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Shrinking the Size of Hydrogen Evolution Catalysts by Carbon Coating

20 Nov 2018

Hydrogen gas is a zero-emission energy resource promising to replace diminishing fossil fuels. The electrolysis of water is a sustainable way to acquire hydrogen gas, but this non-spontaneous process demands electricity to proceed. Therefore, hydrogen evolution reaction (HER) catalysts are used to reduce the energy cost or overpotential of the electrolysis.

Researchers are pursuing ultrafine nanoparticles as HER catalysts due to their high catalytic activity. For example, the HER catalytic activities of Ru nanoparticles are reportedly 100-200% higher than those of bulk Ru catalysts. Unfortunately, the preparation of well-dispersed nanoparticles is challenging because nanoparticles are prone to aggregate together.

Recently in ChemComm, Fuqiang Chu, Yong Qin and coworkers from Changzhou University, China addressed the challenge. They utilized a Ru-based coordination complex and cyanuric acid as the reactants, and synthesized high-performance HER catalysts composed of ~2 nm Ru nanoparticles uniformly dispersed on graphene sheets. During the thermal annealing step in the synthesis, the ligands of the complex and the cyanuric acid both decompose to nitrogen-doped carbon shells covering the as-formed Ru nanoparticles. These shells serve as spacers that prevent particle aggregation (Figure 1).

Figure 1. An illustration of the synthesis of carbon-coated Ru ultrafine nanoparticles on graphene sheets. Tris(2,2′-bipyrindine) ruthenium dichloride is the precursor of the Ru nanoparticles.

In both the acidic and the alkaline electrolytes, the 2 nm Ru particles (RuNC-2) display lower overpotentials and higher current densities than the 5 nm Ru particles (Figure 2) without the carbon coating (RuNC-5). Remarkably, the 2 nm particles showed comparable performance to the benchmark Pt catalyst in the acidic electrolyte (the red and black curves in Figure 2a).

Figure 2. Linear sweep voltammograms of ~3 nm Pt nanoparticles (PtNC), 2 nm Ru nanoparticles (RuNC-2) and 5 nm Ru nanoparticles (RuNC-5) in (a) 0.5 M H₂SO₄ and (b) 1 M KOH aqueous solutions.

The concept of the in-situ generation of protective coatings could inspire the synthesis of other ultra-small nanoparticles to potentially push the HER catalytic performance to new heights.

To find out more please read:

An Ultrafine Ruthenium Nanocrystal with Extremely High Activity for the Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Yutong Li, Fuqiang Chu, Yang Liu, Yong Kong, Yongxin Tao, Yongxin Li and Yong Qin

Chem. Commun., 2018, DOI: 10.1039/c8cc08276f

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Copper A3 Coupling using a Switchable Homogeneous/Heterogeneous Catalyst

06 Nov 2018

A MOC, I learned this week, is a metal-organic cage. I was familiar with MOMs, MOFs and MOBs, but MOCs were a new one. A MOM (metal-organic material) is a coordination-driven assembly constructed from metal nodes linked by organic ligands. MOMs encompass both MOFs (metal-organic frameworks) and MOCs (metal-organic cages). A MOF is an extended network with the potential for inner porosity, and a MOC is a discrete metal-ligand cluster. And that’s just about as far down the nomenclature rabbit hole I’m willing to go. If you’re keeping up you’ll realise that I forgot one! A MOB is a crowd of graduate students competing for free coffee at the public seminar.

Dong and co-workers at Shandong Normal University designed and prepared a MOM catalyst constructed from copper(II) nodes and a tripodal ligand consisting of a phenylic wheel functionalised with diketones. In chloroform these two components arrange into discrete MOC assemblies containing two tripodal ligands and three copper ions. The copper ions in the cluster are each coordinated to two diketone moieties (in a acetylacetonate-like fashion) in a quasi-square planar arrangement.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

An interesting property of the material is that it can switch between the MOC form, soluble in halogenated solvents, and an insoluble MOF that assembles upon addition of 1,4-dioxane. 1,4-Dioxane is both an anti-solvent and a ligand; coordination between copper and 1,4-dioxane binds the discrete MOC cages to each other, arranging them into the extended MOF structure. This behaviour can be exploited to prepare a practical catalyst that combines the benefits of both homogeneous and heterogeneous catalysis, namely that homogeneous catalysts are generally more efficient, selective and easier to study, but heterogeneous catalysis are easier to recover and recycle. What better way to solve this problem than with a catalyst that is homogeneous during the reaction conditions, but heterogeneous when it comes to product separation?

Reversible metal-organic cage MOC(top left)-MOF(top right) metal-organic framework transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

Reversible MOC(top left)-MOF(top right) transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

The authors used the A³ coupling reaction to demonstrate this concept in a catalytic reaction. The A³ reaction is a transition metal-catalysed, multi-component coupling reaction between aldehydes, alkynes and amines. The products are propargylamines, practical synthetic intermediates for the synthesis of nitrogen heterocycles. The A³ reaction has been extensively studied and can be effected by a wide range of transition metal catalysts. Its versatility makes it a popular choice as a model catalytic reaction to demonstrate innovative ideas in catalytic design – as the authors have done here.

Coordination-driven assemblies have a unique potential for the synthesis of differentially soluble materials, used by the authors for novel catalytic design. Whether this particular metal-ligand combination can be applied to other copper catalysed reactions remains to be seen, nevertheless the principle offers an innovative approach that augments the range of methods striving to bridge the gap between homogeneous and heterogeneous catalysis.

To find out more please read:

Cu₃L₂ metal-organic cages for A³-coupling reactions: reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery

Gong-Jun Chen, Chao-Qun Chen, Xue-Tian Li, Hui-Chao Ma and Yu-Bin Dong.
Chem. Commun., 2018, 54, 11550-11553
DOI: 10.1039/c8cc07208f

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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The Birth of a Semiconducting Metal Organic Framework by Sulfur Coordination

22 Oct 2018

Metal organic frameworks (MOFs) are crystalline nanomaterials composed of metal ions or clusters coordinated with organic ligands. Owing to the versatility of their building blocks, MOFs have multiple functionalities and can serve as gas separators, sensors, catalysts, electrode materials etc. Now the structure diversity of MOFs is further enriched by Wu and coworkers from Soochow University, China. Specifically, the researchers synthesized a semiconducting MOF with tetra-coordinated sulfur units. This breakthrough was recently published in ChemComm.

The uniqueness of the synthesized semiconducting MOF (MCOF-89) is its square-planar tetra-coordinated metal-sulfur structure, which is observed in MOFs for the first time. It was believed that putting a sulfur atom next to a metal node of MOFs was extremely difficult, because of the large discrepancy in bonding energy between metal-sulfur bonds and conventional metal-carboxylate bonds. Incorporating sulfur atoms thereby could undermine the structural stability of MOFs.

The authors addressed this challenge by designing a tetra-coordination environment as illustrated in Figure 1. The four manganese-sulfur bonds effectively reinforced the unstable S coordination. MCOF-89 was synthesized via a solvothermal reaction with Mn(CH₃COO)₂ and thiourea as the Mn and S sources, respectively.

Figure 1. The structure of MCOF-89. The illustration on the left is a three-dimensional lattice structure (the red, green and yellow balls represent oxygen, manganese and sulfur), and the structure on the right shows the Mn-S square-planar tetra-coordination configuration (M = manganese).

The synthesized S-incorporated MOF is a semiconductor with a bandgap of 2.82 eV. Additionally, this MOF is photoactive and is able to generate a photocurrent of ~1.9 µA/cm² upon light irradiation.

This work exemplifies how molecular design can lead to the discovery of novel MOFs with extraordinary structures. It could also inspire other synthesis protocols toward various metal-chalcogenide-containing MOFs with unexpected properties.

To find out more please read:

A Semiconducting Metal-Chalcogenide–Organic Framework with Square-Planar Tetra-Coordinated Sulfur

Huajun Yang, Min Luo, Zhou Wu, Wei Wang, Chaozhuang Xue and Tao Wu

Chem. Commun., 2018, 54, 11272-11275

About the blogger:

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MOFS, ZMOFS and Automobiles

05 Sep 2018

Mohamed Eddaoudi and co-workers at KAUST have synthesised a porous metal organic framework (MOF) constructed from carboxylic acid-functionalised imidazole linkers coordinated to yttrium and potassium cations. The researchers classified this material as a zeolite-like MOF (ZMOF) due to its topological resemblance to the naturally occurring zeolite mineral analcime.

The material’s architecture, with cylindrical channels and a pore aperture measuring 3.8 x 6.2 Å, promised utility as a molecular sieve, and the authors showed the ZMOF could be used to sort small chain alkanes based on their level of branching. Linear and mono-branched pentanes and butanes were adsorbed by the material for different lengths of time (linear isomers were retained longer than their branched counterparts) allowing kinetic separation, while the di-branched alkane 2,2,4-trimethylpentane was excluded entirely. The authors anticipate that this material could have practical applications in crude oil refining, to upgrade petroleum into more energy-efficient fuels with reduced emissions.

ZMOF zeolite-like metal organic framework crystal structure with analcime (ana) topology showing channels and pore aperture.

ZMOF crystal structure with analcime (ana) topology showing channels and pore aperture.

The petroleum used to power internal combustion engines consists of a mixture of low molecular weight, linear and branched alkanes. The research octane number (RON) is a standard measure of petroleum performance, and indicates how much pressure a fuel can withstand before self-igniting (knocking) in the engine. High compression engines, which are more energy efficient and release less emissions than regular engines, require high RON fuels.

The RON increases with the proportion of branched alkanes, so can be improved by supplementing fuels with branched isomers obtained by catalytic isomerisation. This process generates a mixture of linear and branched alkanes, so the desired products must be isolated via fractional distillation, which is energy intensive. This creates a dilemma: high RON fuels are more energy efficient, but their energy-intensive production reduces the net benefit.

The authors envisaged an energy-efficient strategy for increasing the RON of petroleum fuels: A low RON fuel is pumped into the engine, where it encounters a separation chamber consisting of ZMOF-based membranes. The membrane excludes and redirects di-branched alkanes, which have a very high RON, to the internal combustion engine. The low RON fraction, consisting of mono-branched and linear alkanes, passes through the ZMOF pores to undergo further reforming processes downstream. In other words: low RON fuels go in, but high RON fuels are combusted.

Scheme showing how ZMOF materials could be used to upgrade gasoline by separating alkanes based on their level of branching. zeolite-like metal organic framework petroleum reforming

Scheme showing the RON of common small-chain alkanes and the use of ZMOF membranes in upgrading gasoline by separating alkanes based on their level of branching

In this work the authors show the potential of ZMOFs to maximise the energetic potential and reduce emissions of petroleum based fuels, while also offering a glimpse of the more general strategy of energy-efficient separations of chemically-similar molecules using tailored materials.

To find out more please read:

Upgrading gasoline to high octane number using zeolite-like metal organic framework molecular sieve with ana-topology

M. Infas H. Mohideen, Youssef Belmabkhout, Prashant M. Bhatt, Aleksander Shkurenko, Zhijie Chen, Karim Adil, Mohamed Eddaoudi.
Chem. Commun., 2018, 54, 9414-9417
DOI: 10.1039/c8cc04824j

About the author

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Come for the colour changing crystals, stay for the science

31 May 2018

Synthesis of copper bimetallic complexes from imidazolyl ligands, and the solvatochromic materials formed upon crystallization and solvent guest-exchange. The solvatochromic behaviour was quantified with visible-region diffuse reflectance spectra.

During the first inorganic chemistry course I took during my undergraduate degree, our professor started the class by passing around some mineral samples, promising us that if we pursued the chemistry of metals we could work with beautifully coloured crystals every day. At the time, colour seemed like such a trite detail amongst the complexity of the subject. Why would you choose a field of study based on something so simple? Well, after a PhD dominated by pale yellow oils, I think I get it now.

Nikolayenko and Barbour at the University of Stellenbosch in South Africa bring us colour! The authors synthesised organometallic copper complexes, which crystallise to form porous single crystals that drastically change colour upon absorption of various solvents. The authors investigated the solvatochromic mechanism using X-ray crystallography, EPR, UV-visible spectroscopy and DFT calculations. Solvatochromic materials are not just made to look pretty; they have potential to be used as sensitive, selective and recyclable sensors to detect solvent vapours with useful applications in industrial process risk management, chemical threat detection and environmental monitoring.

The researchers synthesised a series of complexes comprised of a bidentate ligand with 2-methylimidazolyl groups coordinated to copper(II) ions. The complexes stack to form channels in the crystal, capable of trapping solvent molecules to give different coloured crystals: DMSO and THF-containing crystals are green (λ_max = 574 nm and 540 nm, respectively), those containing acetonitrile are red (λ_max = 624 nm), and crystals trapping acetone, ether and pentane are yellow (λ_max = 588), orange (λ_max = 598 nm) and red/brown (λ_max = 592 nm), respectively.

The authors revealed a correlation between the size of the solvent guest, coordination geometry of the copper complex, and the ligand field splitting. Small guests such as acetonitrile minimally perturb the metallocyclic framework, preserving a rhombic ligand field geometry (large δ_xy of g values in the EPR spectrum), small ligand d-orbital splitting and red-shifted optical spectra. Large guests such as THF have the opposite effect, giving ligand field geometries approaching tetragonal (small δ_xy), large ligand field d-orbital splitting and blue-shifted optical spectra.

By delving into the complexity beneath a seemingly simple phenomenon, Nikolayenko, Barbour and their co-workers have shown using a series of single-crystal complexes that there is nothing simple about colour (and nothing trite about detail).

To find out more please read:

Supramolecular solvatochromism: mechanistic insight from crystallography, spectroscopy, and theory

Varvara I. Nikolayenko, Lisa M. van Wyk, Orde Q. Munro, Leonard J. Barbour.
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c8cc02197j

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Ruthenium Currency for a Hydrogen Fuel Economy

02 May 2018

A group of researchers at the Chinese Academy of Sciences and Southwest University want us to kick the fossil fuels habit. Their research comes to us from China, a country using roughly one quarter of the world’s yearly energy consumption, and where the finite nature of fossil fuels is a very real threat to energy supply security. Leading in energy use, China also leads the world in electricity production from renewable sources and investment in clean energy projects.

Hydrogen is considered a viable alternative to fossil fuels as it is energy rich, more so than petrol or ethanol at 39 kWh/kg (petrol: 13 kWh/kg, ethanol: 8.2 kWh/kg), and upon combustion emits only water vapour. However, hydrogen is often obtained from fossil fuels, and it will only be a practical option for the world’s future energy needs if it can be produced from a renewable source.

Preparation of the Ru2P/reduced graphene oxide electrocatalyst for the hydrogen evolution reaction

Preparation of the Ru₂P/reduced graphene oxide catalyst

To this end, water splitting offers a solution. In a water electrolysis cell, hydrogen is produced at the cathode via the hydrogen evolution reaction (HER, 2H⁺ + 2e^– –> H₂), and molecular oxygen is produced at the anode (2H₂O –> O₂ + 4H⁺ + 4e^–). It is ideal in theory, but high energy efficiencies are required to make water splitting viable, and this relies on the development of catalytic electrodes to minimize overpotentials required to drive the reaction. Currently, state of the art HER electrocatalysts use platinum, which is expensive and rare. Furthermore, platinum catalysts are most efficient in an acidic electrolyte and proceed 2-3 times slower in alkaline solutions. On the other hand, the best oxygen evolution catalysts perform better in alkaline environments. Using an alkaline electrolyte has overall advantages as it is less corrosive, thus increasing the stability and lifetime of the electrolytic cell.

The authors have developed a HER catalyst, using ruthenium, with overpotentials and current densities superior to Pt/C in both alkaline and acidic conditions.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru2P on reduced graphene oxide catalyst.

DFT calculation to probe the hydrogen adsorption energies on the active catalytic surface of the Ru₂P catalyst. a) and b) front and side views of the calculated Ru₂P/reduced graphene oxide surface. c) free energy diagram for the HER with different catalysts.

The electrocatalyst is comprised of small, uniform Ru₂P nanoparticles (~2-4 nm) evenly distributed on reduced graphene oxide sheets. The activity of the prepared catalyst (1.0 mg cm^-2) for the HER was measured in an acidic medium (0.5 M H₂SO₄) and the overpotential to achieve a current density of -10 mA cm^-2 was -22 mV, superior to Pt/C (-27 mV). In an alkaline environment (1.0 M KOH) catalyst performance was enhanced, with an overpotential of -13 mV (29 mV lower than Pt/C). High Faradaic efficiencies of more than 98% were measured in both acidic and alkaline solutions. Additionally, analysis was undertaken to further understand how the structure and composition of the catalyst influences its activity. Double layer capacitance measurements gave clues about the catalyst surface, while theoretical DFT calculations were used to study H-adsorption energies.

There is no way to avoid the reality that ruthenium is also a rare and costly metal, and for this reason may not hold the key to solving our energy woes. However, of real value are the insights gained from probing the structure function relationship of this highly active catalyst, which may guide the synthesis of rationally-designed catalysts using inexpensive and abundant materials.

To find out more please read:

Ultrasmall Ru₂P nanoparticles on graphene: a highly efficient hydrogen evolution reaction electrocatalyst in both acidic and alkaline media

Tingting Liu, Shuo Wang, Qiuju Zhang, Liang Chen, Weihua Hu, Chang Ming Li.
Chem. Commun., 2018, 54, 3343-3346
DOI: 10.1039/c8cc01166d

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Hiding Carbon Dioxide in Oxazolidinones

01 Feb 2018

Sometimes it feels as though the pinnacle of synthetic achievement is represented by 20 step total syntheses (with 10 contiguous stereocentres and 5 fused rings…). The level of chemical complexity that can be fashioned from simple building blocks is undoubtedly impressive, but amid such feats it is important not to lose sight of the elegance and worth of simple chemistry, especially when it aims to play a part in resolving profound challenges. One such challenge, which will increasingly confront future generations, is how to reduce the load of carbon dioxide in the atmosphere. One solution is to ‘fix’ carbon dioxide by integrating it into chemical building blocks of added complexity in a sustainable way.

The porosity and high surface area of metal organic frameworks (MOFs), a class of three-dimensional coordination networks, proffers them as ideal materials for capture and storage of carbon dioxide. A team of researchers have designed a MOF which consumes carbon dioxide in a different way: by transformation into value-added chemicals. The group have developed a catalytic MOF embedded with lewis-acidic copper centres capable of converting aziridines to oxazolidinones by the addition of carbon dioxide. Oxazolidinones are used as auxiliaries in chiral synthesis, and are structural components of some antibiotics.

The MOF, termed MMPF-10, is a metal-metalloporphyrin framework constructed from a copper-bound porphyrin ring chemically modified to incorporate 8 benzoic acid moieties, generating an octatopic ligand. These carboxylic acids groups form a second complex with copper in situ, termed a ‘paddlewheel’ for its appearance, with the formula [Cu₂(CO₂)₄]. The resulting network contains hexagonal channels measuring 25.6 x 15.6 Å flanked by four of each of the two copper complexes. With 0.625 % of the catalyst at room temperature, 1 bar CO₂pressure, and in a solvent free environment, MMPF-10 catalyses the transformation of 1-methyl-2-phenylaziridine to yield 63% of the product.

metal-metalloporphyrin MOF catalyses catalyzes carbon dioxide fixation aziridines to oxazolidinones

Topology of MMPF-10 showing hexagonal channels in a) and c), and pentagonal cavities in b). Turquoise: copper, red: oxygen, grey: carbon, blue: nitrogen.

This work, a simple reaction to prepare oxazolidinones, shows that carbon dioxide can be fixed in specialised synthetic building blocks in a sustainable way. This is the way the first paragraph ended, ‘in a sustainable way’, because the challenge of developing such a reaction is two-fold: it must use carbon dioxide, and the reaction conditions must be sustainable. There will be no beneficial offset if the reaction uses a lot of energy, requires many resources, or generates larges quantities of waste. In this reaction the researchers have remained mindful of developing a mild, solvent-free reaction with low catalyst loading employing an earth abundant metal, reflecting an earnest aim to develop practical and sustainable chemistry.

To find out more please read:

A metal-metalloporphyrin framework based on an octatopic porphyrin ligand for chemical fixation of CO₂ with aziridines

Xun Wang, Wen-Yang Gao, Zheng Niu, Lukasz Wojtas, Jason A. Perman, Yu-Sheng Chen, Zhong Li, Briana Aguila and Shengqian Ma
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c7cc08844b

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Elucidating the Stability of Two Metal-Organic Frameworks toward Carbon Dioxide Sorption: A Comparative Study

14 Aug 2017

Metal-organic frameworks (MOFs) are coordination networks consisting of organic ligands and metal cores. They possess crystalline structures with metal complexes as the basic building blocks. These complexes assemble together and extend periodically to form the MOF structures. MOFs represent a family of highly porous materials with ultrahigh surface area (typically >1000 m² g^-1). Other attractive characteristics for MOFs are abundant active metal cores and unique porous structures with tunable pore width, useful for gas storage applications.

Capturing carbon dioxide has evolved into an intriguing research area, mainly due to environmental concerns triggered by high levels of greenhouse gas emissions. Some MOFs have already been explored as carbon dioxide storage materials and exhibited storage capability exceeding that of conventional absorbents (e.g. amines). Aside from the absorption capacity of carbon dioxide, the performance stability over prolonged operation periods is another figure of merit for MOF-based absorbents. However, there are limited studies in this area. Now for the first time, research groups led by Zeng and Zhao from National University of Singapore compared the performance stability of two representative MOFs, HKUST-1 and UiO-66(Zr). The unit cell of the two MOFs are shown in the inset of Figure a.

The two aforementioned MOFs were subjected to 500 carbon dioxide absorbing and desorbing cycles (Figure a). The carbon dioxide uptake amount of the two MOFs was gauged at specific cycle numbers (Figure b). Whilst HKUST-1 displayed a consistent decreasing storage capacity with increasing cycle number, the capacity of UiO-66(Zr) fluctuated but remained relatively constant. The results clearly indicate that HKUST-1 is more vulnerable and instable than UiO-66(Zr) during long-term working cycles.

The authors then investigated the mechanisms associated with the different stability performances. They first observed that the surface area of HKUST-1 decreased 24% to 1270 m² g^-1 after the stability test, whereas that of UiO-66(Zr) remained relatively intact. Moisture-induced structural collapse was excluded as a possible reason by carrying out a control experiment with ultra-pure and dry hydrogen gas. The authors then exploited multi-frequency atomic force microscopy and concluded that the difference in elastic modulus of the two MOF crystals played an important role in determining the corresponding MOF durability. UiO-66(Zr) has an elastic modulus (ca. 28 GPa) much higher than that of HKUST-1 (ca. 19 GPa), meaning that the former is more elastic than the latter. The high elasticity of UiO-66(Zr) can efficiently buffer the volumetric deformation caused by carbon dioxide absorption and desorption, preventing UiO-66(Zr) crystals from structural failure.

Figure. (a) Illustration of one cycle of the carbon dioxide absorption-desorption test. The inset shows where one carbon dioxide molecule resides in the corresponding MOFs. (b) The evolution of carbon dioxide uptake capacity (blue) and surface area (black) of HKUST-1 and UiO-66(Zr).

This work is expected to provide general guidelines on studying the structural stability of other MOFs with applications associated with gas storage and separation.

To find out more please read:

Structure Failure Resistance of Metal-organic Frameworks toward Multiple-cycle CO₂ Sorption

Zhigang Hu, Yao Sun, Kaiyang Zeng, and Dan Zhao

DOI: 10.1039/c7cc04313a

About the author:

Tianyu Liu is a Ph.D. in chemistry graduated from University of California-Santa Cruz. He is passionate about scientific communication to introduce cutting-edge researches to both the general public and the scientists with diverse research expertise. He is a web writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Coordinating nature and photochemistry to create hydrogen

28 Aug 2015

When we look to our future energy resources, the need to realise new means of renewable energy is immediately obvious. Much research is being carried out around the world into the development of systems that can generate energy – from H₂ to biofuels to solar fuels – all of which place great importance on high efficiency and sustainability.

Looking at the world around us for inspiration, the obvious candidate is the photosynthetic process, where visible light is employed to convert CO₂ and H₂O into chemical energy. This process involves the transport of electrons through a complex series of intricately aligned porphyrin-related and protein biomolecules. We can explore the development of a system that mimics the behaviour of natural systems, with respect to the relay of electrons along a series of molecules, or, alternatively, we can take the components in these systems and exploit their properties in combination with other electronically-active but non-natural molecules.

Upon photoexcitation of [Ru(bpy)3]2+, electron transfer through a ferredoxin scaffold to a cobaloxime catalyst facilitates the production of hydrogen. It is the latter approach which Lisa Utschig and her team from Argonne National Laboratory, near Chicago in the US, employed to generate a molecular system capable of photocatalysing the production of hydrogen. In their biohybrid system, the photosensitiser ruthenium(II) tris(bipyridine), ferredoxin (a water-soluble electron transfer protein), and cobaloxime (a cobalt(II)-based catalyst), were combined to generate a miniature reaction center that mimics those which occur in biological systems. However, the Utschig group’s system has a smaller molecular weight, which allows for characterisation of the electronic processes that occur in the system.

Lisa and her colleagues found that the presence of ferredoxin in the catalytic system acted as a scaffold to stabilise the charge-separated state necessary for electron transfer and the desired production of H_2.They also observed that the catalytic behaviour of the Ru(II)–Co(II) pair was only possible in the presence of ferredoxin, which acted to extend the lifetime of the otherwise transient Co(I), allowing the desired reaction to occur.

In order to fully understand and enhance the properties of the molecular systems developed to fulfil the increasing need for energy alternatives, we need to be able to probe the structure and processes that occur in the molecule; the use of smaller analogs to those that exist in nature offers a means by which to achieve this goal. The photoactivated catalyst discussed in this work is an important step forward in the development of an optimized system for use in solar fuel production.

Read this hot ChemComm article in full:
Aqueous light driven hydrogen production by a Ru–ferredoxin–Co biohybrid
S. R. Soltau, J. Niklas, P. D. Dahlberg, O. G. Poluektov, D. M. Tiede, K. L. Lulfort and L. M. Utschig
Chem. Commun., 2015, 51, 10628–10631
DOI: 10.1039/C5CC03006D

Biography

Anthea Blackburn is a guest web writer for Chemical Science. She hails originally from New Zealand, and is a recent graduate student of Northwestern University in the US, where she studied under the tutelage of Prof. Fraser Stoddart (a Scot. There, she exploited supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states.

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Rotaxane Pulley – To Me, To You

10 Apr 2015

Mechanically interlocked molecules have received ever increasing focus over the last number of years due to their potential to mimic the function of macroscopic devices in the molecular world.

Examples include molecular elevators and molecular muscles and with this Communication Zheng Meng and Chuan-Feng Chen of the CAS Key Laboratory of Molecular Recognition and Function at the Chinese Academy of Sciences in Beijing have added pulley-like shuttling motion to the toolkit.

Molecular pulley system powered by acid and base

Using their previously reported* triptycene-derived crown ether host and combining it with a linear guest with three dibenzylammonium and three N-methyltriazolium sites, they have made a molecular pulley system that mimics the plain rotary motion and linear translocation of full sized pulleys. The movement is powered by acid or base leading to one end of the cable-like guest moving towards the host while the other moves away (picture).

The researchers have not only added to the toolbox of molecular motion components but also provided new insights towards further developing molecular machines.

If you want to make your own molecular pulley read the article today!

To read the details, check out the ChemComm article in full – it’s free to access until 10th May:
A molecular pulley based on a triply interlocked [2]rotaxane
Zheng Meng and Chuan-Feng Chen
Chem. Commun., 2015, 51, Advance Article
DOI: 10.1039/C5CC01301A

*(a) C. F. Chen, Chem. Commun., 2011, 47, 1674–1688 RSC; (b) Y. Han, Z. Meng, Y. X. Ma and C. F. Chen, Acc. Chem. Res., 2014, 47, 2026–2040

**Access is free through a registered RSC account – click here to register

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Chemical Communications Blog

Archive for the ‘Inorganic’ Category

Shrinking the Size of Hydrogen Evolution Catalysts by Carbon Coating

Copper A3 Coupling using a Switchable Homogeneous/Heterogeneous Catalyst

The Birth of a Semiconducting Metal Organic Framework by Sulfur Coordination

MOFS, ZMOFS and Automobiles

Come for the colour changing crystals, stay for the science

Ruthenium Currency for a Hydrogen Fuel Economy

Hiding Carbon Dioxide in Oxazolidinones

Elucidating the Stability of Two Metal-Organic Frameworks toward Carbon Dioxide Sorption: A Comparative Study

Coordinating nature and photochemistry to create hydrogen

Rotaxane Pulley – To Me, To You

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