAP is led by a team from Caltech, led by Professor Nathan Lewis and brings together more than 120 scientists and engineers from Caltech and its lead partner, Lawrence Berkeley National Laboratory. JCAP also draws on the expertise and capabilities of key partners from Stanford University, the University of California at Berkeley, UCSB, UCI, and UCSD, and the Stanford Linear Accelerator. In addition, JCAP serves as a central hub for other solar fuels research teams across the United States, including 20 DOE Energy Frontier Research Center. The program has a budget of $122M over five years, subject to Congressional appropriation

Also in 2010, a team led by professor David Wendell at the University of Cincinnati successfully demonstrated photosynthesis in an artificial construct consisting of enzymes suspended in frog foam.

In 2011, Daniel Nocera and his research team announced the creation of the first practical artificial leaf. In a speech at the 241st National Meeting of the American Chemical Society, Nocera described an advanced solar cell the size of a poker card capable of splitting water into oxygen and hydrogen, approximately ten times more efficient than natural photosynthesis. The cell is mostly made of inexpensive materials that are widely available, works under simple conditions, and shows increased stability over previous catalysts: in laboratory studies, the authors demonstrated that an artificial leaf prototype could operate continuously for at least forty-five hours without a drop in activity. In May 2012, Sun Catalytix, the startup based on Nocera's research, stated that it will not be scaling up the prototype as the device offers few savings over other ways to make hydrogen from sunlight.