Na3V2(PO4)3 Cathode for Room-Temperature Solid-State Sodium-Ion Batteries: Advanced In Situ Synchrotron X-ray Studies to Understand Intermediate Phase Evolution.

Sodium-ion batteries (NIBs) can use elements that are abundantly present in Earth's crust and are technologically feasible for replacing lithium-ion batteries (LIBs). Hence, NIBs are essential components for sustainable energy storage applications. All-solid-state sodium batteries are among the most capable substitutes to LIBs because of their potential to have low price, great energy density, and consistent safety. Nevertheless, more advancements are needed to improve the electrochemical performance of the Na3V2(PO4)3 (NVP) cathode for NIBs, especially with regard to rate performance and operational lifespan. Herein, a core-shell NVP/C structure is accomplished by adopting a solid-state method. The initial reversible capacity of the NVP/C cathode is 106.6 mAh/g (current rate of C/10), which approaches the theoretical value (117.6 mAh/g). It also exhibits outstanding electrochemical characteristics with a reversible capacity of 85.3 mAh/g at 10C and a cyclic retention of roughly 94.2% after 1100 cycles. Using synchrotron-based operando X-ray diffraction, we present a complete examination of phase transitions during sodium extraction and intercalation in NVP/C. To improve safety and given its excellent ionic conductivity and broad electrochemical window, a Na superionic conductor (NASICON) solid electrolyte (Na3.16Zr1.84Y0.16Si2PO12) has been integrated to obtain an all-solid-state NVP/C||Na battery, which provides an exceptional reversible capacity (95 mAh/g at C/10) and long-term cycling stability (retention of 78.3% after 1100 cycles).

Highly integrated autonomous lab-on-a-chip device for on-line and in situ determination of environmental chemical parameters.

The successful integration of sample pretreatment stages, sensors, actuators and electronics in microfluidic devices enables the attainment of complete micro total analysis systems, also known as lab-on-a-chip devices. In this work, we present a novel monolithic autonomous microanalyzer that integrates microfluidics, electronics, a highly sensitive photometric detection system and a sample pretreatment stage consisting on an embedded microcolumn, all in the same device, for on-line determination of relevant environmental parameters. The microcolumn can be filled/emptied with any resin or powder substrate whenever required, paving the way for its application to several analytical processes: separation, pre-concentration or ionic-exchange. To promote its autonomous operation, avoiding issues caused by bubbles in photometric detection systems, an efficient monolithic bubble removal structure was also integrated. To demonstrate its feasibility, the microanalyzer was successfully used to determine nitrate and nitrite in continuous flow conditions, providing real time and continuous information.

Biofunctionalized self-propelled micromotors as an alternative on-chip concentrating system.

Sample pre-concentration is crucial to achieve high sensitivity and low detection limits in lab-on-a-chip devices. Here, we present a system in which self-propelled catalytic micromotors are biofunctionalized and trapped acting as an alternative concentrating mechanism. This system requires no external energy source, which facilitates integration and miniaturization.

Trapping self-propelled micromotors with microfabricated chevron and heart-shaped chips.

We demonstrate that catalytic micromotors can be trapped in microfluidic chips containing chevron and heart-shaped structures. Despite the challenge presented by the reduced size of the traps, microfluidic chips with different trapping geometries can be fabricated via replica moulding. We prove that these microfluidic chips can capture micromotors without the need for any external mechanism to control their motion.

Ultracompact three-dimensional tubular conductivity microsensors for ionic and biosensing applications.

We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection = 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.

Thermal activation of catalytic microjets in blood samples using microfluidic chips.

We demonstrate that catalytic microjet engines can out-swim high complex media composed of red blood cells and serum. Despite the challenge presented by the high viscosity of the solution at room temperature, the catalytic microjets can be activated at physiological temperature and, consequently, self-propel in diluted solutions of blood samples. We prove that these microjets self-propel in 10× diluted blood samples using microfluidic chips.

Microreactor with integrated temperature control for the synthesis of CdSe nanocrystals.

The recent needs in the nanosciences field have promoted the interest towards the development of miniaturized and highly integrated devices able to improve and automate the current processes associated with efficient nanomaterials production. Herein, a green tape based microfluidic system to perform high temperature controlled synthetic reactions of nanocrystals is presented. The device, which integrates both the microfluidics and a thermally controlled platform, was applied to the automated and continuous synthesis of CdSe quantum dots. Since temperature can be accurately regulated as required, size-controlled and reproducible quantum dots could be obtained by regulating this parameter and the molar ratio of precursors. The obtained nanocrystals were characterized by UV-vis and fluorescence spectrophotometry. The band width of the emission peaks obtained indicates a narrow size distribution of the nanocrystals, which confirms the uniform temperature profile applied for each synthetic process, being the optimum temperature at 270 °C (full width at half maximum = 40 nm). This approach allows a temperature controlled, easy, low cost and automated method to produce quantum dots in organic media, enhancing its application from laboratory-scale to pilot-line scale processes.

Compact and autonomous multiwavelength microanalyzer for in-line and in situ colorimetric determinations.

Nowadays, the attainment of microsystems that integrate most of the stages involved in an analytical process has raised an enormous interest in several research fields. This approach provides experimental set-ups of increased robustness and reliability, which simplify their application to in-line and continuous biomedical and environmental monitoring. In this work, a novel, compact and autonomous microanalyzer aimed at multiwavelength colorimetric determinations is presented. It integrates the microfluidics (a three-dimensional mixer and a 25 mm length "Z-shape" optical flow-cell), a highly versatile multiwavelength optical detection system and the associated electronics for signal processing and drive, all in the same device. The flexibility provided by its design allows the microanalyzer to be operated either in single fixed mode to provide a dedicated photometer or in multiple wavelength mode to obtain discrete pseudospectra. To increase its reliability, automate its operation and allow it to work under unattended conditions, a multicommutation sub-system was developed and integrated with the experimental set-up. The device was initially evaluated in the absence of chemical reactions using four acidochromic dyes and later applied to determine some key environmental parameters such as phenol index, chromium(VI) and nitrite ions. Results were comparable with those obtained with commercial instrumentation and allowed to demonstrate the versatility of the proposed microanalyzer as an autonomous and portable device able to be applied to other analytical methodologies based on colorimetric determinations.

A monolithic continuous-flow microanalyzer with amperometric detection based on the green tape technology.

The development of micro total analysis systems (muTAS) has become a growing research field. Devices that include not only the fluidics and the detection system but also the associated electronics are reported scarcely in the literature because of the complexity and the cost involved for their monolithic integration. Frequently, dedicated devices aimed at solving specific analytical problems are needed. In these cases, low-volume production processes are a better alternative to mass production technologies such as silicon and glass. In this work, the design, fabrication, and evaluation of a continuous-flow amperometric microanalyzer based on the green tape technology is presented. The device includes the microfluidics, a complete amperometric detection system, and the associated electronics. The operational lifetime of the working electrode constitutes a major weak point in electrochemical detection systems, especially when it is integrated in monolithic analytical devices. To increase the overall system reliability and its versatility, it was integrated following an exchangeable configuration. Using this approach, working electrodes can be readily exchanged, according to the analyte to be determined or when their surfaces become passivated or poisoned. Furthermore, the electronics of the system allow applying different voltamperometric techniques and provide four operational working ranges (125, 12.5, 1.25, and 0.375 microA) to do precise determinations at different levels of current intensity.

Vortex configuration flow cell based on low-temperature cofired ceramics as a compact chemiluminescence microsystem.

The integration of optical detection methods in continuous flow microsystems can highly extend their range of application, as long as some negative effects derived from their scaling down can be minimized. Downsizing affects to a greater extent the sensitivity of systems based on absorbance measurements than the sensitivity of those based on emission ones. However, a careful design of the instrumental setup is needed to maintain the analytical features in both cases. In this work, we present the construction and evaluation of a simple miniaturized optical system, which integrates a novel flow cell configuration to carry out chemiluminescence (CL) measurements using a simple photodiode. It consists of a micromixer based on a vortex structure, which has been constructed by means of the low-temperature cofired ceramics (LTCC) technology. This mixer not only efficiently promotes the CL reaction due to the generated high turbulence but also allows the detection to be carried out in the same area, avoiding intensity signal losses. As a demonstration, a flow injection system has been designed and optimized for the detection of cobalt(II) in water samples. It shows a linear response between 2 and 20 microM with a correlation of r > 0.993, a limit of detection of 1.1 microM, a repeatability of RSD = 12.4%, and an analysis time of 17 s. These results demonstrate the suitability of the proposal to the determination of compounds involved in CL reactions by means of an easily constructed versatile device based on low-cost instrumentation.

Miniaturized total analysis systems: integration of electronics and fluidics using low-temperature co-fired ceramics.

The advantages of microanalyzers, usually fabricated in silicon, glass, or polymers, are well-known. The design and construction of fluidic platforms are well-developed areas due to the perfectly established microfabrication technologies used. However, there is still the need to achieve devices that include not only the fluid management system but also the measurement electronics, so that real portable miniaturized analyzers can be obtained. Low-temperature co-fired ceramics technology permits the incorporation of actuators, such as micropumps and microvalves, controlled either magnetically, piezoelectrically, or thermally. Furthermore, electronic circuits can be also easily built exploiting the properties of these ceramics and the fact that they can be fabricated using a multilayer approach. In this work, taking advantage of the possibility of combining fluidics and electronics in a single substrate and using the same fabrication methodology, a chemical microanalyzer that integrates microfluidics, the detection system, and also the data acquisition and digital signal processing electronics is presented. To demonstrate the versatility of the technology, two alternative setups have been developed. In the first one, a modular configuration is proposed. In this case, the same electronic module can be used to determine different chemical parameters by simply exchanging the chemical module. In the second one, the monolithic integration of all the elements was accomplished, allowing the construction of compact and dedicated devices. Chloride ion microanalyzers have been constructed to demonstrate the operability of both device configurations. In all cases, the results obtained showed adequate analytical features.