Foot of the Wave Analysis for Mechanistic Elucidation and Benchmarking Applications in Molecular Water Oxidation Catalysis

Abstract

The description of the foot of the wave analysis (FOWA) applied to the electrocatalytic oxidation of water to dioxygen is reported for cases where the rate determining step is first order and second order with regard to catalyst concentration. This coincides with the so called water nucleophilic attack (WNA) and interaction of two M-O units (I2M) mechanism respectively. The newly adapted equations are applied to a range of relevant molecular catalysts both in homogeneous and heterogeneous phase and the kinetic parameters, including apparent rate constants and turnover frequencies, are determined. In this respect the application of FOWA at different catalyst concentrations allows elucidating the reaction mechanism that operates in each case. In addition catalytic Tafel plots are used for assessing the performance of several molecular water oxidation catalysts (WOCs) as a function of overpotential under analogous conditions and thus can be used for benchmarking purposes. While this had been earlier carried out for oxide based WOCs, now it is the first time reported for molecular WOCs.

Hydrogen Bonding Rescues Overpotential in Seven-Coordinated Ru Water Oxidation Catalysts

“…25 Using this methodology we obtain a TOFmax = 0.4 s -1 for 2 IV (O) whereas for 4 IV (O) under the same conditions and at nearly the same overpotential we get a TOFmax = 7,900 s -1 , that is more than 4 orders of magnitude higher. A catalytic Tafel plot is also reported in Figure 2C Mononuclear mono-aqua Ru complexes containing polypyridyl type of ligands such as 2 II (H2O), can undergo a series of electron transfer and/or PCET processes to reach high oxidation states that are capable of promoting the oxidation of water to dioxygen.…”

Catalytic Oxidation of Water to Dioxygen by Mononuclear Ru Complexes Bearing a 2,6‐Pyridinedicarboxylato Ligand

“…A foot‐of‐the‐wave analysis (FOWA) of the catalytic current (see Figure ) for the mixture of 1‐O and 2‐O , gives a TOF max value of 2.4–3.4×10 3 s −1 for the catalytic process for 2‐O , assuming that the initial current at the foot is solely attributed to the fastest WOC.…”

Electrochemical and Kinetic Insights into Molecular Water Oxidation Catalysts Derived from Cp*Ir(pyridine‐alkoxide) Complexes

“…Several electrochemical methods for estimating the amount of solution‐phase catalyst contributing to the current measured to extract their intrinsic rate constant have been described, but very few apply to water oxidation in aqueous solution where substrate‐limited plateau currents are not achievable. Foot‐of‐the‐wave analysis (FOWA) has recently been applied to WOCs as a tool to extract rate constants at the onset of the electrocatalysis by correlating the catalytic current with that of another reversible (pre‐catalytic) redox feature of the catalyst ,. Although these values often greatly over‐estimate the true performance of the catalyst at higher potentials as required for practical application, FOWA is a useful tool for evaluating and comparing performance during molecular electrocatalyst development.…”