Molecular Electrochemical Catalysis of CO-to-Formaldehyde Conversion with a Cobalt Complex.

Formox, a highly energy-intensive process, currently serves as the primary source of formaldehyde (HCHO), for which there is a crucial and steadily growing chemical demand. The alternative electrochemical production of HCHO from C1 carbon sources such as CO2 and CO is still in its early stages, with even the few identified cases lacking mechanistic rationalization. In this study, we demonstrate that cobalt phthalocyanine (CoPc) immobilized on multiwalled carbon nanotubes (MW-CNTs) constitutes an excellent electrocatalytic system for producing HCHO with productivity through the direct reduction of CO, the two-electron reduction product of CO2. By carefully adjusting both the pH and the applied potential, we identified conditions that enable the production of HCHO with a partial current density of 0.64 mA cm-2 (17.5% Faradaic efficiency, FE) and a total FE of 61.2% for the liquid products (formaldehyde and methanol). A reduction mechanism is proposed.

Kinetics of N2 Release from Diazo Compounds: A Combined Machine Learning-Density Functional Theory Study.

Diazo compounds are commonly employed as carbene precursors in carbene transfer reactions during a variety of functionalization procedures. Release of N2 gas from diazo compounds may lead to carbene formation, and the ease of this process is highly dependent on the characteristics of the substituents located in the vicinity of the diazo moiety. A quantum mechanical density functional theory assisted by machine learning was used to investigate the relationship between the chemical features of diazo compounds and the activation energy required for N2 elimination. Our results suggest that diazo molecules, possessing a higher positive partial charge on the carbene carbon and more negative charge on the terminal nitrogen, encounter a lower energy barrier. A more positive C charge decreases the π-donor ability of the carbene lone pair to the π* orbital of N2, while the more negative N charge is a result of a weak interaction between N2 lone pair and vacant p orbital of the carbene. The findings of this study can pave the way for molecular engineering for the purpose of carbene generation, which serves as a crucial intermediate for many chemical transformations in synthetic chemistry.

Density functional theory and machine learning for electrochemical square-scheme prediction: an application to quinone-type molecules relevant to redox flow batteries.

Proton-electron transfer (PET) reactions are rather common in chemistry and crucial in energy storage applications. How electrons and protons are involved or which mechanism dominates is strongly molecule and pH dependent. Quantum chemical methods can be used to assess redox potential (Ered.) and acidity constant (pKa) values but the computations are rather time consuming. In this work, supervised machine learning (ML) models are used to predict PET reactions and analyze molecular space. The data for ML have been created by density functional theory (DFT) calculations. Random forest regression models are trained and tested on a dataset that we created. The dataset contains more than 8200 quinone-type organic molecules that each underwent two proton and two electron transfer reactions. Both structural and chemical descriptors are used. The HOMO of the reactant and LUMO of the product participating in the oxidation reaction appeared to be strongly associated with Ered.. Trained models using a SMILES-based structural descriptor can efficiently predict the pKa and Ered. with a mean absolute error of less than 1 and 66 mV, respectively. Good prediction accuracy of R2 > 0.76 and >0.90 was also obtained on the external test set for Ered. and pKa, respectively. This hybrid DFT-ML study can be applied to speed up the screening of quinone-type molecules for energy storage and other applications.

Temperature-Controlled Syngas Production via Electrochemical CO2 Reduction on a CoTPP/MWCNT Composite in a Flow Cell.

The mixture of CO and H2, known as syngas, is a building block for many substantial chemicals and fuels. Electrochemical reduction of CO2 and H2O to syngas would be a promising alternative approach for its synthesis due to negative carbon emission footprint when using renewable energy to power the reaction. Herein, we present temperature-controlled syngas production by electrochemical CO2 and H2O reduction on a cobalt tetraphenylporphyrin/multiwalled carbon nanotube (CoTPP/MWCNT) composite in a flow cell in the temperature range of 20-50 °C. The experimental results show that for all the applied potentials the ratio of H2/CO increases with increasing temperature. Interestingly, at -0.6 V RHE and 40 °C, the H2/CO ratio reaches a value of 1.2 which is essential for the synthesis of oxo-alcohols. In addition, at -1.0 V RHE and 20 °C, the composite shows very high selectivity toward CO formation, reaching a Faradaic efficiency of ca. 98%. This high selectivity of CO formation is investigated by density functional theory modeling which underlines that the potential-induced oxidation states of the CoTPP catalyst play a vital role in the high selectivity of CO production. Furthermore, the stability of the formed intermediate species is evaluated in terms of the pKa value for further reactions. These experimental and theoretical findings would provide an alternative way for syngas production and help us to understand the mechanism of molecular catalysts in dynamic conditions.

A comparison study of C19T (T = C, Cr, Ti, Fe, and Ni) nanocages by first-principle DFT calculation for removal of ozone-destroyer pollutants.

In the present work, the interaction of dichloromethane (CH2Cl2) and chloroform (CHCl3) on C20 and C19T (T = Cr, Ti, Fe, Ni) has been studied by density functional theory (DFT). The results have been investigated by binding energy, net charge transfer, electrical and thermodynamic properties, and frontier orbitals. Although the complexes of CH2Cl2 and CHCl3 on free C20 nanocages showed slightly binding energy (- 0.029 and - 0.006 eV, respectively), doping of Cr, Ti, Fe, Ni transition metal atoms on C20 nanocage improved the binding energy. The best binding energy was attributed to the adsorption of CH2Cl2 on C19Cr (- 0.755 eV). Based on ESP maps, doping of Cr, Ti, Fe, and Ni is the cause of strong electrophilic region creation which is very useful for adsorption process CH2Cl2 and CHCl3 on nanocages. Also, natural bond orbital (NBO) analysis showed that the best charge transfer was 0.253 eV which was related to the formation of C19Fe-CHCl3 complex. In addition, the least HOMO-LUMO energy gap between free nanocages (C20, C19Cr, C19Ti, C19Fe, and C19Ni) is 4.05 eV (C19Ti). The thermodynamic investigations indicated that due to the negative enthalpy, all of the studied adsorption processes were exothermic.

Structural, optical, photoluminescence and antibacterial properties of copper-doped silver sulfide nanoparticles.

The Ag2S and Cu doped Ag2S nanoparticles were prepared by simple chemical co-precipitation method and characterized by XRD, SEM, EDX, TEM, PL and UV-vis spectra. The photocatalytic activity of Ag2S and Cu doped Ag2S nanoparticles were investigated with Ofloxacin antibiotic, which is part of the fluoroquinolone family. The morphological study indicated that the products were spherical shape in with diameter size of 30nm. The photocatalytic results demonstrated that the Cu doping increased the photocatalytic efficiency of Ag2S nanoparticles. The outcome of antibacterial experiment under visible light irradiation indicate that the Cu doped Ag2S nanoparticles represent increased antibacterial performance compared with un-doped Ag2S nanoparticles.