Designed Synthesis and Catalytic Mechanisms of Non‐Precious Metal Single‐Atom Catalysts for Oxygen Reduction Reaction

Abstract

ORR is proceeded through a two-electron (2e − ) or four-electron (4e − ) pathway. [2][3][4][5] Due to the requirement of high energy conversion efficiency for energy devices, the 4e − pathway directly reducing O 2 to H 2 O is the ideal reaction process. Heretofore, precious metal Pt is still considered as an excellent catalyst for high-efficiency 4e − pathway. [6] However, the high-cost and scarcity limit the extensive use of Pt in practical applications. Thus, development of low-cost and non-precious metal catalysts for energy devices is an intuitively effective strategy.According to the principle that the active sites can be increased by reducing the geometry size, single-atom catalysts (SACs) could expose abundant active sites with maximum atomic utilization and unique physico-chemical properties. [7] It has been presented as a kind of new catalyst members and shows more excellent activity, selectivity, and stability compared with traditional catalysts. Since Thomas et al. first discovered the SACs in 1995, the SACs have been attracting a great deal of attention. [8] In 2000, Heiz et al. prepared SACs containing ≈1-30 Pd atoms for catalyzing acetylene cyclization polymerization reactions. [9] Subsequently, the research of SACs has been rapidly developed into a frontier topic in the field of catalysis since the concept of "single-atom catalysis" was first mentioned by Zhang et al. in 2001. [10] Soon afterwards, Zhang and co-workers proposed an Au-alloyed Pd SACs for ullmann organocatalytic reaction. [11] Subsequently, the Rh SACs loaded on ZnO nanowires could be used to industrially catalyze hydroformylation of olefins by Zhang et al. [12] It showed high activity and selectivity for the hydroformylation of propylene by Zeng et al. [13] Besides, the SACs can be used to catalyze other important electrocatalytic reactions, such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and carbon dioxide reduction reaction (CO 2 RR). For instance, Yu et al. reported that Pt SAC supported on N-doped mesoporous hollow carbon spheres could exhibit excellent HER activity. [14] Wei and co-workers. dispersed Co-P 4 active sites on g-C 3 N 4 as for photocatalytic water splitting reaction. [15] Moreover, Wang et al. used DFT to study a series of transition metals SACs (Fe, Co, Ni, Cu) supported on N-doped graphene, proving that Co-N 4 SAC performed the most excellent OER activity. [16] Wang et al. synthesized Fe SAC on carbonbase with high-efficiency CO 2 RR catalytic activity. [17] Oxygen reduction reaction (ORR) is the important half-reaction for metal-air batteries and fuel cells (FCs), which plays the decisive role for the performance of whole devices. Developing high-efficiency non-precious metal ORR catalysts is urgent and still challenging. Single-atom catalysts (SACs) are considered to be one of the promising substitutes for Pt due to their maximum atom utilization efficiency and mass activity. Despite considerable efforts in preparing various SACs, the reaction mechanism and intrinsic activity modulat...

Recent advances of biomass derived carbon-based materials for efficient electrochemical energy devices

“…In addition to anodic oxidation reaction, ORR occurs at the cathode of fuel cell, which is an important reaction for fuel cell energy conversion. 121,122 The reaction path is relatively complex, the intermediates are generated more, and the intrinsic kinetic rate is slow, so the efficiency of ORR restricts the development of fuel cells. 123 ORR involves either a direct 4e À process or two 2e À processes.…”

Regulating the N Coordination Environment of Co Single-Atom Nanozymes for Highly Efficient Oxidase Mimics

“…Single-atom catalysts (SACs), featuring atomically dispersed metal active sites anchored on the nitrogen-doped carbon texture (M–N–C), have been successfully applied as highly efficient catalysts due to their unique electronic and geometric structures. − Through mimicking the highly evolved catalytic active centers of natural metalloenzymes, single-atom nanozymes have been regarded as potential replacements for natural metalloenzymes and demonstrated outstanding performance for many important biochemical reactions. − More interestingly, the homogeneous active sites of single-atom nanozymes could maximize the efficiency of atomic utilization of metal atoms. , Meanwhile, the well-defined atomic structures and coordination environments could provide an ideal model system for further understanding of the relationship between their structure and performance. − To this end, the study of highly efficient single-atom nanozymes with multiple enzyme-like activities and promising applications has received extensive attention.…”

PEGylated Ni Single-Atom Catalysts as Ultrasensitive Electrochemiluminescent Probes with Favorable Aqueous Dispersibility for Assaying Drug-Resistant Pathogens

“…Typically, SACs are prepared by calcining metal precursors on the carriers to promote the formation and improve stability of atomically dispersed metal active centers. − However, high-temperature calcination inevitably destroys the hydrophilic groups of SACs and lowers their aqueous dispersibility. Thus, it is a huge challenge to apply SACs as signal probes to tag biorecognition molecules for bioassay although they have displayed high catalytic activity superior to natural enzymes and regular nanomaterials.…”