Using Coordination Chemistry Concepts to Unravel Electronic Properties of SACs in Bidimensional Materials

Abstract

Single atom catalysts (SACs) embedded in bidimensional (2D) materials are commonly viewed as chemically doped 2D systems whose electronic properties can be discussed in terms of solid state physics, where the doping atoms are perturbating agents to the semimetallic (graphene) or insulating (h-BN) character of the 2D material. In this Perspective, we present a different and closer viewpoint, where the SAC electronic properties are interpreted in terms of coordination chemistry concepts, as the transition metal (TM) atom is complexed by a giant macrocycle, which is the defective 2D layer. In the crystal/ligand field theories, both electrostatic and covalent interactions between SAC and the surrounding 2D material are accounted for defining the splitting and mixing of the TM d states. This analysis reveals the key role played by the type of 2D material not only in determining spin and charge of SAC but also in stabilizing several SAC oxidative states via charge delocalization for an enhanced catalytic activity.

Electronic Properties of Single-Atom Metal Catalysts Supported on Nitrogen-Doped Carbon

“…Alternatively, due to the similarities to organometallic complexes, 10,26,27 the crystal and ligand field theories can also be applied for the classification and energetics of the dstates splitting of the metal centers. 28 Among the most relevant properties, it is known that depending on the work function of the host, the charge of the metal can be modified, 29,30 instance, the Fe 3+/2+ reduction potential is more negative than the Fermi level of the carbon support stabilizing Fe 3+ states on carbons with pyrrolic N ligands. 31 Coordination of the host can also alter the electron spin configurations of FeN 4 and CoN 4 , affecting their electrochemical properties.…”

New Insights into the Physicochemical and Electrochemical Characterization of Gold Phthalocyanine-Based Materials

“…1,3,[10][11][12] Kotiaho et al 13 have spectroscopically studied the photoinduced processes in phthalocyanine-functionalized gold nanoparticles (Pc-AuNPs) and found a slower relaxation compared to AuNPs, confirming the energy transfer from the photoexcited phthalocyanine to gold. The properties of MPc-based materials can be elegantly tuned by changing the central metal and/or making the peripheral substitution, [1][2][3][4]13,14 which also allows to increase the solubility of MPc complexes. 3,[15][16][17] Specifically, various MPc (M = Co, Fe, Ni, Zn, etc.)…”

“…10 have been widely studied in electrochemistry as molecular materials or as the basis for single atom metal catalyst (SACs) due to M−N 4 −C centers. 5,14,18 For example, a Fe and Zncontaining nitrogen-doped carbon framework after co-pyrolysis of FePc and ZnPc results in a half-wave potential (E 1/2 ) of 0.9 V RHE in 0.1 M KOH (up to 53 mV superior to Pt/C), a 4-electron transfer oxygen reduction reaction (ORR), and fair electrochemical stability. 19 AuPc-based materials have received little attention, however, the mononuclear Au(+II) has a potential in catalysis and medicinal chemistry.…”

“…18 The mastery of a method for the synthesis of AuPc-based materials and the knowledge of their electrochemistry could make it possible to develop single atom catalysts (SACs). 14,18,26 In fact, out of 210 SACs models for the on-site O 2 -to-H 2 O 2 electroconversion, density functional theory (DFT) calculations suggest that among 149 thermodynamically and electrochemically stable SACs, Au-N 4 -C (see Scheme 1) derived from AuPc-based materials would be a candidate if experimentally synthesized. 18 Hence, before exploring AuPc-based materials for SACs, which have the unique advantage of requiring only small amount of the noble metal, it is essential to master a replicable synthesis methodology, and to know the detailed physico-chemistry and electrochemistry of the parent materials.…”