Hot Article – Page 28

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Nanorobots powered from beneath the skin

15 Jul 2011

Science fiction comes to life with the latest nanodevice that sits underneath the skin and converts near-infrared (NIR) light energy into electrical power. This is a promising wireless electrical power source for biological nanorobots for use within the human body, say scientists in Taiwan.

The nanodevice is an organic photovoltaic device (OPV) designed by Fang-Chung Chen and his team from National Chiao Tung University, in Hsinchu. OPVs are more commonly known for their applications in solar cell technology converting sunlight into electricity.

Here, Chen has developed an OPV device that uses NIR light, enabling the energy conversion to occur underneath the skins surface as biological tissues are highly transparent to NIR light. Made up of several layers; including indium tin oxide (ITO)-coated glass, anodic buffer, polymer/fullerene-mixed layer and calcium/aluminium cathode, the device is small, the shape of a fibre, and is ideal for a biological environment.

laser photovoltaic device

The device, the size of a fibre, converts NIR radiation from a laser into electrical power

To test their theory, Chen’s team covered the OPV device with a 3mm layer of porcine skin and fired a NIR laser on it at the maximum threshold tolerated by human skin. The team measured the OPV electrical output as 0.32µW, which is more than enough to drive many biological nanodevices at the same time – the typical power needed for one nanodevice is approximately 10nW.

Yang Yang, Director of the Nano Renewable Energy Center, at the University of California, Los Angeles in the US, says: ‘This is a very interesting and smart design, which will be potentially important and useful for medical applications. Chen has created a new direction for OPVs.’

‘In addition to tissue repair or medical target identification, this OPV device could act as an energy source to trigger biomedical functions of the nanorobots, or more straightforward applications in neurostimulation,’ Chen tells Chemistry World. ‘Imagine that, with this approach, we might be able to use optical methods, non-intrusively, to trigger the electrical stimulation deep inside the body to inhibit pain or to control the disease directly,’ he adds.

Emma Shiells

Read the Energy & Environmental Science article:

Near-infrared laser-driven polymer photovoltaic devices and their biomedical applications
Jyh-Lih Wu, Fang-Chung Chen, Ming-Kai Chuang and Kim-Shih Tan
Energy Environ. Sci., 2011
DOI: 10.1039/c1ee01723c

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The rise of the sodium ion battery

14 Jul 2011

A nanostructured material has been used as an anode in a sodium ion battery for the first time and its performance is better than all carbon materials tested so far, say researchers from Germany.

With the increasing demand for large scale stationary storage systems, cheap sodium-based systems have become attractive. Graphite, the standard anode material in lithium ion batteries is not suitable for a sodium-based system because sodium cannot be inserted between graphite layers. Instead, the team have made a porous carbon material to capture the sodium. The resulting material has excellent rate capability at room temperature, says the team.

Read the Energy & Environmental Science article today:

Room-temperature Sodium-ion batteries: Improving the rate capability of carbon anode materials by templating strategies
S Wenzel, T Hara, J Janek and P Adelhelm, Energy Environ. Sci., 2011
DOI: 10.1039/c1ee01744f

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Themed issue: Biomimetic approaches to artificial photosynthesis

13 Jul 2011

We are delighted to present the current issue of Energy & Environmental Science as a themed issue on biomimetic approaches to artificial photosynthesis, Guest Edited by Leif Hammarström and Michael R. Wasielewski.

The issue includes a lively mix of reviews, Perspective feature articles, Communications and full papers. Take a look at the great issue today, including:

Review
Spectroscopically characterized intermediates of catalytic H2 formation by [FeFe] hydrogenase models
Stefanie Tschierlei, Sascha Ott and Reiner Lomoth, Energy Environ. Sci., 2011, 4, 2340

Perspective
Artificial photosynthetic systems. Using light and water to provide electrons and protons for the synthesis of a fuel
Christian Herrero, Annamaria Quaranta, Winfried Leibl, A. William Rutherford and Ally Aukauloo, Energy Environ. Sci., 2011, 4, 2353

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A step forward for space power

29 Jun 2011

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.

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

28 Jun 2011

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

27 Jun 2011

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

23 Jun 2011

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 splitting It 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

16 Jun 2011

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?

16 Jun 2011

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

10 Jun 2011

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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