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

Abstract

In this manuscript, an electrochemical architecture is designed that controls the kinetics of proton transfer to metal triazole complexes for electrocatalytic O2 and CO2 reduction. Self-assembled monolayers of these catalysts are attached to a glassy carbon electrode and covered with a lipid monolayer containing proton carriers, which acts as a proton-permeable membrane. The O2 reduction voltammograms on carbon are similar to those obtained on membrane-modified Au electrodes, which through the control of proton transfer rates, can be used to improve the selectivity of O2 reduction. The improved voltage stability of the carbon platforms allows for the investigation of a CO2 reduction catalyst inside a membrane. By controlling proton transfer kinetics across the lipid membrane, it is found that the relative rates of H2, CO, and HCOOH production can be modulated. It is envisioned that the use of these membrane-modified carbon electrodes will aid in understanding catalytic reactions involving the transfer of multiple protons and electrons.

Proton Removal Kinetics That Govern the Hydrogen Peroxide Oxidation Activity of Heterogeneous Bioinorganic Platforms

“…By the slowing down and speeding up of H + delivery, a Cu-based O 2 reduction electrocatalyst can toggle between the 1e – pathway to form deleterious superoxide and the 4e – 4H + pathway to generate water exclusively as the desired product . Additionally, a Ag-based CO 2 reduction electrocatalyst has been embedded in a HBM system to steer the product selectivity from CO to formate through control of the transmembrane H + shuttling rate . HBMs have also been repurposed to interrogate stoichiometric redox reactions involving quinone and ferrocene SAMs. , The “flip-flop” diffusion mechanism of proton carriers has also been examined and validated through biophysical and computational methods. , A HBM system can further be used as a broad-based bioelectroanalytical platform to assay the lipid permeability of a range of biologically relevant anions …”

“…However, thiol-based Au SAMs suffer from narrow electrochemical stability, rendering HBMs difficult to apply further to study anodic processes . Because inert glassy carbon (GC) electrodes exhibit wide redox potential windows for practical electrochemical investigations, GC is a suitable candidate substrate for surface modification to fabricate C-based HBMs. ,,− Electrografting is one attractive surface modification method to anchor organic moieties onto GC via amines, diazoniums salts, , and alkynyl linkages . Previously, amine-modified GC electrodes have been designed to enable O 2 reduction and dihydrogen (H 2 ) evolution. ,, …”

“…31 Additionally, a Ag-based CO 2 reduction electrocatalyst has been embedded in a HBM system to steer the product selectivity from CO to formate through control of the transmembrane H + shuttling rate. 51 HBMs have also been repurposed to interrogate stoichiometric redox reactions involving quinone and ferrocene SAMs. 52,53 The "flip-flop" diffusion mechanism of proton carriers has also been examined and validated through biophysical and computational methods.…”

Electrocatalytic CO2 Reduction by Self-Assembled Monolayers of Metal Porphyrins

“…For molecular catalysts, CO 2 reduction is frequently performed using carbon electrodes that contain a binder like Nafion to attach the catalyst to the electrode. Using a dropcast method, a porous multilayer catalyst architecture is formed, which is beneficial for high current density applications, but complicates electrode surface structure . The binder in the electrode matrix also affects the rate of proton transfer and CO 2 diffusion to the catalyst.…”

“…Using a dropcast method, a porous multilayer catalyst architecture is formed, which is beneficial for high current density applications, but complicates electrode surface structure. 12 The binder in the electrode matrix also affects the rate of proton transfer and CO 2 diffusion to the catalyst.…”