Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H+/4 e− process, while oxygen can be fully reduced to water by a 4 e−/4 H+ process or partially reduced by fewer electrons to reactive oxygen species such as H2O2 and O2
−. We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media. Furthermore, our combined kinetic, spectroscopic, and electrochemical study of manganese corroles adsorbed on different electrode materials (down to a submolecular level) reveals mechanistic details of the oxygen evolution and reduction processes.
Abstract[NiFe]‐hydrogenase enzymes are efficient catalysts for H2 evolution but their synthetic models have not been reported to be active under aqueous conditions so far. Here we show that a close model of the [NiFe]‐hydrogenase active site can work as a very active and stable heterogeneous H2 evolution catalyst under mildly acidic aqueous conditions. Entry in catalysis is a NiIFeII complex, with electronic structure analogous to the Ni‐L state of the enzyme, corroborating the mechanism modification recently proposed for [NiFe]‐hydrogenases.
Considering the importance of water
splitting as the best solution
for clean and renewable energy, the worldwide efforts for development
of increasingly active molecular water oxidation catalysts must be
accompanied by studies that focus on elucidating the mode of actions
and catalytic pathways. One crucial challenge remains the elucidation
of the factors that determine the selectivity of water oxidation by
the desired 4e–/4H+ pathway that leads
to O2 rather than by 2e–/2H+ to H2O2. We now show that water oxidation
with the cobalt–corrole CoBr8 as electrocatalyst
affords H2O2 as the main product in homogeneous
solutions, while heterogeneous water oxidation by the same catalyst
leads exclusively to oxygen. Experimental and computation-based investigations
of the species formed during the process uncover the formation of
a Co(III)–superoxide intermediate and its preceding high-valent
Co–oxyl complex. The competition between the base-catalyzed
hydrolysis of Co(III)–hydroperoxide [Co(III)–OOH]− to release H2O2 and the electrochemical
oxidation of the same to release O2 via [Co(III)–O2
•]− is identified as the
key step determining the selectivity of water oxidation.
The protonation state of thiols in self-assembled monolayers (SAMs) on Ag and Au surfaces and nanoparticles (NPs) has been an issue of contestation. It has been recently demonstrated that deuterating the thiol proton produces ostentatious changes in the Raman spectra of thiols and can be used to detect the presence of the thiol functional group. Surface enhanced Raman spectroscopy (SERS) of H/D substituted aliphatic thiols on Ag surfaces clearly shows the presence of S-H vibration between 2150-2200 cm(-1) which shifts by 400 cm(-1) upon deuteration and a simultaneous >20 cm(-1) shift in the C-S vibration of thiol deuteration. Large shifts (>15 cm(-1)) in the C-S vibration are also observed for alkyl thiol SAMs on Au surfaces. Alternatively, neither the S-H vibration nor the H/D isotope effect on the C-S vibration is observed for alkyl thiol SAMs on Ag/Au NPs. XPS data on Ag/Au surfaces bearing aliphatic thiol SAMs show the presence of both protonated and deprotonated thiols while on Ag/Au NPs only deprotonated thiols are detected. These data suggest that aliphatic thiol SAMs on Au/Ag surfaces are partially protonated whereas they are totally deprotonated on Au/Ag NPs. Aromatic PhSH SAMs on Ag/Au surfaces and Ag/Au NPs do not show these vibrations or H/D shifts as well indicating that the thiols are deprotonated at these interfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.