Lab-on-a-chip and miniaturized systems have gained significant popularity motivated by marked differences in material performance at the micro-to-nano-scale realm. However, to fully exploit micro-to-nano-scale chemistry, solvent volatility and lack of reproducibility need to be overcome. Here, we combine the non-volatile and versatile nature of ionic liquids with microcontact printing in an attempt to establish a facile protocol for high throughput fabrication of open microreactors and microfluidics. The micropatterned ionic liquid droplets have been demonstrated as electrochemical cells and reactors for microfabrication of metals and charge transfer complexes, substrates for immobilization of proteins and as membrane-free high-performance amperometric gas sensor arrays. The results suggest that miniaturized ionic liquid systems can be used to solve the problems of solvent volatility and slow mass transport in viscous ionic liquids in lab-on-a-chip devices, thus providing a versatile platform for a diverse number of applications.
From a safety perspective, it is vital to have fast responding gas sensors for toxic and explosive gases in the event of a gas leak. Amperometric gas sensors have been developed for such a purpose, but their response times are often relatively slow-on the order of 50 seconds or more. In this work, we have developed sensors for hydrogen gas that demonstrate ultra-fast response times. The sensor consists of an array of gold microchannel electrodes, electrodeposited with platinum nanoparticles (PtNP) to enable hydrogen electroactivity. Very thin layers (~9 µm) of room temperature ionic liquids (RTILs) result in an extremely fast response time of only 2 seconds, significantly faster than the other conventional electrodes examined (unmodified Pt electrode, and PtNP modified Au electrode). The RTIL layer in the microchannels is much thinner than the channel length, showing an interesting yet complex diffusion pattern and characteristic thin-layer behavior. At short times (e.g. on the timescale of cyclic voltammetry), the oxidation current is smaller and steady-state in nature, compared to macrodisk electrodes. At longer times (e.g. using long-term chronoamperometry), the diffusion layer is large for all surfaces and extends to the liquid/gas phase boundary, where the gas is continuously replenished from the flowing gas stream. Thus, the current response is the largest on the microchannel electrode, resulting in the highest sensitivity and lowest limit of detection for hydrogen. These microchannel electrodes appear to be highly promising surfaces for the ultrafast detection of hydrogen gas, particularly at relevant concentrations close to, or below, the lower explosive limit of 4 vol-% H 2.
Ionic liquid (IL)‐based microchannels sensors have been fabricated and employed for the detection of toxic ammonia (NH3) and hydrogen chloride (HCl) gases, with enhanced sensitivity and response times compared to conventional electrodes. Electrochemical techniques were employed to understand the behaviour of these highly toxic gases in two ionic liquids, [C4mpyrr][NTf2] and [C2mim][NTf2], on a gold modified microchannels electrode. The limits of detection (LODs) obtained in [C4mpyrr][NTf2] for NH3 (3.7 ppm) and in [C2mim][NTf2] for HCl (3.6 ppm) were lower than the current Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) for the two gases (25 ppm for NH3 and 5 ppm for HCl). The response time of the sensor is 15 s with a sensitivity of 143 nA ppm−1 and 14 nA ppm−1 for HCl and NH3, respectively. These results demonstrate the superiority of IL‐based microchannels sensors for detecting toxic gases, when compared to commercially available sensors or traditional IL‐based sensor designs, where high sensitivity or fast response time is still a challenge.
High hydro-active Al-3Ga-3In-3Sn alloys were prepared by coupling alloying and mechanical milling methods. NiCl2 was added to the alloy during ball milling as the catalyst. XRD, SEM, and XAFS were used for the characterization of the hydro-active alloy. The hydrogen generation properties were systematically investigated in tap water at room temperature. The results show that the hydrogen generation rate is 11.02 L∙min−1∙g−1, and the conversion yield is 90.25% for the Al-3Ga-3In-3Sn-2NiCl2 composite with a ball milling time of 2 h at room temperature in tap water. The hydrolysis reaction contains the expansion of the Al-based phase into a nano-sized layer and the further hydrolysis reaction of the layered Al phase with water. The activation mechanism was also investigated, and the activation of Al was attributed to the Al-Ni galvanic with the existing Cl−, which leads to a faster hydrolysis reaction rate for ball-milled powder with NiCl2.
In this study, a “membrane‐less and spill‐less” gas‐sensing device has been evaluated for the electrochemical detection of oxygen. Iron oxide magnetic nanoparticles were prepared by chemical co‐precipitation and used to prepare an aqueous ferrofluid. The iron oxide nanoparticles were subsequently stabilised and passivated with a cationic polymer, namely, poly(diallyldimethyl ammonium chloride). The resulting ferrofluid was evaluated as an electrolyte for the analytical quantification of oxygen on screen‐printed carbon electrodes. An applied magnetic field immobilised the ferrofluid electrolyte in place to result in a “membrane‐less and spill‐less” ferrofluid‐based gas sensor. The polymer poly(diallyldimethyl ammonium chloride) was found to result in an apparent enhancement in the electrocatalysis of the system towards the oxygen reduction reaction. Furthermore, as the strength of the applied magnetic field was increased, the oxygen reduction current also increased owing to the response of the polymer‐coated nanoparticles. The oxygen reduction current was linear from 0 to 100 % oxygen content.
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