Solar-driven conversion processes yielding fuels and commodity chemicals could provide an alternative to mankind’s currently unsustainable use of fossil fuels [1].  Photoelectrochemical (PEC) 

Achieving a viable solar-driven EC CO2 reduction energy conversion efficiency requires minimizing potential losses in all aspects of the device including the cathode, anode, electrolyte, and membrane.  Achieving selective products requires management of multi-electron transfer reactions [4].  Strategies to optimize each component of a CO2 electrolyzer cell to obtain high selectivity and energy conversion efficiency at low overpotential will be described.  An overall cell design which has efficient gas to liquid mass transfer of CO2 is employed [5].  Use of a CsHCO3 buffered electrolyte increases selectivity to C2+ products such as ethylene and ethanol [6,7].  A nanostructured IrOx anode has been synthesized, which shows superior stability and high performance for oxygen evolution in the pH range of interest for CO2 reduction.  Use of a bimetallic CuAg nanocoral type cathode enables selectivity to hydrocarbons and oxygenates over a wide range of pH and cell voltage conditions.  

Solar-driven CO2 reduction is accomplished by coupling the optimized electrolyzer to cell to Si solar cells.  1 sun efficiencies of over 4% for the production of hydrocarbons and oxygenates (e.g. ethylene, ethanol, propanol) are achieved.  Notably, the overall system also functions at >3% conversion efficiency at illumination intensities down to 0.3 suns.  Use of a 4-terminal III-V/Si tandem cell leads to a conversion efficiency to hydrocarbons and oxygenates of over 5% [8].  

Finally, methods to achieve product separation [9] will be discussed in the context of an overall life cycle assessment of the system.