Catechols play an important role in many natural systems. They are known to readily interact with both organic (e.g., amino acids) and inorganic (e.g., metal ions, metal oxides) compounds, thereby providing a powerful system for protein curing. Catechol crosslinked protein networks, such as sclerotized cuticle and byssal threads of the mussel, have been shown to exhibit excellent mechanical properties. A lot of effort has been devoted to mimicking the natural proteins using synthetic catechol-functionalized polymers. Despite the success in developing catechol-functionalized materials, the crosslinking chemistry of catechols is still a subject of debate. To develop materials with controlled and superior properties, a clear understanding of the crosslinking mechanism of catechols is of vital importance. This review describes the crosslinking pathways of catechol and derivatives in both natural and synthetic systems. We discuss existing pathways of catechol crosslinking and parameters that affect the catechol chemistry in detail. This overview will point towards a rational direction for further investigation of the complicated catechol chemistry.

Reducing the heat generated in traditional electronics is a chief motivation for the development of spin-based electronics, called spintronics. Spin-based transistors that do not strictly rely on the raising or lowering of electrostatic barriers can overcome scaling limits in charge-based transistors. Spin transport in semiconductors might also lead to dissipation-less information transfer with pure spin currents. Despite these thermodynamic advantages, little experimental literature exists on the thermal aspects of spin transport in solids. A recent and surprising exception was the discovery of the spin-Seebeck effect, reported as a measurement of a redistribution of spins along the length of a sample of permalloy (NiFe) induced by a temperature gradient. This macroscopic spatial distribution of spins is, surprisingly, many orders of magnitude larger than the spin diffusion length, which has generated strong interest in the thermal aspects of spin transport. Here, the spin-Seebeck effect is observed in a ferromagnetic semiconductor, GaMnAs, which allows flexible design of the magnetization directions, a larger spin polarization, and measurements across the magnetic phase transition. This effect is observed even in the absence of longitudinal charge transport. The spatial distribution of spin currents is maintained across electrical breaks, highlighting the local nature of this thermally driven effect.

several excellent reviews. [9][10][11][12] Recently, it was emphasized by Waite that catechol moieties alone are insufficient to ensure proper underwater adhesion and that the performance is a complex interplay between DOPA and its local environment. [13] Therefore, attention is shifted to include other (noncovalent) interactions used in these natural glues, and much progress has been made in understanding both their performance and delivery process. [14] In this review, we take the sandcastle worm and mussel as a basis for inspiration. We discuss (noncovalent) interactions found in these natural adhesive systems and extend our discussion to additional supramolecular moieties that can be used to control the adhesive and cohesive performance of synthetically designed adhesives. In Section 2, we examine the natural systems and identify the versatile supramolecular interactions used in such protein-based adhesives. These include electrostatic interactions, hydrogen bonding, hydrophobic forces, π-π interactions, metal coordination, cation-π complexation, and dynamic covalent linkages. The use of these interactions in synthetic adhesive systems is explored in the subsequent sections. Section 3 is devoted to the different interactions that catechols (the functional group of DOPA) display to bond to a submerged substrate or to provide cohesive properties to the adhesive. Despite the fact that catechols have already been the topic of many excellent reviews, [9,13,17] we believe that catechols play a pivotal role in both the sandcastle worm and the mussel adhesive systems and, therefore, should not be omitted from this review. In Section 4, we discuss the use of electrostatic interactions in protein-based and synthetic adhesive formulations for wet conditions. These interactions can be tailored to a wide distribution of bond strengths and thus can be tuned to change multi ple mechanical properties, which is essential for design of an adhesive. Besides the effect on the adhesive and cohesive properties, we highlight work where electrostatic interactions cause liquid-liquid phase separation in aqueous polymer solutions. The resulting (complex) coacervate is a concentrated, liquid, yet water-insoluble phase of the adhesive material, which can act as a powerful delivery tool for underwater adhesives. Hydrogen bonding in adhesives is explored in Section 5. The use of hydrogen bonding to adjust the viscoelastic properties of adhesives has been identified decades, ago, and hydrogen bonding moieties are commonly used in pressure sensitive adhesives (PSAs). However, besides simple, single hydrogen bonding motifs, many interesting alternative Nature has developed protein-based adhesives whose underwater performance has attracted much research attention over the last few decades. The adhesive proteins are rich in catechols combined with amphiphilic and ionic features. This combination of features constitutes a supramolecular toolbox, to provide stimuli-responsive processing of the adhesive, to secure strong adhesion to a variety of...

The integrated hybrid architectures composed of edge site-enriched nickel–cobalt sulfide (Ni–Co–S) nanoparticles and graphene as advanced materials for asymmetric supercapacitors are configured, delivering a superb rate capability.

port at high-rate. [ 2 ] The ion transport is shown in the following equation L D τ = / 2 A general approach is developed for the synthesis of 2D porous carbon nanosheets (PCNS) from bio-sources derived carbon precursors (gelatin) by an integrated procedure of intercalation, pyrolysis, and activation. Montmorillonite with layered nanospace is used as a nanotemplate or nanoreactor to confi ne and modulate the transformation of gelatin, further leading to the formation of 2D nanosheet-shaped carbon materials. The as-made 2D PCNS exhibits a signifi cantly improved rate performance, with a high specifi c capacitance of 246 F g −1 and capacitance retention of 82% at 100 A g −1 , being nearly twice that of microsized activated carbon particulates directly from gelatin (131 F g −1 , 44%). The shortened ion transport distance in the nanoscaled dimension and modulated porous structure is responsible for such an enhanced superior rate capability. More importantly, the present strategy can be extended to other bio-sources to create 2D PCNS as electrode materials with high-rate performance. This will also provide a potential strategy for confi guring 2D nanostructured carbon electrode materials with a short ion transport distance for supercapacitors and other carbon-related energy storage and conversion devices.

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Effectively active oxygen evolution reaction (OER) electrocatalysts are highly desired for water splitting. Herein, the design and fabrication of nanometersized Fe-modulated CoOOH nanoparticles by a novel conversion tailoring strategy is reported for the first time and these nanoparticles are assembled on graphene matrix to construct 2D nanohybrids (FeCoOOH/G) with ultrasmall particles and finely modulated local electronic structure of Co cations. The Fe components are capable of tailoring and converting the micrometer-sized sheets into nanometer-sized particles, indicative of ultrasensitive Fe-triggered behavior. The as-made FeCoOOH/G features highly exposed edge active sites, well-defined porous structure, and finely modulated electron structure, together with effectively interconnected conducting networks endowed by graphene. Density functional theory calculations have revealed that the Fe dopants in the FeCoOOH nanoparticles have an enhanced adsorption capability toward the oxygenated intermediates involved in OER process, thus facilitating the whole catalytic reactions. Benefiting from these integrated characteristics, the as-made FeCoOOH/G nanohybrids as an oxygen evolution electrocatalyst can deliver a low overpotential of 330 mV at 10 mA cm −2 and excellent electrochemical durability in alkaline medium. This strategy provides an effective, durable, and nonprecious-metal electrocatalyst for water splitting.

The design and fabrication of 2D nanostructure electrodes with desired electrochemical activities is highly demanded for electrocatalysis and supercapacitors. Herein, the tuned fabrication of ultrathin and tortuous nickel/cobalt-layered double hydroxide (NiCo-LDH) nanosheets via a graphene oxide (GO) surface-confined strategy is reported, yielding nanosheets with a thickness of 1.7-1.8 nm that is duplicated from the graphene oxides in terms of both the lateral size and the shape. It has been found that the C/O functional groups on the GO surface have functioned to promote the oxidation of Co 2+ to Co 3+ , and to transform the β-phase NiCo-hydroxide (NiCo-OH) into the LDH-phase with tuned homogenous composition and geometry. The ultrathin NiCo-LDH nanosheets mimic the morphology and size of the graphene due to the surface-confined and/or surface-guided growth. The as-obtained NiCo-LDH-graphene (NiCo-LDH-G) nanosheets exhibit a superior electrocatalytic activity for oxygen evolution reaction, evidenced by a small overpotential of 0.337 V (@10 mA cm −2 in 0.1 m KOH electrolyte), and a high charge storage capability of 1489 F g −1 as electrodes for supercapacitors. This 2D surface-confined growth strategy may pave a way for the fabrication of ultrathin 2D materials including but not limited to transition metal hydroxides for high-performance electrochemical applications.