Isolated Single Atoms Anchored on N-Doped Carbon Materials as a Highly Efficient Catalyst for Electrochemical and Organic Reactions

Abstract

Single-atom catalysts (SACs) with atomic dispersion and coordinated unsaturated active sites have sparked gigantic attention, focusing on high activity, selectivity, atom utilization, and a unique metal−support coordination environment. However, isolated single atoms possess high surface free energy, especially under harsh reaction conditions, and tend to migrate and agglomerate into clusters or nanoparticles in an elusive manner. Herein, we have integrated different types of N-doped carbon (N-C) materials as Lewis base sites to anchor dispersed metal atoms. The lone pairs of electrons donated by N-rich materials effectively resist metal sintering. The matrix includes organic compounds, MOFs, N-doped graphene, g-C 3 N 4 , and biomass. Furthermore, we also emphasized the application of N-C material-based SACs in ORR, OER, HER, organic reactions, and CO 2 RR. Beneficially, these establish a definitive correlation between construction strategy and catalytic performance. Finally, we review the staged challenges and development opportunities confronted by SACs and pave the way for balancing the electronic structure and catalytic properties of SACs supported on derived N-C materials.

Revealing the Real Role of Nickel Decorated Nitrogen‐Doped Carbon Catalysts for Electrochemical Reduction of CO2 to CO

“…However, to the best of our knowledge, it is difficult to prepare solely nitrogen‐doped carbon‐encapsulated Ni NPs without the formation of Ni‐N x sites during the high‐temperature carbonization process because Ni atoms are prone to coordinate with N atoms and form single Ni‐N x sites at high temperatures. [ 15 ] Moreover, Javier Pérez‐Ramírez and co‐workers also doubted this idea as they mentioned in one of their recent papers that “a few studies have claimed that nickel nanoparticles intentionally coated with a thick (nitrogen‐doped) carbon layer can exhibit eCO 2 RR activity. [ 16 ] However, the presence of atomically dispersed nickel could not be excluded from the data presented.” Thus, the question remains of whether nitrogen‐doped carbon‐encapsulated Ni NPs are truly active for the electroreduction of CO 2 to CO in the complete absence of single Ni atoms and lack of comprehensive study and solid evidence.…”

Single atom catalysts by atomic diffusion strategy

“…In addition, during the synthesis process, as the load continues to increase, metal atoms are prone to migration and agglomeration, which leads to the formation of clusters or nanoparticles. This is one of the reasons why most synthesis methods enhance the stability of metal atoms at the expense of metal loading [15,16,20,59,111]. Therefore, it is still challenging to synthesize single-atom catalysts with high loading and high stability.…”

Electrocatalytic acidic oxygen evolution reaction: From nanocrystals to single atoms

“…[ 123,124 ] As we all know, metals, metal oxides, and nonmetals (such as N‐doped C materials, carbon nanotubes, graphene) can all act as supports for single atoms. [ 125 ] However, due to the tendency of metal ions to aggregate, proper synthesis methods are particularly important for the preparation of highly reactive SAC. [ 126,127 ]…”