ChemSusChem

The front cover shows a flow system that operates with a highly effective immobilized peptidic catalyst, reported by Helma Wennemers and co-workers from the ETH Zürich, Switzerland on page 242. More than 600 turnovers and high stereoselectivities are achieved on a scale of >450 mmol (>100 g), without a significant drop of the activity or stereoselectivity of the immobilized peptidic catalyst. This high efficiency and sustainability of a flow system is unprecedented in the very active field of enamine catalysis and opens the way for more practical applications.

“This is the first example of highly stereo- and chemoselective enamine catalysis in a continuous flow reactor on a scale of >100 g (>450 mmol).” This and more about the story behind the front cover research can be found on p. 212.

The truth about carbonylations: Palladium-catalyzed oxidative carbonylation reactions have undergone a rapid development during recent years. Nowadays, a plethora of palladium catalysts and reaction protocols are available for the synthesis of carbonyl-containing products, which are important intermediates in the manufacture of dyes, pharmaceuticals, agrochemicals, and other industrial products. Herein, we summarize the developments of oxidative carbonylation transformations of alkenes, alkynes, arenes, and organometalic reagents.

Pep talk: An immobilized peptidic catalyst achieves more than 600 turnovers in a continuous-flow system, allowing the production of chiral γ-nitroaldehydes with excellent stereoselectivities on a scale of >450 mmol (>100 g). Such a high efficiency opens the way for more practical applications of enamine catalysis.

Oppan quantized style: By adding a gold precursor at its cathode, a microbial fuel cell (MFC) is demonstrated to form gold nanoparticles that can be used to simultaneously produce bioelectricity and hydrogen. By exploiting the quantized capacitance charging effect, the gold nanoparticles mediate the production of hydrogen without requiring an external power supply, while the MFC produces a stable power density.

Pulp & Oil: We report the unprecedented formation of de-aromatized lignin oil together with a white polysaccharide fraction when lignocellulose is treated with peracids, which are formed in situ by enzymes. A preliminary characterization of the lignin oil is provided, together with the evidence that the delignified lignocellulose is accessible to cellulases to afford fermentable sugars. As a first proof-of-concept, the reported approach may bring promising new research lines in the future.

Sensing the sun: Incorporation of a cyanomethyl benzoic acid electron acceptor into donor–π–acceptor sensitizers for dye-sensitized-solar cell is shown to lead to devices with improved conversion efficiency when compared with more widely used cyanoacetic acid acceptor.

Titanium nitride electrocatalyst: TiN nanoparticles on a carbon nanotube–graphene hybrid support are fabricated and utilized as a new counter electrode material for quantum-dot-sensitized solar-cell applications. The new material exhibits enhanced power-conversion efficiency (relative to the state-of-the-art Au electrode), which is ascribed to a reduced charge-transfer resistance and a larger surface area relative to the Au electrode.

All-vanadium redox flow batteries are considered to be one of the most promising technologies for large-scale stationary energy storage. Nevertheless, constant capacity decay severely jeopardizes their long-term stability. The capacity-decay mechanism of vanadium flow batteries using a Nafion membrane is investigated and elucidated. Capacity-restoration methods are proposed and experimentally validated.

Cross my heart: New cross-linked high-temperature electrolytes based on sulfone polybenzimidazole and poly(vinylbenzyl chloride) are developed. The cross-linked membranes exhibit excellent stability towards radical oxidation, high resistance to acid swelling, and improved mechanical strength, which allows higher acid doping levels, increased proton conductivity, and significantly improved fuel cell performance and durability.

Nanovoid photoanode: A facile method to improve the efficiency of solar energy conversion systems by minimizing the charge-carrier diffusion length and increasing the light absorption is proposed. The Bi₂WO₆ nanovoid array photoanode shows a much higher photocurrent density and photon-to-H₂ conversion efficiency than planar Bi₂WO₆ photoanodes.

Photorechargeability in the dark! Insights into the self-photorechargeability phenomenon of WO₃ is covered in this work. The proposed mechanism is studied by investigating the intercalation and de-intercalation of alkali cations through cyclic voltammetry studies. Maximum charge capacity is also monitored to optimise the charge storage ability. The stored electrons are also successfully utilised for H₂ generation in the absence of light illumination.

WO_xbefore Pt: Ordered mesoporous tungsten suboxide (m-WO_3−x) is synthesized by using a hard template and a partial reduction process. The m-WO_3−x is used as an alternative catalyst for a counter electrode (CE) instead of Pt for iodine-free electrolyte (T₂/T⁻)-based dye-sensitized solar cells. The catalytic activity of m-WO_3−x CE is superior to that of conventional Pt CEs.

Membrane power: The use of a new tetrasulfonated monomer to prepare segmented sulfonated aromatic polysulfones, instead of traditional disulfonated ones, facilitates ionic cluster formation in proton-exchange membranes. This results in durable fuel-cell membranes with improved water-uptake characteristics and significantly enhanced proton conductivity.

Nanotube films help capture the sun: Carbon nanotube–silicon solar cells are a recently investigated photovoltaic architecture with demonstrated high efficiencies. Hybrid solar-cell devices with an efficiency of approximately 9.7 %, and comprising a thin film of polyaniline deposited on silicon and covered by a single-walled carbon nanotube film are fabricated and characterized.

Breakthrough barrier: Quaternized poly(tetramethyl diphenyl ether sulfone) membranes synthesized through a bromination route are introduced into a vanadium flow battery (VFB) as an anion-conductive membrane separator (see picture), with a higher battery efficiency than commercial Nafion 115 owing to outstanding selectivity between proton and vanadium ions.

Unusually active ceramics: This study analyses the role of a reactive ceramic powder during the thermal treatment of the thermoplastic feedstock. BSCF (Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ) in contrast to other ceramics, clearly participates in the decomposition reaction of polystyrene (PS). Owing to the release of oxygen by BSCF, the decomposition mechanism of PS in contact with the powder is changed from a pyrolytic to a thermoxidative mechanism.

ZrPped up! Oxazolidinones are synthesized by treating glycerol carbonate or glycerol with urea in the presence of γ-Zr phosphate as the catalyst. Increasing the temperature increases the conversion yield, but the selectivity decreases, making the separation process more difficult. Two isomers, 6 and 6′, are formed from glycerol carbonate with a quasi-molar ratio, whereas the formation of 6′ is preferred when starting from glycerol.

Hot catalyst with microwaves: An alternative way to supply thermal energy to liquids is by microwave heating. However, the combination of well-defined, structured nanoparticles with microwaves allows even more promising catalyst heating without arcing effects and bulk liquid heating. Ullmann-type CO coupling has been performed in a microwave flow process with high yields.

Magnetic carbon-nanotube-based M²⁺scavenger: An enhanced supramolecular material based on magnetic carbon nanotubes able to exert M²⁺-depolluting action in water solutions is described. Its strong decontamination activity, combined with easy recyclability, makes this material an appropriate candidate for efficient bulk wastewater treatment.

Turn waste into value: A low value by-product of the bioethanol production from lignocellulosic biomass is successfully employed as precursor for the synthesis of porous nanostructured carbon materials through hydrothermal carbonization (HTC). Silica-nanoparticle templates and chemical activation are used to introduce tailored porosity within the HTC carbon structure, which is beneficial to their performance as electrode in supercapacitors.

Formic acid for fuel: 5-(Hydroxymethyl)furfural (HMF) produced from the dehydration of sugars is coupled with petrochemically derived arenes. The resulting materials are approximately equal by mass of bio- and petro-derived precursors, which are suitable precursors to C₁₂–C₁₄ fuels by subsequent hydrodeoxygenation.