Redox Processes at Semiconductors-Gerischer Model and Beyond

What X‐Ray Absorption Spectroscopy Can Tell Us About the Active State of Earth‐Abundant Electrocatalysts for the Oxygen Evolution Reaction**

“… [129] The nature of the redox couples directly relates to an atomistic understanding of the key steps of the catalytic mechanism, e.g., of the rate‐limiting step as shown in Figure 8 , and their midpoint potential is crucial to understand charge transfer from/to semiconductors, e.g., in the framework of the Marcus–Gerischer theory. [ 138 , 139 , 140 ] Identification of the relevant redox couples is thus a natural choice for mechanistic discussions and has led to the recent insight that the OER is a first‐order reaction with respect to the Mn density of states, while the ORR is of second order. [141] Moreover, the Mn 3+/4+ redox couple is essential for the evolution of oxygen in natural photosynthesis as well as for electrodeposited Mn oxides [142] because Mn 4+ together with Mn 3+ has been proposed as a necessity for the OER and because its midpoint potential is similar to that of the OER.…”

“…Alternatively, the redox couples can be identified by fitting the oxidation state from XAS to (modified) Nernst equations [129] . The nature of the redox couples directly relates to an atomistic understanding of the key steps of the catalytic mechanism, e.g., of the rate‐limiting step as shown in Figure 8, and their midpoint potential is crucial to understand charge transfer from/to semiconductors, e.g., in the framework of the Marcus–Gerischer theory [138–140] . Identification of the relevant redox couples is thus a natural choice for mechanistic discussions and has led to the recent insight that the OER is a first‐order reaction with respect to the Mn density of states, while the ORR is of second order [141] .…”

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

“…12−15 This model was first described in the 1960s by the combined theoretical work of Marcus and Gerischer 12,13 and continued to be disseminated in modern research publications and textbooks of electron transfer theories. 14,15 This energetic requirement is suitable for optimization of single electron transfers of importance to regenerative solar cells, 16 yet remains challenging for important multi-electron catalysis such as water oxidation and carbon dioxide reduction. Herein, we report electron transfer, photovoltage, and kinetic behavior of illuminated p-Si electrolyte interfaces in contact with redox active species that accept multiple electrons.…”

“…Hybrid photoelectrodes comprised of a narrow bandgap semiconductor with an integrated molecular catalyst are actively being investigated for the generation of fuels from chemical feedstocks and sunlight. − The interfacial electron transfer processes that govern the efficiency of such hybrids are understood through a model that requires isoenergetic transfer between the catalyst and photogenerated carriers at the fixed energetic position of the conduction or valence band edge. − This model was first described in the 1960s by the combined theoretical work of Marcus and Gerischer , and continued to be disseminated in modern research publications and textbooks of electron transfer theories. , This energetic requirement is suitable for optimization of single electron transfers of importance to regenerative solar cells, yet remains challenging for important multi-electron catalysis such as water oxidation and carbon dioxide reduction. Herein, we report electron transfer, photovoltage, and kinetic behavior of illuminated p-Si electrolyte interfaces in contact with redox active species that accept multiple electrons.…”

Was uns die Röntgenabsorptionsspektroskopie über den aktiven Zustand von Elektrokatalysatoren für die Sauerstoffentwicklungsreaktion lehrt**

“…B. im Rahmen der Marcus-Gerischer-Theorie Lit. [138][139][140]. Die Identifizierung der relevanten Redoxpaare ist daher eine natürliche Wahl für mechanistische Diskussionen und hat jüngst zu der Erkenntnis geführt, dass die OER eine Reaktion erster Ordnung in Bezug auf die Mn-Zustandsdichte ist, während die ORR eine Reaktion zweiter Ordnung ist.…”