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A bifunctional electrocatalyst based on heteroatoms doped VS2 was developed for electrocatalytic water splitting.

In this work, a facile and cost-effective approach to assemble metallic wires into two-dimensional (2D) and three-dimensional (3D) freestanding geometries by room-temperature welding is demonstrated. The low melting point of gallium (29.8 °C) enables the welding at room temperature without the aid of high-energy sources required for high-melting-point metals and alloys. The welding enables assembly of solid gallium wires into 2D and 3D geometries that could create freestanding architectures with multiple junctions along any inclined direction. These 2D and 3D freestanding metallic structures are freeze-cast in soft elastomers to obtain stretchable and soft devices: a 2D stretchable resistive and capacitive sensor patterned with parallel metal lines, a 2D stretchable capacitive sensor patterned with an interdigitated metal structure with capacitive changes on stretching in both x- and y-axes, and a 3D compressive sensor by assembly of liquid metal helices, which could sense foot pressure compression. We also developed a facile method to interconnect between soft circuits and external electronics, suppressing stress during mechanical deformation.

Shape memory composites are fascinating materials with the ability to preserve deformed shapes that recover when triggered by certain external stimuli. Although elastomers are not inherently shape memory materials, the inclusion of phase-change materials within the elastomer can impart shape memory properties. When this filler changes the phase from liquid to solid, the effective modulus of the polymer increases significantly, enabling stiffness tuning. Using gallium, a metal with a low melting point (29.8 °C), it is possible to create elastomeric materials with metallic conductivity and shape memory properties. This concept has been used previously in core-shell (gallium-elastomer) fibers and foams, but here, we show that it can also be implemented in elastomeric films containing microchannels. Such microchannels are appealing because it is possible to control the geometry of the filler and create metallically conductive circuits. Stretching the solidified metal fractures the fillers; however, they can heal by body heat to restore conductivity. Such conductive, shape memory sheets with healable conductivity may find applications in stretchable electronics and soft robotics.

In this work, we introduce liquid metal patterned stretchable and soft capacitive sensor with enhanced dielectric properties enabled by graphite nanofiber (GNF) fillers dispersed in polydimethylsiloxane (PDMS) substrate. We oxidized gallium-based liquid metal that exhibited excellent wetting behavior on the surface of the composites to enable patterning of the electrodes by a facile stencil printing. The fluidic behavior of the liquid metal electrode and modulated dielectric properties of the composite (k = 6.41 ± 0.092@6 wt % at 1 kHz) was utilized to fabricate stretchable and soft capacitive sensor with ability to distinguish various hand motions.

This study describes buckling instabilities mediated via surface roughness to generate hierarchical structures on a metal (aluminum)/polymer (polystyrene) laminated composite bilayer film on a rigid substrate. Buckling instability is a non-lithographic approach to generate microscale features in thin films. Metals can buckle over the surface due to compressive stress arising from differences in thermal expansion of the individual layers. The topographies of the buckles characterized by wavelength and amplitude can be manipulated by varying the thickness of the layers and the extent of thermal annealing time. Here, the pre-buckled surface on the laminated composite bilayer film formed via two–step molding resulted in hierarchical patterns via surface roughness-mediated buckling instability. The negative replica of the buckles was generated by poly(dimethyl siloxane) (PDMS) and the positive replica of the buckles was fabricated via molding using a PDMS negative replica onto the PS film. The metal layer was subsequently formed on the PS film and the laminated composite bilayer film enabled patterns with hierarchical topography following thermal treatment. The hierarchically structured surfaces exhibit moderately enhanced hydrophilicity and the elastomeric replica with hierarchical buckles showed stretchable hydrophobicity up to 120% stretching due to partial preservation of the pre-structured buckles on the surface.