Archive for June, 2011

Energy & Environmental Science new record Impact Factor of 9.4

New citation data just released by Thomson ISI shows the new Impact Factor of Energy & Environmental Science to be 9.446.

Energy & Environmental Science is not only still the #1 ranking journal in its ISI subject category, but now is one of the top-ranking chemistry journals.

The fantastic news demonstrates that the journal continues to attract and publish outstanding research, which appeals to its community-spanning international readership.

We wish to thank all our Board members, authors and referees for their continuing support – your input has made the journal what it is.

Please do continue to submit your best work to Energy & Environmental Science.We look forward to further success in the months and years ahead.

With our best wishes,

Energy & Environmental Science Editorial Office

Find out more about RSC Publishing’s 2010 Impact Factors

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A step forward for space power

US scientists have gained insights into how to improve polymer solar cells’ stability in space to power shuttles.

Inorganic solar cells have been investigated as power sources for spacecraft, and they are efficient, but they are heavy, so are costly to launch. Because of this, the power gains are marginal.

Organic polymer solar cells are light and flexible, making them attractive for use in satellites. But, these cells would degrade when exposed to the x-ray radiation present in space, making them inefficient. The x-rays pass through the relatively transparent polymer layer, causing a loss in voltage in the device.

Yang Yang from the University of California, Los Angeles, and Roderick Devine from the Air Force Research Laboratory at Kirtland Air Force Base, New Mexico, have discovered that the interface between the photoactive polymer layer and the electrode of the cell is the key to the cell’s reaction to x-rays.  

Satellite

Polymer solar cells are lightweight so can be transported to space at a fraction of the cost of inorganic cells that are being investigated as power sources for spacecraft

 The team saw that a charge accumulating at the interface after radiation exposure was causing the loss of voltage and that by modifying the interface, they could lessen this accumulation and improve the cell’s stability. They tested different electrode interfaces – Ca/Al, Al and LiF/Al compared to TiO2:Cs/Al and ZnO/Al interfaces – and found that the metal-oxide/metal interfaces were less susceptible to radiation.

Jianyong Ouyang from the National University of Singapore, an expert in polymeric electronic materials and devices, is impressed by Yang’s research. ‘The work is practically significant in that it provides guidance for improving polymer solar cells,’ he says.

‘In the immediate future, we will continue to focus our efforts on the interface to gain a greater understanding and control of its properties,’ concludes Yang.

Catherine Bacon

Read the Energy & Environmental Science article:

Interface design to improve stability of polymer solar cells for potential space applications
Ankit Kumar, Nadav Rosen, Roderick Devine and Yang Yang
Energy Environ. Sci., 2011, DOI: 10.1039/c1ee01368h

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Nanogenerators for environmental sensors

A nanomaterial-based, self-powered sensor that detects mercury in water has been developed by teams from the US and Korea.

Most environmental sensors need to be wired to a power supply, which can be expensive in terms of parts and labour. There is also the potential for contamination from batteries. Solar energy is a more attractive, and greener, alternative, but it relies on weather conditions and time of day. 

Instead, Zhong Lin Wang, from the Georgia Institute of Technology, Atlanta, US, and colleagues have made a standalone sensor that harvests energy from movements occurring in its surroundings. They created a nanogenerator to harvest the energy using zinc oxide nanowires (ZnO NW). The nanowires are piezoelectric, which means that they accumulate charge when they are moved, and they’re environmentally friendly.

Zinc oxide nanowires and gold film on flexible substrates

Left: zinc oxide nanowires on a flexible substrate (top) with a gold film electrode (bottom); right: zinc oxide nanowires

 The team made the device by placing the nanowires onto a flexible substrate, with the ends of the wires in contact with a gold film electrode. When the nanowires were compressed as a result of movement, electrons flowed along the wires to the gold conductor. With successive compression and release, the electrons flowed back and forth, producing an electrical current. The output was stored in a capacitor to power the sensor to detect pollutants periodically. The sensor was made from single walled carbon nanotubes that turn on an LED indicator. Wang tested the device in water and found that the LED lit up in the presence of mercury ions, and the mercury concentration was indicated by the intensity of the LED. 

‘What’s most exciting is that we have built a self-powered system that is driven by energy harvested from the environment that can work independently and sustainably,’ says Wang.  In the future, Wang hopes to apply the nanogenerators in other areas besides environmental sensing. ‘There are potential applications in wireless biosensing, sensor networks, personal electronics and even national security,’ he says. His team is also looking at harvesting energy from the environment in other ways such as turbulence in water or air flow and sonic waves.

Jun Liu, from the Pacific Northwest National Laboratory, Richland, US, who works on the synthesis and applications of nanostructured materials for energy was impressed with the device and says that the research has great potential for practical applications. ‘Some biomedical applications or remote area sensing make it difficult to provide the power for very small devices. Fully functional and standalone nanodevices will be handy for these applications,’ he says.

Rebecca Brodie

Read the Energy & Environmental Science article:

Self-powered environmental sensor system driven by nanogenerators
Minbaek Lee, Joonho Bae, Joohyung Lee, Churl-Seung Lee, Seunghun Hong and Zhong Lin Wang
Energy Environ. Sci., 2011, DOI: 10.1039/c1ee01558c

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Polymeric complexes for lithium storage

Organic materials look to finally fulfil their potential as electrodes after scientists in France and China create a new type of lithium storage material that uses polymeric complexes. 

Structure of the material showing the lithium storage sites (pink balls).

Although previous attempts at making lithium storage materials (important for lithium ion batteries) from polypyrrole complexes have failed due to their negligible storage capacity, Qingyu Kong and Zhaoxiang Wang et al. have modified traditional polymerisation and reduction processes to make a polypyrrole–iron–oxygen complex that has overcome previous problems. 

The multilayered material possesses strong intralayer Fe–N coordination, which endows it with high specific capacity. In addition, the high reversibility of the Fe–O–Fe interactions during cycling means the material has high stability. Finally, the conducting polypyrrole matrix gives the material an excellent rate performance. 

Read about this exciting new find here.

Polypyrrole-iron-oxygen coordination complex as high performance lithium storage material
Qingyu Kong and Zhaoxiang Wang et al.
Energy Environ. Sci., 2011 DOI: 10.1039/C1EE01275D

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Water splitting using bacteriorhodopsin/TiO2 nanotubes

HOT paper:

This Energy & Environmental Science article reports for the first time the use of bacteriorhodopsin(bR)/TiO2 hybrid electrodes in photoelectrochemical water oxidation cells.

water splittingIt is thought the proton pumping property of bR can be used in a variety of applications, especially those related to third generation photovoltaic cells.

Read this HOT article today:

Bacteriorhodopsin/TiO2 nanotube arrays hybrid system for enhanced photoelectrochemical water splitting
Nageh K. Allam, Chun-Wan Yen, Rachel D. Near and Mostafa A. El-Sayed
Energy Environ. Sci., 2011, DOI: 10.1039/C1EE01447A

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Not a basic fuel cell

A hydrogen peroxide fuel cell has been operated under acidic conditions for the first time by scientists in Japan and Korea.

Hydrogen peroxide can be a benign energy carrier because it can be produced by the two-electron reduction of oxygen and can also generate electricity by hydrogen peroxide fuel cells. Electrochemical oxygen reduction takes place in acidic conditions with high current efficiencies, but all hydrogen peroxide fuel cells, until now, have operated under basic conditions.

The acidic fuel cell’s open current potential was a dramatic improvement over fuel cells operated under basic conditions, say the researchers.

Read the paper today -
Protonated iron-phthalocyaninate complex used for cathode material of a hydrogen peroxide fuel cell operated under acidic conditions
Y Yamada, S Yoshida, T Honda and S Fukuzumi
Energy Environ. Sci., 2011, DOI: 10.1039/c1ee01587g

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What’s the best choice for supercapacitors: graphene or graphene oxide?

Graphene oxide may be a better choice as an electrode for supercapacitors than graphene because it exhibits higher capacitance, shorter processing time and is cheaper than graphene, say researchers from China.

Supercapacitors are promising energy storage devices for electric vehicles because of their high power densities and long cyclic lives.

Graphene, a two-dimensional nanosheet of graphite, has been the material of choice for supercapacitors because it possesses superior electrical conductivity, a high theoretical surface area and chemical tolerance. But, owing to the unavoidable aggregation of graphene nanosheets, the surface area is usually much lower than the theoretical one and its capacitance is generally in the range 100–200 F g-1.

Graphene oxide is an intermediate during the synthesis of graphene. Despite the fact that some graphene oxide-based nanocomposites have performed well in supercapacitors, it has been said that graphene oxide is not suitable as an electrode material because of its poor conductivity, but the team contradict this with their findings.

Read the article in full:
What Is the Choice for Supercapacitors: Graphene or Graphene Oxide?
B Xu, S Yue, Z Sui, X Zhang, S Hou, G Cao and Y Yang
Energy Environ. Sci., 2011, DOI: 10.1039/c1ee01198g

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Energy & Environmental Science Most-Read Articles for Q1 2011

Top 25 most-read Energy & Environmental Science articles for Q1

Review of solutions to global warming, air pollution, and energy security
Mark Z. Jacobson
DOI: 10.1039/B809990C

Graphene based new energy materials
Yiqing Sun, Qiong Wu and Gaoquan Shi
DOI: 10.1039/C0EE00683A

Organic tandem solar cells: A review
Tayebeh Ameri, Gilles Dennler, Christoph Lungenschmied and Christoph J. Brabec
DOI: 10.1039/B817952B

Bulk nanostructured thermoelectric materials: current research and future prospects
A. J. Minnich, M. S. Dresselhaus, Z. F. Ren and G. Chen
DOI: 10.1039/B822664B

Flexible energy storage devices based on graphene paper
Hyeokjo Gwon, Hyun-Suk Kim, Kye Ung Lee, Dong-Hwa Seo, Yun Chang Park, Yun-Sung Lee, Byung Tae Ahn and Kisuk Kang
DOI: 10.1039/C0EE00640H

Carbon nanotubes for lithium ion batteries
Brian J. Landi, Matthew J. Ganter, Cory D. Cress, Roberta A. DiLeo and Ryne P. Raffaelle
DOI: 10.1039/B904116H

Development and challenges of LiFePO4 cathode material for lithium-ion batteries
Li-Xia Yuan, Zhao-Hui Wang, Wu-Xing Zhang, Xian-Luo Hu, Ji-Tao Chen, Yun-Hui Huang and John B. Goodenough
DOI: 10.1039/C0EE00029A

Graphene-based nanomaterials for energy storage
Martin Pumera
DOI: 10.1039/C0EE00295J

Highly active cobalt phosphate and borate based oxygen evolving catalysts operating in neutral and natural waters
Arthur J. Esswein, Yogesh Surendranath, Steven Y. Reece and Daniel G. Nocera
DOI: 10.1039/C0EE00518E

Nanostructured silicon for high capacity lithium battery anodes
Jeannine R. Szczech and Song Jin
DOI: 10.1039/C0EE00281J

Development of alternative photocatalysts to TiO2: Challenges and opportunities
María D. Hernández-Alonso, Fernando Fresno, Silvia Suárez and Juan M. Coronado
DOI: 10.1039/B907933E

CO2 capture by solid adsorbents and their applications: current status and new trends
Qiang Wang, Jizhong Luo, Ziyi Zhong and Armando Borgna
DOI: 10.1039/C0EE00064G

Vertically-aligned nanostructures of ZnO for excitonic solar cells: a review
Irene Gonzalez-Valls and Monica Lira-Cantu
DOI: 10.1039/B811536B

Carbon nanostructures for energy
Nazario Martin, Dirk M. Guldi, Andreas Hirsch
DOI: 10.1039/C1EE90001C

Catalytic routes for the conversion of biomass into liquid hydrocarbon transportation fuels
Juan Carlos Serrano-Ruiz and James A. Dumesic
DOI: 10.1039/C0EE00436G

Green energy storage materials: Nanostructured TiO2 and Sn-based anodes for lithium-ion batteries
Da Deng, Min Gyu Kim, Jim Yang Lee and Jaephil Cho
DOI: 10.1039/B823474D

The role of buffer layers in polymer solar cells
Riccardo Po, Chiara Carbonera, Andrea Bernardi and Nadia Camaioni
DOI: 10.1039/C0EE00273A

Electrospun nanofibers in energy and environmental applications
V. Thavasi, G. Singh and S. Ramakrishna
DOI: 10.1039/B809074M

Olivine LiFePO4: development and future
Yonggang Wang, Ping He and Haoshen Zhou
DOI: 10.1039/C0EE00176G

Nanostructured carbon-based electrodes: bridging the gap between thin-film lithium-ion batteries and electrochemical capacitors
Seung Woo Lee, Betar M. Gallant, Hye Ryung Byon, Paula T. Hammond and Yang Shao-Horn
DOI: 10.1039/C0EE00642D

Microalgae as biodiesel & biomass feedstocks: Review & analysis of the biochemistry, energetics & economics
Peter J. le B. Williams and Lieve M. L. Laurens
DOI: 10.1039/B924978H

High-performance Si microwire photovoltaics
Michael D. Kelzenberg, Daniel B. Turner-Evans, Morgan C. Putnam, Shannon W. Boettcher, Ryan M. Briggs, Jae Yeon Baek, Nathan S. Lewis and Harry A. Atwater
DOI: 10.1039/C0EE00549E

Bulk-heterojunction hybrid solar cells based on colloidal nanocrystals and conjugated polymers
Yunfei Zhou, Michael Eck and Michael Krüger
DOI: 10.1039/C0EE00143K

An overview of CO2 capture technologies
Niall MacDowell, Nick Florin, Antoine Buchard, Jason Hallett, Amparo Galindo, George Jackson, Claire S. Adjiman, Charlotte K. Williams, Nilay Shah and Paul Fennell
DOI: 10.1039/C004106H

Design of solid catalysts for the conversion of biomass
Roberto Rinaldi and Ferdi Schüth
DOI: 10.1039/B902668A

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HOT Communication: Polymer/nanocrystal (NC) hybrid solar cells

Polymer/nanocrystal (NC) hybrid solar cells with an efficiency of 2.14% were fabricated from aqueous CdTe NCs and poly(p-phenylenevinylene) precursor.

Polymer NC solar cell

Read this ‘HOT’ Communication:
Efficient polymer/nanocrystal hybrid solar cells fabricated from aqueous materials
Weili Yu, Hao Zhang, Zhanxi Fan, Junhu Zhang, Haotong Wei, Ding Zhou, Bin Xu, Fenghong Li, Wenjing Tian and Bai Yang
Energy Environ. Sci., DOI: 10.1039/C1EE01485D

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An electric partnership

Researchers in the US have uncovered an intriguing electrochemical partnership between two bacteria, which boosts their combined ability to generate an electric current when they are grown in a bioelectrochemical reactor. The work could lead to more efficient reactors, as well as throwing light on the ecological relationship between microbes in the wider environment.

Certain microbes can metabolise organic waste in a way that releases electrons, which can be transferred to an electrode and used to generate electric power or in electrochemical reactions to make useful products. One common bacterium that has been investigated in such bioelectrochemical systems is Pseudomonas aeruginosa.  In some natural environments, such as marine sediments, P. aeruginosa is found to be associated with another microbe, Enterobacter aerogenes. On the face of things, such a partnership appears unlikely as each bacterium has apparently different metabolic preferences. Now, a team led by Lars Angenent at Cornell University, Ithaca, has shown why these organisms can live in harmony in an energetically efficient way.

‘We found that when you feed a sugar such as sucrose to the mixed colony, this is fermented by E. aerogenes and one of the fermentation products is 2,3-butanediol,’ says Angenent. ‘This in turn is a substrate for P. aeruginosa. But not only does the alcohol act as a nutrient for Pseudomonas, it also stimulates it to produce redox mediators called phenazines.’

Bioelectrochemical systems with the bacteria P. aeruginosa with glucose (right) and 2,3-butanediol (left)

The current produced by a culture of P. aeruginosa with 2,3-butanediol (left) was increased two-fold compared with glucose (right) as the carbon source, owing to enhanced phenazine production

 

Phenazines are three-ringed nitrogen-containing compounds that can ‘traffic’ electrons. One particular phenazine that 2,3-butanediol stimulates P. aeruginosa to produce in excess is pyocyanin. This is used by E. aerogenes to increase its efficiency of metabolism of its sugar substrate from relatively inefficient fermentation to respiration, which generates electrons that can be fed into the electrode of the reactor.

The team found that when the two organisms are together, they produce 14 times more electric current than when on their own. Feeding a monoculture of P. aeruginosa with 2,3-butanediol results in a doubling of electric current, while exposing E. aerogenes to pyocyanin causes its current production to rise almost 20-fold. The study is the first to demonstrate metabolite based ‘inter-species communication’ in bioelectrochemical systems, resulting in enhanced electrochemical activity, says Angenent, adding: ‘It also explains how an inconsequential fermenter can become an important electrode-respiring bacterium within an ecological network at the anode.’

Korneel Rabaey, who works at the Advanced Water Management Centre at the University of Queensland in Australia, says: ‘As microbial populations will be essential for stable current generation, particularly when waste feedstocks are used as a fuel, understanding what drives high current output and stable community performance is an essential part in the development of this technology.’

Simon Hadlington

Link to journal article

Metabolite-based mutualism between Pseudomonas aeruginosa PA14 and Enterobacter aerogenes enhances current generation in bioelectrochemical systems
Arvind Venkataraman, Miriam A. Rosenbaum, Sarah D. Perkins, Jeffrey J. Werner and Largus T. AngenentEnergy Environ. Sci., 2011
DOI: 10.1039/c1ee01377g

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