Which is Best for ORR: Single Atoms, Nanoclusters, or Coexistence?

Recently, a diverse array of novel metal‐nitrogen‐carbon (M‐N‐C) single‐atom catalysts (SACs) have rapidly evolve, particularly in the realm of oxygen reduction reaction (ORR). Despite the plethora of proposed design and improvement strategies for SACs, a comprehensive review systematically compiling the components in M‐N‐C from a unified perspective is notably absent. For the first time, a thorough examination of each component in M‐N‐C is conducted, focusing on the perspective of entropy increase in the active sites of SACs. For the single M‐N4 sites and the whole M‐N‐C system, an increase in entropy implies an elevated degree of disorder and chaos. Broadly, the entropy‐increasing modification of M (single mental sites) and guest groups entails an augmentation of chaos, with the most effective co‐catalytic synergy achieved by establishing multiple active sites through a “cocktail effect”. Concerning N (nitrogen and other heteroatoms) and C (carbon supports), the entropy increase modification induces heightened disorder, with symmetry breaking more likely to drive M‐N4 toward adsorbing oxygen molecules to attain an equilibrium symmetric structure. All these innovative design strategies have led to a remarkable improvement in the ORR activity and stability and offer a guiding criterion for the future preparation of SACs.

Recent Design Strategies for M‐N‐C Single‐Atom Catalysts in Oxygen Reduction: An Entropy Increase Perspective

Yan,

Chen,

Chen

2024

OH‐Induced Surface Reconstitution in Single Atoms and Clusters Integrated Electrocatalysts for Self‐Adaptive Oxygen Electrocatalysis

Qi,

Yu,

Gan

et al. 2024

The integration of atom clusters and single atoms into a unified system represents a desirable approach for attaining enhanced catalytic performance. Nonetheless, the controllable synthesis of a single‐atom and nanocluster integrated system (SA‐NC) faces considerable challenges, and the mechanisms underlying the catalytic activity remain poorly understood. In this research, a cobalt‐based catalyst containing both coordinatively unsaturated single‐atom (CoN3) and small nanoclusters (Co@SA‐NC) is synthesized. The Co@SA‐NC not only facilitates charge and mass transfer due to the interconnected long‐range micromorphology, thus endowing efficient oxygen electrocatalytic reaction (ORR/OER), but also undergoes surface reconfiguration upon OH adsorption at high potentials in alkaline ORR/OER conditions. More appealingly, this OH‐involved reconfigured adaptive structure promotes optimization of energy barriers owing to the dynamic regulation from the bridged OH between Co single‐atom and cluster in the whole reaction process. Specific to the application metrics, a zinc–air battery assembled using the Co@SA‐NC catalyst exhibit targeted power density enhancement with 270 mW cm−2 in an alkaline medium. This work offers an effective insight into the study of SA‐NC catalytic reaction pathways for efficient ORR/OER catalysis.

Rapid Hole Transfer and Molecular Enrichment at Amorphous‐Crystalline Interfaces of Pt_0.25%/TO(B)‐FCP for Efficient Photocatalysis

Sun,

Xia,

et al. 2024

The construction of amorphous‐crystalline interfaces of heterogeneous metal oxide systems is an effective approach to modulate the interfacial adsorption behavior and carrier transfer pathways for the photocatalytic process. In this work, the amorphous‐crystalline interface is constructed by covalently linking a flexible crosslinked polymer (FCP) layer to a Pt0.25%/TO(B) substrate. Adsorption‐photodegradation experiments show that Pt0.25%/TO(B)‐FCP can ultimately enrich bisphenol A molecules to the interface within 5 min and in situ‐photodegrade >97.0% of bisphenol A within 10 min (50 ppm), which is 6.21 times than pure TO(B). In addition to the efficient accumulation of BPA molecules, the rapid hole transfer pathway at the amorphous‐crystalline interface is revealed by theoretical calculations, Kelvin probe force microscopy, and photoelectrochemical characterization. The coexistence of Pt single atoms (SAs) and nanoclusters (NCs) optimizes the transfer kinetics and reduces the energy barrier of photogenerated holes of TO(B). Meanwhile, the covalent hole transfer channels between the FCP layer and Pt0.25%/TO(B) significantly accelerate the separation and transfer of photogenerated carrier, promoting the photodegradation of adsorbed BPA molecules.