The Role of Defect Sites in Nanomaterials for Electrocatalytic Energy Conversion

Abstract

The development of advanced catalysts for efficient electrochemical energy conversion technologies to alleviate the reliance on fossil fuels has attracted considerable interest in the last decades. Insight into the roles of reactive sites in nanomaterials is significant for understanding and implementing the design principles of nanocatalysts. Recently, the essential role of defects, including vacancies, reconstructed defects, and doped non-metal (or metal)-defect-based motifs, have been widely demonstrated to promote the diverse electrochemical processes (e.g., O 2 [or CO 2 ] reduction reactions and H 2 [or O 2 ] evolution reactions). Nevertheless, the in-depth exploration of the underlying defect electrocatalytic mechanism is still in its infancy. This review summarizes the state-ofthe-art defect engineering strategies for designing highly efficient electrochemical nanocatalysts with special emphasis on the correlation between defect structures and electrocatalytic properties. Finally, some perspectives on the challenges and future research directions in this promising area are presented.

Edge‐Rich Fe−N4 Active Sites in Defective Carbon for Oxygen Reduction Catalysis

“…The metal atom center in such metal−N−C catalysts should not be recognized as an isolated active site, which is coordinated with surrounding nonmetal atoms and serves as a whole to catalyze reaction. [ 5 ] For instance, Zn and Cr atoms, generally considered to be inactive toward ORR in nature, were validated to become excellent ORR active centers when immobilized in N‐modified divacancies (ND) of carbon substrates with four coordination atoms, emphasizing the significant role of defects in formation of active sites. [ 6 ] Among all the PGM‐free ORR catalysts, Fe−N−C materials attract most interest due to their manifested best performance under the acidic condition.…”

“…[ 23 ] The real‐time H 2 O 2 yield and electron transfer number ( n ) were further probed by rotating ring‐disk electrode (RRDE), confirming a direct four electron process toward ORR for the best catalyst Fe−N 4 −C‐60, with n value close to 4 and an extremely low H 2 O 2 yield (less than 0.5%) (Figure S15, Supporting Information). [ 5b ] Working stability is another critical metric aside from activity to affect the practical application of ORR electrocatalysts. Considering the structural difference between e‐ND−Fe and c‐ND−Fe, the ORR durability for both Fe−N 4 −C‐60 and Fe−N 4 −C‐20 catalysts should be evaluated and compared.…”

Multidimensional Ordered Bifunctional Air Electrode Enables Flash Reactants Shuttling for High‐Energy Flexible Zn‐Air Batteries

“…As shown in Figure 3d, the Co Kedge absorption edge position of MPZCC@CNT appears between those of pure Co and CoO, indicating a Co valence between Co 0 and Co 2+ . [42] Specifically, these components reduce electron density of neighboring C atoms, which promotes the capturing of oxygen involved reactants and assures fast electrocatalytic oxygen redox kinetics for ORR and OER. [40] Such chemical bonding configuration of CoN x can create additional defects in the carbon lattices, which is identified by the Raman spectra.…”

Defect engineering of nonprecious metal based catalysts for oxygen evolution reaction

“…Among them, the point defects have been intensively studied, as they can significantly affect the chemical and physical properties of the 2D nanomaterials 89 90 . Likewise, the charge distribution of edge carbon differs from that basal plane carbon.…”

“…The spectra from PAS can provide direct information about the components with different positron lifetimes, so that the various defect types and their corresponding concentrations can be studied (even at ppm level) 89 . In this way, PAS can be a strong technique to study defects in materials.…”