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Title: Molecular Electrocatalysts for Oxidation of Hydrogen Using Earth-Abundant Metals: Shoving Protons Around with Proton Relays

Journal Article · · Accounts of Chemical Research

Sustainable, carbon-neutral energy is needed to supplant the worldwide reliance on fossil fuels, to address the persistent problem of increasing emissions of CO2. Solar and wind energy are intermittent, highlighting the need to develop energy storage on a huge scale. Electrocatalysts provide a way to convert between electrical energy generated by renewable energy sources and chemical energy in the form of chemical bonds. Here, the oxidation of hydrogen to give two electrons and two protons is carried out in fuel cells, but the typical catalyst is platinum, a precious metal of low earth-abundance and high cost. In nature, hydrogenases based on iron or iron/nickel reversibly oxidize hydrogen with remarkable efficiency and rates. Functional models of these enzymes are synthesized with the goal of achieving electrocatalytic H2 oxidation using inexpensive, earth-abundant metals along with a key feature identified in the [FeFe]-hydrogenase: an amine base positioned near the metal. The diphosphine ligands PR2NR'2 (1,5-diaza-3,7-diphosphacyclooctane with alkyl or aryl groups on the P and N) are used as ligands in Ni, Fe and Mn complexes. The pendant amines promote binding and heterolytic cleavage of H2, placing the hydride on the metal and the proton on the amine. The pendant amines also serve as proton relays, accelerating intramolecular and intermolecular proton transfers. Electrochemical oxidations and deprotonations by an exogeneous amine base lead to catalytic cycles for oxidation of H2 (1 atm) at room temperature for catalysts derived from [Ni(PCy2NR'2)2]2+, CpC6F5Fe(PtBu2NBn2)H and MnH(PPh2NBn2)(bppm)(CO) [bppm = (PArF2)2CH2)]. The Mn cation [Mn(PPh2NBn2)(bppm)(CO)]+ mediates the rapid (>104 s-1 at -95 °C), reversible heterolytic cleavage of H2. Obtaining the optimal benefit of pendant amines incorporated into the ligand requires that the pendant amine be properly positioned to interact with a M-H or M(H2) bond. In addition, ligands are ideally selected such that the hydride acceptor ability of the metal and the basicity of a pendant are tuned to give low barriers for heterolytic cleavage of the H-H bond and for subsequent proton transfer reactions. Using these principles allows the rational design of electrocatalysts for H2 oxidation using earth-abundant metals.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC05-76RL01830
OSTI ID:
1582563
Report Number(s):
PNNL-SA-108095
Journal Information:
Accounts of Chemical Research, Vol. 48, Issue 7; ISSN 0001-4842
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 123 works
Citation information provided by
Web of Science

References (51)

Powering the planet: Chemical challenges in solar energy utilization journal October 2006
Low-platinum and platinum-free catalysts for the oxygen reduction reaction at fuel cell cathodes journal January 2011
A review on non-precious metal electrocatalysts for PEM fuel cells journal January 2011
Platinum Availability for Future Automotive Technologies journal November 2012
Hydrogenases journal March 2014
Structure/Function Relationships of [NiFe]- and [FeFe]-Hydrogenases journal October 2007
A Mixed-Valent, Fe(II)Fe(I), Diiron Complex Reproduces the Unique Rotated State of the [FeFe]Hydrogenase Active Site journal June 2007
Catalytic Activation of H 2 under Mild Conditions by an [FeFe]-Hydrogenase Model via an Active μ-Hydride Species journal September 2013
Small molecule mimics of hydrogenases: hydrides and redox journal January 2009
Redox-Switched Oxidation of Dihydrogen Using a Non-Innocent Ligand journal January 2008
Combining acid–base, redox and substrate binding functionalities to give a complete model for the [FeFe]-hydrogenase journal October 2011
Electrons from hydrogen journal January 2009
A Dinuclear Ni( -H)Ru Complex Derived from H2 journal April 2007
A Functional [NiFe]Hydrogenase Mimic That Catalyzes Electron and Hydride Transfer from H2 journal February 2013
[NiFe]Hydrogenase from Citrobacter sp. S-77 Surpasses Platinum as an Electrode for H 2 Oxidation Reaction journal June 2014
Enzymes as Working or Inspirational Electrocatalysts for Fuel Cells and Electrolysis journal July 2008
Measurement of the Hydride Donor Abilities of [HM(diphosphine) 2 ] + Complexes (M = Ni, Pt) by Heterolytic Activation of Hydrogen journal March 2002
Fundamentals of H 2 Binding and Reactivity on Transition Metals Underlying Hydrogenase Function and H 2 Production and Storage journal October 2007
Mechanism of Heterolysis of H 2 by an Unsaturated d 8 Nickel Center: via Tetravalent Nickel? journal January 2010
Thermally stable N2 and H2 adducts of cationic nickel(ii) journal January 2012
Synthesis, Structure, and Reactivity of a Nickel Dihydrogen Complex journal November 2012
Hydrogen Oxidation and Production Using Nickel-Based Molecular Catalysts with Positioned Proton Relays journal January 2006
Nature of hydrogen interactions with Ni(II) complexes containing cyclic phosphine ligands with pendant nitrogen bases journal March 2007
Two Pathways for Electrocatalytic Oxidation of Hydrogen by a Nickel Bis(diphosphine) Complex with Pendant Amines in the Second Coordination Sphere journal June 2013
Controlling proton movement: electrocatalytic oxidation of hydrogen by a nickel( ii ) complex containing proton relays in the second and outer coordination spheres journal January 2014
Stabilization of Nickel Complexes with Ni 0 ···H–N Bonding Interactions Using Sterically Demanding Cyclic Diphosphine Ligands journal December 2011
The Role of Pendant Amines in the Breaking and Forming of Molecular Hydrogen Catalyzed by Nickel Complexes journal April 2012
Moving Protons with Pendant Amines: Proton Mobility in a Nickel Catalyst for Oxidation of Hydrogen journal September 2011
Proton Delivery and Removal in [Ni(P R 2 N R 2 ) 2 ] 2+ Hydrogen Production and Oxidation Catalysts journal November 2012
Solvent and electrolyte effects on Ni(P R 2 N R′ 2 ) 2 -catalyzed electrochemical oxidation of hydrogen journal January 2014
Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production journal April 2012
Proton-Coupled Electron Transfer journal April 2012
Mechanistic Insights into Catalytic H 2 Oxidation by Ni Complexes Containing a Diphosphine Ligand with a Positioned Amine Base journal April 2009
Reversible Electrocatalytic Production and Oxidation of Hydrogen at Low Overpotentials by a Functional Hydrogenase Mimic journal February 2012
Amino acid modified Ni catalyst exhibits reversible H 2 oxidation/production over a broad pH range at elevated temperatures journal November 2014
The organometallic active site of [Fe]hydrogenase: Models and entatic states journal March 2003
Structural and Functional Analogues of the Active Sites of the [Fe]-, [NiFe]-, and [FeFe]-Hydrogenases journal June 2009
Synthesis, Characterization, and Reactivity of Fe Complexes Containing Cyclic Diazadiphosphine Ligands: The Role of the Pendant Base in Heterolytic Cleavage of H 2 journal March 2012
Perfluoroaryl-substituted cyclopentadienyl complexes of transition metals journal May 2006
An iron complex with pendent amines as a molecular electrocatalyst for oxidation of hydrogen journal February 2013
Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H 2 journal May 2015
Heterolytic Cleavage of Hydrogen by an Iron Hydrogenase Model: An Fe-H⋅⋅⋅H-N Dihydrogen Bond Characterized by Neutron Diffraction journal April 2014
Dihydrogen Bonding:  Structures, Energetics, and Dynamics journal July 2001
Hydrogens detected by subatomic resolution protein crystallography in a [NiFe] hydrogenase journal January 2015
Iron Complexes for the Electrocatalytic Oxidation of Hydrogen: Tuning Primary and Secondary Coordination Spheres journal March 2014
Increasing the rate of hydrogen oxidation without increasing the overpotential: a bio-inspired iron molecular electrocatalyst with an outer coordination sphere proton relay journal January 2015
Reversible Displacement of Polyagostic Interactions in 16e [Mn(CO)(R 2 PC 2 H 4 PR 2 ) 2 ] + by H 2 , N 2 , and SO 2 . Binding and Activation of η 2 -H 2 trans to CO Is Nearly Invariant to Changes in Charge and cis Ligands journal March 1999
Synthesis, Structures, and Reactions of Manganese Complexes Containing Diphosphine Ligands with Pendant Amines journal October 2010
Rapid, Reversible Heterolytic Cleavage of Bound H 2 journal July 2013
Heterolytic cleavage of H 2 by bifunctional manganese( i ) complexes: impact of ligand dynamics, electrophilicity, and base positioning journal January 2014
Production of hydrogen by electrocatalysis: making the H–H bond by combining protons and hydrides journal January 2014

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Noncovalent Immobilization of Molecular Electrocatalysts for Chemical Synthesis: Efficient Electrochemical Alcohol Oxidation with a Pyrene-TEMPO Conjugate journal June 2017
H 2 Oxidation Electrocatalysis Enabled by Metal-to-Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction journal September 2018
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First-row transition metal complexes of ENENES ligands: the ability of the thioether donor to impact the coordination chemistry journal January 2016
Evaluation of attractive interactions in the second coordination sphere of iron complexes containing pendant amines journal January 2019
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Photochemically Driven Reverse Water-Gas Shift at Ambient Conditions mediated by a Nickel Pincer Complex journal July 2018
Syntheses, crystal structures, and electrochemical studies of dinuclear coordination compounds with the Fe 2 (CO) 6 core journal October 2016
Electrocatalytic H 2 Evolution by the Co‐Mabiq Complex Requires Tempering of the Redox‐Active Ligand journal June 2019
H 2 Oxidation Electrocatalysis Enabled by Metal-to-Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction journal September 2018
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On the concept of frustrated Lewis pairs
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