Electrochemical Potential-Driven Shift of Frontier Orbitals in M–N–C Single-Atom Catalysts Leading to Inverted Adsorption Energies

Abstract

Electronic structure is essential to understanding the catalytic mechanism of metal single-atom catalysts (SACs), especially under electrochemical conditions. This study delves into the nuanced modulation of "frontier orbitals" in SACs on nitrogen-doped graphene (N−C) substrates by electrochemical potentials. We observe shifts in Fermi level and changes of d-orbital occupation with alterations in electrochemical potentials, emphasizing a synergy between the discretized atomic orbitals of metals and the continuous bands of the N−C based environment. Using O 2 and CO 2 as model adsorbates, we highlight the direct consequences of these shifts on adsorption energies, unveiling an intriguing inversion of adsorption energies on Co/N−C SAC under negative electrochemical potentials. Such insights are attributed to the role of the d xz and d z 2 orbitals, pivotal for stabilizing the π* orbitals of O 2 . Through this exploration, our work offers insights on the interplay between electronic structures and adsorption behaviors in SACs, paving the way for enhanced catalyst design strategies in electrochemical processes.

Tip‐like Fe−N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

“…Through the differential charge density, T−Fe SAC shows a more balanced electron intensity and a larger total charge transfer to adsorbed O 2 * at Fe sites, promoting the transition from associative to dissociative process (Figure S21) [33] . From the DOS diagram, the orbitals of O 2 interact intensively with Fe d xz and d z 2 orbitals in T−Fe SAC, effectively weakening σ bonding and reducing the splitting energy of O−O bond, leading to the sufficient activation of O 2 (Figure S22) [34] …”

“…[33] From the DOS diagram, the orbitals of O 2 interact intensively with Fe d xz and d z 2 orbitals in TÀ Fe SAC, effectively weakening σ bonding and reducing the splitting energy of OÀ O bond, leading to the sufficient activation of O 2 (Figure S22). [34] To verify the pathway transition experimentally, in situ ATR-SEIRAS as a molecular-level detector was adopted to track the evolution of oxygen-related intermediates over solid-liquid interfaces under realistic working conditions. As illustrated in Figure 4b, the two catalysts exhibit a readily identifiable O 2 * peak (~1,120 cm À 1 ) that emerged at all the potential ranges, indicating the efficient adsorption of reactant molecules.…”

Bidirectional electron transfer boosts Li–CO2 electrochemistry

“…In reality, the electrochemical reactions are conducted under constant potential conditions, and diverse electrode potentials will affect the double layer at the interface and also affect the electronic structure of the catalyst itself. 74 But the constant potential effects on the BET behavior and aprotic Li–CO 2 electrochemical performance are still a mystery. It was subsequently solved by using the CPM on the basis of an implicit solvation model.…”

Tip‐like Fe−N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

“…[33] From the DOS diagram, the orbitals of O 2 interact intensively with Fe d xz and d z 2 orbitals in TÀ Fe SAC, effectively weakening σ bonding and reducing the splitting energy of OÀ O bond, leading to the sufficient activation of O 2 (Figure S22). [34] To verify the pathway transition experimentally, in situ ATR-SEIRAS as a molecular-level detector was adopted to the evolution of oxygen-related intermediates over solid-liquid interfaces under realistic working conditions. As illustrated in Figure 4b, the two catalysts exhibit a readily identifiable O 2 * peak (~1,120 cm À 1 ) that emerged at all the potential ranges, indicating the efficient adsorption of reactant molecules.…”