Cations determine the mechanism and selectivity of alkaline ORR on Pt(111)
The proton-coupled electron transfer (PCET) mechanism of the oxygen reduction reaction (ORR) is a long-standing enigma in electrocatalysis.
physics.chem-ph↗
arXiv subjects
Ken Sakaushi
Publications and source records attributed to Ken Sakaushi.
Cation-Dependent Nonadiabaticity in Proton-Coupled Electron Transfer at Electrified Solid-Liquid Interfaces
Here we report an observation of cation-dependent nonadiabaticity in a proton-coupled electron transfer electrode process (PCET) during hydrogen evolution at electrified interfaces of Au(111) single-crystal electrode and electrolytes by employing electrochemical kinetic isotope effect analysis at ultra-clean/well-defined systems to investigate quantum-to-classical transition (QCT) in highly accuracy.
physics.chem-ph↗
Quantum Proton Tunneling in Multi-electron/-proton Transfer Electrode Processes
Quantum proton tunneling (QPT) in the two representative multi-electron/-proton transfer electrode processes, i.e. hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), was investigated by using polycrystalline platinum (pcPt) and gold (pcAu) electrodes at 298 kelvin (K). In order to observe quantum effects in the electrode processes, the hydrogen/deuterium kinetic isotope effect constant ratio (= KH/D) was measured in a variety of conditions. In this Contribution, it is shown that the QPT in surface electrochemical system is highly affected by a choice of system. Although several systems show a clear manifestation of QPT in the electrode processes and primitive interpretations can be given to these observations, it is still challenge to derive a fine molecular-level picture on the results including several complicated effects. However, based on the observations, a selection of a full QPT path may be strongly affected by the different microscopic proton transfer mechanisms, i.e. proton transfer from hydronium ion or water molecule.
physics.chem-ph↗
Observation of Kinetic Isotope Effect in Electrocatalysis with Fully Deuterated Ultrapure Electrolytes
Kinetic isotope effect (KIE) is a common physicochemical effect to elucidate complicated microscopic reaction mechanism in biological, chemical and physical systems. Especially, the exchange of hydrogen to deuterium is a standard approach to investigate kinetics and pathways of a wide spectrum of key reactions involving proton transfer. However, KIE in electrocatalysis is still challenge. One main reason is owing to the high sensitivity to impurities in electrochemical systems. Aiming to establish an appropriate approach to observe KIE in electrocatalysis, we investigated KIE in electrocatalysis by using fully deuterated ultrapure electrolytes. With these electrolytes, we studied oxygen reduction reaction with platinum catalyst, which is well-known to be sensitive to impurity, as the model systems. In conclusion, the electrode processes in these systems can be strongly influenced by a purity of a selected deuterated electrolyte, especially in case of alkaline conditions. Therefore a highly pure deuterated electrolyte is indispensable to study microscopic electrode processes of electrocatalysis by analyzing KIE. This work shows a key criterion and methods to observe a reliable KIE in electrocatalytic systems, and therefore, provides a general approach to investigate complicated multielectron- and multiproton-transfer processes using not only standard electrochemical technique but also surface sensitive spectrometry.
physics.chem-ph↗
Quantum-to-Classical Transition of Proton-Transfer in Electrocatalytic Oxygen Reduction
The four-electron oxygen reduction reaction on Pt catalyst in alkaline solution undergoes proton transfer via tunneling mechanism. The hydrogen/deuterium kinetic isotopic rate constant ratio (kH/kD ) = 32 in a low overpotential region, indicating the importance of the quantum-proton-tunneling at the rate-determining step (RDS). However, kH/kD goes down to 3 in a high overpotential region, suggesting the classical proton-transfer (PT) scheme. Therefore, there is a quantum-to-classical transition of PT process as a function of potential, which is confirmed by theoretical study.
physics.chem-ph↗
Polymeric Frameworks as Organic Semiconductors with Controlled Electronic Properties
The rational assembly of monomers, in principle, enables the design of a specific periodicity of polymeric frameworks, leading to a tailored set of electronic structure properties in these solid-state materials. The further development of these emerging systems requires a combination of both experimental and theoretical studies. Here, we investigated the electronic structures of two-dimensional polymeric frameworks based on triazine and benzene rings, by means of electrochemical techniques. The experimental density of states was obtained from quasi-open-circuit voltage measurements through galvanostatic intermittent titration technique, which we show to be in excellent agreement with first principles calculations performed for two and three-dimensional structures of these polymeric frameworks. These findings suggest that the electronic properties do not only depend on the number of stacked layers but also on the ratio of the different aromatic rings.
cond-mat.mtrl-sci↗