Anchoring of Transition Metals to Graphene Derivatives as an Efficient Approach for Designing Single‐Atom Catalysts

Abstract

Graphene derivatives with anchored metal atoms represent a promising class of single‐atom catalysts (SACs). To elucidate factors determining the bond strength between metal atoms and graphene derivatives, a series of late 3d and 4d elements, including the iron triad, light platinum group elements, and coinage metals (Fe, Co, Ni, Ru, Rh, Pd, Cu, Ag, and Au), in different oxidation states (from 0 to +III) bonded to either cyanographene (CG) or graphene acid (GA) is explored. The vast diversity of N···Me and O···Me bond dissociation energies is related to charge transfer between the metal and substrate. The ability of CG and GA to reduce metal cations and oxidize metal atoms is attributed to the π‐conjugated lattice of the graphene derivatives. The binding energies of core electrons of the anchored metals are predicted to enable experimental identification via X‐ray photoelectron spectroscopy. The anchoring of metals is accompanied by either complete or partial spin quenching, leading in most cases to the same oxidation state of the metal regardless of its initial charge. The identified features can be utilized in designing new materials with a high potential in heterogenous SACs as well as electrochemical and spintronic applications.

Single Co‐Atoms as Electrocatalysts for Efficient Hydrazine Oxidation Reaction

“…The positive binding affinity of Co 2+ cations to GCN was recently rationalized in terms of efficient charge transfer from the substrate to metal cations. [ 43 ] The reaction mechanism consists of four deprotonation steps (in basic environment) and four electrochemical oxidation steps ( Figure ). In total, four electrons are released.…”

Graphene Acid: A Versatile 2D Platform for Catalysis

“…Interestingly, very recently the anchoring of single‐atom transition metals to GA for catalysis purposes has been also investigated theoretically: [23] they calculated the bond dissociation energy and charge exchange, solvent effects on the coordination of the metal (Fe, Co, Ni, Ru, Rh, Pd, Cu, Ag, and Au in different oxidation states) to GA and the XPS binding energy of the hypothetical hybrids for their easy identification. Authors considered the calculated samples stable enough to be considered suitable single atom catalysis, although they admitted that some competitive phenomena could experimentally occur.…”

Emerging graphene derivatives as active 2D coordination platforms for single-atom catalysts

“…They also offer a broad portfolio of homogeneously distributed functionalities covalently grafted onto the graphene lattice, and their further functionalization via the chemistry of the attached functionalities. 45 Thanks to these properties, FG-derived materials can be efficiently utilized as supporting materials for SACs 12,[44][45][46][47][48] because introduced functional groups can immobilize SMSs and avoid undesirable processes such as the formation of larger metal clusters and the leaching of metal particles during reactions.…”

“…Such functionality can anchor transition metal atoms, which can be utilized in SACs. 12,47 It also creates a strong bond with silver nanoparticles, which hampers the defense mechanism of silver-resistant bacteria. 77 The nitrile groups in GCN can be readily hydrolyzed into carboxyl (-COOH) groups, thus forming graphene acid (GA) 43,78 that may be also utilized as a ligand for anchoring transition metals 45 or as a recyclable substrate for water remediation or retrieval of precious metals from waste.…”

“…The amount of the transferred charge correlates with the electron affinity of the bare metal cation and with the dissociation energy of the GCN/GA⋯Me bond. 47 Interestingly, the analysis of spin populations of the metal atoms/cations anchored to GCN/GA demonstrated that their oxidation states were often the same despite their different initial charges. In the case of cation pairs Fe 2+ /Fe 3+ , Co 2+ /Co 3+ , and Cu + /Cu 2+ , this feature, in combination with high bond dissociation energy, could be used for designing new mixed-valence SACs.…”