Ni/Co/Co3O4@C nanorods derived from a MOF@MOF hybrid for efficient overall water splitting.

The design of nanostructured materials for efficient bifunctional electrocatalysts has gained tremendous attention, yet developing a fast and effective synthesis strategy remains a challenge. Here, we present a fast and scalable synthetic method of Ni/Co/Co3O4@C nanorods for efficient overall water splitting. Using microwave synthesis, we first produced a unique Ni-MOF@Co-MOF in a few minutes. Subsequently, we transformed the MOF@MOF into hybrid Ni/Co/Co3O4 nanoparticles covered with graphitic carbon in a few seconds using laser-scribing. The prepared bimetallic catalysts showed remarkably low overpotentials of 246 mV for the oxygen evolution reaction (OER) and 143 mV for the hydrogen evolution reaction (HER) at a current density of 30 mA cm-2. An electrolyzer assembled with the bimetallic catalysts delivered a high current density of 20 mA cm-2 at a voltage of 1.6 V and exhibited good durability (nearly 91.6% retention even after a long-running operation of 24 h at a voltage of 1.52 V). Our proposed method could serve as a powerful method for creating various multimetallic hybrid nanocatalysts with unique hierarchical structures from diverse MOFs.

Graphitic Carbon with MnO/Mn7 C3 Prepared by Laser-Scribing of MOF for Versatile Supercapacitor Electrodes.

Pseudocapacitive materials encapsulated in conductive carbon matrix are of paramount importance to develop energy storage devices with high performance and long lifespan. Here, via simple laser-scribing, the Mn-based metal-organic framework [EG-MOF-74(Mn)] is transformed into pseudocapacitive hybrid MnO/Mn7 C3 encapsulated in highly conductive graphitic carbon. It is revealed that the rapid carbothermic reduction of MnO (C + MnO → C' + Mn7 C3 + CO) leads to the formation of the intermediate pseudocapacitive MnO/Mn7 C3 and the concurrent catalytic graphitization of disordered carbon. This reaction produces a new type of pseudocapacitive material in the form of MnO/Mn7 C3 fully embedded in highly conductive graphitic carbon. Thanks to the synergistic effect of the MnO/Mn7 C3 nanoparticles and the graphitic carbon, the composite exhibits a high specific capacitance of 403 F g-1 with excellent stability. Asymmetric coin-cell supercapacitors based on the composite demonstrate high energy (29.2 Wh kg-1 ) and power densities (8000 W kg-1 ) with a long lifespan. Prototypes of flexible paper-based supercapacitors made of the composite also show great potential toward applications of flexible electronics.

Highly dispersive Co3O4 nanoparticles incorporated into a cellulose nanofiber for a high-performance flexible supercapacitor.

Transition metal oxides used as electrode materials for flexible supercapacitors have attracted huge attention due to their high specific capacitance and surface-to-volume ratio, specifically for cobalt oxide (Co3O4) nanoparticles. However, the low intrinsic electronic conductivity and aggregation of Co3O4 nanoparticles restrict their electrochemical performance and prevent these electrode materials from being commercialized. Herein, a facile, advantageous, and cost effective sol-gel synthetic route for growing Co3O4 nanoparticles uniformly over a low cost and eco-friendly one-dimensional (1D) hydrophilic cellulose nanofiber (CNF) surface has been reported. This exhibits high conductivity, which enables the symmetric electrode to deliver a high specific capacitance of ∼214 F g-1 at 1 A g-1 with remarkable cycling behavior (∼94% even after 5000 cycles) compared to that of pristine CNF and Co3O4 electrodes in an aqueous electrolyte. Furthermore, the binder-free nature of 1D Co3O4@CNF (which was carbonized at 200 °C for about 20 min under a H2/Ar atmosphere) shows great potential as a hybrid flexible paper-like electrode and provides a high specific capacitance of 80 F g-1 at 1 A g-1 with a superior energy density of 10 W h kg-1 in the gel electrolyte. This study provides a novel pathway, using a hydrophilic 1D CNF, for realizing the full potential of Co3O4 nanoparticles as advanced electrode materials for next generation flexible electronic devices.

Prolonged Biodegradation and Improved Mechanical Stability of Collagen via Vapor-Phase Ti Stitching for Long-Term Tissue Regeneration.

Collagen, one of the most popular biomedical materials, exhibits rapid biodegradation accompanied by a notable decrease of mechanical stability in the human body. This is a key challenge for its use in large-sized tissue regeneration, which takes a long time. In order to resolve this problem, we introduced vapor-phase titanium (Ti) derivatives into the interchain regions in collagen via TiO2 atomic layer deposition (ALD), which has been widely used for thin-film deposition. The introduced Ti simultaneously enhanced both the tensile strength (∼384.45 MPa) and Young's modulus (∼1.56 GPa) by approximately 29 and 26% compared to the pristine commercial collagen membrane. In vitro tests demonstrated that approximately 31% of Ti-infiltrated collagen is retained after 4 weeks, whereas the pristine commercial collagen rapidly degrades by up to 90% within 1 week. The in vivo biodegradation rate was greatly improved and inversely proportional to the number of TiO2 ALD cycles. Moreover, bone mineralization, which is observed during the late stage of bone healing, appeared only in the Ti-infiltrated collagen. We believe that our simple vapor-phase treatment method could be widely used with xenograft materials, which typically require adequate biodegradation rates and stable mechanical properties.

Tough and Immunosuppressive Titanium-Infiltrated Exoskeleton Matrices for Long-Term Endoskeleton Repair.

Although biodegradable membranes are essential for effective bone repair, severe loss of mechanical stability because of rapid biodegradation, soft tissue invasion, and excessive immune response remain intrinsically problematic. Inspired by the exoskeleton-reinforcing strategy found in nature, we have produced a Ti-infiltrated chitin nanofibrous membrane. The membrane employs vapor-phase infiltration of metals, which often occurs during metal oxide atomic layer deposition (ALD) on organic substrates. This metal infiltration manifests anomalous mechanical improvement and stable integration with chitin without cytotoxicity and immunogenicity. The membrane exhibits both impressive toughness (∼13.3 MJ·m-3) and high tensile strength (∼55.6 MPa), properties that are often mutually exclusive. More importantly, the membrane demonstrates notably enhanced resistance to biodegradation, remaining intact over the course of 12 weeks. It exhibits excellent osteointegrative performance and suppresses the immune response to pathogen-associated molecular pattern molecules indicated by IL-1ß, IL-6, and granulocyte-macrophage colony-stimulating factor expression. We believe the excellent chemico-biological properties achieved with ALD treatment can provide insight for synergistic utilization of the polymers and ALD in medical applications.

Dynamics of GeSbTe phase-change nanoparticles deposited on graphene.

Phase-change Ge2Sb2Te5 nanoparticles (NPs), that are promising for next-generation phase-change memory and other emerging optoelectronic applications, have been deposited on graphene support layers and analyzed using advanced transmission electron microscopy techniques allowing high quality atomic resolution imaging at accelerating voltages as low as 40 kV. The deposition results in about three times higher NP coverage on suspended graphene than on graphene containing an amorphous background support. We attribute this to the variation in surface energy of suspended and supported graphene, indicating that the former harvests NPs more effectively. Hydrocarbon contamination on the graphene profoundly enhances the mobility of the NP atoms and after prolonged (weeks) exposure to air resulted in more severe oxidation and spreading of NPs on the suspended graphene than on supported graphene because the network of hydrocarbons develops more extensively on the suspended rather than on the supported graphene. Due to this oxidation, GeO x shells are formed out of NPs having a uniform composition initially. The present work provides new insights into the structure and stability of phase-change NPs, graphene and their combinations.

Activated Carbon Textile via Chemistry of Metal Extraction for Supercapacitors.

Carbothermic reduction in the chemistry of metal extraction (MO(s) + C(s) → M(s) + CO(g)) using carbon as a sacrificial agent has been used to smelt metals from diverse oxide ores since ancient times. Here, we paid attention to another aspect of the carbothermic reduction to prepare an activated carbon textile for high-rate-performance supercapacitors. On the basis of thermodynamic reducibility of metal oxides reported by Ellingham, we employed not carbon, but metal oxide as a sacrificial agent in order to prepare an activated carbon textile. We conformally coated ZnO on a bare cotton textile using atomic layer deposition, followed by pyrolysis at high temperature (C(s) + ZnO(s) → C'(s) + Zn(g) + CO(g)). We figured out that it leads to concurrent carbonization and activation in a chemical as well as mechanical way. Particularly, the combined effects of mechanical buckling and fracture that occurred between ZnO and cotton turned out to play an important role in carbonizing and activating the cotton textile, thereby significantly increasing surface area (nearly 10 times) compared with the cotton textile prepared without ZnO. The carbon textiles prepared by carbothermic reduction showed impressive combination properties of high power and energy densities (over 20-fold increase) together with high cyclic stability.

A robust and conductive metal-impregnated graphene oxide membrane selectively separating organic vapors.

A small amount of Zn impregnated by ALD triggered enhancement of the mechanical as well as electrical properties of the graphene oxide (GO) membrane. In addition, the Zn-impregnated membranes selectively separated diverse organic vapors while maintaining high water permeability.