One pot electrochemical synthesis of poly(melamine) entrapped gold nanoparticles composite for sensitive and low level detection of catechol

A simple and cost effective synthesis of nanomaterials with advanced physical and chemical properties have received much attention to the researchers, and is of interest to the researchers from different disciplines. In the present work, we report a simple and one pot electrochemical synthesis of poly(melamine) entrapped gold nanoparticles (PM-AuNPs) composite. The PM-AuNPs composite was prepared by a single step electrochemical method, wherein the AuNPs and PM were simultaneously fabricated on the electrode surface. The as-prepared materials were characterized by various physicochemical methods. The PM-AuNPs composite modified electrode was used as an electrocatalyst for oxidation of catechol (CC) due to its well-defined redox behavior and enhanced electro-oxidation ability towards CC than other modified electrodes. Under optimized conditions, the differential pulse voltammetry (DPV) was used for the determination of CC. The DPV response of CC was linear over the concentration ranging from 0.5 to 175.5 μM with a detection limit of 0.011 μM. The PM-AuNPs composite modified electrode exhibits the high selectivity in the presence of range of potentially interfering compounds including dihydroxybenzene isomers. The sensor shows excellent practicality in CC containing water samples, which reveals the potential ability of PM-AuNPs composite modified electrode towards the determination of CC in real samples

The effects of morphology, microstructure and mixed-valent states of MnO2 on the oxygen evolution reaction activity in alkaline anion exchange membrane water electrolysis

In this work, we focused on the evaluation of oxygen evolution reaction (OER) activity of three different shapes of α-MnO2 nanowires (NWs), nanorods (NRs) and nanotubes (NTs) in alkaline anion exchange water electrolyser. We have attempted to separate the effect of shape, surface area, Mn3+ content and crystal facets on OER activity and stability. X-ray Photoelectron Spectroscopy (XPS) measurements showed that NTs had the highest surface concentration of Mn3+ on the as prepared samples with average Mn oxidation state of 3.33. However, after activation an increase in the average oxidation state of all three shapes to 3.9 was confirmed by XPS. X-Ray Diffraction (XRD) showed surface restructuring after testing. MnO2 NWs showed the highest OER mass activity of 60.6 A g−1 (10 mA cm−2 at 1.67 V (RHE)) due to the higher surface area of 72.2 m2 g−1. While NTs showed the highest specific activity due to highest content of 211 facet, high Mn3+ surface concentration/surface defects. Similar trend was observed in electrolyser testing with 2 mg cm−2 loading. Poor electronic conductivity of MnO2 resulted in decrease in performance with increased loading to 4 mg cm−2. All the studied shapes showed good stability over 36 h of electrolyser testing

Development of α‐MnO2 Nanowire with Ni and (Ni, Co) – Cation Doping as an Efficient Bifunctional Oxygen Evolution and Oxygen Reduction Reaction Catalysts

Manganese oxides (MnO 2 ) with nanowire morphology materials are a promising candidate for improving oxygen evolution and oxygen reduction reaction (OER/ORR) performance. In this work, we developed transition metal cation doping strategy into the α-MnO 2 tunnel structure to tune the Mn oxidation states and control the uniform nanowire morphology, crystalline structure in order to investigate the effect of doping over bifunctional activity. The single Ni 2+ cation doping in α-MnO 2 with various loading concentrations resulted in 8Ni-MnO 2 exhibiting remarkable OER and ORR activity owing to their excessive concentration of Mn 3+ and Mn 4+ octahedral sites respectively. Further, Co 2+ cation doping in 8Ni-MnO 2 leads to an enhanced synergistic effect that significantly improves the fraction of Mn 3+ quantity which is confirmed by average oxidation state. For, electrochemical OER performance of 8Co-8Ni-MnO 2 exhibits a potential of 1.77 V, Tafel slope value of 68 mV dec -1 and lower charge transfer resistance and it is active in ORR with more positive onset potential of 0.90 V, half-wave potential of 0.80 V, better current density (4.7 mA cm -2 ) and a four-electron pathway. Moreover, bifunctional activity (ΔE = E OER @10 mA cm -2 – ORR@E 1/2 ) of 8Co-8Ni-MnO 2 demonstrated 0.97 V, indicates an excellent activity in alkaline electrolyte solution

One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

The valorization of CO2 via renewable energy sources allows one to obtain carbon-neutral fuels through its hydrogenation, like methane. In this study, Ni0.05Ce0.95O2−δ catalysts were prepared using a simple one-pot hydrothermal method yielding nanorod and nanocube particles to be used for the methanation reaction. Samples were characterized by XRD, BET, TEM, H2-TPR, and H2-TPD experiments. The catalytic activity tests revealed that the best performing catalyst was Ni0.05Ce0.95O2−δ, with nanorod morphology, which gave a CO2 conversion of 40% with a selectivity of CH4 as high as 93%, operating at 325 ◦C and a GHSV of 240,000 cm3 h−1 g−1. However, the lower activation energy was found for Ni0.05Ce0.95O2−δ catalysts with nanocube morphology. Furthermore, an in operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed flowing CO2:H2 or CO:H2 mixture, showing that the main reaction pathway, for the CO2 methanation, is the direct hydrogenation of formate intermediate

One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

The valorization of CO2 via renewable energy sources allows one to obtain carbon-neutral fuels through its hydrogenation, like methane. In this study, Ni0.05Ce0.95O2−δ catalysts were prepared using a simple one-pot hydrothermal method yielding nanorod and nanocube particles to be used for the methanation reaction. Samples were characterized by XRD, BET, TEM, H2-TPR, and H2-TPD experiments. The catalytic activity tests revealed that the best performing catalyst was Ni0.05Ce0.95O2−δ, with nanorod morphology, which gave a CO2 conversion of 40% with a selectivity of CH4 as high as 93%, operating at 325 °C and a GHSV of 240,000 cm3 h−1 g−1. However, the lower activation energy was found for Ni0.05Ce0.95O2−δ catalysts with nanocube morphology. Furthermore, an in operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed flowing CO2:H2 or CO:H2 mixture, showing that the main reaction pathway, for the CO2 methanation, is the direct hydrogenation of formate intermediate

Dual Heteroatom-Doped Carbon Monoliths Derived from Catalyst-free Preparation of Porous Polyisocyanurate for Oxygen Reduction Reaction

Tris­(4-isocyanatophenyl)­methane (TIPM) and <i>N</i>,<i>N</i>′-dimethylformamide react at room temperature with no externally added catalyst to yield polyisocyanurate (PIR) gels. The obtained PIR gels were converted to N- and S-doped porous carbon monoliths by thermal treatment at 1000 °C with elemental sulfur under inert conditions. The PIR linkage acts as precursor for carbon and nitrogen, and %S doping was varied by changing the concentrations of elemental sulfur during pyrolysis. The optimized concentration of sulfur (5.6%) into the carbon matrix displayed excellent oxygen reduction activity with direct four-electron transfer relative to its pristine counterparts by (1) introducing micro- and mesopores in addition to the already existing macropores by etching the carbon surface (confirmed by N₂ sorption isotherms and microscopic images) with the increase in the external surface area providing more active centers and efficient diffusion of electrolyte ions, (2) providing more – C–S–C– active species than oxidized sulfur species (confirmed by XPS and FT-IR) with more oxygen adsorption sites, and (3) filling the micropores of the carbon as a monolayer, affording increased electronic conductivity to the amorphous carbon. This simple and facile method of incorporating N- and S- together into the porous carbon matrix can be considered as an alternate for nonprecious metal catalysts for oxygen reduction reaction

Physiochemical Investigation of Shape-Designed MnO₂ Nanostructures and Their Influence on Oxygen Reduction Reaction Activity in Alkaline Solution

In this work, five types of MnO₂ nanostructres (nanowires, nanotubes, nanoparticles, nanorods, and nanoflowers) were synthesized with a fine control over their α-crystallographic form by hydrothermal method. The electrocatalytic activities of these materials were examined toward oxygen reduction reaction (ORR) in alkaline medium. Numerous characterizations were correlated with the observed activity by analyzing their crystal structure (TGA, XRD, TEM), material morphology (FE-SEM), porosity (BET), inherent structural nature (IR, Raman, ESR), surfaces (XPS), and electrochemical properties (Tafel, Koutecky–Levich plots and % of H₂O₂ produced). Moreover, X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) analysis were employed to study the structural information on the MnO₂ coordination number as well as interatomic distance. These combined results show that the electrocatalytic activities are significantly dependent on the nanoshapes and follow an order nanowire > nanorod > nanotube > nanoparticle > nanoflower. α-MnO₂ nanowires possess enhanced electrocatalytic activity compared to other shapes, even though the nanotubes possess a much higher BET surface area. In the ORR studies, α-MnO₂ nanowires displayed Tafel slope of 65 mV/decade, n-value of 3.5 and 3.6% of hydrogen peroxide production. The superior ORR activity was attributed to the fact that it possesses active sites composed with two shortened Mn–O bonds along with a Mn–Mn distance of 2.824 Å, which provides an optimum requirement for the adsorbed oxygen in a bridge mode favoring the direct 4 electron reduction. In accordance with the first principles based density functional theory (DFT), the enhancement in ORR activity is due to the less activation energy needed for the reaction by the (211) surface than all other surfaces