Featured Research

from universities, journals, and other organizations

Best of both worlds: Solar hydrogen production breakthrough

Date:
July 29, 2013
Source:
Helmholtz Association of German Research Centres
Summary:
Using a simple solar cell and a photo anode made of a metal oxide, scientists have successfully stored nearly five percent of solar energy chemically in the form of hydrogen. This is a major feat as the design of the solar cell is much simpler than that of the high-efficiency triple-junction cells based on amorphous silicon or expensive III-V semiconductors that are traditionally used for this purpose.

When light hits the system, an electrical potential builds up. The metal oxide layer acts as a photo anode and is the site of oxygen formation. It is connected to the solar cell by way of a conducting bridge made of graphite (black). Since only the metal oxide layer is in contact with the electrolyte, the silicon solar cell remains safe from corrosion. A platinum spiral serves as the cathode where hydrogen is formed.
Credit: Image courtesy of Helmholtz Association of German Research Centres

Using a simple solar cell and a photo anode made of a metal oxide, HZB and TU Delft scientists have successfully stored nearly five percent of solar energy chemically in the form of hydrogen. This is a major feat as the design of the solar cell is much simpler than that of the high-efficiency triple-junction cells based on amorphous silicon or expensive III-V semiconductors that are traditionally used for this purpose. The photo anode, which is made from the metal oxide bismuth vanadate (BiVO4) to which a small amount of tungsten atoms was added, was sprayed onto a piece of conducting glass and coated with an inexpensive cobalt phosphate catalyst.

Related Articles


"Basically, we combined the best of both worlds," explains Prof. Dr. Roel van de Krol, head of the HZB Institute for Solar Fuels: "We start with a chemically stable, low cost metal oxide, add a really good but simple silicon-based thin film solar cell, and -- voilà -- we've just created a cost-effective, highly stable, and highly efficient solar fuel device."

Thus the experts were able to develop a rather elegant and simple system for using sunlight to split water into hydrogen and oxygen. This process, called artificial photosynthesis, allows solar energy to be stored in the form of hydrogen. The hydrogen can then be used as a fuel either directly or in the form of methane, or it can generate electricity in a fuel cell. One rough estimate shows the potential inherent in this technology: At a solar performance in Germany of roughly 600 Watts per square meter, 100 square meters of this type of system is theoretically capable of storing 3 kilowatt hours of energy in the form of hydrogen in just one single hour of sunshine. This energy could then be available at night or on cloudy days.

Metal oxide as photo anode prevents corrosion of the solar cell

Van de Krol and his team essentially started with a relatively simple silicon-based thin film cell to which a metal oxide layer was added. This layer is the only part of the cell that is in contact with the water, and acts as a photo anode for oxygen formation. At the same time, it helps to prevent corrosion of the sensitive silicon cell. The researchers systematically examined and optimized processes such as light absorption, separation of charges, and splitting of water molecules. Theoretically, a solar-to-chemical efficiency of up to nine percent is possible when you use a photo anode made from bismuth vanadate, says van de Krol. Already, they were able to solve one problem: Using an inexpensive cobalt phosphate catalyst, they managed to substantially accelerate the process of oxygen formation at the photo anode.

A new record: More than 80 percent of the incident photons contribute to the current!

The biggest challenge, however, was the efficient separation of electrical charges within the bismuth vanadate film. Metal oxides may be stable and cheap, but the charge carriers have a tendency to quickly recombine. This means they are no longer available for the water splitting reaction. Now, Van de Krol and his team have figured out that it helps to add wolfram atoms to the bismuth vanadate film. "What's important is that we distribute these wolfram atoms in a very specific way so that they can set up an internal electric field, which helps to prevent recombination," explains van de Krol. For this to work, the scientists took a bismuth vanadium wolfram solution and sprayed it onto a heated glass substrate. This caused the solution to evaporate. By repeatedly spraying different wolfram concentrations onto the glass, a highly efficient photo-active metal oxide film some 300 nanometers thick was created. "We don't really understand quite yet why bismuth vanadate works so much better than other metal oxides. We found that more than 80 percent of the incident photons contribute to the current, an unexpectedly high value that sets a new record for metal oxides" says van de Krol. The next challenge is scaling these kinds of systems to several square meters so they can yield relevant amounts of hydrogen.


Story Source:

The above story is based on materials provided by Helmholtz Association of German Research Centres. Note: Materials may be edited for content and length.


Journal Reference:

  1. Fatwa F. Abdi, Lihao Han, Arno H. M. Smets, Miro Zeman, Bernard Dam, Roel van de Krol. Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode. Nature Communications, 2013; 4 DOI: 10.1038/ncomms3195

Cite This Page:

Helmholtz Association of German Research Centres. "Best of both worlds: Solar hydrogen production breakthrough." ScienceDaily. ScienceDaily, 29 July 2013. <www.sciencedaily.com/releases/2013/07/130729111927.htm>.
Helmholtz Association of German Research Centres. (2013, July 29). Best of both worlds: Solar hydrogen production breakthrough. ScienceDaily. Retrieved October 30, 2014 from www.sciencedaily.com/releases/2013/07/130729111927.htm
Helmholtz Association of German Research Centres. "Best of both worlds: Solar hydrogen production breakthrough." ScienceDaily. www.sciencedaily.com/releases/2013/07/130729111927.htm (accessed October 30, 2014).

Share This



More Earth & Climate News

Thursday, October 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Deadly Mudslide in Sri Lanka Buries Houses

Deadly Mudslide in Sri Lanka Buries Houses

AP (Oct. 29, 2014) — A mudslide triggered by monsoon rains buried scores of workers' houses at a tea plantation in central Sri Lanka on Wednesday, killing at least 10 people and leaving more than 250 missing, an official said. (Oct. 29) Video provided by AP
Powered by NewsLook.com
Galapagos Tortoises Bounce Back, But Ecosystem Lags

Galapagos Tortoises Bounce Back, But Ecosystem Lags

Newsy (Oct. 29, 2014) — The Galapagos tortoise has made a stupendous recovery from the brink of extinction to a population of more than 1,000. But it still faces threats. Video provided by Newsy
Powered by NewsLook.com
Saharan Solar Project to Power Europe

Saharan Solar Project to Power Europe

Reuters - Business Video Online (Oct. 29, 2014) — A solar energy project in the Tunisian Sahara aims to generate enough clean energy by 2018 to power two million European homes. Matt Stock reports. Video provided by Reuters
Powered by NewsLook.com
Obama: The US Will Not 'run and Hide' From Ebola

Obama: The US Will Not 'run and Hide' From Ebola

AP (Oct. 29, 2014) — Surrounded by health care workers in the White House East Room, President Barack Obama said the U.S. will likely see additional Ebola cases in the weeks ahead. But he said the nation can't seal itself off in the fight against the disease. (Oct. 29) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



    Save/Print:
    Share:  

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile iPhone Android Web
    Follow Facebook Twitter Google+
    Subscribe RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins