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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Collection of Review Articles on Photoelectrochemical Water Splitting in Energy & Environmental Science

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hydrogen, photoelectrochemistry, solar fuels, water splitting

A leading journal in the area of clean energy technology, Energy & Environmental Science (EES), recently published a special issue that contains a series of 5 review articles on photoelectrochemical (PEC) water splitting for the production of hydrogen from sunlight.  Collectively the articles provide an overview of the state of the art in PEC technology, current understanding of PEC operation, characterization techniques for the development of PEC materials, and highlight key challenges and opportunities in the field.

You can find all of the articles on this page:   http://pubs.rsc.org/en/journals/journalissues/ee#!recentarticles&adv

as well as an editorial that summarizes the different articles and state of the field: http://pubs.rsc.org/en/content/articlelanding/2015/ee/c5ee90047f#!divAbstract

New record for direct solar water splitting efficiency: 14%!

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benchmark efficiency, energy storage, hydrogen, solar fuels

“Surpassing the 17 year record of 12.4 percent, the new efficiency level of 14 percent helps build a promising future for solar hydrogen production” -ECS News

http://www.ecsblog.org/record-breaking-energy-efficiency-levels/

direct link to nature communications paper here:

http://www.nature.com/ncomms/2015/150915/ncomms9286/full/ncomms9286.html#affil-auth

Dr. Yiying Wu’s Reddit AMA

Tags

batteries, outreach, reddit, solar, solar fuels

Dr. Yiying Wu from Ohio State posted an AMA (Ask Me Anything) yesterday on Reddit’s science forum, where he answers questions about his work on solar batteries. This is a great way to increase public awareness of solar battery research, and is worth checking out if you have the time.

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

Germany’s upcoming solar eclipse

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electric grid, energy storage, Germany, solar, solar fuels, solar intermittency

We often talk about solar intermittency being a major challenge for wide-spread adoption of solar energy, and a major motivating factor for developing solar fuels technology. Solar intermittency is especially problematic for electric grid operators, who try to constantly balance electricity demand and supply.  Grid-scale energy storage is one solution to this problem, but currently no economical options exist except for a few places that are well-suited for pumped hydro storage.

The resiliency of Germany’s power grid – which gets the highest percentage of its electricity from solar in the world at 7% – may get a huge test this coming week when a major solar eclipse is supposed to occur.  An eclipse can cause a lot more trouble than clouds because it can suddenly affect a very large area of land, resulting in a much more rapid “turn off” and “turn on” of solar-electricity being produced.

The following article gives a more detailed description of what the eclipse means for Germany’s electric grid, and includes a nice plot of the expected solar electric output during the course of the day:

http://www.motherjones.com/environment/2015/03/solar-eclipse-germany-power

February Journal club article

Tags

hydrogen, silicon photoelectrochemistry, solar fuels

nature communications paper on MIS photocathode with STO insulator:

http://www.nature.com/nnano/journal/v10/n1/full/nnano.2014.277.html

Back-Illuminated Photoelectrodes

Tags

back-illumination, Silicon, solar fuels

A recent publication in Energy & Environmental Science out of the Technical University of Denmark investigates the use of back-illuminated Silicon-based photocathodes for photoelectrochemical cells:

http://pubs.rsc.org/en/Content/ArticleLanding/2014/EE/C4EE03723E#!divAbstract

Many photoelectrochemical reactor/cell designs based on tandem (2 absorber) stacks employ Si as the bottom component, meaning that light will first pass through the back contact of this cell rather than the front surface where the electrochemical reaction is taking place.

Despite the practical necessity of back illumination in many PEC device designs, back illumination brings with it several challenges, including lower current density due to bulk recombination and complications associated with using a transparent conducting back contact.