A team at the Joint Center for Artificial Photosynthesis (JCAP) at Lawrence Berkeley National Laboratory and UC Berkeley is proposing an artificial photosynthesis scheme for direct synthesis and separation to almost pure ethanol with minimum product crossover using saturated salt electrolytes.
In a paper in the RSC journal Energy & Environmental Science, Professor Alexis Bell and postdoc Meenesh Singh describe the novel design of an integrated artificial photosynthetic system that continuously produces >90 wt% pure ethanol using a polycrystalline copper cathode and an IrO2 anode at a current density of 0.85 mA cm-2. The annual production rate of > 90 wt% ethanol using such a photosynthesis system operating at 10 mA cm-2 (12% solar-to-fuel (STF) efficiency) can be 15.27 million gallons per year per square kilometer, corresponding to 7% of the industrial ethanol production capacity of California, they suggest.
Alcohols are particularly attractive products for artificial photosynthesis of liquid fuels because of their high energy density and market value per amount of energy input, they note. (Other work at JCAP has investigated the electrochemical reduction of CO2 to methanol.)
The major challenges in the photo/electrochemical synthesis of alcohols from sunlight, water and CO2 are low product selectivity, high membrane fuel-crossover losses, and the high cost of product separation from the electrolyte.
In the proposed system, the ethanol produced in the saturated salt electrolytes can be readily phase separated into a microemulsion, which can be collected as pure products in a liquid-liquid extractor.
JCAP was established by the US Department of Energy in 2010 as an Energy Innovation Hub, with the goal of developing an integrated solar energy-to-chemical fuel conversion system and moving this system from the bench-top discovery phase to a scale where it can be commercialized. (Earlier post.)
The program’s first phase focused on solar H2 generation, which was completed in September 2015. In April 2015, the DOE refunded JCAP for another five years with $75 million. (Earlier post.)
Led by the California Institute of Technology, JCAP has an integral partnership with the Lawrence Berkeley National Laboratory. Additionally, JCAP draws on the expertise and capabilities of key collaborators from the University of California campuses at Irvine (UCI) and San Diego (UCSD), and the SLAC National Accelerator Laboratory.
Meenesh R. Singh and Alexis T. Bell (2015a) “Design of an Artificial Photosynthetic System for Production of Alcohols in High Concentration from CO2” Energy & Environmental Science doi: 10.1039/C5EE02783G
Meenesh R. Singh, Ezra L. Clark, and Alexis T. Bell (2015b) “Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels” PNAS doi: 10.1073/pnas.1519212112