March 25, 2015 | Leave a Comment
The A*STAR experimental analysis and computer simulations reveal new insights into the process by which ethanol produced from waste biomass can be converted into hydrogen in the presence of a catalyst. The new insights should aid the design of more efficient catalysts for hydrogen production.
Hydrogen gas is an environmentally friendly alternative to fossil fuels. Today using a process known as steam reforming, hydrogen is obtained by with steam to break up hydrocarbon compounds – most commonly, methane in natural gas. But ethanol produced by fermenting waste biomass is potentially a cleaner starting material for this process.
Despite having been extensively studied in recent years, steam reforming of ethanol is currently too inefficient to produce hydrogen on an industrial scale. This stems partly from the complexity of its reaction, which can yield a range of different products.
Jia Zhang of the A*STAR Institute of High Performance Computing in Singapore explains, “Our lack of understanding of the detailed reaction mechanism hinders further improvement of a catalyst for the reaction. The reaction was a black box before we started exploring it.”
Now, Zhang and her co-workers have used experiments and computer simulations to probe how ethanol breaks down into hydrogen on rhodium catalysts supported on zirconia-based oxides. These nanosized catalysts had previously been shown to be highly active for this reaction.
The team used gas chromatography and mass spectrometry in real time to monitor the intermediate species that form as the reaction proceeds. The measurements revealed that the C2H4O species is an important intermediate. Of the two possible structures this species can adopt, acetaldehyde (CH3CHO) was identified as the most probable one by the team’s computer calculations. The calculations also showed that water plays an unexpectedly important role in controlling the reaction pathway.
Based on the new knowledge, the team proposed a mechanism for the reaction under their chosen conditions. Hydrogen is produced at most stages along the pathway, including the final step in which carbon monoxide reacts with water to produce hydrogen and carbon dioxide. The team’s calculations showed that the success of this final step is critical in determining the amount of hydrogen produced by steam reforming.
Zhang said, “Our theoretical simulations and experimental analysis provide important information on the reaction mechanism. This is a fundamental step forward in our understanding of the catalyst, which is the basis of catalyst design.”
The team’s ultimate goal is to design catalysts that can produce hydrogen more cheaply and efficiently than current catalysts.
The hydrogen for fuel effort is getting paved with lots of small but important steps that could well lead to low cost hydrogen. It surprises the uninitiated with all the possible sources from waste material, to biomass, splitting water and so on. It looks more promising all the time. Solve the production cost issue over enough sources and the two other problems of low cost fuel cells to use the hydrogen and safely store it without it escaping and the hydrogen economy could get real and big, fast.
The Agency for Science, Technology and Research (A*STAR) has announced an oxide/carbon composite outperforms expensive platinum composites in oxygen chemical reactions for green energy devices. Electrochemical devices are essential for a green energy evolution in which clean alternatives replace carbon-based fuels.
Green energy device market growth requires conversion systems that produce hydrogen from water or rechargeable batteries that can store clean energy in cars. The Singapore-based researchers have developed improved catalysts as electrodes for more efficient and durable green energy devices.
The group’s paper, “Dual-Phase Spinel MnCo2O4and Spinel MnCo2O4/Nanocarbon Hybrids for Electrocatalytic Oxygen Reduction and Evolution” has been published in the American Chemical Society journal Applied Materials & Interfaces.
Electrochemical devices such as batteries use chemical reactions to create and store energy. One of the cleanest reactions is the conversion from water into oxygen and hydrogen. Using energy from the sun, water can be converted into those two elements, which then store this solar energy in gaseous form. Burning or reoxidizing hydrogen leads to a chemical reaction that produces water.
For technical applications looking for electrons rather than heat, the conversion from hydrogen and oxygen into water is done in fuel cells, while some rechargeable batteries use chemical reactions based on oxygen to store and release energy. A crucial element for both types of devices is the cathode, which is the electrical contact where these reactions take place.
For a well-functioning cathode, the electronic energy levels of the cathode material need to be well matched to the energies required for the oxygen reactions. An ideal material for such reactions is MnCo2O4, a spinel oxide, which has the advantage that its energy states can be fine tuned by adjusting its composition.
The research team, which included Zhaolin Liu and colleagues from the A*STAR Institute of Materials Research and Engineering with colleagues from Nanyang Technological University and the National University of Singapore, combined nanometer-sized crystals of this material with sheets of carbon or carbon nanotubes.
These composites offer several benefits including low cost and high efficiency.
Liu said, “The cost is estimated to be tens of times cheaper than the platinum/carbon composites used at present.” Because platinum is expensive, intensive efforts are being made to find alternative materials for batteries.
The A*STAR researchers fabricated these composites using a scalable chemical synthesis method and studied their performance in oxygen reactions. In these tests, the composites clearly outperformed the platinum-based alternatives. They were more efficient than the platinum-based solutions, with comparable devices in the lab lasting about five times longer, for more than 64 charge-discharge cycles.
While these are still research laboratory results, the first results for full battery prototypes are encouraging, comments Liu. “We envisage a 100-watt rechargeable battery stack in one to two years and a 500-watt one in one to three years.”
The team is off to a great start on what one would hope is a grand success. Much of the technology for hydrogen is held back by the immense barrier of platinum’s cost. And as rare as platinum is, added to its demand would only exacerbate the problem. Lets hope the team’s effort to “harden up” their discovery bears fruit and soon.
University of New South Wales (UNSW) scientists have developed a highly efficient oxygen-producing catalyzing electrode for splitting water. The electrode has the potential to be scaled up for industrial production of the energy fuel hydrogen. The new technology is based on an inexpensive, specially coated foam material that lets the bubbles of oxygen escape quickly. Unlike other water electrolysers that use precious metals as catalysts, the electrode is made entirely from two non-precious and abundant metals – nickel and iron.
Associate Professor Chuan Zhao, of the UNSW School of Chemistry said, “Our electrode is the most efficient oxygen-producing electrode in alkaline electrolytes reported to date, to the best of our knowledge. It is inexpensive, sturdy and simple to make, and can potentially be scaled up for industrial application of water splitting.”
Inefficient and costly oxygen-producing electrodes are one of the major barriers to the widespread commercial production of hydrogen by electrolysis, where the water is split into hydrogen and oxygen using an electrical current.
Unlike other water electrolysers that use precious metals as catalysts, the new UNSW electrode is made entirely from two non-precious and abundant metals – nickel and iron.
Commercially available nickel foam, which has holes in it about 200 micrometers across, or twice the diameter of a human hair, is electroplated with a highly active nickel-iron catalyst, which reduces the amount of electricity needed for the water-splitting to occur.
This ultra-thin layer of a nickel-iron composite also has tiny pores in it, about 50 nanometers across.
Associate Professor Zhao explained, “The three-dimensional architecture of the electrode means it has an enormous surface area on which the oxygen evolution reaction can occur.”
“The larger bubbles of oxygen can escape easily through the big holes in the foam. As well, the smaller holes make the electrode surface ‘wetter’, so the bubbles do not stick to it, which is a common problem that makes electrodes less efficient.”
Hydrogen production is a rapidly growing industry, but the majority of hydrogen is still produced using fossils fuels such as natural gas, oil and coal, because those sources are still cheaper than electrolysis of water.
Hydrogen can be a great fuel for powering mobile devices or vehicles, and storing electricity generated from renewable energy, such as solar.
Associate Professor Zhao said, “I think this electrode has great potential for the industrial-scale production of hydrogen. Our next goal is to understand the science behind it and to further improve its performance. Cleaner sources of fuel like hydrogen will be particularly important for reducing carbon dioxide emissions and solving the air pollution problems from the burning of fossil fuels such as coal.”
Like almost all water splitting research the matter of separating the elements and material handling are not covered. Oxygen and hydrogen gases combine very easily releasing a great deal of energy, so getting the water apart and the elements safely separate would make a process that can attract interest.
For now the team is looking at the science and the paper does include worthwhile electric requirements that could be used as comparison to existing processes. Whether that’s enough to compete with fossil fuels that release the hydrogen at very low or no oxygen content in the process is yet to be discovered.
Researchers at Brown University Institute for Molecular and Nanoscale Innovation have come up with a new way of making thin perovskite films for solar cells at room temperature. In just five years of development hybrid perovskite solar cells have attained power conversion efficiencies that took decades to achieve with the top-performing silicon semiconductor materials used to generate electricity from sunlight.
The first perovskite cells introduced in 2009 managed an efficiency of only about 4 percent, far below the 25 percent efficiency boasted by standard silicon cells. But by last year, perovskite cells had been certified as having more than 20-percent efficiency.
Perovskites, a class of crystalline materials that when made into films are excellent light absorbers and are much cheaper to make than the silicon wafers used in standard solar cells.
There are a number of different ways to make perovskite films, but nearly all of them require heat. Perovskite precursor chemicals are dissolved into a solution, which is then coated onto a substrate. Heat is applied to remove the solvent, leaving the perovskite crystals to form in a film across the substrate.
Nitin Padture, professor of engineering and director of the Institute for Molecular and Nanoscale Innovation at Brown University said, “People have made good films over relatively small areas – a fraction of a centimeter or so square. But they’ve had to go to temperatures from 100 to 150º C, and that heating process causes a number of problems.”
For example, the crystals often form unevenly when heat-treated, leaving tiny pinholes in the film. In a solar cell, those pinholes can reduce efficiency. Heat also limits the substrates on which films can be deposited. Flexible plastic substrates, for example, cannot be used because they are damaged by the high temperatures.
Yuanyuan Zhou, a graduate student in Padture’s lab, started looking for a way to make perovskite crystal thin films without having to apply heat. He came up with what is known as a solvent-solvent extraction (SSE) approach.
The team’s paper has been published in the Royal Society of Chemistry’s Journal of Materials Chemistry A showing the technique produces high-quality crystalline films with precise control over thickness across large areas.
Zhou’s method has perovskite precursors dissolved in a solvent called NMP and coated onto a substrate. Then, instead of heating, the substrate is bathed in diethyl ether (DEE), a second solvent that selectively grabs the NMP solvent and whisks it away. What’s left is an ultra-smooth film of perovskite crystals. With no heating involved, the crystals can be formed on virtually any substrate, even heat-sensitive polymer substrates used in flexible photovoltaics.
Another advantage is that the entire SSE crystallization process takes less than two minutes, compared to an hour or more for heat-treating. That makes the process more amenable to mass production because it can be done in an assembly line kind of process.
Zhou’s work looks even better because the SSE approach also enables films to be made very thin while maintaining high quality. Standard perovskite films are generally on the order of 300 nanometers thick. But Zhou has been able to make high quality films as thin as 20 nanometers. The SSE films could also be made larger, several centimeters square without generating the disabling pinholes.
Zhou said, “Using the other methods, when the thickness gets below 100 nanometers you can hardly make full coverage of film. You can make a film, but you get lots of pinholes. In our process, you can form the film evenly down to 20 nanometers because the crystallization at room temperature is much more balanced and occurs immediately over the whole film upon bathing.”
Initial testing of cells made with SSE films showed conversion efficiency of over 15 percent. Solar cells based on semitransparent 80-nanometer films made using the process were shown to have higher efficiency than any other ultra-thin film.
One has to think that a lot of research and development folks are going to be reading this team’s study paper.
March 17, 2015 | 2 Comments
Carnegie Institution’s Rebecca R. Hernandez (now at University of California Berkley), Madison K. Hoffacker, and Chris Field found that the amount of energy that could be generated from solar equipment constructed on and around existing infrastructure in California would exceed the state’s demand by up to five times.
The team offers that further development of solar energy is complicated by the need to find space for solar power-generating equipment without significantly altering the surrounding environment.
Ms. Hernandez explained, “Integrating solar facilities into the urban and suburban environment causes the least amount of land-cover change and the lowest environmental impact.”
Just over 8 percent of all of the terrestrial surfaces in California have been developed by people, from cities and buildings to park spaces. Residential and commercial rooftops present plenty of opportunity for power generation through small and utility-scale solar power installations. Other compatible opportunities are available in open urban spaces such as parks.
Likewise, there is opportunity for additional solar construction in undeveloped sites that are not ecologically sensitive or federally protected, such as degraded lands.
“Because of the value of locating solar power-generating operations near roads and existing transmission lines, our tool identifies potentially compatible sites that are not remote, showing that installations do not necessarily have to be located in deserts,” Hernandez said.
This study included the two principle kinds of solar technologies, the photovoltaics, that use semiconductors and are similar to the solar panels found in consumer electronics, and concentrated solar power, which uses enormous curved mirrors to focus the sun’s rays.
A mix of both options would be possible, as best suits each particular area of installation, whether it is on a rooftop, in a park, on degraded lands, or anywhere else deemed compatible or potentially compatible. They found that small and utility-scale solar power could generate up to 15,000 terawatt-hours of energy per year using photovoltaic technology and 6,000 terrawatt-hours of energy per year using concentrating solar power technology.
Overall the team found that California has about 6.7 million acres (27, 286 square kilometers) of land that is compatible for photovoltaic solar construction and about 1.6 million acres (6,274 square kilometers) compatible for concentrating solar power. There is also an additional 13.8 million acres (55,733 square kilometers) that is potentially compatible for photovoltaic solar energy development with minimal environmental impact and 6.7 million acres (27,215 square kilometers) also potentially compatible for concentrating solar power development.
The team’s work shows it is possible to substantially increase the fraction of California’s energy needs met by solar, without converting natural habitat and causing adverse environmental impact and without moving solar installations to locations remote from the consumers.
“As California works to meet requirements that 33 percent of retail electricity be provided by renewable sources by 2020 and that greenhouse-gas emissions be 80 percent below 1990 levels by 2050, our research can help policymakers, developers, and energy stakeholders make informed decisions,” said Field, director of Carnegie’s Department of Global Ecology. “Furthermore, our findings have implications for other states and countries with similarly precious environmental resources and infrastructural constraints.”
Its quite a refreshing review, especially for the green crowd folks. Noticeably absent though, is the financial impact, the storage needed to provide power overnight and cloudy days and the means by which all of this is capitalized.
At the spending pace and the sheer size of the budget for the State of California burning through taxpayers money they would hardly notice the funding of most if not all the responsible fusion projects across the country. If anyone needs fusion to get to commercial breakeven its California taxpayers and ratepayers.