Cobalt and Nickel Diimine-Dioxime Complexes as Molecular Electrocatalysts for Hydrogen Evolution with Low Overvoltages

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 49; pp. 20627 - 20632
• Main Authors: Jacques, Pierre-André, Artero, Vincent, Pécaut, Jacques, Fontecave, Marc, Lehn, Jean-Marie P.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 08.12.2009; National Acad Sciences
• Subjects: Alternative energy; Biochemistry; Biochemistry, Molecular Biology; Catalysis; Chemical reactions; Chemical Sciences; Cobalt; Cobalt - chemistry; Coordination chemistry; Crystallography, X-Ray; Electricity; Electrocatalysis; Electrochemistry; Electrodes; Electrolysis; Evolution; Hydrogen; Hydrogen - analysis; Imines - chemistry; Life Sciences; Ligands; Molecular evolution; Nickel; Nickel - chemistry; Organometallic Compounds - chemistry; Overvoltage; Oxidation-Reduction; Oximes; Oximes - chemistry; Physical Sciences; Precipitates; Protons; hydrogenase; cobaloxime; electrocatalysis; bio-inspired chemistry; hydrogen evolution reaction
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0907775106

Hydrogen production through the reduction of water appears to be a convenient solution for the long-run storage of renewable energies. However, economically viable hydrogen production requests platinum-free catalysts, because this expensive and scarce (only 37 ppb in the Earth's crust) metal is not a sustainable resource [Gordon RB, Bertram M, Graedel TE (2006) Proc Natl Acad Sei USA 103:1209-1214]. Here, we report on a new family of cobalt and nickel diimine-dioxime complexes as efficient and stable electrocatalysts for hydrogen evolution from acidic nonaqueous solutions with slightly lower overvoltages and much larger stabilities towards hydrolysis as compared to previously reported cobaloxime catalysts. A mechanistic study allowed us to determine that hydrogen evolution likely proceeds through a bimetallic homolytic pathway. The presence of a proton-exchanging site in the ligand, furthermore, provides an exquisite mechanism for tuning the electrocatalytic potential for hydrogen evolution of these compounds in response to variations of the acidity of the solution, a feature only reported for native hydrogenase enzymes so far.