Importance of Ligand Effects Breaking the Scaling Relation for Core–Shell Oxygen Reduction Catalysts

Abstract

Tremendous recent efforts have been made toward developing highly active oxygen reduction reaction (ORR) catalysts with a minimized usage of noble metal Pt by using Pt alloys and core–Pt shell structures. A main computational framework for such a goal has been the search for a new material with the *OH binding slightly weaker than Pt based on the conventional volcano relation of ORR activity versus *OH binding energy. In this work, by using carbides and nitrides as core materials, we demonstrate that the conventional scaling relation between *OH and *O can be completely broken owing to a significant ligand–Pt orbital interactions in the core–Pt shell structure, and in such cases, the usual catalyst design strategy of tuning the *OH binding energy of Pt to a weaker leg of the volcano can mislead the prediction. In these cases, one needs to consider all reaction intermediates to appropriately predict the activity of ORR catalysts. We additionally show that, although the transition metal nitrides and carbides studied here as core materials all induce an undesired tensile strain to the Pt overlayers with a stronger *OH binding, a proper tuning of the ligand (core) effects in the Pt1 and Pt2 overlayers core–shell configurations can lead to an activity comparable to or slightly better than Pt.

Single Metal Atoms Anchored in Two‐Dimensional Materials: Bifunctional Catalysts for Fuel Cell Applications

“…Today, despite limited supply and cost, platinum‐based catalysts remain the widely viable materials for ORR due to their superior activity. Various Pt‐based alloys, core–shell structures and nanostructure catalysts have been extensively investigated to enhance Pt use and improve the intrinsic catalytic activity. Although the kinetics of hydrogen oxidation reaction (HOR) at the anode side is at least six orders of magnitude faster than that of cathode reaction, the use of Pt‐based catalysts holds back the large‐scale commercialization of PEMFC.…”

Activating Transition Metal Dichalcogenides by Substitutional Nitrogen‐Doping for Potential ORR Electrocatalysts

“…In order to get a desirable fuel cell performance, major emphasis has been given to enhancing the slow kinetics of oxygen reduction reaction (ORR) at the cathode that requires approximately eight times higher Pt loading (∼0.4 mg cm −2 ) when compared to the anode of a PEMFCs . Since Pt is a rare earth metal with a very high price tag, intensive research efforts are underway with an aim to either reduce Pt loading in the cathode or to replace it completely with an efficient, cheap and more abundant alternative for their large‐scale realization …”

“…[14][15][16] Since Pt is a rare earth metal with a very high price tag, intensive research efforts are underway with an aim to either reduce Pt loading in the cathode or to replace it completely with an efficient, cheap and more abundant alternative for their large-scale realization. [17][18][19][20][21][22][23][24][25][26][27][28][29] An encouraging progress has been made on the search for an optimal ORR electrocatalyst considering two-dimensional (2D) nanosheets such as graphene, boron nitride, etc. and their nanoribbons owing to their low cost, high durability, and vast abundance.…”

Gold and gold-palladium branched nanocrystals for applications in plasmonic catalysis and electrocatalysis

“…This is a shortrange effect and is only effective at most three atomic layers. 25 The geometric effects can be caused by the surface strain in which the atomic arrangement of the surface can be compressed or expanded due to the difference of the lattice parameter of the core and shell. This effect alters the d-band center due to the decreased (expanded) or increased (compressed) of the overlap of the d orbitals of the metallic atoms.…”

“…This effect alters the d-band center due to the decreased (expanded) or increased (compressed) of the overlap of the d orbitals of the metallic atoms. 18,25 It is noteworthy that, in addition to their widespread use in nanocatalysis, metallic nanoparticles have also been widely explored in electrocatalysis, especially in the context of fuel cells for clean energy generation/conversion. 26 In this sense, the electrooxidation of alcohols have been studied because they are possible substitutes for hydrogen in fuel cells.…”