24 August 2015

New record energy efficiency for artificial photosynthesis

artificial photosynthesis
A new world-record 22 percent conversion efficiency for solar-powered hydrogen production has been claimed by researchers from Australia's Monash University (Credit: Shutterstock)

As the world moves towards developing new avenues of renewable energy, the efficiencies of producing fuels such as hydrogen must increase to the point that they rival or exceed those of conventional energy sources to make them a viable alternative. Now researchers at Monash University in Melbourne claim to have created a solar-powered device that produces hydrogen at a world-record 22 percent efficiency, which is a significant step towards making cheap, efficient hydrogen production a reality.

Efficiency records for solar-powered hydrogen production have continued to rise over the years, and much more rapidly as the technology and techniques improve. Even as late as December last year a report says a solar-driven hydrogen record efficiency at the time of just 12.3 percent, so this new record shows a very healthy 10 percent improvement on that and beats out the previous record of 18 percent.

Splitting water using electricity to produce hydrogen and oxygen has been an established scientific technique for many decades. However, the rate at which hydrogen has been produced in this way has not been commercially viable due to the relatively low conversion rates compared to the input energy costs. Ideally, solar-powered water-splitting would be one of the best ways to produce hydrogen as its energy input cost is effectively zero.

On the downside, however, the low efficiencies of past solar devices have kept this technology largely in its infancy. The Monash researchers believe that may all soon change as increased efficiencies in the process and in the devices themselves improve.

"Electrochemical splitting of water could provide a cheap, clean and renewable source of hydrogen as the ultimately sustainable fuel." said Professor Leone Spiccia from the School of Chemistry at Monash who led the research. "This latest breakthrough is significant in that it takes us one step further towards this becoming a reality."

According to the researchers, the breakthrough is significantly attributable to the leading-edge capabilities of the group in which they work and a growing expertise in tuning the processes and materials used in water splitting.

To help achieve the required solar-input efficiencies, the team utilized the very best commercial-grade multi-junction (indium gallium phosphide, gallium arsenide, and germanium) solar cells available to ensure the maximum sunlight to electricity conversion.

However, an even greater contribution to efficiency was on the material side, where the use of expanded foam nickel electrodes increased the available electrolysis surface area with such efficiency that the electrolyte in which they were immersed was simply local river water with the addition of a standard pH buffer (generally a salt solution containing sodium phosphate and sodium chloride).

In this combination of high-efficiency cells and high-yield electrodes, the team claims the 22 percent record for conventional solar-cell to electrochemical production of hydrogen.

What the eventual limit of such technologies is a largely moot point at this stage and largely reliant on the increasing efficiency of solar-cell light conversion factors. Advances in such things as perovskite solar-cells may assist in this regard and, compared to some other methods of sunlight-powered water-splitting yet to fully prove their mettle, may achieve the necessary breakthrough point to tip the balance in favor of cheap, abundant hydrogen fuel.

"Hydrogen can be used to generate electricity directly in fuel cells," said Professor Doug MacFarlane, ARC Laureate Fellow and leader of the Energy Program of the ARC Centre of Excellence for Electromaterials Science at Monash. "Cars driven by fuel cell electric engines are becoming available from a number of car manufacturers. Hydrogen could even be used as an inexpensive energy storage technology at the household level to store energy from roof-top solar cells."

The results of the research were recently published in the journal Energy and Environmental Science.

Source: Monash University, gizmag


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