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With growing research interest in liquid metals, such as Ga and Ga-based alloys, understanding their behaviours at reduced dimensions is becoming of more fundamental significance, especially for exploiting their properties in a variety of applications. Mechanical sonication is a common technique used for micronising bulk liquid metals into smaller sized particles. One distinct characteristic of Ga and Ga-based liquid metal alloy particles, micronised via sonication, is the formation of native oxygen species such as GaOOH and Ga2O3. However, the nitridation of these particles has not been reported. In this work, we demonstrate a room temperature nitridation process during the micronisation of eutectic Ga–In alloy (EGaIn). Characterisations reveal that the sonication in the N-containing precursors of PVP and N2 results in the formation of GaN within the GaOOH crystallites that separate themselves from the bulk of EGaIn during sonication. As a model example of the applicability of such particles, low-detection-limit biosensing by photoluminescence of the obtained particles is demonstrated. The work shows a room temperature pathway for the creation of GaN that can be further investigated, expanded upon, and implemented for different future applications.

One of the major challenges in the development of soft electronics is to devise scalable and automated strategies for the microfabrication of deformable and flexible electronic components and sensors. Liquid metals have demonstrated unique characteristics suitable for such applications. To date, conductive patterning using liquid metals has mainly focused on writing or injection of liquid metals into prefabricated channels, requiring multiple complicated procedures and reliance on specific inks formulae. Here a new strategy has been introduced for direct patterning of liquid metal particles onto substrates via UV photolithography. A variety of different tracks, patterns and sensors, on both rigid and flexible substrates, are demonstrated using a dispersion of eutectic alloy of gallium and indium in photoresist, to present the extent of capability of the introduced method. The method provides simple, effective, high-resolution and precision patterning of liquid metals for the emerging fields of soft electronics and sensors.

Cellulose-based supercapacitors display important advantages in comparison with devices fabricated with other materials, regarding environmental friendliness, flexibility, cost and versatility. Recent progress in the field has been mainly focused on the utilization of cellulose fibres as: structural mechanical reinforcement of electrodes; precursors of electrically active carbon-based materials; or primary electrolytes that act as reservoirs of secondary electrolytes. In this work, a flexible, lightweight, robust, portable and manageable all-carboxymethyl cellulose symmetric supercapacitor has been obtained by assembling two electrodes based on carboxymethyl cellulose hydrogels to a solid electrolytic medium formulated with the same material. Hydrogels, which were made by cross-linking carboxymethyl cellulose paste with citric acid in water, rendered not only effective solid electrolytic media by simply loading NaCl but also electroactive electrodes. For the latter, conducting polymer microparticles, which were loaded into the hydrogel network during the physical cross-linking step, were appropriately connected through the in situ anodic polymerization of a similar conducting polymer in aqueous medium, thus creating conduction paths. The performance of the assembled supercapacitors has been proved by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. This design opens a new window for the green and mass production of flexible cellulose-based supercapacitors

We report a green carbon capture and conversion technology offering scalability and economic viability for mitigating CO2 emissions. The technology uses suspensions of gallium liquid metal to reduce CO2 into carbonaceous solid products and O2 at near room temperature. The nonpolar nature of the liquid gallium interface allows the solid products to instantaneously exfoliate, hence keeping active sites accessible. The solid co-contributor of silver-gallium rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano dimensional triboelectrochemical reactions. By altering the secondary solvent and changing the reactor height, the dissolution and conversion efficiency can be tuned. The optimum reactor height is only 27 cm, when gallium/silver fluoride mix at 7:1 mass ratio is employed as the reaction material. At CO2 input of ~8 sccm, 92% efficiency was obtained at the record low input energy of 228.5 kW∙h for the capture and conversion of a tonne of CO2. The potential impact of this green technology is remarkable, likely benefiting a variety of industries and offering an economical solution for CO2 capture and conversion.

Room-temperature synthesis of 2D graphitic materials (2D-GMs) remains an elusive aim, especially with electrochemical means. Here, it is shown that liquid metals render this possible as they offer catalytic activity and an ultrasmooth templating interface that promotes Frank-van der Merwe regime growth, while allowing facile exfoliation due to the absence of interfacial forces as a nonpolar liquid. The 2D-GMs are formed at low onset potential and can be in situ doped depending on the choice of organic precursors and the electrochemical set-up. The materials are tuned to exhibit porous or pinhole-free morphologies and are engineered for their degree of oxidation and number of layers. The proposed liquid-metal-based room-temperature electrochemical route can be expanded to many other 2D materials.

We report the reduction of poly(3,4-ethylenedioxythiophene) (PEDOT) films with a cationic 1,4-diazabicyclo[2.2.2]octane-based ionene bearing N,N0-(meta-phenylene)dibenzamide linkages (mPI). Our main goal is to obtain n-doped PEDOT using a polymeric dopant agent rather than small conventional tetramethylammonium (TMA), as is usual. This has been achieved using a three-step process, which has been individually optimized: (1) preparation of p-doped (oxidized) PEDOT at a constant potential of +1.40 V in acetonitrile with LiClO4 as the electrolyte; (2) dedoping of oxidized PEDOT using a fixed potential of 1.30 V in water; and (3) redoping of dedoped PEDOT applying a reduction potential of 1.10 V in water with mPI. The resulting films display the globular appearance typically observed for PEDOT, with mPI being structured in separated phases forming nanospheres or ultrathin sheets. This organization, which has been supported by atomistic molecular dynamics simulations, resembles the nanosegregated phase distribution observed for PEDOT p-doped with poly(styrenesulfonate). Furthermore, the doping level achieved using mPI as the doping agent is comparable to that achieved using TMA, even though ionene provides distinctive properties to the conducting polymer. For example, films redoped with mPI exhibit much more hydrophilicity than the oxidized ones, whereas films redoped with TMA are hydrophobic. Similarly, films redoped with mPI exhibit the highest thermal stability, while those redoped with TMA show thermal stability that is intermediate between those of the latter and the dedoped PEDOT. Overall, the incorporation of an mPI polycation as the n-dopant into PEDOT has important advantages for modulating the properties of this emblematic conducting polymer.

A green carbon capture and conversion technology offering scalability and economic viability for mitigating CO2 emissions is reported. The technology uses suspensions of gallium liquid metal to reduce CO2 into carbonaceous solid products and O2 at near room temperature. The nonpolar nature of the liquid gallium interface allows the solid products to instantaneously exfoliate, hence keeping active sites accessible. The solid co-contributor of silver-gallium rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano-dimensional triboelectrochemical reactions. When a gallium/silver fluoride mix at 7:1 mass ratio is employed to create the reaction material, 92% efficiency is obtained at a remarkably low input energy of 230 kWh (excluding the energy used for dissolving CO2 ) for the capture and conversion of a tonne of CO2 . This green technology presents an economical solution for CO2 emissions.

Gallic acid, a natural phenolic compound, efficiently establishes surface complexes with liquid gallium leading to the formation of an aqueous gallium dispersion via sonication. The surface functionalised gallium particles thus obtained were easily impregnated into paper membranes that could be turned from insulating to conductive by pressure induced deformation of the embedded particles.

Colloidal liquid metal alloys of gallium, with melting points below room temperature, are potential candidates for creating electrically conductive and flexible composites. However, inclusion of liquid metal micro- and nanodroplets into soft polymeric matrices requires a harsh auxiliary mechanical pressing to rupture the droplets to establish continuous pathways for high electrical conductivity. However, such a destructive strategy reduces the integrity of the composites. Here, this problem is solved by incorporating small loading of nonfunctionalized graphene flakes into the composites. The flakes introduce cavities that are filled with liquid metal after only relatively mild press-rolling (0.1 MPa) to form electrically conductive continuous pathways within the polymeric matrix, while maintaining the integrity and flexibility of the composites. The composites are characterized to show that even very low graphene loadings (≈0.6 wt%) can achieve high electrical conductivity. The electrical conductance remains nearly constant, with changes less than 0.5%, even under a relatively high applied pressure of30 kPa. The composites are used for forming flexible electrically-conductive tracks in electronic circuits with a self-healing property. The demonstrated application of co-fillers, together with liquid metal droplets, can be used for establishing electrically-conductive printable-composite tracks for future large-area flexible electronics.

Different carboxymethyl cellulose sodium salt (NaCMC)-based pastes and hydrogels, both containing a salt as supporting electrolyte, have been prepared and characterized as potential solid state electrolyte (SSE) for solid electrochemical supercapacitors (ESCs).The characteristics of the NaCMC-based SSEs have been optimized by examining the influence of five different factors in the capacitive response of poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes: i) the chemical nature of the salt used as supporting electrolyte; ii) the concentration of such salt; iii) the concentration of cellulose used to prepare the paste; iv) the concentration of citric acid employed during NaCMC cross-linking; and v) the treatment applied to recover the supporting electrolyte after washing the hydrogel. The specific capacitance of the device prepared using the optimized hydrogel as SSE is 81.5 and 76.8¿F/g by means of cyclic voltammetry and galvanostatic charge/discharge, respectively, these values decreasing to 60.7 and 75.5¿F/g when the SSE is the paste.

Flexible and lightweight electrodes were prepared using a two-step process. First, poly(3,4-ethylenedioxythiophene) (PEDOT) microparticles were loaded into poly-y-glutamic acid (y-PGA) hydrogel matrix during the reaction of the biopolymer chains with the cross-linker, cystamine. After this, PEDOT particles dispersed inside the hydrogel were used as polymerization nuclei for the chronoamperometric synthesis of poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PHMeDOT) in aqueous solution. After characterization of the resulting electrode composites, electrochemical studies revealed that the capacitive properties drastically depend on the polymerization time used to produce PHMeDOT inside the loaded hydrogel matrix. Specifically, flexible electrodes obtained using a polymerization time of 7 h exhibit an specific capacitance of 45.4 ± 0.7 mF/cm2 from cyclic voltammetry and charge–discharge long-term stability. The applicability of these electrodes in lightweight and flexible energy-harvesting systems useful for energy-autonomous, low-power, disposable electronic devices has been proved powering a LED bulb.

Three isomeric ionene polymers containing 1,4-diazabicyclo[2.2.2]octane (DABCO) and N,N’-(x-phenylene)dibenzamide (x= ortho- / meta- / para-) linkages have been used as dopant agents to produce n-doped poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes by reducing already dedoped conducting polymer (CP) films. This work focuses on the influence of the ionene topology in both the properties of n-doped PEDOT:ionene electrodes and the success of the in situ thermal gelation of the ionene inside the CP matrix. The highest doping level is reached for the para-isomeric ionene-containing electrode, even though the content of ortho- and meta-topomers into the corresponding n-doped PEDOT:ionene electrodes is greater. Thus, many of the incorporated ionene units are not directly interacting with CP chains and, therefore, do not play an active role as n-dopant agent but they are crucial for the in situ formation of ionene hydrogels. The effect of the ionene topology is practically inexistent in properties like the specific capacitance and wettability of PEDOT:ionene films, and it is small but non-negligible in the electrochemical and thermal stability. In contrast, the surface morphology, topography, and distribution of dopant molecules significantly depend on the ionene topology. In situ thermal gelation was successful in PEDOT films n-doped with the ortho- and para-topomers, even though this assembly process was much faster for the former than for the latter. The gelation considerably improved the mechanical response of electropolymerized PEDOT film, which was practically non-existent before it. Molecular dynamics simulations prove that the strength and abundance of PEDOT···ionene specific interactions (i.e. ¿-¿ stacking, N–H···S hydrogen bonds and both N+···O and N+···S interactions) are higher for the meta-isomeric ionene, for which the in situ gelation was not achieved, than for the ortho- and para-ones.

Flexible symmetric supercapacitor prototypes composed of electrodes that were prepared by polymerizing poly(hydroxymethyl-3,4-ethylenedioxythiophene) inside a poly-¿-glutamic acid (¿PGA) biohydrogel matrix, previously loaded with microparticles of poly(3,4-ethylenedioxythiophene) (PEDOT) and alumina (Al2O3), have been fabricated and characterized. Prototypes have been assembled in a totally solid, compact and lightweight configuration, where the supporting electrolytic medium is a ¿PGA hydrogel prepared in presence of NaHCO3. The elements of the prototypes have been characterized and their optimized to obtain the highest specific capacitance. The electrochemical performances of the prototypes have been investigated by cyclic voltammetry, charge-discharge galvanostatic cycles and electrochemical impedance spectroscopy. After 2000 charge-discharge cycles (i.e. 60.000¿s of continuous operation), the loss of specific capacitance is of only 8%, revealing an excellent stability. Results are very promising for the development of compact, flexible, lightweight and biocompatible supercapacitors to be employed like energy-autonomous electronic devices.

Metal foams are highly sought-after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low-melting-point liquid metal is devised for the single-step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low-melting-point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron- to micron-sized open-cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo-electrocatalysis, bacteria electrofiltration, and CO2 electroconversion. In particular, the Field's metal-based foams show exceptional CO2 electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low-temperature post transition and transition metal alloys.

Composites formed by poly(3,4-ethylenedioxythiophene) and alumina (PEDOT/Al2O3) have been prepared by in situ anodic polymerization. For this purpose, the stability of 1:1 and 4:1 monomer:alumina aqueous solutions has been examined as a function of the pH (2.3, 4.0, 7.0, 8.8, or 10.8). Results indicate that the monomer behaves as a dispersant that remains stable at the studied basic pHs despite they are close to the isoelectric point of alumina. Although the thermal stability of the composites is considerably affected by the pH of the reaction medium, its influence on the surface morphology is very small. Independently, of the synthetic conditions, the electrochemical properties were better for PEDOT/Al2O3 than for pure PEDOT, reflecting that alumina particles promote the charge mobility. The highest specific capacitance (SC; 141 F/g), which was 55% higher than that obtained for pure PEDOT, was achieved for the composite prepared at pH = 8.8 using a 4:1 monomer:alumina ratio. These conditions favor the participation of OH– groups as secondary doping agents without degrading the polymer matrix and enhance the specific surface of the films, facilitating the ionic mobility. On the other hand, application of a multi-step polymerization strategy has shown that interfaces originated by consecutive steps enhance the SC. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017