Archive for August, 2013

Enabling long shelf lifetime by purification of PBDTTPD

Organic solar cells have attracted wide interest in the scientific community as a possible alternative for silicon based photovoltaics in certain areas. While laboratory efficiency of organic devices went beyond 10 % within the last years, lifetime issues such as rapid performance degradation remain to be solved.

Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities

In a recent article, Mateker et al. examined the performance degradation of solar cells made of the commonly used polymers PBDTTPD and PC61BM. Earlier findings indicated that cells made with PBDTTPD of high average molecular weight (Mw) degraded even in inert atmosphere and darkness while those of low Mw did not.

By intentional contamination with the small molecule TPD, the researchers demonstrated the influence of such impurities onto device performance. As a consequence, high weight PBDTTPD was thoroughly purified. Devices utilizing this filtered polymer demonstrated shelf lifetimes beyond 111 days.

The performance reduction of the unfiltered high Mw polymer is attributed by the researchers to small molecules which form a layer at the cathode contact of the cell. This layer was indicated by the widely known S-shaped JV-characteristic.  Such features are developed within less a week of storage in darkness. By removing the old and evaporating a new cathode layer, device performance was partially recovered and the standard solar cell JV-curve shape was re-established.

Intentional introduction of TPD (a building block of PBDTTPD and thus a possible residue of the synthesising reactions) into the low Mw polymer created the same behaviour as for the unfiltered high Mw counterpart. In consequence, the authors removed small molecule impurities from the high Mw polymer by size exclusion chromatography (SEC) and demonstrated the excellent improvement of device lifetime.

Read more detail in the article:

Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities
William R. Mateker, Jessica D. Douglas, Clément Cabanetos, I. T. Sachs-Quintana, Jonathan A. Bartelt, Eric T. Hoke, Abdulrahman El Labban, Pierre M. Beaujuge, Jean M. J. Fréchet and Michael D. McGehee
DOI: 10.1039/C3EE41328D

By Sebastian Axmann

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This week’s HOT article

Take a look at this exciting article that has been recently published online

Black anatase titania enabling ultra high cycling rates for rechargeable lithium batteries
Seung-Taek Myung, Masaru Kikuchi, Chong Seung Yoon, Hitoshi Yashiro, Sun-Jae Kim, Yang-Kook Sun and Bruno Scrosati
Energy Environ. Sci., 2013, Advance Article
DOI: 10.1039/C3EE41960F

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Meet Chengdu Liang: Energy & Environmental Science’s newest Advisory Board member

Chengdu Liang

Energy & Environmental Science (EES) is delighted to welcome Dr Chengdu Liang as an Advisory Board member.

Chengdu Liang is a scientist at the Center for Nano-phase Materials Sciences, Oak Ridge National Laboratory, USA. His research focusses on energy conversion and storage, catalytic nanomaterials, mesoporous materials and metal and metal oxide/sulfide nanoparticles. He is well known for his work on developing lithium-sulfur batteries and lithium-ion batteries.Energy & Environmental Science

On behalf of Chengdu Liang and the Editor-in-Chief Nathan Lewis (Caltech) we invite you to submit your best research to Energy & Environmental Science.

EES publishes outstanding, community-spanning, agenda-setting research covering all aspects of energy and environmental research. With an Impact Factor of 11.65, which is rising fast, it the ideal place to publish your work.

So you can see for yourself the quality of work in EES, we have collected together some recent articles in Dr Liang’s exciting research fields, with a selection available to read for free for a limited period.

Reviews

FREE: Na-ion batteries, recent advances and present challenges to become low cost energy storage systems
Verónica Palomares, Paula Serras, Irune Villaluenga, Karina B. Hueso, Javier Carretero-González and Teófilo Rojo
DOI: 10.1039/C2EE02781J

FREE: Mg rechargeable batteries: an on-going challenge
Hyun Deog Yoo, Ivgeni Shterenberg, Yosef Gofer, Gregory Gershinsky, Nir Pour and Doron Aurbach
DOI: 10.1039/C3EE40871J

FREE: The pursuit of rechargeable solid-state Li–air batteries
Fujun Li, Hirokazu Kitaura and Haoshen Zhou
DOI: 10.1039/C3EE40702K

FREE: Update on Na-based battery materials. A growing research path
Verónica Palomares, Montse Casas-Cabanas, Elizabeth Castillo-Martínez, Man H. Han and Teófilo Rojo
DOI: 10.1039/C3EE41031E

FREE: Room-temperature stationary sodium-ion batteries for large-scale electric energy storage
Huilin Pan, Yong-Sheng Hu and Liquan Chen
DOI: 10.1039/C3EE40847G

FREE: Challenges of non-aqueous Li–O2 batteries: electrolytes, catalysts, and anodes
Fujun Li, Tao Zhang and Haoshen Zhou
DOI: 10.1039/C3EE00053B

FREE: High temperature sodium batteries: status, challenges and future trends
Karina B. Hueso, Michel Armand and Teófilo Rojo
DOI: 10.1039/C3EE24086J

FREE: Electrical energy storage for transportation—approaching the limits of, and going beyond, lithium-ion batteries
Michael M. Thackeray, Christopher Wolverton and Eric D. Isaacs
DOI: 10.1039/C2EE21892E

FREE: Ti-based compounds as anode materials for Li-ion batteries
Guan-Nan Zhu, Yong-Gang Wang and Yong-Yao Xia
DOI: 10.1039/C2EE03410G

FREE: Lithium-ion batteries. A look into the future
Bruno Scrosati, Jusef Hassoun and Yang-Kook Sun
DOI: 10.1039/C1EE01388B

FREE: Challenges in the development of advanced Li-ion batteries: a review
Vinodkumar Etacheri, Rotem Marom, Ran Elazari, Gregory Salitra and Doron Aurbach
DOI: 10.1039/C1EE01598B

Original research

Controlled synthesis of hierarchical CoxMn3−xO4 array micro-/nanostructures with tunable morphology and composition as integrated electrodes for lithium-ion batteries
Le Yu, Lei Zhang, Hao Bin Wu, Genqiang Zhang and Xiong Wen (David) Lou
DOI: 10.1039/C3EE41181H

CuO/PVDF nanocomposite anode for a piezo-driven self-charging lithium battery
Xinyu Xue, Ping Deng, Shuang Yuan, Yuxin Nie, Bin He, Lili Xing and Yan Zhang
DOI: 10.1039/C3EE41648H

Synthesis of Mo2N nanolayer coated MoO2 hollow nanostructures as high-performance anode materials for lithium-ion batteries
Jun Liu, Shasha Tang, Yakun Lu, Gemei Cai, Shuquan Liang, Wenjun Wang and Xiaolong Chen
DOI: 10.1039/C3EE41006D

Charge transport in lithium peroxide: relevance for rechargeable metal–air batteries
Maxwell D. Radin and Donald J. Siegel
DOI: 10.1039/C3EE41632A

Towards high energy density sodium ion batteries through electrolyte optimization
Alexandre Ponrouch, Rémi Dedryvère, Damien Monti, Atif E. Demet, Jean Marcel Ateba Mba, Laurence Croguennec, Christian Masquelier, Patrik Johansson and M. Rosa Palacín
DOI: 10.1039/C3EE41379A

A membrane-free lithium/polysulfide semi-liquid battery for large-scale energy storage
Yuan Yang, Guangyuan Zheng and Yi Cui
DOI: 10.1039/C3EE00072A

Lithium metal fluorosulfate polymorphs as positive electrodes for Li-ion batteries: synthetic strategies and effect of cation ordering
Rajesh Tripathi, Guerman Popov, Brian L. Ellis, Ashfia Huq and L. F. Nazar
DOI: 10.1039/C2EE03222H

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Solar Energy for Afterhours

Sr- and Mn-doped LaAlO3−δ for solar thermochemical H2 and CO productionA major drawback to solar energy is the fact that it places us at the mercy of nature’s schedule. To get around this we need some method of storing it such as converting it into fuel. Whereas electric storage requires batteries, fuel storage only needs barrels and tanks. In a paper recently published in EES, researchers at Sandia National Labs demonstrated an improved method of converting solar energy directly into fuel.

The researchers identified an improved catalyst that splits water (or carbon dioxide) after heating by concentrating solar: using mirrors or lenses to shine lots of sunlight on one spot to get it really hot. At high temperatures (traditionally above 1500°C), oxygen is liberated from the catalyst. The catalyst is then cooled (traditionally to 800°C) and exposed to water vapor (or carbon dioxide gas). Starved for oxygen, the catalyst steals it from the water (or carbon dioxide) to leave hydrogen (or carbon monoxide). These products may either be directly used as fuel or for synthesis of more traditional fuels such as gasoline.

The improved catalyst is from a class of materials called “perovskite oxides” and contains a mix of strontium, lanthanum, manganese, aluminum and oxygen. Compared to traditional catalysts that use cerium or iron, this improved catalyst performs over a smaller range of temperatures: 1350°C for oxygen liberation and 1000°C for hydrogen (or carbon monoxide) production. This decrease in temperature range is important to ensuring the life of the catalyst, which (cycled every 5 minutes for 8 hours per day, 300 days per year over 10 years) must be sturdy enough to withstand 300-thousand cycles. It is anticipated that further exploration into this class of catalysts will yield further improvements.

Read the article in EES today:

Sr- and Mn-doped LaAlO3−δ for solar thermochemical H2 and CO production
Anthony H. McDaniel, Elizabeth C. Miller, Darwin Arifin, Andrea Ambrosini, Eric N. Coker, Ryan O’Hayre, William C. Chueh and Jianhua Tong
DOI: 10.1039/C3EE41372A

Robert Coolman EES guest web-writerBy Robert Coolman

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Hydrogen from the sun: the feasibility of industrial-scale photocatalytic H2 production

Chemists and chemical engineers from Cal-Tech, Stanford, and the US Department of Energy collaborated to investigate four methods of industrial-scale hydrogen gas generation directly from sunlight, via photocatalysis.

The lowest-tech solution, giant ‘baggies’ containing water and a photocatalytic slurry that co-generate hydrogen and oxygen, is the least expensive option, but in terms of land use is surprisingly as efficient as higher-tech panel-based options. Though this is a technical report, anyone interested in renewable energy and the hydrogen economy on a larger scale would find this interesting.

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry

Hydrogen is the single most promising fuel for the future economy. Although >95% of it is presently made by steam reforming, it can be generated independently from fossil fuels. Thermal reforming of biofuels, renewably powered electrolysis, and photolytic generation together represent the possibilities for renewable H2 generation, and this paper investigates the viability of the last, modelling the scale-up of present technologies for H2 generation to ten tonnes per day. The US Department of Energy (DoE) guidelines set $2-4/kg H2 as a reasonable threshold for viability; based on an ideal location for gathering solar energy, the authors found that two of the four designs viably meet this goal.

Photocatalysis couples the hydrogen evolution reaction (HER) to the oxygen evolutio
lving the proposed overall efficiency. The first design predominates, and is proposed to produce H2 at $1.60/kg.n reaction (ORR). Two designs are based on slurries of photocatalytically active particles in water-filled HDPE bags. The single-bed system evolves H2 and O2 simultaneously, posing an explosive risk and requiring separation, but is simple and cost-effective. The dual-bed system evolves the two gases separately, but requires both the redox reaction of an efficiently redox-cycling ‘mediator’ (e.g. Fe2+/Fe3+) to be coupled to the OER and HER reactions and porous bridges between half-cells to transport the mediator between the cells, significantly complicating the design and halving the efficiency.

The other two designs are based on panels composed of two photocatalytically active layers between a transparent anode exposed to the sun where the HER occurs and a metal cathode where the OER occurs. The third design involves flat panels. The fourth design uses cylindrical parabolas for a 10:1 light concentration to increase efficiency. In both designs, the two reactions are inherently separated, and although panels are more efficient for the area collecting sunlight, panel spacing makes their footprint larger. Of these, the parabolic design predominates, producing at $3.20/kg.

Thus, both the giant baggie and concentrator panel options are economically viable – the baggies are cheaper, but the panels have fewer unknowns in terms of their safety, lifetime, and mass production. Compare these efficiencies with those of electrolyzer apparatuses paired to solar electrical generation, a further study the authors recommend, and we’ll have a good picture of the future of renewable fuel generation.

Read the article in EES:

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry
Blaise A. Pinaud, Jesse D. Benck, Linsey C. Seitz, Arnold J. Forman, Zhebo Chen, Todd G. Deutsch, Brian D. James, Kevin N. Baum, George N. Baum, Shane Ardo, Heli Wang, Eric Miller and Thomas F. Jaramillo
DOI: 10.1039/C3EE40831K, Analysis

Benjamin Britton new EES guest web writerBy Benjamin Britton

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A Symphony of Components: Hierarchical CoxMn3-xO4 Electrodes

While the idea of micro/ nanostructured electrode materials has been very effective for developing high-performance lithium-ion batteries, integrated 3D electrodes with hierarchical arrays are the boutique avenues going forward. A recent Energy and Environmental Science paper by Yu et al presents morphology-controlled tunable CoxMn3-xO4 structures that exhibit interesting electrochemical performance.

Controlled synthesis of hierarchical CoxMn3−xO4 array micro-/nanostructures with tunable morphology and composition as integrated electrodes for lithium-ion batteries

The strategy of growing electroactive nanostructures on conductive substrates to form integrated 3D electrodes is interesting not only from a device-design standpoint but also for efficient electron transport, as noted by the authors. The synthesis strategy used is robust and well controlled. I find their approach and implementation of direct growth of free-standing and tailored CoxMn3-xO4 structures on current-collecting substrates to be an important and logical step towards integrated electrodes for high performance energy storage devices.

Electrode materials for lithium-ion batteries are the poster child for structure-performance relationships. The interplay between electrochemical performance and morphology of the assembled structure is intriguing and for me makes a strong case for studying these materials in-operation. How does each of the components alter during charging-recharging, what is their role and could the entire framework look like a symphony?

Intrigued by this symphony? Read the paper!

Controlled synthesis of hierarchical CoxMn3−xO4 array micro-/nanostructures with tunable morphology and composition as integrated electrodes for lithium-ion batteries
Le Yu, Lei Zhang, Hao Bin Wu, Genqiang Zhang and Xiong Wen (David) Lou
DOI: 10.1039/C3EE41181H

Prineha Narang EES guest web writer

By Prineha Narang

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Reengineering Photosynthesis

In a recent paper in Energy & Environmental Science, UCLA Parsons Foundation Professor James C. Liao and his lab report the metabolic engineering of cyanobacteria to efficiently produce photosynthetic n-butanol.

Oxygen-tolerant coenzyme A-acylating aldehyde dehydrogenase facilitates efficient photosynthetic n-butanol biosynthesis in cyanobacteriaThe production of sustainable energy and fuels is one of the great challenges facing chemistry today.  There are many approaches to this immense task, including the engineering of photosynthetic organisms to directly produce chemical fuels.

Ethanol is great for many reasons, but n-butanol is a better target for renewable fuel systems, as it can be blended seamlessly into the current fossil fuel infrastructure.  Unfortunately for synthetic biologists, the microbe that best produces n-butanol is a strict anaerobe, while the cyanobacterial photosynthetic machinery is responsible for the better part of the molecular oxygen in Earth’s atmosphere (For the record, this blogger is in favor of cyanobacterial oxygen evolution).

The authors of this paper find a clever way around this fundamental incompatability by using a different, air-tolerant enzyme for a key step in the biosynthetic pathway.  A propionaldehyde oxidation catalyst (PduP) demonstrated catalytic reduction of butyryl-CoA to n-butyraldehyde, which could subsequently be converted to n-butanol.  This is just one of 7 enzymes from 7 different organisms functioning in concert to produce the photosynthetic butanol.  Much of this process has been previously been reported by the Liao group.

The challenges in stitching together these genomes are enormous.  After all, no enzyme works in a vacuum (no offense, computationalists), and getting the right cocktail of expressed enzymes and complementary cofactors requires well-engineered organisms.   Even the best systems have yields discussed in milligrams per liter per day.  And even then, the butanol produced is toxic to the cells that make it.

Using synthetic biology to properly engineer these organisms will render them hardly recognizable.  The challenges are daunting, but the possibilities seem limitless.  By combining enzymes from many different organisms, each evolved over billions of years for efficient catalysis, or even human-designed enzymes tailored to exotic new schemes, metabolic engineers could produce stripped-down microbial factories to fuel our transportation and synthesize fine chemicals.  Perhaps, given the diversity of life and biochemistry on Earth, microbial engineering could one day be used to bioterraform the solar system for human colonization!  Well, I can dream, right?

Read Liao and co-workers’ article in EES:

Oxygen-tolerant coenzyme A-acylating aldehyde dehydrogenase facilitates efficient photosynthetic n-butanol biosynthesis in cyanobacteria
Ethan I. Lan, Soo Y. Ro and James C. Liao
DOI: 10.1039/C3EE41405A

EES guest web writer Michael Doud By Michael Doud

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