Title: Identifying and Breaking Scaling Relations in Molecular Catalysis of Electrochemical Reactions

Abstract

Improving molecular catalysis for important electrochemical proton-coupled electron transfer (PCET) reactions, such as the interconversions of H⁺/H₂, O₂/H₂O, CO₂/CO, and N₂/NH₃, is an ongoing challenge. Synthetic modifications to the molecular catalysts are valuable but often show trade-offs between turnover frequency (TOF) and the effective overpotential required to initiate catalysis (η_eff). Herein, we derive a new approach for improving efficiencies—higher TOF at lower η_eff—by changing the concentrations and properties of the reactants and products, rather than by modifying the catalyst. The dependence of TOF on η_eff is shown to be quite different upon changing, for instance, the pK_a of the acid HA versus the concentration or partial pressure of a reactant or product. Using the electrochemical reduction of dioxygen catalyzed by iron porphyrins in DMF as an example, decreasing [HA] 10-fold lowers η_eff by 59 mV and decreases the TOF by a factor of 10. Alternatively, a 10-fold decrease in K_a(HA) also lowers η_eff by 59 mV but only decreases the TOF by a factor of 2. This approach has been used to improve a catalytic TOF by 10⁴ vs the previously reported scaling relationship developed via synthetic modifications to the catalyst. The analysis has the potential to predict improved efficiencymore » and product selectivity of any molecular PCET catalyst, based on its mechanism and rate law.« less

Authors:

Pegis, Michael L.  ^[1];

• Search DOE PAGES for author "Pegis, Michael L."
• Search DOE PAGES for ORCID "0000-0001-6686-1717"

Wise, Catherine F. ^[1]; Koronkiewicz, Brian ^[1]; Mayer, James M.  ^[1]

• Search DOE PAGES for author "Mayer, James M."
• Search DOE PAGES for ORCID "0000-0002-3943-5250"

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+ Show Author Affiliations

1. Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States

Publication Date:

Wed Jul 19 00:00:00 EDT 2017

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)

OSTI Identifier:

1374929

Alternate Identifier(s):

OSTI ID: 1469826

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Published Article

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Name: Journal of the American Chemical Society Journal Volume: 139 Journal Issue: 32; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous); catalysis (heterogeneous); solar (fuels); bio-inspired; energy storage (including batteries and capacitors); hydrogen and fuel cells; charge transport; materials and chemistry by design; synthesis (novel materials)