Study on the Structure‐Activity Relationship Between Single‐Atom, Cluster and Nanoparticle Catalysts in a Hierarchical Structure for the Oxygen Reduction Reaction

Abstract

Literature reports have shown that in primary structures, single‐atom catalysts exhibit better performance than cluster and nanoparticles due to their maximum atom utilization and the fine‐tuning of the electronic structure of the active sites. Hierarchical structures have recently been extensively studied because of increased active sites and orderliness of channels significantly improves the catalytic performance compare to primary structures especially in nanoparticles, however, the different sized effect of catalysts research has not been reported. Herein, a unique hollow double‐shell structure (a distinct cavity‐containing) is used as a hierarchical model to study the possible difference between single atom, cluster, and nanoparticle and to establish the corresponding structure‐activity relationship. Three Co catalysts are prepared: single atoms (Co‐Catalyst‐1), clusters (Co‐Catalyst‐2, 0.5–1 nm), and nanoparticles (Co‐Catalyst‐3, ≈5 nm) and their oxygen‐reduction capacity is evaluated. The unique electronic interactions, the strong electron‐withdrawing ability of N in Co–N4 (Co‐Catalyst‐1), attract electrons from the electrode to Co, specifically by expediting the generation and transformation of the rate‐determining step intermediates *OOH. The variant spatial structure which is caused by Co atom aggregation, and led to surface area, pore size, and carbon disorder, is a distinct, therefore significant variation in mass and charge transport efficiency, and activities.

ZIF-Derived Co/Zn Bimetallic Catalytic Membrane with Abundant CNTs for Highly Efficient Reduction of p-Nitrophenol

“…The mesoporous structure is on account of the aggregation of small particles of Co metal, which leaves nanopores in the initial position. The produced CNTs should also be an important reason for the formation of mesoporous structure . For Co0.2Zn0.4- T ( T = 770, 870, 920, 1020) powders, all samples exhibit combined hybrid type-I and IV isotherms (Figure b), indicating that all the powdered catalysts are microporous/mesoporous composite structural materials, in good agreement with the data of pore size (Figure d) .…”

“…Nitrogen sorption measurements were conducted to investigate the porous structures of the powdered catalysts. The as-synthesized Co0Zn0.6–920 exhibits a type I isotherm, indicating that its pore structure is mainly microporous (<2 nm) (Figure a,c) . The combined hybrid type-I and IV isotherms with a hysteresis loop indicate the coexistence of micropores and mesopores in Co0.2Zn0.4–920 and Co0.6Zn0–920 (Figure a,c) .…”

“…The as-synthesized Co0Zn0.6−920 exhibits a type I isotherm, indicating that its pore structure is mainly microporous (<2 nm) (Figure 5a,c). 57 The combined hybrid type-I and IV isotherms with a hysteresis loop indicate the coexistence of micropores and mesopores in Co0.2Zn0.4−920 and Co0.6Zn0−920 (Figure 5a,c). 57 The microporous structure is mostly contributed by the removal of methanol and 2methylimidazole from the precursor.…”

“…57 The combined hybrid type-I and IV isotherms with a hysteresis loop indicate the coexistence of micropores and mesopores in Co0.2Zn0.4−920 and Co0.6Zn0−920 (Figure 5a,c). 57 The microporous structure is mostly contributed by the removal of methanol and 2methylimidazole from the precursor. The mesoporous structure is on account of the aggregation of small particles of Co metal, which leaves nanopores in the initial position.…”

Size Sensitivity of Supported Palladium Species on Layered Double Hydroxides for the Electro-oxidation Dehydrogenation of Hydrazine: From Nanoparticles to Nanoclusters and Single Atoms

“…After normalizing to Pd mass, the ECSA of Pd SAs/NiFe (31.8 cm 2 ) was 1.9 times that of Pd NCs/NiFe (16.8 cm 2 ) and 5.7 times that of Pd NPs/NiFe (5.6 cm 2 ), implying the exposed active sites with the order of Pd SAs/NiFe > Pd NCs/NiFe > Pd NPs/NiFe. 38 Nevertheless, the reaction activity of Pd SAs/NiFe was nearly negligible (0.12 A mg Pd −1 at 0.35 V vs RHE). When the Pd species varied from SAs to NCs and NPs, the reaction activity can be enhanced largely to 4.3 A mg Pd −1 for Pd NCs/NiFe and 0.6 A mg Pd −1 for Pd NPs/NiFe under the same conditions, respectively.…”