Recent developments in hydrogen evolving molecular cobalt(II)–polypyridyl catalysts

Abstract

The search for efficient noble metal-free hydrogen-evolving catalysts is the subject of intense research activity. A new family of molecular cobalt(II)-polypyridyl catalysts has recently emerged. These catalysts prove more robust under reductive conditions than other cobalt-based systems and display high activities under fully aqueous conditions. This review discusses the design, characterization, and evaluation of these catalysts for electrocatalytic and light-driven hydrogen production. Mechanistic considerations are addressed and structure-catalytic activity relationships identified in order to guide the future design of more efficient catalytic systems.

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water

“…1,2 From the first report of a functional water splitting cell using UV light as energy source and metallic platinum as a cathode for the hydrogen evolution catalysis, 3 significant progress has been made towards the construction of cells that use a wider range of the UV-visible-NIR spectrum with increasing solar to hydrogen conversion efficiencies. 4 They use a variety of configurations taking advantage of photovoltaics and photoelectrochemical technologies or both combined. An important element for the optimum performance and competitive cost of these cells is the hydrogen evolving catalyst (HEC) of the reductive half-cell, responsible for the H-H bond formation.…”

“…In this context, the use of molecular cobalt-based catalysts, stabilized by nitrogen donor ligands, has proven to be a good alternative given the high turnover numbers and stability achieved under catalytic conditions. [4][5][6][7][8][9] The catalyst precursor [LCo III Cl 2 ] + (L = macrocyclic ligand) in Scheme 1 belongs to this family of HEC and has been used in electrochemical as well as photochemical catalysis showing excellent results. [10][11][12][13][14] In contrast to many other molecular HEC that are active only in organic solvents, complex [LCo III Cl 2 ] + works in pure aqueous conditions showing remarkable stability over a period of several hours.…”

New Cobalt‐Bisterpyridyl Catalysts for Hydrogen Evolution Reaction

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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. [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. The substituents of the ligands were found to greatly affect the catalytic performances of the systems, in terms of stability and overpotential.

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“…[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. 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.…”

A Poly(cobaloxime)/Carbon Nanotube Electrode: Freestanding Buckypaper with Polymer‐Enhanced H2‐Evolution Performance

“…[1][2][3] Thedevelopment of low-cost catalysts,such as those based on the earth-abundant 3d transition metals Co,Ni, and Fe, offers ap romising route to compete with the performance of the current benchmark catalysts,i ncluding expensive platinum and fragile H 2 -producing enzymes known as hydrogenases. [4][5][6][7][8] Many molecular cobalt-containing H 2 evolution catalysts have been reported, [9] and cobaloximes and their derivatives are among the most widely studied. [10][11][12][13] Thea dvantages of cobaloximes are their facile synthesis and the tunability of their catalytic properties by modifying the substituents on the equatorial and/or axial ligands.…”