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Concerted Proton–Electron Transfer Minimizes Substituent Effects on Adsorbed Phthalocyanine Electrocatalysis

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.5c16528· OSTI ID:3018338
Molecularly modified electrodes (MMEs) are potent electrocatalysts, but few principles exist for their rational design. Electrocatalysis by soluble molecules depends strongly on substituents that tune the catalyst redox potential (E1/2), but it is unclear if this parameter similarly impacts MME catalysis. Herein, we employ the hydrogen evolution reaction (HER) as a test case for comparing carbon-adsorbed cobalt phthalocyanine (CoPc/C) and cobalt hexadecafluoro-phthalocyanine (CoFPc/C). By correlating HER activity and voltammetric data to total Co surface concentration across a wide range of catalyst loadings, we find that only 5–25% of adsorbed Co sites contribute to the Co(II/I) redox wave and that this subpopulation poorly correlates with catalytic activity. Instead, in the low-loading limit, catalytic activity correlates linearly with the majority Co(II/I)-silent Co population, revealing per-site turnover frequency (TOF) values for HER. Despite a 230 mV difference in Co(II/I) redox potentials, CoPc/C and CoFPc/C display TOF values differing by less than a factor of 3 when compared over a wide potential range. Mechanistic studies point to an inner-sphere concerted proton–electron transfer step as rate-determining, suggesting that the Co–H bond dissociation free energy (BDFE) rather than the Co(II/I) E1/2 is thermodynamically relevant. Computational studies indicate that the fluoro-substituents lead to compensatory changes in Co(II/I) E1/2 and Co(I) basicity, leaving the Co–H BDFE largely unchanged between CoPc and CoFPc and thereby manifesting in similar catalytic rates. Furthermore, these results highlight the limited effect of E1/2-tuning on MME catalytic activity and motivate the development of methods to directly alter active site–substrate BDFE.
Research Organization:
Massachusetts Institute of Technology, Cambridge, MA (United States)
Sponsoring Organization:
National Science Foundation Graduate Research Fellowship; USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0020973; SC0021173
OSTI ID:
3018338
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society; ISSN 0002-7863; ISSN 1520-5126
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

References (78)

Elements of Molecular and Biomolecular Electrochemistry: An Electrochemical Approach to Electron Transfer Chemistry journal June 2019
Splitting Water with Cobalt journal July 2011
Reactivity Descriptors for the Activity of Molecular MN4 Catalysts for the Oxygen Reduction Reaction journal September 2016
Aqueous Electrochemical Reduction of Carbon Dioxide and Carbon Monoxide into Methanol with Cobalt Phthalocyanine journal November 2019
Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO2 Reduction to Methanol journal December 2023
Surface Immobilization of Molecular Electrocatalysts for Energy Conversion journal March 2017
Mitigating Cobalt Phthalocyanine Aggregation in Electrocatalyst Films through Codeposition with an Axially Coordinating Polymer journal June 2024
Coordination chemistry in two dimensions: chemically modified electrodes journal May 1988
Spectroscopic and electrochemical studies of transition metal tetrasulfonated phthalocyanines journal December 1985
Hexadecafluoro- and octacyano phthalocyanines as electrocatalysts for the reduction of dioxygen journal January 1991
Selective electroacatalysis for CO2 reduction in the aqueous phase using cobalt phthalocyanine/poly-4-vinylpyridine modified electrodes journal April 1995
Catalytic activity of cobalt and iron phthalocyanines or porphyrins supported on different carbon nanotubes towards oxygen reduction reaction journal November 2011
Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions journal December 2010
Surface chemistry of porphyrins and phthalocyanines journal November 2015
Explaining Kinetic Isotope Effects in Proton-Coupled Electron Transfer Reactions journal April 2025
Molecular Control of Heterogeneous Electrocatalysis through Graphite Conjugation journal November 2019
Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications journal December 2021
Independent Tuning of the pKa or the E1/2 in a Family of Ruthenium Pyridine–Imidazole Complexes journal June 2023
DFT Study on the Mechanism of the Electrochemical Reduction of CO 2 Catalyzed by Cobalt Porphyrins journal February 2016
Phthalocyanine and Metal Phthalocyanines Adsorbed on Graphene: A Density Functional Study journal June 2019
Kinetic and Thermodynamic Control in Porphyrin and Phthalocyanine Self-Assembled Monolayers journal September 2017
Simple Preparation and Characterization of Hybrid Cobalt Phthalocyanine on Multiwalled Carbon Nanotube Electrodes journal March 2024
Tuning Electrode Reactivity through Organometallic Complexes journal June 2023
Electrochemical CO2 Reduction to Methanol by Cobalt Phthalocyanine: Quantifying CO2 and CO Binding Strengths and Their Influence on Methanol Production journal December 2023
Poly(ionic liquid) Ionomers Help Prevent Active Site Aggregation, in Single-Site Oxygen Reduction Catalysts journal May 2024
Nonadiabatic Proton-Coupled Electron Transfer at a Graphitic Surface Immobilized Cobalt Porphyrin journal September 2024
Shallow Rate-Redox Potential Scaling in Aqueous Molecular Oxygen Reduction Electrocatalysis Across a Family of Iron Macrocycles journal December 2024
Reaction Pathways of Hydrogen-Evolving Electrocatalysts: Electrochemical and Spectroscopic Studies of Proton-Coupled Electron Transfer Processes journal May 2016
Effects of Substrate and Polymer Encapsulation on CO 2 Electroreduction by Immobilized Indium(III) Protoporphyrin journal April 2018
Concerted Proton-Coupled Electron Transfer to a Graphite Adsorbed Metalloporphyrin Occurs by Band to Bond Electron Redistribution journal April 2023
Homogenous Electrocatalytic Oxygen Reduction Rates Correlate with Reaction Overpotential in Acidic Organic Solutions journal October 2016
Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O 2 Reduction with a Mononuclear Cobalt Porphyrin Catalyst journal June 2019
Molecular Catalysts Boost the Rate of Electrolytic CO 2 Reduction journal April 2020
Bond Strengths of Toluenes, Anilines, and Phenols:  To Hammett or Not journal May 2004
Chemically modified electrodes journal May 1980
Proton-Coupled Electron Transfer journal November 2007
Acid and Basic Catalysis. journal October 1928
Experimental criterion for the absence of artifacts in the measurement of rates of heterogeneous catalytic reactions journal November 1982
Electrochemical parametrization of metal complex redox potentials, using the ruthenium(III)/ruthenium(II) couple to generate a ligand electrochemical series journal March 1990
Catalytic pathways for the electroreduction of oxygen by iron tetrakis(4-N-methylpyridyl)porphyrin or iron tetraphenylporphyrin adsorbed on edge plane pyrolytic graphite electrodes journal October 1990
Reduction potentials for substituted benzyl radicals: pKa values for the corresponding toluenes journal January 1989
Chronopotentiometric Studies on the Oxidation of Ferrocene, Ruthenocene, Osmocene and Some of their Derivatives1 journal November 1960
Electrocatalytic Hydrogen Evolution at Low Overpotentials by Cobalt Macrocyclic Glyoxime and Tetraimine Complexes journal July 2007
[Ni(P Ph 2 N C6H4X 2 ) 2 ] 2+ Complexes as Electrocatalysts for H 2 Production: Effect of Substituents, Acids, and Water on Catalytic Rates journal April 2011
Turnover Numbers, Turnover Frequencies, and Overpotential in Molecular Catalysis of Electrochemical Reactions. Cyclic Voltammetry and Preparative-Scale Electrolysis journal June 2012
Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation journal September 2020
Catalyst Aggregation Matters for Immobilized Molecular CO2RR Electrocatalysts journal February 2023
Bonds over Electrons: Proton Coupled Electron Transfer at Solid–Solution Interfaces journal March 2023
Impact of the Surface Microenvironment on the Redox Properties of a Co-Based Molecular Cathode for Selective Aqueous Electrochemical CO2-to-CO Reduction journal May 2024
Proton-Coupled Electron Transfer Mechanisms for CO2 Reduction to Methanol Catalyzed by Surface-Immobilized Cobalt Phthalocyanine journal July 2024
In Situ Generated CO Enables High-Current CO2 Reduction to Methanol in a Molecular Catalyst Layer journal May 2024
Medium Effects Are as Important as Catalyst Design for Selectivity in Electrocatalytic Oxygen Reduction by Iron–Porphyrin Complexes journal March 2015
Perturbing the Copper(III)–Hydroxide Unit through Ligand Structural Variation journal December 2015
Donor-Dependent Kinetics of Interfacial Proton-Coupled Electron Transfer journal February 2016
Identifying and Breaking Scaling Relations in Molecular Catalysis of Electrochemical Reactions journal August 2017
Molecular Cobalt Catalysts for O 2 Reduction: Low-Overpotential Production of H 2 O 2 and Comparison with Iron-Based Catalysts journal November 2017
Proton Discharge on a Gold Electrode from Triethylammonium in Acetonitrile: Theoretical Modeling of Potential-Dependent Kinetic Isotope Effects journal December 2018
Graphite Conjugation Eliminates Redox Intermediates in Molecular Electrocatalysis journal July 2019
Electrocatalytic reduction of carbon dioxide to carbon monoxide and methane at an immobilized cobalt protoporphyrin journal September 2015
In-situ spectroscopic probe of the intrinsic structure feature of single-atom center in electrochemical CO/CO2 reduction to methanol journal June 2023
Domino electroreduction of CO2 to methanol on a molecular catalyst journal November 2019
Adsorbed cobalt porphyrins act like metal surfaces in electrocatalysis journal May 2022
Metal surfaces catalyse polarization-dependent hydride transfer from H2 journal April 2023
The solvation environment of molecularly dispersed cobalt phthalocyanine determines methanol selectivity during electrocatalytic CO2 reduction journal July 2024
CO2-to-methanol electroconversion on a molecular cobalt catalyst facilitated by acidic cations journal July 2024
Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions journal January 2013
Toward the rational benchmarking of homogeneous H 2 -evolving catalysts journal January 2014
Highly efficient electrocatalytic hydrogen evolution from neutral aqueous solution by a water-soluble anionic cobalt( ii ) porphyrin journal January 2015
Boosting hydrogen evolution by using covalent frameworks of fluorinated cobalt porphyrins supported on carbon nanotubes journal January 2019
The Brønsted relation – recent developments journal January 1973
Proton transfer kinetics of transition metal hydride complexes and implications for fuel-forming reactions journal January 2023
A mechanism review of metal phthalocyanines as single-atomic catalysts in electrochemical energy conversion journal January 2025
Some applications of the transition state method to the calculation of reaction velocities, especially in solution journal January 1935
Inertia and driving force of chemical reactions journal January 1938
A Synthetic Nickel Electrocatalyst with a Turnover Frequency Above 100,000 s-1 for H2 Production journal August 2011
Surface Functionalization of Electrodes with Molecular Reagents journal January 1986
A molecular mediator for reductive concerted proton-electron transfers via electrocatalysis journal August 2020
Electrochemical Hydrogen Evolution by Cobalt (II) Porphyrins: Effects of Ligand Modification on Catalytic Activity, Efficiency and Overpotential journal January 2018

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