7 research outputs found
Ligand Tuning in Pyridine-Alkoxide Ligated Cp*Ir III Oxidation Catalysts
Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation behavior, and oxidation kinetics. Application of these precursors to catalytic C–H oxidation of ethyl benzenesulfonate with aqueous sodium periodate showed that the ligand substitution pattern, solution pH, and solvent all have pronounced influences on initial rates and final conversion values. Correlation with O2 evolution profiles during C–H oxidation catalysis showed these competing reactions to occur sequentially, and demonstrates how it is possible to tune the activity and selectivity of the active species through the N^O ligand structure
Ligand Tuning in Pyridine-Alkoxide Ligated Cp*Ir III Oxidation Catalysts
Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation behavior, and oxidation kinetics. Application of these precursors to catalytic C–H oxidation of ethyl benzenesulfonate with aqueous sodium periodate showed that the ligand substitution pattern, solution pH, and solvent all have pronounced influences on initial rates and final conversion values. Correlation with O2 evolution profiles during C–H oxidation catalysis showed these competing reactions to occur sequentially, and demonstrates how it is possible to tune the activity and selectivity of the active species through the N^O ligand structure
Kinetics versus Charge SeparationSeparation: Improving the Activity of Stoichiometric and Non-Stoichiometric Hematite Photoanodes Using a Molecular Iridium Water Oxidation Catalyst
Oxygen-deficient
iron oxide thin films, which have recently been
shown to be highly active for photoelectrochemical water oxidation,
were surface-functionalized with a monolayer of a molecular iridium
water oxidation cocatalyst. The iridium catalyst was found to dramatically
improve the kinetics of the water oxidation reaction at both stoichiometric
and nonstoichiometric α-Fe<sub>2</sub>O<sub>3‑x</sub> surfaces. This was found to be the case in both the dark and in
the light as evidenced by cyclic voltammetry, Tafel analysis, and
electrochemical impedance spectroscopy (EIS). Oxygen evolution measurements
under working conditions confirmed high Faradaic efficiencies of 69–100%
and good stability over 22 h of operation for the functionalized electrodes.
The resulting ∼200–300 mV shift in onset potential for
the iridium-functionalized sample was attributed to improved interfacial
charge transfer and oxygen evolution kinetics. Mott–Schottky
plots revealed that there was no shift in flat-band potential or change
in donor density following functionalization with the catalyst. The
effect of the catalyst on thermodynamics and Fermi level pinning was
also found to be negligible, as evidenced by open-circuit potential
measurements. Finally, transient photocurrent measurements revealed
that the tethered molecular catalyst did improve charge separation
and increase charge density at the surface of the photoanodes, but
only at high applied biases and only for the nonstoichiometric oxygen-deficient
iron oxide films. These results demonstrate how molecular catalysts
can be integrated with semiconductors to yield cooperative effects
for photoelectrochemical water oxidation
Graphite-protected CsPbBr3 perovskite photoanodes functionalised with water oxidation catalyst for oxygen evolution in water
Metal-halide perovskites have been widely investigated in the photovoltaic sector due to their promising optoelectronic properties and inexpensive fabrication techniques based on solution processing. Here we report the development of inorganic CsPbBr3-based photoanodes for direct photoelectrochemical oxygen evolution from aqueous electrolytes. We use a commercial thermal graphite sheet and a mesoporous carbon scaffold to encapsulate CsPbBr3 as an inexpensive and efficient protection strategy. We achieve a record stability of 30 h in aqueous electrolyte under constant simulated solar illumination, with currents above 2 mA cm-2 at 1.23 VRHE. We further demonstrate the versatility of our approach by grafting a molecular Ir-based water oxidation catalyst on the electrolyte-facing surface of the sealing graphite sheet, which cathodically shifts the onset potential of the composite photoanode due to accelerated charge transfer. These results suggest an efficient route to develop stable halide perovskite based electrodes for photoelectrochemical solar fuel generation.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 665992 </p