Controlling Proton and Electron Transfer Rates to Enhance the Activity of an Oxygen Reduction Electrocatalyst

Abstract

An electrochemical approach is developed that allows for the control of both proton and electron transfer rates in the O2 reduction reaction (ORR). A dinuclear Cu ORR catalyst was prepared that can be covalently attached to thiol‐based self‐assembled monolayers (SAMs) on Au electrodes using azide–alkyne click chemistry. Using this architecture, the electron transfer rate to the catalyst is modulated by changing the length of the SAM, and the proton transfer rate to the catalyst is controlled with an appended lipid membrane modified with proton carriers. By tuning the relative rates of proton and electron transfer, the current density of the lipid‐covered catalyst is enhanced without altering its core molecular structure. This electrochemical platform will help identify optimal thermodynamic and kinetic parameters for ORR catalysts and catalysts of other reactions that involve the transfer of both protons and electrons.

Membrane-Modified Metal Triazole Complexes for the Electrocatalytic Reduction of Oxygen and Carbon Dioxide

“…The enhancement of current elicited by the proton carrier is due to a change in the ORR mechanism as demonstrated in previous work (Tse et al, 2016 ; Gautam et al, 2018 ). In the presence of lipid layer without proton carrier, the hydrophobic nature of the lipid impedes proton transfer to the catalyst, which causes the ORR to proceed primarily via a 1 e − pathway to yield superoxide.…”

Brønsted Acid Scaling Relationships Enable Control Over Product Selectivity from O2 Reduction with a Mononuclear Cobalt Porphyrin Catalyst

“…Mononuclear Co- Efforts to control ORR product selectivity with molecular catalysts include diverse catalyst classes, including Fe, 32−34 Cu, 35,36 and Mn 37−39 complexes. New catalyst designs c o m m o n l y f e a t u r e m u l t i n u c l e a r m e t a l c o mplexes 11,13,[20][21][22]35,36,40 or implement other approaches to control the relative rates of electron 41−43 and/or proton transfer 26,27,34,43,44 as a means to facilitate O−O cleavage and avoid H 2 O 2 generation. Elucidation of the factors that contribute to product selectivity are complicated, however, by the manner in which these catalysts are studied.…”

Mechanistic Insights into Surfactant-Modulated Electrode–Electrolyte Interface for Steering H2O2 Electrosynthesis

“…For example, the organic proton donor serves as a proton relay to accelerate the proton transfer process. 21,22 The incorporation of polar, charged, or ionizable groups near porphyrin metal sites promotes protoncoupled electron activation of small molecules. 23 Pt and Au electrodes that are modified with ionic liquids exhibit faster rates of proton-coupled electron transfer.…”

“…45 The weakened interfacial hydrogen-bond network leads to a decreased availability of protons, thereby favoring two-electron ORR toward H 2 O 2 . 21,22 Interfacial Investigation via Electrochemical Impedance Spectroscopy. To further clarify the role of DTAB on interfacial mass transfer and charge transfer processes, electrochemical impedance spectroscopy (EIS) measurement was conducted (see Experimental procedures (SI) for details).…”

“…The interfacial hydrogen-bond network significantly affects the interfacial proton transfer process. ,, Some methods based on electrode modification have been reported to modulate the kinetics of proton transfer at the electrode–electrolyte interface. For example, the organic proton donor serves as a proton relay to accelerate the proton transfer process. , The incorporation of polar, charged, or ionizable groups near porphyrin metal sites promotes proton-coupled electron activation of small molecules . Pt and Au electrodes that are modified with ionic liquids exhibit faster rates of proton-coupled electron transfer .…”