GWU Researcher Developing Efficient Solar Chemical Process for Generation of Energetic Molecules and Conversion of CO2
Dr. Stuart Licht (earlier post) at George Washington University is developing a solar-driven process that, he says, could efficiently replace current industrial processes for the production of certain energetic molecules such as hydrogen, metals and chlorine, which are responsible for a large component of anthropogenic CO2. It can also convert captured anthropogenic CO2, generated by burning fossil fuels, to CO and O2 via high-temperature electrolysis. A paper on his work is in press for the ACS’ Journal of Physical Chemistry, C.
One third of the global industrial sector’s annual emission of 1x1010 metric tons of CO2 is released in the production of metals and chlorine. This, together with the additional CO2 from electrical generation, heating and transportation, comprise the majority of CO2 emissions.
The STEP (Solar Thermal Electrochemical Photo) process fundamentally captures sunlight more efficiently than photovoltaics by using the full (UV, visible and infrared) sunlight. More than 50% of solar energy is captured and used. Conventional photovoltaics lose much of the visible sunlight, and can not use the infrared sunlight at all.
STEP distinguishes radiation that is intrinsically energy sufficient to drive photovoltaic charge transfer and applies all excess solar thermal energy to heat the electrolysis reaction chamber and to decrease the energy of endothermic electrolysis reactions.
The process comprises five basic steps:
- sunlight harvesting and concentration,
- electron/hole separation and electronic charge transfer driven by superbandgap energy in the photovoltaic,
- transfer of sub-bandgap and excess super-bandgap radiation to step up heat to the electrolysis chamber,
- high-temperature, low-energy electrolysis forming energy-rich products, and
- cycle completion by preheating of the electrolysis reactant through heat exchange with the energetic electrolysis products.
Solar heating can decrease the energy to drive a range of electrolysis processes. The electrochemical driving force for a variety of chemicals of widespread use by society will be shown to significantly decrease with increasing temperature...As an example of the STEP solar energy efficiency gains, this study focuses on CO2 splitting potentials....these potentials (black circles in the figure [at right]) decrease more rapidly with temperature than those for water splitting, signifying that the STEP process may be readily applied to CO2 electrolysis.—Licht, 2009
A molten carbonate bath electrolysis cell, fed by CO2, generates CO—an important syngas component and, which when reacted with H2, forms methanol. Molten alkali carbonate electrolyte fuel cells typically operate at 650 °C. Licht plans a follow-up study to present experimental measurements of the CO2 splitting electrochemical potential (to CO or solid C), with increasing temperature.
In addition to the removal of CO2, the STEP process is shown to be consistent with the efficient solar generation of a variety of metals, as well as chlorine, in place of conventional industrial processes. In total, these processes are responsible for the majority of anthropogenic CO2 release, and their replacement by STEP processes will end the root cause of anthropogenic global warming.
The STEP process occurs at solar energy conversion efficiency greater than attainable by photovoltaics alone. This study provides a path for a transition beyond the fossil fuel, electrical or hydrogen economy, to a renewable chemical economy based on the direct formulation of the materials needed by society.—Licht, 2009
Stuart Licht (2009) STEP (Solar Thermal Electrochemical Photo) Generation of Energetic Molecules: A Solar Chemical Process to End Anthropogenic Global Warming. Journal of Physical Chemistry, C, in press. doi: 10.1021/jp9044644