Recently, Professor Ruqiang Zou’s group in the College of Engineering made great achievements in the synthesis of large carbon networks with hierarchical porosity and atomically dispersed metal sites, which demonstrated superior electrocatalytic performance towards oxygen reduction reaction. This work is published in Angewandte Chemie and is chosen as the inner cover (DOI: 10.1002/anie.201811126 and 10.1002/ange.201811126).
Three-dimensional (3D) carbon networks with hierarchical porosity are attracting considerable attention in the field of energy storage and conversion. Compared with typical carbonaceous nanoparticles, which suffer from insufficient contact and poor conductivity, 3D carbon networks with hierarchical porosity can provide consecutive electrical conductivity and porous channels for fast electron transfer and effective mass transport. To acquire desirable electrochemical features, these carbon networks have been extensively explored as supports to load various active components, especially metal sites. Recently, single-atom catalysts are attracting increasing interests owing to their high catalytic activity from the atomically dispersed metal sites (ADMSs). Integration of ADMSs into 3D carbon networks is a new frontier in material research; however, it remains to be a challenge. Developing a simple and scalable synthetic strategy is particularly desirable.
Metal-organic frameworks (MOFs), an emerging class of porous crystalline materials, have flourished as attractive precursors for the fabrication of various nanostructured materials. Generally, carbonization of MOFs will produce shrinked particles, sintered aggregations, or collapsed structures. Thus far, only a few ADMS-decorated materials derived from MOFs have been reported, which are generally limited to small particles due to the shrinkage upon pyrolysis. Breakthroughs, which are based on new type of MOFs and synthetic concept, are urgently expected in order to fabricate ADMS-decorated hierarchically porous carbon networks in a large size.
In order to integrate ADMSs to 3D carbon networks, Ruqiang Zou’s group fabricate submillimeteric carbon networks with hierarchical porosity and ADMSs from energetic MOFs (EMOFs). Specifically, Zn-based triazole-rich EMOFs doped with Co and/or Fe ions were used as precursors. Upon one-step pyrolysis, Zn nodes are reduced and evaporated, while the energetic triazole ligands decompose and release a large amount of gases, foaming the hierarchicaly porous carbon networks. Meanwhile, the homogeneously dispersed target metal ions (Fe and/or Co ions) are transformed into ADMSs. The as-obtained CoFe@C is composed of hierarchically porous carbon networks with high conductivity and active Fe and Co ADMSs, which exhibits superior electrocatalytic performance towards oxygen reduction reaction.
Schematic illustration of 3D carbon networks with hierarchical porosity and ADMSs
The first author and co-first author of this work are Ruo Zhao and Zibin Liang, Ph.D. candidates in Zou’s group. This work is supported by the National Natural Science Foundation of China (51772008), the National Key Research and Development Program of China (2017YFA0206701), National Program for Support of Top-notch Young Professionals, Changjiang Scholar Program.