Modification of Microelectrode Arrays with High Surface Area Dendritic Platinum 3D Structures: Enhanced Sensitivity for Oxygen Detection in Ionic Liquids

Materials for Chemical Sensing: A Comprehensive Review on the Recent Advances and Outlook Using Ionic Liquids, Metal–Organic Frameworks (MOFs), and MOF-Based Composites

The ability to measure and monitor the concentration of specific chemical and/or gaseous species (i.e., “analytes”) is the main requirement in many fields, including industrial processes, medical applications, and workplace safety management. As a consequence, several kinds of sensors have been developed in the modern era according to some practical guidelines that regard the characteristics of the active (sensing) materials on which the sensor devices are based. These characteristics include the cost-effectiveness of the materials’ manufacturing, the sensitivity to analytes, the material stability, and the possibility of exploiting them for low-cost and portable devices. Consequently, many gas sensors employ well-defined transduction methods, the most popular being the oxidation (or reduction) of the analyte in an electrochemical reactor, optical techniques, and chemiresistive responses to gas adsorption. In recent years, many of the efforts devoted to improving these methods have been directed towards the use of certain classes of specific materials. In particular, ionic liquids have been employed as electrolytes of exceptional properties for the preparation of amperometric gas sensors, while metal–organic frameworks (MOFs) are used as highly porous and reactive materials which can be employed, in pure form or as a component of MOF-based functional composites, as active materials of chemiresistive or optical sensors. Here, we report on the most recent developments relative to the use of these classes of materials in chemical sensing. We discuss the main features of these materials and the reasons why they are considered interesting in the field of chemical sensors. Subsequently, we review some of the technological and scientific results published in the span of the last six years that we consider among the most interesting and useful ones for expanding the awareness on future trends in chemical sensing. Finally, we discuss the prospects for the use of these materials and the factors involved in their possible use for new generations of sensor devices.

Core@shell PtAuAg@PtAg Hollow Nanodendrites as Effective Electrocatalysts for Methanol and Ethylene Glycol Oxidation

Pt-based catalysts with core@shell structures are widely used in alcohol oxidations due to their excellent catalytic performance. In this work, we synthesized a series of core@shell PtAuAg@PtAg hollow nanodendrites (HNDs) with different compositions by a simple seed-mediated method. The PtAuAg@PtAg HNDs with a hollow core and dendritic shell exhibit excellent catalytic performance for ethylene glycol oxidation reaction (EGOR) and methanol oxidation reaction (MOR). Among these, Pt₃₈Au₂₉Ag₃₃ HNDs have the highest mass activity (12364.0 mA mg_Pt^-1/3278.0 mA mg_Pt^-1) for EGOR and MOR, which is 4.2 times and 5.3 times higher than that of commercial Pt/C (2941.0 mA mg_Pt^-1/617.6 mA mg_Pt^-1), respectively. More importantly, after successive cyclic voltammetry tests, the retained mass activities of Pt₃₈Au₂₉Ag₃₃ HNDs are 3913.8 mA mg_Pt^-1 and 348.3 mA mg_Pt^-1, which are much higher than that of commercial Pt/C as well. The excellent catalytic performance of PtAuAg@PtAg HNDs can be attributed to the structure of HNDs, which can greatly increase the surface area and active sites, as well as the electronic and synergistic effects among Pt, Au, and Ag. This research may provide new ideas for the development of high-efficiency hollow catalytic materials for EGOR and MOR.

Formation of 3-Dimensional Gold, Copper and Palladium Microelectrode Arrays for Enhanced Electrochemical Sensing Applications

Microelectrodes offer higher current density and lower ohmic drop due to increased radial diffusion. They are beneficial for electroanalytical applications, particularly for the detection of analytes at trace concentrations. Microelectrodes can be fabricated as arrays to improve the current response, but are presently only commercially available with gold or platinum electrode surfaces, thus limiting the sensing of analytes that are more electroactive on other surfaces. In this work, gold (Au), copper (Cu), and palladium (Pd) are electrodeposited at two different potentials into the recessed holes of commercial microelectrode arrays to produce 3-dimensional (3D) spiky, dendritic or coral-like structures. The rough fractal structures that are produced afford enhanced electroactive surface area and increased radial diffusion due to the 3D nature, which drastically improves the sensitivity. 2,4,6-trinitrotoluene (TNT), carbon dioxide gas (CO₂), and hydrogen gas (H₂) were chosen as model analytes in room temperature ionic liquid solvents, to demonstrate improvements in the sensitivity of the modified microelectrode arrays, and, in some cases (e.g., for CO₂ and H₂), enhancements in the electrocatalytic ability. With the deposition of different materials, we have demonstrated enhanced sensitivity and electrocatalytic behaviour towards the chosen analytes.