Electrochemical CO2 reduction has promise as a technology that could help society reach carbon neutrality while producing valuable fuels and chemicals. Herein, the electrochemical synthesis of methyl formate, a product not observed in aqueous CO2 electrolysis, has been analyzed by a rigorous technoeconomic model to evaluate its commercial viability. Methyl formate synthesis has been demonstrated with high faradaic efficiency through the electroreduction of CO2 in methanol. Four competing approaches were analyzed: (1) electroreduction of captured CO2 in a dual CH3OH/H2O electrolyzer, (2) direct electroreduction of flue gas CO2 in a dual CH3OH/H2O electrolyzer, (3) electroreduction of captured CO2 in a CH3OH/CH3OH electrolyzer, and (4) electroreduction of captured CO2 in a H2O/H2O electrolyzer with a downstream CH3OH reactor. Sensitivity analyses, cost contour plots, and comparison plots were generated. The dual methanol/water electrolysis approach was the most cost competitive, with a levelized cost of methyl formate below the present market price. The all-methanol electrolysis route was more expensive due to increased methanol consumption and greater distillation costs. Methyl formate production through aqueous CO2 electrolysis to formic acid with a secondary esterification reaction was by far the most expensive approach, primarily due to the energy-intensive nature of distilling formic acid from water.

In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (H 2 DMTH, H 2 L 1 ). The neutral complexes NiL 1 and PdL 1 were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The pK a of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL 1 and 13.03 for PdL 1 . Cyclic voltammograms of both NiL 1 and PdL 1 in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at −1.83 and −1.79 V (vs ferrocenium/ferrocene) for NiL 1 and PdL 1 , respectively. A quasireversible, ligand-centered event is observed at −2.43 and −2.34 V for NiL 1 and PdL 1 , respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s −1 at an overpotential of 0.74 V for NiL 1 and 8280 s −1 at an overpotential of 0.44 V for PdL 1 . Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.

In this study, a series of thiosemicarbazonato−hydrazinatopyridine metal complexes were evaluated as CO 2 capture agents. The complexes incorporate a non-coordinating, basic hydrazinatopyridine nitrogen in close proximity to a Lewis acidic metal ion allowing for metal−ligand cooperativity. The coordination of various metal ions with (diacetyl-2-(4-methyl-thiosemicarbazone)-3-(2-hydrazinopyridine) (H 2 L 1 ) yielded ML 1 (M = Ni(II), Pd(II)), ML 1 (CH 3 OH) (M = Cu(II), Zn(II)), and [ML 1 (PPh 3 ) 2 ]BF 4 (M = Co(III)) complexes. The ML 1 (CH 3 OH) complexes reversibly capture CO 2 with equilibrium constants of 88 ± 9 and 6900 ± 180 for Cu(II) and Zn(II), respectively. Ligand effects were evaluated with Zn(II) through variation of the 4-methyl-thiosemicarbazone with 4-ethyl (H 2 L 2 ), 4-phenethyl (H 2 L 3 ), and 4-benzyl (H 2 L 4 ) derivatives. The equilibrium constant for CO 2 capture increased to 11,700 ± 300, 15,000 ± 400, and 35,000 ± 200 for ZnL 2 (MeOH), ZnL 3 (MeOH), and ZnL 4 (MeOH), respectively. Quantification of ligand basicity and metal ion Lewis acidity shows that changes in CO 2 capture affinity are largely associated with ligand basicity upon substitution of Cu(II) with Zn(II), while variation of the thiosemicarbazone ligand enhances CO 2 affinity by tuning the metal ion Lewis acidity. Overall, the Zn(II) complexes effectively capture CO 2 from dilute sources with up to 90%, 86%, and 65% CO 2 capture efficiency from 400, 1000, and 2500 ppm CO 2 streams.

Addition of the potassium dichalcogenidodiphenylphosphinate salts, KE 2 PPh 2 (E=S, Se), to either the THF solvate of vanadium (III) chloride or unsolvated chromium(III) chloride results in rapid ligand substitution and the formation of a series of closelyrelated trivalent, neutral mononuclear complexes, M(E 2 PPh 2 ) 3 (M=V, Cr; E=S, Se), isolated in modest to good yield. The metal dichalcogenidophosphinate complexes reported herein were characterized by IR, UV-vis, and 1 H NMR spectroscopies, and their solid-state molecular structures were determined by single-crystal X-ray crystallography. Importantly, the comparative analysis includes the structural and spectroscopic studies of two rare V(III) dithio-and diseleno-phosphinate VE 6 cores, as well as, two previously known CrE 6 analogues. In the solid-state the title complexes exhibit trigonal distortion from octahedral with torsion angles ranging from 43(2) to 50.3(6)°and structural parameters consistent with ligation of progressively 'softer' chalcogen-donors.