Reorganization Energies for Interfacial Proton-Coupled Electron Transfer to a Water Oxidation Catalyst

Kessinger, Matthew C.; Soudackov, Alexander V.; Schneider, Jenny; Bangle, Rachel E.; Hammes‐Schiffer, Sharon; Meyer, Gerald J.

doi:10.1021/jacs.2c09672

Cited by 9 publications

(30 citation statements)

References 73 publications

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“…Furthermore, we employ this model to describe experimentally measured pH-dependent kinetic data for a representative interfacial electrochemical PCET reaction, namely, reduction of a Ru-based water oxidation catalyst attached to a tin-doped In 2 O 3 (ITO) surface. 19 Our model explains the origins of the previously observed weak pH dependence of PCET for this system using physically meaningful parameters. Moreover, our model's predicted behavior for a wider pH range is then confirmed by additional experiments.…”

Section: ■ Introductionmentioning

confidence: 51%

“…When the pH increases from 3 to 5, the maximum rate constant only decreases by around 3-fold rather than decreasing 100-fold, as would be expected according to a model based on a single PCET pathway with H 3 O + as the proton donor, or being pH-independent, as would be expected according to a model based on a single PCET pathway with H 2 O as the proton donor. 19 Here, we focus on the PCET process associated with the reduction of the Ru III catalyst 37−44 attached to ITO. The two ET and two EPT channels, as well as Ox, OxH + , Red − , and RedH for this process, are depicted in Figure 3.…”

Section: Red (E) and K Imentioning

confidence: 99%

“…The two ET and two EPT channels, as well as Ox, OxH + , Red − , and RedH for this process, are depicted in Figure 3. As no buffer solution was added in the experiments, 19 the diagram in Figure 1 gives a complete set of the possible ET and EPT channels in this system, which is recreated using system-specific notation in Figure 4. The experimental rate constant was obtained by analyzing the absorbance change of the Ru II catalyst (the product) as a function of time.…”

Section: Red (E) and K Imentioning

confidence: 99%

“…These examples include the homogeneous oxidation of tyrosine 13−15 and tryptophan, 16−18 as well as the interfacial reduction of Ru-based water oxidation catalysts. 19 However, an explanation for these weak pH dependencies remains elusive. Herein, we will show that the weak pH dependence of some PCET reactions can be explained in terms of a competition among multiple mechanisms.…”

Section: ■ Introductionmentioning

confidence: 99%

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General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

Cui,

Soudackov,

Kessinger

et al. 2023

J. Am. Chem. Soc.

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The pH dependence of proton-coupled electron transfer (PCET) reactions, which are critical to many chemical and biological processes, is a powerful probe for elucidating their fundamental mechanisms. Herein, a general, multichannel kinetic model is introduced to describe the pH dependence of both homogeneous and electrochemical PCET reactions. According to this model, a weak pH dependence can arise from the competition among multiple sequential and concerted PCET channels involving different forms of the redox species, such as protonated and deprotonated forms, as well as different proton donors and acceptors. The contribution of each channel is influenced by the relative populations of the reactant species, which often depend strongly on pH, leading to complex pH dependence of PCET apparent rate constants. This model is used to explain the origins of the experimentally observed weak pH dependence of the electrochemical PCET apparent rate constant for a ruthenium-based water oxidation catalyst attached to a tin-doped In 2 O 3 (ITO) surface. The weak pH dependence is found to arise from the intrinsic differences in the rate constants of participating channels and the dependence of their relative contributions on pH. This model predicts that the apparent maximum rate constant will become pH-independent at higher pH, which is confirmed by experimental measurements. Our analysis also suggests that the dominant channels are electron transfer at lower pH and sequential PCET via electron transfer followed by fast proton transfer at higher pH. This work highlights the importance of considering multiple competing channels simultaneously for PCET processes.

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Section: ■ Introductionmentioning

confidence: 51%

Section: Red (E) and K Imentioning

confidence: 99%

Section: Red (E) and K Imentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

Cui,

Soudackov,

Kessinger

et al. 2023

J. Am. Chem. Soc.

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“…Indeed, a recent study of a molecular water oxidation catalyst reported that a 0.19 Å change in a Ru−O bond length, for Ru III -OH → Ru II -OH 2 , corresponded to a λ i = 0.54 eV change in inner-sphere reorganization. 77 An inner-sphere reorganization energy of this magnitude would explain the unusually large total reorganization energy measured for this sensitizer.…”

Section: ■ Introductionmentioning

confidence: 89%

Impact of Molecular Orientation on Lateral and Interfacial Electron Transfer at Oxide Interfaces

Loague

Keller

Müller

et al. 2023

ACS Appl. Mater. Interfaces

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Molecular dyes, called sensitizers, with a cis-[Ru(LL)(dcb)(NCS) 2 ] structure, where dcb is 4,4′-(CO 2 H) 2 -2,2′-bipyridine and LL is dcb or a different diimine ligand, are among the most optimal for application in dye-sensitized solar cells (DSSCs). Herein, a series of five sensitizers, three bearing two dcb ligands and two bearing one dcb ligand, were anchored to mesoporous thin films of conducting tin-doped indium oxide (ITO) or semiconducting TiO 2 nanocrystallites. The number of dcb ligands impacts the surface orientation of the sensitizer; density functional theory (DFT) calculations revealed an ∼1.6 Å smaller distance between the oxide surface and the Ru metal center for sensitizers with two dcb ligands. Interfacial electron transfer kinetics from the oxide material to the oxidized sensitizer were measured as a function of the thermodynamic driving force. Analysis of the kinetic data with Marcus−Gerischer theory indicated that the electron coupling matrix element, H ab , was sensitive to distance and ranged from H ab = 0.23 to 0.70 cm −1 , indicative of nonadiabatic electron transfer. The reorganization energies, λ, were also sensitive to the sensitizer location within the electric double layer and were smaller, with one exception, for sensitizers bearing two dcb ligands λ = 0.40−0.55 eV relative to those with one λ = 0.63−0.66 eV, in agreement with dielectric continuum theory. Electron transfer from the oxide to the photoexcited sensitizer was observed when the diimine ligand was more easily reduced than the dcb ligand. Lateral self-exchange "hole hopping" electron transfer between surface-anchored sensitizers was found to be absent for sensitizers with two dcb ligands, while those with only one were found to hop with rates similar to those previously reported in the literature, k hh = 47−89 μs −1 . Collectively, the kinetic data and analysis reveal that interfacial kinetics are highly sensitive to the surface orientation and sensitizers bearing two dcb ligands are most optimal for practical applications of DSSCs.

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Kinetic Properties of Oxygen Evolution Reaction Catalysis in Hematite

Snir

Toroker

2023

Advcd Theory and Sims

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Water splitting is a promising method for hydrogen generation, but current catalytic reactions suffer from low efficiency. One possible reason for such inefficiency is a high kinetic barrier for water oxidation, and there is a lack of direct and efficient method to calculate the barrier for each reaction. In this paper, the inner sphere component of the reorganization energy that contributed to the activation energies is calculated. A novel algorithm is used for calculating the reorganization energy based on Marcus theory combined with the climbing image nudged elastic band method used to find transition states and activation energies of the oxygen evolution reaction steps, which allows the calculation of the activation energy at different potentials and without simulating solvation in order to obtain the inner sphere component alone arising from the reorganization of the ionic surface. The new method is tested in both acidic and basic conditions and with explicit water molecules, as well as implicit solvation. It is discovered that the reaction involving the transition of the *O intermediate into *OOH has the highest activation energy of all steps, thus explaining the high coverage of the *O intermediate found by experiments.

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Reorganization Energies for Interfacial Proton-Coupled Electron Transfer to a Water Oxidation Catalyst

Cited by 9 publications

References 73 publications

General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System

Impact of Molecular Orientation on Lateral and Interfacial Electron Transfer at Oxide Interfaces

Kinetic Properties of Oxygen Evolution Reaction Catalysis in Hematite

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