Carbon-supported first-row transition metal complexes drive electroreduction of CO 2 to CO in aqueous medium with remarkable activity and selectivity. However, their durability under negative potentials is quite low and the deactivation mechanisms are still not clear. Herein, we present an in-depth mechanistic study on the stability of Co porphyrin-based catalysts during CO 2 reduction in an aqueous electrolyte. The mechanisms of the degradation reactions were evaluated for Co tetraphenylporphyrin (CoTPP) using a combination of spectral, electrochemical, and theoretical methods. Our evidence shows that two major pathways contribute to the gradual activity loss. The first route is oxidative and yields the catalytically inactive complex [Co III TPP]OH. The second pathway is based on reductive carboxylation of the porphyrin ring via transient formation of [Co 0 TPP] 2− and [Co 0 TPP-CO] 2− . The latter reaction disrupts the π-system of the porphyrin structure and leads to the complete disintegration of the macrocyclic core. In contrast to the earlier reports, we found that the direct poisoning by CO, demetallation, and reduction to chlorins play no significant role in the deactivation process. It was further determined that the bulky donating functional groups disfavor the formation of dianionic species and restrict access of CO 2 to the vulnerable meso-position of the porphyrin ligand, thus improving the catalyst stability. The effect was found to be especially strong for the −OMe-substituted complex CoTPP-(OMe) 8 that shows excellent reusability under overpotentials below 500 mV. In turn, electronegative substituents such as fluorine suppress the activity of the catalyst and provide no advantages in terms of durability.

The knowledge of nonequilibrium electron transfer rates is paramount for the design of modern hybrid electrocatalysts. Herein, we propose a general simulation-based approach to interpret variable-frequency square wave voltammetry (VF-SWV) for heterogeneous materials featuring reversible redox behavior. The resistive and capacitive corrections, inclusion of the frequency domain, and statistical treatment of the surface redox kinetics are used to account for the non-ideal nature of electrodes. This approach has been validated in our study of Co II /Co I redox transformation for Co tetraphenylporphyrin (CoTPP) immobilized on carbon cloth and multiwalled carbon nanotubes (CNTs) -one of the most active heterogeneous molecular catalysts in carbon dioxide (CO 2 ) electroreduction. It is demonstrated that the modeling of experimental data furnishes the capacitance of the surface double layer C, uncompensated resistance R u , symmetry coefficients α, kinetic constants k 0 , and equilibrium redox potentials E 0 in one experiment. Moreover, the proposed method yields a stochastic map of the redox kinetics rather than a single value, thus exposing the inhomogeneous nature of the electrochemically active layer. The computed parameters are in excellent agreement with the results of the classic methods such as cyclic voltammetry and fall in line with the reported CoTPP catalytic activity. Thus, VF-SWV is suitable for the study of high-level composites such as covalent organic frameworks and organometallic-CNT mixtures. The resulting insights into the electron transfer mechanisms are especially useful for the rational development of the catalyst−support interfaces and immobilization methods.

The immobilization of enzymes in metal–organic frameworks (MOFs) with preserved biofunctionality paves a promising way to solve problems regarding the stability and reusability of enzymes. However, the rational design of MOF-based biocomposites remains a considerable challenge as very little is known about the state of the enzyme, the MOF support, and their host–guest interactions upon immobilization. In this study, we elucidate the detailed host–guest interaction for MOF immobilized enzymes in the biointerface. Two enzymes with different sizes, lipase and insulin, have been immobilized in a mesoporous PCN-333(Al) MOF. The dynamic changes of local structures of the MOF host and enzyme guests have been experimentally revealed for the existence of the confinement effect to enzymes and van der Waals interaction in the biointerface between the aluminum oxo-cluster of the PCN-333 and the -NH 2 species of enzymes. This kind of host–guest interaction renders the immobilization of enzymes in PCN-333 with high affinity and highly preserved enzymatic bioactivity.

Entropy benchmarking of different sized molecules in aqueous phase is carried out for known solvation models, where we compare geometry and solvation cavity packing parameters, which allows us to improve the accuracy of the obtained entropy values using empirical corrections. A comparison of solvation entropy models is conducted for a benchmarking set of 56 molecules, showing how an accurate description of cavitation entropy and its hindrance on other entropy values is important for large-sized solute molecules. Finally, we compare reaction free energies with entropies calculated using the most accurate solvation model considered, where we demonstrate a significant improvement in the accuracy relative to experimental values.

MetalÀ organic frameworks (MOFs) as solid acid catalysts provide active sites with definite structures. Here, Zr 6-based MOF-808 and its derivatives were studied as catalysts for glycerol dehydration, the products of which (acrolein vs. acetol) are very sensitive to the nature of the catalytic acid sites. Evolving MOF-808 into MOF-808-S with a 120 % increase in the number of Brønsted OH À /H 2 O coordinated to Zr IV and a vanished Lewis acidity by steam treatment, the post-synthetically modified catalyst presented 100 % conversion of glycerol, 91 % selectivity to acrolein, and 0 % selectivity to acetol within the active window. Real-time analysis of the product composition indicated the in situ MOF structural evolution. Overall, the specific MOF-substrate interaction characterized by the probe reaction provides more understandings on the structural evolution of the MOFs and their impact on the performance as solid acid catalysts.