Martin R. Lohe

Vertically oriented cobalt selenide/NiFe layered-double-hydroxide nanosheets supported on exfoliated graphene foil: an efficient 3D electrode for overall water splitting

Developing cost-effective electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in basic media is critical to renewable energy conversion technologies. Here, we report a ternary hybrid that is constructed by in situ growth of cobalt selenide (Co0.85Se) nanosheets vertically oriented on electrochemically exfoliated graphene foil, with subsequent deposition of NiFe layered-double-hydroxide by a hydrothermal treatment. The resulting 3D hierarchical hybrid, possessing a high surface area of 156 m2 g−1 and strong coupling effect, exhibits excellent catalytic activity for OER, which only requires overpotentials of 1.50 and 1.51 V to attain current densities of 150 and 250 mA cm−2, respectively. These overpotentials are much lower than those reported for other non-noble-metal materials and Ir/C catalysts. The hybrid also efficiently catalyzes HER in base with a current density of 10 mA cm−2 at an overpotential of −0.26 V. Most importantly, we achieve a current density of 20 mA cm−2 at 1.71 V by using the 3D hybrid as both a cathode and an anode for overall water splitting, which is well comparable to the integrated performance of Pt/C and Ir/C catalysts.

Imine-linked polymer-derived nitrogen-doped microporous carbons with excellent CO2 capture properties.

A series of nitrogen-doped microporous carbons (NCs) was successfully prepared by direct pyrolysis of high-surface-area microporous imine-linked polymer (ILP, 744 m(2)/g) which was formed using commercial starting materials based on the Schiff base condensation under catalyst-free conditions. These NCs have moderate specific surface areas of up to 366 m(2)/g, pore volumes of 0.43 cm(3)/g, narrow micropore size distributions, and a high density of nitrogen functional groups (5.58-8.74%). The resulting NCs are highly suitable for CO2 capture adsorbents because of their microporous textural properties and large amount of Lewis basic sites. At 1 bar, NC-800 prepared by the pyrolysis of ILP at 800 °C showed the highest CO2 uptakes of 1.95 and 2.65 mmol/g at 25 and 0 °C, respectively. The calculated adsorption capacity for CO2 per m(2) (μmol of CO2/m(2)) of NC-800 is 7.41 μmol of CO2/m(2) at 1 bar and 25 °C, the highest ever reported for porous carbon adsorbents. The isosteric heats of CO2 adsorption (Qst) for these NCs are as high as 49 kJ/mol at low CO2 surface coverage, and still ~25 kJ/mol even at high CO2 uptake (2.0 mmol/g), respectively. Furthermore, these NCs also exhibit high stability, excellent adsorption selectivity for CO2 over N2, and easy regeneration and reuse without any evident loss of CO2 adsorption capacity.

Highly porous nitrogen-doped polyimine-based carbons with adjustable microstructures for CO2 capture

A series of highly porous nitrogen doped porous carbons (NPCs) have been successfully prepared using a novel porous polyimine as the precursor. The resulting NPCs have a high specific surface area of up to 3195 m2 g−1, high pore volume and micropore volume (up to 1.58 and 1.38 cm3 g−1, respectively), narrow micropore size distributions, and adjustable nitrogen (1.52–5.05 wt%) depending on the activation temperatures (600–750 °C). The CO2 uptakes of the NPCs prepared at higher temperatures (700–750 °C) are lower than those prepared at milder conditions (600–650 °C). At 1 bar, NPC-650 demonstrates the best CO2 capture performance and could efficiently adsorb CO2 molecules of 3.10 mmol g−1 (136 mg g−1) and 5.26 mmol g−1 (231.3 mg g−1), at 25 and 0 °C, respectively. The NPCs also show good a initial CO2/N2 adsorption selectivity of up to 23.4 and an adsorption ratio of CO2/N2 (6.6) at 1 bar. Meanwhile, these NPCs exhibit a high stability and facile regeneration/recyclability without evident loss of the CO2 capture capacities.

Fine tuning of the metal–organic framework Cu3(BTC)2 HKUST-1 crystal size in the 100 nm to 5 micron range

Cu3(BTC)2 (BTC = 1,3,5-benzene tricarboxylate) was synthesized from cooled reagents in ethanol–water solvent mixtures and in ethanol solvent at room temperature involving quenching at −196 °C and freeze drying in order to limit crystal growth. These approaches are handy to synthesize this MOF with narrow particle size distribution in the range of 100 nm to 5 microns and to achieve excellent crystallinity and unprecedented porosity. The nano-version of Cu3(BTC)2 outperforms micron size crystals in catalyzing methanolysis of styrene oxide.

New-Generation Graphene from Electrochemical Approaches: Production and Applications

Extensive research suggests a bright future for the graphene market. However, for a long time there has been a huge gap between laboratory-scale research and commercial application due to the challenging task of reproducible bulk production of high-quality graphene at low cost. Electrochemical exfoliation of graphite has emerged as a promising wet chemical method with advantages such as upscalability, solution processability and eco-friendliness. Recent progress in the electrochemical exfoliation of graphite and prospects for the application of exfoliated graphene, mainly in the fields of composites, electronics, energy storage and conversion are discussed.

Structural flexibility and intrinsic dynamics in the M2(2,6-ndc)2(dabco) (M = Ni, Cu, Co, Zn) metal–organic frameworks

The synthesis and structural flexibility of the metal–organic frameworks M2(2,6-ndc)2(dabco) (DUT-8(M), M = Ni, Co, Cu, Zn; 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) as well as their characterization by gas adsorption, 129Xe NMR and 13C MAS NMR spectroscopy are described. Depending on the integrated metal atom the compounds show reversible (DUT-8(Ni), DUT-8(Co)), non-reversible (DUT-8(Zn)) or no (DUT-8(Cu)) structural transformation upon solvent removal and/or physisorption of several gases. DUT-8(Co) exhibits a similar structural transformation by solvent removal and adsorption behavior as observed for DUT-8(Ni). DUT-8(Zn) undergoes an irreversible structural change caused by solvent removal. The non-flexible copper containing MOF reveals the best performance concerning porosity and gas storage capacities within the DUT-8 series. Xenon adsorption studies combined with 129Xe NMR spectroscopy are used to study the flexibility of the DUT-8 compounds. 129Xe chemical shift and line width strongly depend on the metal atom. Solid-state 13C NMR spectroscopy has been applied in order to further characterize the organic parts of the DUT-8 frameworks. While DUT-8(Ni) exhibits narrow, well-resolved lines in its “as made” state, the signals of DUT-8(Co) are broadened and shifted over an unusually wide chemical shift range (−72 to 717 ppm). No detectable signals are found in DUT-8(Cu) indicating significantly changed internal dynamics compared to DUT-8(Ni) and DUT-8(Co).

Magnetic mesoporous bioactive glass scaffolds: preparation, physicochemistry and biological properties

The magnetic 10Fe5Ca MBG scaffolds (Fe3O4-CaO-SiO2-P2O5 system) have been prepared by a combination of polyurethane sponge and P123 as co-templates and an evaporation-induced self-assembly (EISA) process through the substitution of Fe3O4 for CaO in the 15Ca MBG scaffolds (CaO-SiO2-P2O5 system). The structure, magnetic heating, drug release, physicochemical and biological properties were systematically investigated. The results showed that the 10Fe5Ca MBG scaffolds had the interconnected macroporous structure with pore sizes ranging from 200 to 400 μm and the mesoporous wall with a peak pore size of ca. 3.34 nm. Also, the 10Fe5Ca MBG scaffolds exhibited similar mechanical strength, apatite-forming ability and sustained drug release behavior compared to the 15Ca MBG scaffolds. Importantly, the substitution of Fe3O4 for CaO in the MBG scaffolds induced a slower ion dissolution rate and more significant potential to stabilize the pH environment, and facilitated osteoblast cell proliferation, alkaline phosphatase (ALP) activity and osteogenic expression. In particular, the 10Fe5Ca MBG scaffolds could generate heat in an alternating magnetic field. Therefore, the magnetic 10Fe5Ca MBG scaffolds have potential for the regeneration of the critical-size bone defects caused by bone tumors by a combination of magnetic hyperthermia and local drug delivery therapy.

Few-Layer Graphene Shells and Nonmagnetic Encapsulates: A Versatile and Nontoxic Carbon Nanomaterial

In this work a simple and scalable approach to coat nonmagnetic nanoparticles with few-layer graphene is presented. In addition, the easy processing of such nanoparticles to remove their core, leaving only the 3D graphene nanoshell, is demonstrated. The samples are comprehensively characterized, as are their versatility in terms of functionalization and as a material for electrochemical storage. Indeed, these 3D graphene nanostructures are easily functionalized much as is found with carbon nanotubes and planar graphene. Electrochemical investigations indicate these nanostructures are promising for stable long-life battery applications. Finally, initial toxicological investigations suggest no acute health risk from these 3D graphene nanostructures.

Scalable Fabrication and Integration of Graphene Microsupercapacitors through Full Inkjet Printing

A simple full-inkjet-printing technique is developed for the scalable fabrication of graphene-based microsupercapacitors (MSCs) on various substrates. High-performance graphene inks are formulated by integrating the electrochemically exfoliated graphene with a solvent exchange technique to reliably print graphene interdigitated electrodes with tunable geometry and thickness. Along with the printed polyelectrolyte, poly(4-styrenesulfonic acid), the fully printed graphene-based MSCs attain the highest areal capacitance of ∼0.7 mF/cm2, substantially advancing the state-of-art of all-solid-state MSCs with printed graphene electrodes. The full printing solution enables scalable fabrication of MSCs and effective connection of them in parallel and/or in series at various scales. Remarkably, more than 100 devices have been connected to form large-scale MSC arrays as power banks on both silicon wafers and Kapton. Without any extra protection or encapsulation, the MSC arrays can be reliably charged up to 12 V and retain the performance even 8 months after fabrication.

Ultrafast Delamination of Graphite into High-Quality Graphene Using Alternating Currents

To bridge the gap between laboratory-scale studies and commercial applications, mass production of high quality graphene is essential. A scalable exfoliation strategy towards the production of graphene sheets is presented that has excellent yield (ca. 75 %, 1-3 layers), low defect density (a C/O ratio of 21.2), great solution-processability, and outstanding electronic properties (a hole mobility of 430 cm2  V-1  s-1 ). By applying alternating currents, dual exfoliation at both graphite electrodes enables a high production rate exceeding 20 g h-1 in laboratory tests. As a cathode material for lithium storage, graphene-wrapped LiFePO4 particles deliver a high capacity of 167 mAh g-1 at 1 C rate after 500 cycles.