New Cobalt‐Bisterpyridyl Catalysts for Hydrogen Evolution Reaction

Abstract

Preparation of as eries of terpyridyl ligandsb earing different substituents recently led to the synthesis of new cobalt-bisterpyridyl complexes spanning over aw ide range of redox potentials. In this work, we describet he catalytic properties of these complexes for the electroreduction of protons into hydrogen (hydrogen evolution reaction( HER)) in acetonitrile. The substituents of the ligands were found to greatly affect the catalytic performances of the systems, in terms of stability and overpotential. Interestingly,s ystemsb ased on dimethylaminoterpyridine derivatives perform HER with highe fficiency,l ow overpotential and excellent stability. Density functional theory calculations were used to providei nsights into the reaction mechanism of HER catalyzed by these systems, highlighting the role of the ligand for protonactivation.Major efforts are currently employed into the development of green energy technologies based on solar and wind power. However,t hese energy sourcess uffer from low energetic density and intermittency.T oo vercome such failings, ac ommon approachi nvolves storage of the generatede nergy by conversion into chemical energy through the formation of chemical bonds. The best examples of these strategies are the photochemicalo re lectrochemical reduction of protons (2H + )t om olecular hydrogen (H 2 ), allowing energy storagethrough the formation of an HÀHc hemical bond. [1][2][3] The kinetic barrierf or such at ransformation is large, hence,c atalysts are required to lower it.Although metallic platinum remains the most effective catalytic materialf or the hydrogen evolution reaction( HER), its limited availability and high cost justifiest he quest for alternative catalysts based on cheaper and more abundant non-noble metals.C urrent research focuses primarily on two types of compounds:h eterogeneousm aterials and homogeneous metal complexes. Despite being more complex than heterogeneous materials, molecular catalysts are often ideal for fine tuning reactivity through syntheticm odificationso f the ligands. In this context,significant successhas been recently obtained with molecular cobalt complexes,i np articular cobaloximes, cobalt-diimine-dioximes andc obalt-polypyridine complexes. [3][4][5][6][7] The latter possess remarkablea bility to store multiple reducing equivalents, as the ligand not only stabilizes the reduced metal centerb ut also accumulates electrons within its p-conjugated system. Within this class of compounds, our group hasi nvestigated the rarely studied potential of simple and cheap cobalt-bisterpyridine complexes as catalysts for CO 2 and proton reduction. [8] We have shown that these complexes can be graftedo nt he surface of glassy carbon electrodes, on which they display significant HER activity. [9] To optimize such catalysts, we have synthesized av ariety of new terpyridines with different substituents (very few functionalized terpyridine derivatives were commercially available). Synthesis and characterization of the corresponding cobalt complexes (C1-C8 in Figure ...

Solar-driven reduction of aqueous CO2 with a cobalt bis(terpyridine)-based photocathode

“…Its formation would involve the de-coordination of one or two pyridines to create a vacant coordination site and, subsequently, the oxidative addition of CO2. 49 In fact, the d 8 configuration of [Co I ] species is likely to favour a square planar or tetrahedral geometry, as well as increase the lability of the ligand. 50,51 Moreover, the pyridine de-coordination is likely to be stabilised by protonation of its nitrogen atom from the diprotonated phosphonic acid due to the latter's lower pKa value.…”

Alternating substrate/ligand-metal coordination enables a low-energy pathway for C-O bond cleavage in the electrocatalytic reduction of carbon dioxide

“…6 Partial de-coordination of polydentate polypyridyl ligands from metal centers upon reduction have also been postulated earlier by some groups. [70][71][72] However, the synergistic occurrence of these two processes in a single catalytic framework is, to the best of our knowledge, unprecedented.…”

Metal‐Terpyridine Complexes in Catalytic Application – A Spotlight on the Last Decade

“…Thereby, the obtained CO‐to‐H 2 ratio could be adjusted via the applied voltage and the chemical structure of the tpy ligand . In line with these studies, these authors prepared the library of Co(II) complexes 46 (Figure ) and tested them in the electrocatalytic HER from acetic acid in acetonitrile solutions . The ligand architecture had a profound impact on the catalytic performance of the complexes with respect to their stability and overpotential ( e. g ., complex 46 a readily decomposed in the presence of AcOH).…”