Experimental Determination of Enthalpies of Solution of Tetraphenyl Porphyrin (TPP) and Some Metal Derivatives, in Chloroform: Interpretation of the Solvation Processes at a Molecular Level

Construction of Cobalt Porphyrin-Modified Cu2O Nanowire Array as a Tandem Electrocatalyst for Enhanced CO2 Reduction to C2 Products

Here, the molecule-modified Cu-based array is first constructed as the self-supporting tandem catalyst for electrocatalytic CO2 reduction reaction (CO2RR) to C2 products. The modification of cuprous oxide nanowire array on copper mesh (Cu2O@CM) with cobalt(II) tetraphenylporphyrin (CoTPP) molecules is achieved via a simple liquid phase method. The systematical characterizations confirm that the formation of axial coordinated Co-O-Cu bond between Cu2O and CoTPP can significantly promote the dispersion of CoTPP molecules on Cu2O and the electrical properties of CoTPP-Cu2O@CM heterojunction array. Consequently, as compared to Cu2O@CM array, the optimized CoTPP-Cu2O@CM sample as electrocatalyst can realize the 2.08-fold C2 Faraday efficiency (73.2% vs 35.2%) and the 2.54-fold current density (‒52.9 vs ‒20.8 mA cm-2) at ‒1.1 V versus RHE in an H-cell. The comprehensive performance is superior to most of the reported Cu-based materials in the H-cell. Further study reveals that the CoTPP adsorption on Cu2O can restrain the hydrogen evolution reaction, improve the coverage of *CO intermediate, and maintain the existence of Cu(I) at low potential.

Protonation of Planar and Nonplanar Porphyrins: A Calorimetric and Computational Study

Herein, we report the first calorimetric study of the protonation of planar and nonplanar free-base porphyrins: H₂OETPP (strongly saddled by its substituents), H₂T(tBu)P (strongly ruffled by its substituents), and the nominally planar porphyrins (npPs) H₂OEP, H₂TPP, H₂T(nPe)P, and H₂T(iPr)P. The observed enthalpies of protonation in solution (ΔH_protsoln) for formation of the dications in 1,1,2,2-tetrachloroethane with 2% trifluoroacetic acid are -45 ± 1 kcal mol^-1 for the npPs, -52.0 kcal mol^-1 for H₂T(tBu)P, and -70.9 kcal mol^-1 for H₂OETPP. The corresponding enthalpies of protonation (ΔH_DFT) obtained from DFT calculations (-27 ± 5, -42, and -63 kcal mol^-1, respectively) reproduce this trend. The much more negative enthalpy of protonation seen for H₂OETPP is consistent with this molecule being pre-deformed into the saddle structure favored by porphyrin dications. Except for OETPP, the calculated enthalpies of the first protonations (ΔH₁) are significantly more positive than the enthalpies of the second protonations (ΔH₂). In addition, the structural strain energies for the first protonations (ΔE_st(1)) are also significantly more positive than ΔE_st(2). According to the calculations, the monocations thus have higher proton affinities than the corresponding free-base porphyrins due to a structural strain effect, which is consistent with the generally elusive nature of the porphyrin monocation. The recent observations of monocations for free-base porphyrins with a high degree of saddling can be rationalized in terms of ΔH₁ and ΔH₂ being similar; so, the monocation is no longer an unstable intermediate.

Kinetic and thermodynamic processes of organic species at the solution-solid interface: the view through an STM

A focused review is presented on the evolution of our understanding of the kinetic and thermodynamic factors that play a critical role in the formation of well ordered organic adlayers at the solution-solid interface. While the current state of knowledge is in the very early stages, it is now clear that assumptions of kinetic or thermodynamic control are dangerous and require careful confirmation. Equilibrium processes at the solution-solid interface are being described by evolving thermodynamic models that utilize concepts from the thermodynamics of micelles. A surface adsorption version of the Born-Haber cycle is helping to extract the thermodynamic functions of state associated with equilibrium structures, but only a very few systems have been so analyzed. The kinetics of surface phase transformation, especially for polymorphic phases is in an early qualitative stage. Adsorption and desorption kinetics are just starting to be measured. The study of kinetics and thermodynamics for organic self-assembly at the solution-solid interface is experiencing very exciting and rapid growth.