A Copper Complex as Catalyst in Proton Reduction

Substituent Effect on Ligand-Centered Electrocatalytic Hydrogen Evolution of Phosphorus Corroles

There have been few reports on the substituent effect of main-group-element corrole complexes as ligand-centered homogeneous electrocatalysts for the hydrogen evolution reaction (HER). The key to comprehend the catalytic mechanism and develop efficient catalysts is the elucidation of the effects of electronic structure on the performance of energy-related small molecules. In this work, the "push-pull" electronic effect of the substituents on electrocatalytic HER of phosphorus corroles was investigated by using 5,10,15-tris(phenyl) corrole phosphorus (1P), 10-pentafluorophenyl-5,15-bis(phenyl) corrole phosphorus (2P), 10-phenyl-5,15-bis(pentafluorophenyl) corrole phosphorus (3P), 5,10,15-tris(pentafluorophenyl) corrole phosphorus (4P) complexes bearing hydroxyl axial ligands and different numbers of fluorine atoms on the meso-aryl substituents. The results revealed that the catalytic HER activity of phosphorus corroles decreased with the increasing of fluorine atom numbers, it follows in the order 1P>2P>3P>4P. Density functional theory (DFT) calculations show that the corrole 1P has the lowest free energy barrier in catalytic HER.

Electrocatalytic proton reduction by dinuclear cobalt complexes in a nonaqueous electrolyte

Two dinuclear CoII complexes 1 and 2 have been synthesized and characterized using various spectroscopic methods. Both the complexes were employed for H+ reduction in organic media. Faradaic efficiency of 82–90% was obtained for the H2 evolution.

Effect of Counteranions in Electrocatalytic Hydrogen Generation Promoted by Bis(phosphinopyridyl) Ni(II) Complexes

We previously reported the preparation and characterization of a Ni(II) complex capable of electrocatalytic hydrogen generation. The complex [Ni(L_NH2)₂Cl]Cl (1) includes a 6-((diphenylphosphino)methyl)pyridin-2-amine ligand (L_NH2), which has an amino group as a base that acts as a proton transfer site by virtue of its location near the metal center. In order to study the effect of counteranions in hydrogen generation, two additional Ni^II(L_NH2) complexes with weakly coordinating/noncoordinating counteranions, [Ni(L_NH2)₂](OTs)₂ (OTs^- = p-toluenesulfonate) (2) and [Ni(L_NH2)₂](BF₄)₂ (3), were synthesized. Their X-ray crystal structures reveal that the Ni(II) ion is coordinated with two bidentate L_NH2 ligands in both complexes. Complex 2 contains both trans and cis isomers in the unit cell. The former is in an axially elongated square-pyramidal geometry (τ₅ = 0.17), and the latter is in a nearly square planar geometry (τ₄ = 0.11) with two weakly interacting OTs^- anions at the axial sites. Complex 3 has only the cis isomer in the solid state, which is in a nearly square planar geometry (τ₄ = 0.10). These complexes are slightly different from 1, which has a distorted-square-pyramidal geometry (τ₅ = 0.25) with a coordinated chloride anion. UV-vis spectra of 2 and 3 in MeCN show a spectral pattern characteristic of a square-planar Ni(II) complex. These spectra are slightly different from the unique spectrum of 1, which is typical of an axially coordinating Ni(II) species as a result of having a Cl^- anion at the apical position. Electrocatalytic hydrogen generation promoted by these three Ni(II) complexes (1.0 mmol) demonstrates an increase in the catalytic current induced by stepwise addition of HOAc (pK_a = 22.3 in MeCN) as a proton source. The complexes demonstrate turnover frequencies (TOF) of 3800 s^-1 for 1, 5400 s^-1 for 2, and 8800 s^-1 for 3 in MeCN (3 mL) containing 0.1 M [n-Bu₄N](ClO₄) in the presence of HOAc (145 equiv) at overpotentials of ca. 530, 490, and 430 mV, respectively.

Reactivity and Mechanism of Photo- and Electrocatalytic Hydrogen Evolution by a Diimine Copper(I) Complex

The tetrahedral copper(I) diimine complex [Cu(pq)2]BF4 displays high photocatalytic activity for the H2 evolution reaction with a turnover number of 3564, thus representing the first type of a Cu(I) quinoxaline complex capable of catalyzing proton reduction. Electrochemical experiments indicate that molecular mechanisms prevail and DFT calculations provide in-depth insight into the catalytic pathway, suggesting that the coordinating nitrogens play crucial roles in proton exchange and hydrogen formation.

Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes

The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule-material hybrid systems are organized as "dark" cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends the scope of this review to prospects and challenges in targeting catalysis beyond "classical" H2 evolution and CO2 reduction to C1 products, by summarizing cases for higher-value products from N2 reduction, C x>1 products from CO2 utilization, and other reductive organic transformations.

Electrocatalytic reduction of protons to hydrogen by a copper complex of the pentadentate ligand Dmphen-DPA in a nonaqueous electrolyte

An aminopyridine-based copper complex was synthesized and investigated for its electrocatalytic proton reduction activity and the plausible mechanism.

Electrochemical water oxidation using a copper complex

This study highlights the importance of proton coupled electron transfer (PCET) during electrochemical-driven water oxidation catalysis employing a copper complex.