Sunday, December 16, 2018

Researchers Use Jiggly Jell-O To Make Powerful New Hydrogen Fuel Catalyst

The inexpensive new material can split water just as efficiently as costly platinum.

A cheap and effective new catalyst developed by researchers at the University of California, Berkeley, can generate hydrogen fuel from water just as efficiently as platinum, currently the best -- but also most expensive -- water-splitting catalyst out there.

The catalyst, which is composed of nanometer-thin sheets of metal carbide, is manufactured using a self-assembly process that relies on a surprising ingredient: gelatin, the material that gives Jell-O its jiggle.

Two-dimensional metal carbides spark a reaction that splits water into oxygen and valuable hydrogen gas. Berkeley researchers have discovered an easy new recipe for cooking up these nanometer-thin sheets that is nearly as simple as making Jell-O from a box.
An illustration shows hydrogen gas bubbling off of a sheet of metal carbide
Credit : Xining Zang graphic, copyright Wiley

"Platinum is expensive, so it would be desirable to find other alternative materials to replace it," said senior author Liwei Lin, professor of mechanical engineering at UC Berkeley. "We are actually using something similar to the Jell-O that you can eat as the foundation, and mixing it with some of the abundant earth elements to create an inexpensive new material for important catalytic reactions."

This study was made available online in Oct. 2018 in the journal Advanced Materials ahead of final publication in print on Dec. 13.

A zap of electricity can break apart the strong bonds that tie water molecules together, creating oxygen and hydrogen gas, the latter of which is an extremely valuable source of energy for powering hydrogen fuel cells. Hydrogen gas can also be used to help store energy from renewable yet intermittent energy sources like solar and wind power, which produce excess electricity when the sun shines or when the wind blows, but which go dormant on rainy or calm days.

But simply sticking an electrode in a glass of water is an extremely inefficient method of generating hydrogen gas. For the past 20 years, scientists have been searching for catalysts that can speed up this reaction, making it practical for large-scale use.

When magnified, the two-dimensional metal carbides resemble sheets of cellphane.
A black and white image of metal carbide under high magnification.
Credit : Xining Zang photo, copyright Wiley

"The traditional way of using water gas to generate hydrogen still dominates in industry. However, this method produces carbon dioxide as byproduct," said first author Xining Zang, who conducted the research as a graduate student in mechanical engineering at UC Berkeley. "Electrocatalytic hydrogen generation is growing in the past decade, following the global demand to lower emissions. Developing a highly efficient and low-cost catalyst for electrohydrolysis will bring profound technical, economical and societal benefit."

To create the catalyst, the researchers followed a recipe nearly as simple as making Jell-O from a box. They mixed gelatin and a metal ion -- either molybdenum, tungsten or cobalt -- with water, and then let the mixture dry.

"We believe that as gelatin dries, it self-assembles layer by layer," Lin said. "The metal ion is carried by the gelatin, so when the gelatin self-assembles, your metal ion is also arranged into these flat layers, and these flat sheets are what give Jell-O its characteristic mirror-like surface."

Heating the mixture to 600 degrees Celsius triggers the metal ion to react with the carbon atoms in the gelatin, forming large, nanometer-thin sheets of metal carbide. The unreacted gelatin burns away.

The researchers tested the efficiency of the catalysts by placing them in water and running an electric current through them. When stacked up against each other, molybdenum carbide split water the most efficiently, followed by tungsten carbide and then cobalt carbide, which didn't form thin layers as well as the other two. Mixing molybdenum ions with a small amount of cobalt boosted the performance even more.

Molecules in gelatin naturally self-assemble in flat sheets, carrying the metal ions with them (left). Heating the mixture to 600 degrees Celsius burns off the gelatin, leaving nanometer-thin sheets of metal carbide.


Credit : Xining Zang graphic, copyright Wiley

"It is possible that other forms of carbide may provide even better performance," Lin said.

The two-dimensional shape of the catalyst is one of the reasons why it is so successful. That is because the water has to be in contact with the surface of the catalyst in order to do its job, and the large surface area of the sheets mean that the metal carbides are extremely efficient for their weight.

Because the recipe is so simple, it could easily be scaled up to produce large quantities of the catalyst, the researchers say.

"We found that the performance is very close to the best catalyst made of platinum and carbon, which is the gold standard in this area," Lin said. "This means that we can replace the very expensive platinum with our material, which is made in a very scalable manufacturing process."



Contacts and sources:
Kara Manke
University of California, Berkeley

Citation: Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis Xining Zang Wenshu Chen Xiaolong Zou J. Nathan Hohman Lujie Yang Buxuan Li Minsong Wei Chenhui Zhu Jiaming Liang Mohan Sanghadasa Jiajun Gu Liwei Lin http://dx.doi.org/10.1002/adma.201805188




Saturday, December 15, 2018

Organic Food Worse for the Climate

​Organically farmed food has a bigger climate impact than conventionally farmed food, due to the greater areas of land required. This is the finding of a new international study involving Chalmers University of Technology, Sweden, published in the journal Nature. 

​The researchers developed a new method for assessing the climate impact from land-use, and used this, along with other methods, to compare organic and conventional food production. The results show that organic food can result in much greater emissions. 

The crops per hectare are lower in organic farming, which leads to greater indirect carbon dioxide emissions from deforestation.
Illustration

“Our study shows that organic peas, farmed in Sweden, have around a 50 percent bigger climate impact than conventionally farmed peas. For some foodstuffs, there is an even bigger difference – for example, with organic Swedish winter wheat the difference is closer to 70 percent,” says Stefan Wirsenius, an associate professor from Chalmers, and one of those responsible for the study.

The reason why organic food is so much worse for the climate is that the yields per hectare are much lower, primarily because fertilisers are not used. To produce the same amount of organic food, you therefore need a much bigger area of land.

Credit:: Yen Strandqvist

The ground-breaking aspect of the new study is the conclusion that this difference in land usage results in organic food causing a much larger climate impact.

“The greater land-use in organic farming leads indirectly to higher carbon dioxide emissions, thanks to deforestation,” explains Stefan Wirsenius. “The world’s food production is governed by international trade, so how we farm in Sweden influences deforestation in the tropics. If we use more land for the same amount of food, we contribute indirectly to bigger deforestation elsewhere in the world.”

Even organic meat and dairy products are – from a climate point of view – worse than their conventionally produced equivalents, claims Stefan Wirsenius.

“Because organic meat and milk production uses organic feed-stocks, it also requires more land than conventional production. This means that the findings on organic wheat and peas in principle also apply to meat and milk products. We have not done any specific calculations on meat and milk, however, and have no concrete examples of this in the article,” he explains.

A new metric: Carbon Opportunity Cost
The researchers used a new metric, which they call “Carbon Opportunity Cost”, to evaluate the effect of greater land-use contributing to higher carbon dioxide emissions from deforestation. This metric takes into account the amount of carbon that is stored in forests, and thus released as carbon dioxide as an effect of deforestation. The study is among the first in the world to make use of this metric.

Stefan Wirsenius, Associate Professor at the Department of Space, Earth and Environment.
Stefan Wirsenius
Credit:   Johan Bodell


“The fact that more land use leads to greater climate impact has not often been taken into account in earlier comparisons between organic and conventional food,” says Stefan Wirsenius. “This is a big oversight, because, as our study shows, this effect can be many times bigger than the greenhouse gas effects, which are normally included. It is also serious because today in Sweden, we have politicians whoseal goals is to increase production of organic food. If thoseat goals isare implemented, the climate influence from Swedish food production will probably increase a lot.”


So why have earlier studies not taken into account land-use and its relationship to carbon dioxide emissions? 

“There are surely many reasons. An important explanation, I think, is simply an earlier lack of good, easily applicable methods for measuring the effect. Our new method of measurement allows us to make broad environmental comparisons, with relative ease,” says Stefan Wirsenius.



Contacts and sources:
Johanna Wilde / Stefan Wirsenius
Chalmers University of Technology

Citation: Journal Reference: Assessing the efficiency of changes in land use for mitigating climate change.Timothy D. Searchinger, Stefan Wirsenius, Tim Beringer, Patrice Dumas. Nature, 2018; 564 (7735): 249 DOI: 10.1038/s41586-018-0757-z