H2 production vs. CO2 reduction

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CO2, hydrogen, solar, solar fuels

Here is a recent viewpoint article published in ACS Energy Letters discussing the merits of using solar energy (or solar-derived electricity) to 1.) split water for H2 production, or 2.) reduce CO2 into liquid hydrocarbon fuels:

http://pubs.acs.org/doi/abs/10.1021/acsenergylett.6b00377

There is a lot of active research ongoing for both of these pathways, so this is an important discussion to be having.

The article nicely articulates the reasons for not performing CO2 reduction from CO2 captured from coal fired power plants.  However, there are other sources of CO2 as well, such as cement plants, or  capturing CO2 directly from air (so-called negative emissions) as discussed in this article:

http://www.pnas.org/content/109/33/13156

 

 

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Perovskite-based Photovoltaic-Electrolysis device for Reduction of CO2 to CO

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carbon dioxide, carbon monoxide, CO, CO2, perovskite photovoltaics, PV-electrolysis, solar, solar fuels

Researchers in Michael Gratzel’s group at EPFL in Switzerland recently reported a solar-to-chemical conversion efficiency of 6.5% for the reduction of CO2 to carbon monoxide (CO):

http://www.nature.com/ncomms/2015/150611/ncomms8326/abs/ncomms8326.html

This is the best reported solar-to-CO conversion efficiency for solar-driven CO2 reduction, and was achieved with three series connected perovskite photovoltaic (PV) cells. When the electrical output from the PV cells was coupled to an IrO2 anode (for the oxygen evolution reaction) and a roughened gold cathode (for CO2 reduction), the device achieved stable current densities with high selectivity towards CO for almost 20 hours. Thin film perosvkite PV cells have attracted a lot of attention in recent years due to the significant improvement in efficiency (up to 20% now), and they are a natural choice of PV material to couple with electrochemical reactions due to the ability of a single perovskite cell to produce photovoltages above 1.0 V.

(a) Schematic of the device combining photovoltaics with an electrochemical cell. (b) Generalized energy diagram for converting CO₂ into CO with three perovskite solar cells. Image and caption from: http://www.nature.com/ncomms/2015/150611/ncomms8326/abs/ncomms8326.html