Academic literature on the topic 'Redox Reaction and Slow Learners'

Microbial fuel cells are electrochemical devices that use microorganisms as catalysts to produce electricity. Oxygen is the most used electron acceptor in the cathodic reaction of these systems, due to its abundance in the environment and high redox potential; however, the slow kinetics in oxygen reduction constitutes a limitation. Platinum (Pt) is the most widely used catalyst to accelerate the oxygen reduction reaction, but its high cost makes its use on a large scale impossible. In this study, the performance of manganese dioxide (MnO2) as a cathodic catalyst in an H-type microbial fuel cell was examined. The MnO2 layer on the carbon fiber surface was deposited by simply immersing the carbon in an aqueous KMnO4 solution. The microbial fuel cell was characterized by polarization and power curves. A maximum power peak of 6.09 mW/m2 was obtained with a current density of 22 mA/m2, showing that MnO2 can be a low-cost alternative to be used as catalytic material in the cathode of these devices.

Abstract Metal complexes promote catalytic epoxidation in two different ways: (i) by activation of an oxidant and subsequent migration of an oxygen from the oxidant to olefins; (ii) by oxidation of a metal ion by an oxidant to the high-valent metal oxide and subsequent oxygen transfer to olefins with the reduction of metal ion which can be reoxidized to the metal oxide in situ.The former types of reactions are catalyzed mostly by early transition metal complexes and the latter type of reactions mainly by group VII-X transition metal complexes. For example, t-butyl hydroperoxide is activated by O=V(OR)3 or O2Mo(OR)2 and undergoes epoxidation. During these reactions, the oxidation states of the vanadium and molybdenum ions do not change (Scheme 2.1.1). In general, olefins bearing a precoordinating functional group are good substrates for this type of reaction (see Section 2.3), while epoxidation of isolated olefins is rather slow. On the other hand, stereospecific epoxidation of olefins and C—H hydroxylation of alkanes are realized in living cells with the aid of oxidizing enzymes. Based on the clarification of the catalysis of an iron porphyrin complex at the active site of the representative oxidizing enzyme cytochrome P450, investigations into the enantioselective epoxidation of simple olefins with metalloporphyrin complexes or its equivalents as catalysts were commenced. The P-450-catalysed reactions transfer oxygen atoms to substrates via a high-valent oxo iron porphyrin complex that is produced by the complex redox procedure containing the enzymatic reaction with molecular oxygen. However, the formation of the same oxo species can be chemically effected by treatment of an iron porphyrin complex with stoichiometric oxidants such as iodosylbenzene (Scheme 2.1.2). Besides iron porphyrins, many other metal complexes have been found to catalyse oxygen-transfer reactions via the corresponding high-valent metal oxides.

In this contribution, a thermodynamic model-based approach for the optimal design of a solid-state hydrogen storage and release system utilizing the reversible iron oxide/iron thermochemical redox mechanism is presented. Existing storage processes using this mechanism face significant limitations, including low hydrogen conversion, high energy input requirements, limited storage density, and slow charging/discharging kinetics. To address these challenges, a custom thermodynamic model using NIST thermochemistry data is developed, enabling an in-depth analysis of redox reaction equilibria under different conditions. Unlike previous studies, this approach integrates a multi-objective optimization framework that explicitly balances competing objectives: maximizing hydrogen yield while minimizing thermal energy demand. By systematically identifying optimal trade-offs, the study provides new insights into improving process efficiency and reactor design for thermochemical hydrogen storage. These findings contribute to advancing energy-efficient and scalable hydrogen storage technologies.

Abstract The extensive studies of used fuel dissolution inside a failed nuclear waste container have been reviewed. The primary controlling factor is the redox condition set at the fuel surface by water radiolysis, its evolution with time as radiation fields decay, and how it is influenced by the presence of oxidant scavengers, especially H2, produced by corrosion of the steel liner in the container. If the container fails early, and oxidizing conditions are established, dissolution will be a corrosion reaction driven by radiolytically-produced H2O2. As radiation fields decay and conditions become less oxidizing, the corrosion rate will decrease, and its evolution with time, will be influenced by the formation of insoluble UVI corrosion product deposits, stabilized by calcium and silicate in the groundwater. These deposits could partially block fuel corrosion, but also lead to locally acidified sites at which the corrosion rate is increased. These sites would be pores in the deposit and/or flaws in the fuel surface. If the groundwater contains sufficient bicarbonate, deposition would be inhibited and the fuel corrosion possibly accelerated by the formation of bicarbonate-uranyl ion complexes. As conditions become less oxidizing these issues become less important. The generation of acidity within deposits is unlikely, and since corrosion would be limited by the available concentration of oxidants, the influence of bicarbonate on the corrosion rate disappears. For sufficiently low dose rates, a threshold for the transition from corrosion to chemical dissolution has been identified and validated by dissolution rate measurements on used and alpha-doped fuels. Beyond this threshold dissolution will be solubility-controlled and extremely slow. The transition from radiolytic corrosion to chemical dissolution can be rapidly induced by oxidant scavengers, especially H2. Small concentrations of H2 suppress the redox condition to the threshold even for used fuels with high gamma/beta radiation fields. For sufficiently high concentrations, the establishment of the reversible H2/H+ reaction on noble metal epsilon particles can lead to galvanic protection of the fuel against corrosion. It is possible that this effect could lead to protection of the fuel against corrosion almost from the time of container failure. Under these conditions fuel dissolution and radionuclide release would be extremely small.