Electrosynthesis of Metal-Organic Framework Films with Well-Defined Facets.

The deposition of metal-organic framework (MOF) films with defined exposed facets is important to enhance the performance of these films for, for example, catalysis or separations. In this work, MOF films with specific exposed facets are electrodeposited anodically on various substrates (e. g. on copper-sputtered Si wafers, copper meshes, copper foams, and polypropylene membranes). The influence of the deposition parameters, including the pH of the solution, current density, concentration of linker, and solvent, on the exposed facets of the deposited MOFs was investigated. The results suggest that precise control over the supersaturation during anodic deposition is a possible strategy for synthesizing MOF crystals with well-defined exposed facets. This approach provides a powerful toolbox for various applications requiring crystal facet control of MOF films.

Sideways propelled bimetallic rods at the water/oil interface.

The motion of self-propelling microswimmers is significantly affected by confinement, which can enhance or reduce their mobility and also steer the direction of their propulsion. While their interactions with solid boundaries have already received considerable attention, many aspects of the influence of liquid-liquid interfaces (LLI) on active particle propulsion still remain unexplored. In this work, we studied the adsorption and motion of bimetallic Janus sideways propelled rods dispersed at the interface between an aqueous solution of hydrogen peroxide and oil. The wetting properties of the bimetallic rods result in a wide distribution of their velocities at the LLI. While a fraction of rods remain immotile, we note a significant enhancement of motility for the rest of the particles with velocities of up to 8 times higher in comparison to those observed near a solid wall. Liquid-liquid interfaces, therefore, can provide a new way to regulate the propulsion of bimetallic particles.

Electrochemical behavior and electrodeposition of gallium in 1,2-dimethoxyethane-based electrolytes.

The electrochemical behavior and electrodeposition of gallium was studied in a non-aqueous electrolyte comprising of gallium(iii) chloride and 1,2-dimethoxyethane (DME). Electrochemical quartz crystal microbalance (EQCM) and rotating ring disk electrode (RRDE) measurements indicate that reduction of gallium(iii) is a two-step process: first from gallium(iii) to gallium(i), and then from gallium(i) to gallium(0). The morphology and elemental composition of the electrodeposited layer were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Metallic gallium was deposited as spheres with diameters of several hundred nanometers that were stacked on top of each other. X-ray photoelectron spectroscopy (XPS) revealed that each gallium sphere was covered by a thin gallium oxide shell. Electrochemical experiments indicated that these oxide layers are electrically conductive, as gallium can be electrodeposited and partially stripped on or from the layer of spheres below. This was further evidenced by simultaneous electrodeposition of gallium and indium, using indium as a tracer. Electrodeposition of gallium from an O2-containing electrolyte resulted in spheres with smaller diameters. This was due to the formation thicker oxide shells, through which diffusion of gallium atoms that were electrodeposited on the surface, was slower. The concentration of gallium adatoms on top of the gallium spheres to form a new sphere therefore reaches the critical concentration for nucleating a new gallium sphere sooner, leading to smaller spheres.

Cathodic Electrodeposition of MOF Films Using Hydrogen Peroxide.

Metal-organic framework (MOF) films can be made by cathodic electrodeposition, where a Brønsted base is formed electrochemically which deprotonates the MOF linkers that are present in solution as undissociated/partially dissociated weak acids. However, the co-deposition of metal and the narrow range of possible metal nodes limit the scope of this method. In this work, we propose the use of hydrogen peroxide (hydrogen peroxide assisted cathodic deposition or HPACD), to overcome these limitations. Electrochemical measurements indicate that in DMF, hydrogen peroxide is reduced to superoxide anions that deprotonate the carboxylic ligands. This single-electron reduction happens at much higher potentials than all previous reported methods. This prevents the co-deposition of metal and extends the range of possible metal nodes. Various pure MOF films (HKUST-1, MIL-53(Fe) and MOF-5) were prepared via this approach. HPACD was also used for the preparation of patterned MOF films and of flexible Cu-BTC coated paper membranes which reject 99.1 % of Rose Bengal from water with a permeance of 8.4 L m-2 h-1 bar-1 .

Indium electrodeposition from indium(iii) methanesulfonate in DMSO.

The electrochemical behavior and electrodeposition of indium was investigated at 26 °C and 160 °C from a solution composed of indium(iii) methanesulfonate and dimethylsulfoxide (DMSO). Indium(iii) methanesulfonate was synthesized from indium(iii) oxide and methanesulfonic acid (MSA). Cyclic voltammetry, quartz crystal microbalance measurements and rotating ring disk electrode experiments indicated that reduction of indium(iii) to both indium(i) and indium(0) occurs. Yet, reduction to metallic indium was found to be the predominant process. Deposited indium could be stripped to indium(i). This unstable species disproportionated to indium(iii) and indium(0), leading to the formation of micron-sized metallic indium particles in the electrolyte. At 26 °C, indium deposited on glassy carbon as smooth, flat films whereas at 160 °C, it deposits as droplets.

Scalable Electrodeposition of Liquid Metal from an Acetonitrile-Based Electrolyte for Highly Integrated Stretchable Electronics.

The advancement of highly integrated stretchable electronics requires the development of scalable sub-micrometer conductor patterning. Eutectic gallium indium (EGaIn) is an attractive conductor for stretchable electronics, as its liquid metallic character grants it high electrical conductivity upon deformation. However, its high surface tension makes its patterning with sub-micrometer resolution challenging. In this work, this limitation is overcome by way of the electrodeposition of EGaIn. A non-aqueous acetonitrile-based electrolyte that exhibits high electrochemical stability and chemical orthogonality is used. The electrodeposited material leads to low-resistance lines that remain stable upon (repeated) stretching to a 100% strain. Because electrodeposition benefits from the resolution of mature nanofabrication methods used to pattern the base metal, the proposed "bottom-up" approach achieves a record-high density integration of EGaIn regular lines of 300 nm half-pitch on an elastomer substrate by plating on a gold seed layer prepatterned by nanoimprinting. Moreover, vertical integration is enabled by filling high-aspect-ratio vias. This capability is conceptualized by the fabrication of an omnidirectionally stretchable 3D electronic circuit, and demonstrates a soft-electronic analog of the stablished damascene process used to fabricate microchip interconnects. Overall, this work proposes a simple route to address the challenge of metallization in highly integrated (3D) stretchable electronics.

Electrodeposition of indium from non-aqueous electrolytes.

The electrochemical behaviour and deposition of indium in electrolytes composed of 0.4 mol dm-3 In(Tf2N)3 and 0.4 mol dm-3 InCl3 in the solvents 1,2-dimethoxyethane and poly(ethylene glycol) (average molecular mass of 0.400 kg mol-1, PEG400) was investigated. Indium(i) was identified as the intermediate species that disproportionated to indium(iii) and indium(0) nanoparticles. The presence of nanoparticles was verified by TEM analysis. SEM analysis showed that deposits obtained at room temperature from 1,2-dimethoxyethane were rough, while spherical structures were formed in PEG400 at 160 °C.