Electrocatalytic Hydrogen Production with a Molecular Cobalt Complex in Aqueous Solution

Abstract

Herein, we present the synthesis of a cobalt complex with a pentadentate ligand platform and its application in the electrochemical hydrogen evolution reaction (LCF3=2,6‐bis(methoxybis(4‐trifluormethyl‐1H‐imidazol‐2‐yl)methyl)pyridine). The complex is active in neutral to acidic solvent mixtures containing 50 % water. Electronic tuning in the ligand backbone, that is introduction of electron‐withdrawing CF3‐groups, shifts the onset potential of the catalytic wave to less negative potentials. NMR and UV/Vis studies indicate that the CoIII complex is deprotonated twice in the ligand backbone under neutral conditions. Reduction is accompanied by protonation, as indicated by pH‐dependent CV measurements, and the CoI state initiates catalysis. The result suggests that the pentadentate ligand is an ideal platform for cobalt catalysts in the oxidative and reductive water splitting reaction.

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

“…By replacing equatorial pyridine with imidazole, Siewert and co‐workers recently presented the electrocatalytic hydrogen production activity catalyzed by complex 5 in neutral or acidic solvent mixtures . An onset potential of –1.28 V vs. NHE with 50 % FE and a catalytic rate constant of 70 s –1 at –1.42 V were determined for complex 5 in phosphate buffered MeCN/H 2 O (1:1).…”

Strategies for Electrochemically Sustainable H2 Production in Acid

“…[ 157 ] The cobalt complex consists of a pentadentate ligand and can be used at a solvent mixture containing 50% water, delivering a rate constant of 70 s −1 for HER. [ 158 ] In addition to Co‐based complexes, molecular complexes produced by combining nickel with bis(diphenylphosphanyl)amine ligands were demonstrated to be potential homogeneous catalyst for HER, with high TOF (2827–5149 s −1 ) and stability in acidic conditions. [ 159 ] Ni molecular complexes consisting of bis(diphenylphosphanyl)amine ligands also have excellent stability but with relatively lower TOF 368.59–585.17 s –1 in trifluoroacetic acid‐containing solutions.…”

Closed Synthetic Cycle for Nickel‐Based Dihydrogen Formation

“…Hydrogen (H 2 ) is an appealing alternative to carbon-based fuels, and, in this context, the hydrogen economy has given considerable attention to metal hydrides. [1][2][3][4] While cobalt complexes have been extensively studied for hydrogen production, [5][6][7][8][9][10][11][12][13][14][15][16] nickel hydride complexes, obtained by protonation of the corresponding Ni 0 complex, [17][18][19][20][21][22] are currently attracting interest due to their potential to transfer protons, hydrogen atoms, or hydrides. [23][24][25][26][27] In H 2 evolution chemistry, molecular Ni hydride catalysts are known for H 2 production through proton reduction.…”