A Molecular Cobalt Hydrogen Evolution Catalyst Showing High Activity and Outstanding Tolerance to CO and O₂

Abstract

There is a demand to develop molecular catalysts promoting the hydrogen evolution reaction (HER) with a high catalytic rate and a high tolerance to various inhibitors, such as CO and O2. Herein we report a cobalt catalyst with a penta‐dentate macrocyclic ligand (1‐Co), which exhibits a fast catalytic rate (TOF=2210 s−1) in aqueous pH 7.0 phosphate buffer solution, in which proton transfer from a dihydrogen phosphate anion (H2PO4−) plays a key role in catalytic enhancement. The electrocatalyst exhibits a high tolerance to inhibitors, displaying over 90 % retention of its activity under either CO or air atmosphere. Its high tolerance to CO is concluded to arise from the kinetically labile character of undesirable CO‐bound species due to the geometrical frustration posed by the ligand, which prevents an ideal trigonal bipyramid being established.

Structure‐Functional Analysis of Hydrogen Production Catalyzed by Molecular Cobalt Complexes with Pentadentate Ligands in Aqueous Solutions

“…A distorted pentagonal bipyramid Co complex 16 with a nearly coplanar pentaaza‐macrocyclic ligand was reported by Zhong, Lu, Sakai, and co‐workers for electrocatalytic HER in 2019 . A quasi‐reversible couple at E 1/2 = –0.80 V assigned for [Co II (L)(H 2 O) 2 ] 2+ /[Co II (L –· )(H 2 O)] + and an irreversible wave at –1.10 V (vs. NHE) for [Co II (L –· )(H 2 O)] + / [Co 0 (L)] were observed for complex 16 in a neutral aqueous 0.10 m NaClO 4 solution.…”

CH-π interaction boosts photocatalytic CO2 reduction activity in a noble-metal-free system with a molecular cobalt catalyst anchored on carbon nitride

“…The synthesis of Co-N5 consists of a template complexation reaction where 2,6-diacetyl-pyridyl reacts with triethylenetetramine in the presence of Co(II) salts as previously described in the literature. 11 A similar method was used for the synthesis of Co-PYN5 but using the diacetyl reactant functionalized with a pyrene moiety. This generates Co- 11 As a consequence, when one of the aliphatic N of PYN5 is not coordinated, it can also act as a proton acceptor or hydrogen bonding site close to the axial positions where the CO2 reduction transformation will occur and therefore can help to significantly reduce the activation energies for the CO2 reduction reaction as has been recently reported for both reduction and oxidation reactions involving proton transfer steps in the rate determining step.…”

“…11 A similar method was used for the synthesis of Co-PYN5 but using the diacetyl reactant functionalized with a pyrene moiety. This generates Co- 11 As a consequence, when one of the aliphatic N of PYN5 is not coordinated, it can also act as a proton acceptor or hydrogen bonding site close to the axial positions where the CO2 reduction transformation will occur and therefore can help to significantly reduce the activation energies for the CO2 reduction reaction as has been recently reported for both reduction and oxidation reactions involving proton transfer steps in the rate determining step. 42,43 Another interesting feature of the [Co(PYN5)(MeCN)2] 2+ structure is the 119.4 o dihedral angle between the acetyl and pyrene groups due to the steric hindrance produced by the alpha-CH groups of each moiety.…”

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

“…The viability of a hydrogen‐based energy society is depended on efficient and durable production of hydrogen . Recent efforts have resulted in the identification of many molecular catalysts for hydrogen evolution . Despite these achievements, however, understanding and further controlling reaction processes are still highly challenging .…”