Hidden in plain sight: unlocking the full potential of cyclic voltammetry with the thin-film rotating (ring) disk electrode studies for the investigation of oxygen reduction reaction electrocatalysts

Cyclic voltammetry conducted with a thin-film rotating disk electrode, or ring-disk electrode (CV-TF-R(R)DE) is a very popular ‘ex situ’ tool for the rapid screening of electrocatalysts for their activity in oxygen reduction reaction. Despite its popularity and broad use, in most instances only a small part of the information that could be accessed by CV-TF-R(R)DE is actually used by scientists in their research. This work outlines both innovative and more traditional (but half-forgotten) ways of using CV-TF-R(R)DE to its optimal or full potential in the ongoing quest to study the most relevant features of oxygen reduction reaction electrocatalysts and quickly identify the most promising candidates for their applications in fuel cells or other electrochemical devices.     

Approximation of Composition and Temperature Dependent Heat Conductivity and Optimization of Thermoelectric Energy Conversion in Silicon–Germanium Alloys

We analyze the efficiency as thermoelectric energy converter of a silicon–germanium alloy with composition and temperature dependent heat conductivity. The dependency on composition is determined by a non-linear regression method (NLRM), while the dependency on temperature is approximated by a first-order expansion in the neighborhood of three reference temperatures. The differences with respect to the case of thermal conductivity depending on composition only are pointed out. The efficiency of the system is analyzed under the assumption that the optimal energy conversion corresponds to the minimum rate of energy dissipated. The values of composition and temperature which minimize such a rate are calculated as well.     

Green Solvents for Eco-Friendly Synthesis of Dimethindene: A Forward-Looking Approach

Dimethindene is a selective histamine H₁ antagonist and is commercially available as a racemate. Upon analyzing the synthetic pathways currently available for the industrial preparation of dimethindene, we set up a sustainable approach for the synthesis of this drug, switching from petroleum-based volatile organic compounds (VOCs) to eco-friendly solvents, such as 2-methyltetrahydrofuran (2-MeTHF) and cyclopentyl methyl ether (CPME) belonging to classes 3 and 2, respectively. Beyond decreasing the environmental impact of the synthesis (E-factor: 24.1–54.9 with VOCs; 12.2–22.1 with 2-MeTHF or CPME), this switch also improved the overall yield of the process (from 10% with VOCs to 21–22% with 2-MeTHF or CPME) and remarkably simplified the manual operations, working under milder conditions. Typical metrics applied at the first and second pass, according to the CHEM21 metrics toolkit, were also calculated for the whole synthetic procedure of dimethindene, and the results were compared with those of the classical procedure.     

Calculated volume and energy profiles for water exchange on t2g6 rhodium(III) and iridium(III) hexaaquaions: conclusive evidence for an Ia mechanism

An I(a) mechanism was assigned for water exchange on the hexaaquaions Rh(OH(2))(6)(3+) and Ir(OH(2))(6)(3+) on the basis of negative Delta V(++) experimental values (-4.2 and -5.7 cm(3) mol(-1), respectively). The use of Delta V(++) as a mechanistic criterion was open to debate primarily because Delta V(++) could be affected by extension or compression of the nonparticipating ligand bond lengths on going to the transition state of an exchange process. In this paper, volume and energy profiles for two distinct water exchange mechanisms (D and I(a)) have been computed using quantum chemical calculations which include hydration effects. The activation energy for Ir(OH(2))(6)(3+) is 32.2 kJ mol(-1) in favor of the I(a) mechanism (127.9 kJ mol(-1)), as opposed to a D pathway; the value for the I(a) mechanism being close to Delta H(++) and Delta G(++) experimental values (130.5 kJ mol(-1) and 129.9 kJ mol(-1) at 298 K, respectively). Volumes of activation, computed using Connolly surfaces and for the I(a) pathway (DeltaV(++)(calc) = -3.9 and -3.5 cm(3) mol(-1), respectively, for Rh(3+) and Ir(3+)), are in agreement with the experimental values. Further, it is demonstrated for both mechanisms that the contribution to the volume of activation due to the changes in bond lengths between Ir(III) and the spectator water molecules is negligible: -1.8 for the D, and -0.9 cm(3) mol(-1) for I(a) mechanism. This finding clarifies the debate about the interpretation of Delta V(++) and unequivocally confirms the occurrence of an I(a) mechanism with retention of configuration and a small a character for both Rh(III) and Ir(III) hexaaquaions.