Simple Synthesis of Cobalt Carbonate Hydroxide Hydrate and Reduced Graphene Oxide Hybrid Structure for High-Performance Room Temperature NH₃ Sensor

A Flow-Through Membraneless Microfluidic Zinc-Air Cell

In this work, the proof of concept of a functional membraneless microfluidic Zn-air cell (μZAC) that operates with a flow-through arrangement is presented for the first time, where the activity and durability can be modulated by electrodepositing Zn on porous carbon electrodes. For this purpose, Zn electrodes were obtained using chronoamperometry and varying the electrodeposition times (20, 40, and 60 min), resulting in porous electrodes with Zn thicknesses of 3.3 ± 0.3, 11.6 ± 2.4, and 34.8 ± 5.1 μm, respectively. Pt/C was initially used as the cathode to analyze variables, such as KOH concentration and flow rate, and then, two manganese-based materials were evaluated (α-MnO₂ and MnMn₂O₄ spinel, labeled as Mn₃O₄) to determine the effect of inexpensive materials on the cell performance. According to the transmission electron microscopy (TEM) results, α-MnO₂ has a nanorod-like shape with a diameter of 11 ± 1.5 nm, while Mn₃O₄ presented a hemispherical shape with an average particle size of 22 ± 1.8 nm. The use of α-MnO₂ and Mn₃O₄ cathodic materials resulted in cell voltages of 1.39 and 1.35 V and maximum power densities of 308 and 317 mW cm^-2, respectively. The activities of both materials were analyzed through density of state calculations; all manganese species in the α-material MnO₂ presented an equivalent density of states with a reduced orbital occupation to the left of the Fermi energy, which allowed for better global performance above Mn₃O₄/C and Pt/C.

Impedimetric Detection of Ammonia and Low Molecular Weight Amines in the Gas Phase with Covalent Organic Frameworks

Two Covalent Organic Frameworks (COF), named TFP-BZ and TFP-DMBZ, were synthesized using the imine condensation between 1,3,5-triformylphloroglucinol (TFP) with benzidine (BZ) or 3,3-dimethylbenzidine (DMBZ). These materials were deposited, such as films over interdigitated electrodes (IDE), by chemical bath deposition, giving rise to TFP-BZ-IDE and TFP-DMBZ-IDE systems. The synthesized COFs powders were characterized by Powder X-Ray Diffraction (PXRD), Fourier Transform Infrared spectroscopy (FT-IR), solid-state Nuclear Magnetic Resonance (ssNMR), nitrogen adsorption isotherms, Scanning Electron Microscopy (SEM), and Raman spectroscopy, while the films were characterized by SEM and Raman. Ammonia and low molecular weight amine sensing were developed with the COF film systems using the impedance electrochemical spectroscopy (EIS). Results showed that the systems TFP-BZ-IDE and TFP-DMBZ-IDE detect low molecular weight amines selectively by impedimetric analysis. Remarkably, with no significant interference by other atmospheric gas compounds such as nitrogen, carbon dioxide, and methane. Additionally, both COF films presented a range of sensitivity at low amine concentrations below two ppm at room temperature.