Novel microsphere photocatalysts show good performance for water splitting and water cleaning

22 December 2014

Researchers at the National University of Singapore and the Agency for Science, Technology and Research (A*STAR) in Singapore have produced novel microsphere catalysts that can improve water quality in daylight and also generate hydrogen as a green energy source. The novel multielement Au/La-SrTiO₃ microspheres were synthesized by a solvothermal method using monodisperse gold and La-SrTiO₃ nanocrystals as building blocks. A paper on their work was published in Chemistry – An Asian Journal.

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Photocatalytic materials use sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface. In addition to decomposing harmful molecules in water, photocatalysts are used to split water into its components of oxygen and hydrogen.

He-Kuan Luo, Andy Hor and colleagues from the A*STAR Institute of Materials Research and Engineering (IMRE) set out to improve an existing catalyst. Oxygen-based compounds such as strontium titanate (SrTiO₃₎ are promising, as they are robust and stable materials and are suitable for use in water. One of the team’s innovations was to enhance its catalytic activity by adding small quantities of the metal lanthanum, which provides additional usable electrical charges.

Catalysts also need to capture a sufficient amount of sunlight to catalyze chemical reactions. To enable the photocatalyst to harvest more light, the scientists attached gold nanoparticles to the lanthanum-doped SrTiO₃ microspheres. These gold nanoparticles are enriched with electrons and hence act as antennas, concentrating light to accelerate the catalytic reaction.

The porous structure of the microspheres results in a large surface area, as it provides more binding space for organic molecules to dock to. A single gram of the material has a surface area of about 100 square meters. The large surface area plays a critical role in achieving a good photocatalytic activity, noted Luo.

To demonstrate the efficiency of these catalysts, the researchers studied how they decomposed the dye rhodamine B in water. Within four hours of exposure to visible light 92% of the dye was gone—faster than conventional catalysts that lack gold nanoparticles.

Both the conduction and valence bands of Au/La-SrTiO₃ microspheres thus show favorable potential for proton reduction under visible light. The superimposed effect of Au nanoparticles and La doping in Au/La-SrTiO₃ microspheres led to high photocurrent density in photoelectrochemical water splitting and good photocatalytic activity in photodegradation of rhodamine B.

The team showed that the microparticles with gold nanoparticles performed better in water-splitting experiments than those without, further highlighting the versatility and effectiveness of these microspheres.

Resources

• Wang, G., Wang, P., Luo, H.-K. Hor, T. S. A. (2014) “Novel Au/La-SrTiO— microspheres: Superimposed effect of gold nanoparticles and lanthanum doping in photocatalysis,” Chemistry – An Asian Journal 9, 1854–1859 doi: 10.1002/asia.201402007

Lux Research: GaN-on-Si will dominate the GaN power electronics market for the next decade, reaching $1B by 2024

22 December 2014

Emerging materials such as gallium nitride (GaN) and silicon carbide (SiC) look to displace silicon in power electronic applications. While silicon and SiC (SiC-on-SiC) come in only one flavor, GaN comes in many different variants, including GaN-on-Si, GaN-on-SiC, and GaN-on-GaN. In a new report, Lux Research forecasts that the total market for GaN power electronics overall will grow at 32% CAGR, reaching $1.1 billion by 2024, or more than 5% of the total market share.

Each variety of GaN has advantages and disadvantages while also being better suited to different power electronics applications. For example, Lux notes, while GaN-on-Si offers price benefits over the other GaN types, GaN-on-SiC can offer benefits of efficient high-temperature operation.

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Lux forecasts that the GaN-on-silicon (Si) market will grow at more than 30% CAGR to reach nearly $1.0 billion by 2024, representing 90% of the total GaN market. This is largely due to the sheer number of companies developing GaN-on-Si solutions for power electronics markets.

GaN-on-Si in transportation and renewables and grid markets will reach about $380 million and $350 million, respectively, in 2024, proving to be the runaway leaders for adoption of GaN-on-Si.

GaN-on-SiC and GaN-on-GaN will have a limited play in power electronics until SiC and GaN substrates become substantially cheaper.

GaN-on-Si carbide (SiC) will be best adopted in the transportation segment, reaching nearly $100 million in 2024. SiC substrates’ ability to function efficiently at high temperatures will be a key driver for GaN-on-SiC adoption. In contrast, GaN-on-GaN will experience lukewarm adoption across all applications.

The success of GaN-on-Si will attract investments not only from silicon incumbent device manufacturers but also from foundries like Taiwan Semiconductor Manufacturing Company (TSMC) that are already invested in GaN-on-Si for light-emitting diodes (LEDs), Lux said. GaN-on-Si leverages silicon infrastructure, and with foundries becoming increasingly cash-rich, expect to see select foundries move upstream through direct partnerships, investments, or acquisition of device manufacturers in GaN-on-Si longer term.

Siemens unveils first series production EV with RACE architecture and system

22 December 2014

Siemens has unveiled the first electric series production vehicle with the central electronics and software architecture RACE. (Earlier post.) This technology, developed in the research project of the same name, replaces the entire control system with standard hardware and a kind of “operating system for automobiles.”
The basic idea is to control a variety of vehicle functions on a uniform, centralized computer platform instead of providing every system with its own hardware and software as today.

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This is expected to massively reduce the development time for vehicles. Another advantage is that thanks to the standardized software base, additional functions can be retrofitted more easily and cheaply than before. Vehicle weight will also be reduced substantially.

Together with electric car manufacturer StreetScooter, Siemens’ Corporate Technology, global research unit equipped a series production vehicle with RACE technology. The abbreviation translates loosely as “Robust and Reliant Automotive Computing Environment for Future ears.” A modern mid-range car has about 70 control devices installed in it and many meters of cable. There are a larger number of different interfaces and software applications in every vehicle that interoperate without a common software base.

Currently the parking sensor, navigation and air-conditioning system, for example, each need their own control device, which is connected to other control devices.

The complexity of this architecture, which has grown over the years, will become less and less transparent and thus hinder innovation. In vehicles with RACE technology, there is now only one central processing unit controlling all functions. These are designed with multiple redundancy for reasons of safety. Development time for new vehicles has now been reduced by up to 30% thanks to the new capabilities of RACE.

The aim is that new functions should be easy to add in the future as well, in the same way as with Plug Play on a computer. Today, this is hardly possible. To equip a car retroactively, say with a rear view camera, requires a large amount of time and effort for testing. The installation and integration of new hardware in the existing communication system is nearly impossible. The goal is to make this function more easily in the future.

With RACE, tests for new functions can be integrated and performed digitally; new components will be connected to the RACE computer, for example via Ethernet. The component can be used after downloading the new software onto one of the control processors.

Since functions no longer need a permanent connection to a control processor, it will be possible to install, for example, new infotainment or driving and assistance functions in the vehicle, ideally just in the form of software.

Less cable and fewer control devices will also have a positive impact on weight, and make cars less prone to faults. Electric cars in particular will profit from this because it increases their range and reduces running costs. The use of RACE is not, however, restricted to cars. The system architecture is also intended to be transferrable to multiple unit trains, smart grids or other complex systems.

Caltech team proposes taxonomy for solar fuels generators; different approaches to converting sunlight to chemical fuels

22 December 2014

Researchers at the California Institute of Technology are proposing a nomenclature and taxonomy for solar fuels generators—devices that harness energy from sunlight to drive the synthesis of chemical fuels. A number of different approaches to this technology are being pursued, many of which can be differentiated by the physical principles on which they are based, according to the Caltech team, led by Dr. Nathan Lewis.

In an open-access paper published in the RSC journal Energy Environmental Science, Dr. Lewis and colleagues outlined their method of using the source of the asymmetry that separates photogenerated electronics and holes as the basis for their taxonomy. They identify three basic device types: photovoltaic cells, photoelectrochemical cells, and photoelectrosynthetic particulate/molecular photocatalysts.

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An understanding of the inherent operating principles and the advantages and challenges associated with each of these device types will facilitate clear comparisons between devices as well as help guide research efforts toward improving these devices and achieving the ultimate goal of sustainable fuel production.

Illustrations of Nielander et al.’s different categories of solar fuels generators.

(a) Semiconductor/electrolyte junction in the dark and prior to equilibration in which the photovoltage and photocurrent are determined in whole or in part by the difference between Fermi level of the semiconductor (EF) and the electrochemical potential of the electrolyte solution (Eredox), denoted as DE.

(b) Semiconductor buried junction in the dark and prior to equilibration in which the photovoltage and photocurrent are determined by the difference between the Fermi levels (EF) of the two solid-state contacting phases (DE), shown here as two semiconductors. The DE is independent of any difference between the Fermi level of the solid contacting the electrolyte and the electrochemical potential of the electrolyte. The highly doped phase (in red) allows for ohmic contact between it and the contacting electrolyte phase.

(c) Particulate/molecular photocatalysts suspended or dissolved in solution. Each unit individually absorbs light, generates excited carriers and effects the desired chemical reactions at the particulate/molecular electrolyte interface.

Credit: RSC, Nielander et al. Click to enlarge.

All solar fuels generators require an electrical asymmetry to separate and transport photogenerated charge carriers vectorially, the authors explain. Without this vectorial separation and transport, the charge carriers—and the chemical products—would have no net directionality and thus would undergo no net separation. This would result in recombination of charge carriers and/or a loss of chemical potential in the resulting fuel/oxidant mixture.

The required vectorial separation can be effected by chemical and/or electrical potential gradients as well as by kinetic asymmetries at the interface between two unlike materials. We refer to this interface as a “junction”. We note that our usage of the term “junction” differentiates such an interface from an interface between two unlike materials that does not result in an asymmetry which produces a vectorial charge separation.

We propose that the various solar-fuels generators can be differentiated at a fundamental level based on the underlying principles used to accomplish vectorial charge separation and by the method in which the separated charge is used to effect the synthesis of chemical fuels.

Photovoltaic cells (PV). PV cells produce electricity from sunlight are widely available, and are referred to as solar electric cells. PV cells that produce fuels are referred to as “PV-biased electrosynthetic cells” and can consist of any number of buried junctions arranged electrically in series with electrocatalysts submerged in an electrolyte.

In all such systems, the Caltech team explained, the photovoltage generated by the structure is independent of the nature of the electrocatalyst/electrolyte interface.

• Advantages are the high reported solar-to-fuels efficiencies and the independence of the power-producing junction with respect to the formal potential for the reactions of interest.

• Issues include achieving a cost advantage for a system with the functioning photovoltaic cell immersed in the electrolyte, relative to a system that utilizes a discrete photo- voltaic cell in dry conditions wired to a discrete fuel-forming device, as well as finding catalyst/electrolyte interfaces that are transparent, conductive, and stable under operational, fuel- forming conditions.

• Key research needs involve the development of cost-competitive photovoltaic cells, the integration of components, discovery of materials, development of low-cost fabrication methods, and the stabilization of electrodes through the use of materials that act as transparent and conductive protecting layers.

Photoelectrochemical cells. (PEC) Devices utilizing solid/ionic-conductor junctions, also referred to as solid/electrolyte junctions, are called photoelectrochemical (PEC) cells. PEC cells that only produce electricity are referred to as regenerative photoelectrochemical cells.

PEC cells that produce fuels at the semi-conductor/electrolyte junction are referred to as photoelectrosynthetic cells.

The performance of photoelectrodes consisting of semiconductor/electrolyte junctions is determined by the energetics and kinetics of the semiconductor/electrolyte interface. Commonly, an electrocatalyst is incorporated at the semiconductor/electrolyte interface to improve the interfacial charge-transfer kinetics; however, for the device to remain categorized as a PEC cell, the nature of the electrolyte must affect the performance of the cell.

• Advantages of PEC cells are their simplicity of fabrication and the finding that inexpensive polycrystalline semiconductor/electrolyte junctions can often perform nearly as well as their single crystalline counterparts.

• Issues associated with PEC cells include obtaining a combination of materials that are operationally stable and also possess appropriate interfacial energetics and band gaps, as well as the development and integration of electrocatalysts into the semiconductor/electrolyte junction.

• Key research needs for solar fuels generators based on PEC cells involve the discovery and development of semiconducting materials that possess both the proper band gaps for effective sunlight absorption and well-positioned band energetics, and the development of methods for incorporating efficient electrocatalysts into semiconductor/electrolyte interfaces that are stable under operational, fuel-forming conditions.

Photovoltaic-biased photoelectrochemical cells. Coupling a PV cell with a PEC cell results in a cell that contains both a buried junction and a semiconductor/electrolyte junction—a PV-biased PEC cell. Like their parents, PV-biased PEC cells can produce electricity or fuel. PV-biased PEC cells that produce fuels and that include at least one buried junction may fall into a number of categories, which are systematically named based on whether fuel formation occurs at a solid/electrolyte junction in the device and the presence or absence of additional two-terminal regenerative PEC cells.

• PV-biased PEC cells in which fuel formation occurs at the solid/electrolyte junction are “PV-biased photoelectrosynthetic cells”.

• PV-biased PEC cells that produce fuels that are formed away from a solid/electrolyte junction, but include at least one isolated regenerative PEC cell, are referred to as “Regenerative PEC- and PV-biased electrosynthetic cells”.

Photoelectrosynthetic particulate/ molecular photocatalysts. The semiconducting material can be in a dispersed particulate form as opposed to a solid electrode. This approach support both the buried junction and the semiconductor/electrolyte junction motifs.

The particulate versions of PV and PEC cells, as well as the related photo-driven molecular photocatalysts wherein inorganic molecular compounds are dispersed in solution, share many of the same research challenges as their parent categories, with the added challenge of developing methods to physically separate the products of the fuel-forming reactions. The term cell does not apply to particulate schemes that employ neither addressable electrodes nor a built-in means to enforce the separation of products. For these reasons, we consider all three of these strategies to comprise members of the general category of photoelectrosynthetic particulate/molecular photocatalysts.

Resources

• Adam C. Nielander, Matthew R. Shaner, Kimberly M. Papadantonakis, Sonja A. Francis and Nathan S. Lewis (2015) “A taxonomy for solar fuels generators,” Energy Environ. Sci., 8, 16 doi: 10.1039/C4EE02251C

ETH team develops catalytic process to make lactic acid from glycerol biodiesel byproduct; 20% lower CO2 than fermentation pathway

22 December 2014

Researchers at ETH Zürich developed an eco-friendly cascade process to make large amounts of lactic acid from glycerol, a waste by-product in the production of biodiesel. Polylactic acid (PLA) is a promising alternative for making plastics, as it is biodegradable and made from renewable resources. Manufacturers use PLA for disposable cups, bags and other sorts of packaging. The demand for PLA is constantly rising and has been estimated to reach about one megaton per year by 2020.

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The research groups of ETH professors Konrad Hungerbühler and Javier Pérez-Ramírez at the Institute for Chemical and Bioengineering are now introducing a new method to produce lactic acid. The process is more productive, cost-effective and climate-friendly than sugar fermentation, which is the technology currently used to produce lactic acid. The new method’s greatest advantage is that it makes use of a waste feedstock: glycerol.

Glycerol is a by-product in the manufacturing of biodiesel, and as such is not high-grade but contains residues of ash and methanol. This waste substance is becoming more and more abundant, with 3 megatons in 2014 expected to increase to more than 4 megatons by 2020. Because of its impurity, glycerol is not suitable for the chemical or pharmaceutical industry. Moreover, it does not burn well and is thus not a good energy source.

Nobody knows what to do with this amount of waste glycerol. Normally, it should go through waste water treatment, but to save money and because it is not very toxic, some companies dispose of it in rivers or feed it to livestock. But there are concerns about how this affects the animals.

In the ETH cascade procedure, glycerol is first converted enzymatically to an intermediate called dihydroxyacetone, which is further processed to produce lactic acid by means of a heterogeneous catalyst.

The researchers of the Advanced Catalysis Engineering group of professor Pérez-Ramírez designed a tin-containing MFI zeolite catalyst with high reactivity and a long life span. The close collaboration between the two research groups allowed the catalyst to be improved step by step while at the same time performing the life cycle assessment of the procedure as a whole.

By improving several aspects of the catalyst design, the researchers were finally able to surpass sugar fermentation both from an environmental and an economic point of view.

Taking into account the energy saved by using the waste feedstock glycerol and the improved productivity, the new procedure reduces the overall CO₂ emission by 20% compared to fermentation: per kilogram of lactic acid produced, 6 kilograms of CO₂ are emitted with the new method compared to 7.5 kilograms with the conventional technology.

Also, by lowering the overall cost of the process, the researchers calculated a 17-fold increase of the profit possible by using the new process.

Resources

• Morales M, Dapsens PY, Giovinazzo I, Witte J, Mondelli C, Papadokonstantakis S, Hungerbühler K, Pérez-Ramírez J (2014) “Environmental and economic assessment of lactic acid production from glycerol using cascade bio- and chemocatalysis,” Energy Environmental Science, doi: 10.1039/C4EE03352C

Schaeffler to show 48V mild-hybrid SUV concept at NAIAS; phase 2 of development meets 2025 CAFE

22 December 2014

At the 2015 North American International Auto Show (NAIAS) in Detroit in January, Schaeffler will show the second phase of its concept car that meets 2025 CAFE requirements, including its mild hybridization with a 48-volt system. (Earlier post.)

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The vehicle is based on a modern, all-wheel-drive, midsize SUV with an automatic transmission. Last year during NAIAS, Schaeffler showed the first phase of the concept car that demonstrated its low-cost strategy to meet CAFE 2020 guidelines.

the use and optimization of a range of Schaeffler technologies allowed the vehicle’s fuel consumption to be reduced by 15%. These values were initially simulated using Schaeffler calculation programs and verified by Schaeffler’s experts in North America using measurements and test cycles, and then certified by an independent testing institute.

In addition to the 48 volt hybridization, Schaeffler incorporated other innovations, including: a permanent engaged starter; a four-wheel drive disconnect clutch; a thermal management module; as well as extensive damping and friction reduction measures in the drive train.

Additional examples of Schaeffler’s Mobility for Tomorrow strategy will be on display in the company’s Technology Suite, including its Formula-E racing car. This car was specially created for the electrically operated Monoposto Racing Series and has already raced in Asia and South America. Upcoming performances will be in Miami on March 4 and Long Beach in April 2015. Schaeffler is the technology partner of the German ABT team, whose driver, Lucas di Grassi, leads the championship from its beginning.