Confusion over Media Report of M.I.T. "Solar Revolution" Claim?
28 Aug, 2008 03:44 pm
Reports of a new discovery, by a team of MIT researchers, in the popular media are confusing, claiming that a magic "catalyst" has been discovered that can promote artificial photosynthesis, and which will solve the world's energy problems. The reality is less overwhelming and demonstrates a good case for the need for scientific integrity in all reporting of new "discoveries" in the media as in the scientific literature.
The oxygen-producing catalyst is quoted as being made "of cobalt metal(?), phosphate, and an electrode, placed in water". "When electricity - whether from a photovoltaic cell, a wind turbine or any other source - runs through the electrode, the cobalt and phosphate form a thin film on the electrode, and oxygen gas is produced."
I think in reality, for "catalyst" one should read "electrode". What they have actually done is to develop a new anode (positively charged electrode in an electrolytic cell) for the splitting of water by electrolysis. The solution contains Co2+ cations (not cobalt metal) and HPO4]2- anions . The electrode material consists of indium tin oxide upon which becomes absorbed some "cobalt-phosphate" solid when current is passed through it.
It is said [1,2] that the process "can duplicate the water-splitting reaction that occurs during photosynthesis". Well, O.K., that is what photosynthesis does in essence, and then uses the "hydrogen" part, in the form of protons and electrons, to reduce CO2 to form the polysaccharide component of plants, but this is quite a different kind of catalyst, from the chlorophyll magnesium-porphyrin complex that occurs in nature. Chlorophyll does however release oxygen, accounting for the atmospheric burden of the gas, without which organic, surface life would be impossible.
It sounds very innovative and clever and the photosynthesis angle is a nice explanation to use in layman's terms. However, is it true that the discovery means that "solar energy can now be generated on a massive scale as well as rather cheaply"?
I note that platinum is still presumably involved in the process - for the cathode - which will doubtless prove a problem to recover sufficient quantity of per annum to really make a hole in our energy budget using solar-power. I have quoted the abstract of the paper below, which casts a little more light on the subject .
There is a useful article with many comments which I have just found via google .
I think this may be another "solution" where the availability of platinum is the final fence at which the "hydrogen-horse" will fall. Other metals might be used to make the cathode, but none commonly are as efficient as platinum. In fuel-cells too, platinum is the best. Hence, presumably, the final fuel-cell in which the hydrogen and oxygen are combined to make the nocturnal electricity also uses an electrode made of platinum, thus increasing the further burden of demand on this rare metal.
Meanwhile our energy-imperatives, based on fossil-fuels and nuclear, become more pressing.
 "Boffins claim solar energy breakthrough." By Jesse Denzin-Weber. http://www.theinquirer.net/gb/inquirer/news/2008/08/05/major-discovery-field-solar
 "'Major discovery' from MIT primed to unleash solar energy revolution." By Anne Trafton, MIT News Office. http://web.mit.edu/newsoffice/2008/oxygen-0731.html
 published Online July 31, 2008
Science DOI: 10.1126/science.1162018
Submitted on June 19, 2008
Accepted on July 18, 2008
In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+
Matthew W. Kanan 1 and Daniel G. Nocera 1*
1 Department of Chemistry, 6-335, Massachusetts Institute of Technology, Cambridge, MA 02139–4307, USA.
* To whom correspondence should be addressed.
Daniel G. Nocera , E-mail: firstname.lastname@example.org
The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to O2 and H2-equivalents. The realization of artificial systems that perform similar "water splitting" requires catalysts that produce O2 from water without the need for excessive driving potentials. Here, we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing Co2+. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates HPO42– as the proton acceptor in the O2-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.