The oxygen reduction reaction (ORR) is a fundamental reaction for energy storage and conversion. It has mainly relied on platinum-based electrocatalysts, but the chemical doping of carbon-based materials has proven to be a promising strategy for preparing metal-free alternatives. Nitrogen doping in particular provides a diverse range of nitrogen forms. Here, we introduce a new form of nitrogen doping moieties -sp-hybridized nitrogen (sp-N) atoms into chemically defined sites of ultrathin graphdiyne, through pericyclic replacement of the acetylene groups. The as-prepared sp-N-doped graphdiyne catalyst exhibits overall good ORR performance, in particular with regards to peak potential, half-wave potential and current density. Under alkaline conditions it was comparable to commercial Pt/C, and showed more rapid kinetics. And although its performances are a bit lower than those of Pt/C in acidic media they surpass those of other metal-free materials. Taken together, experimental data and density functional theory calculations suggest that the high catalytic activity originates from the sp-N dopant, which facilitates O adsorption and electron transfer on the surface of the catalyst. This incorporation of chemically defined sp-N atoms provides a new synthetic route to high-performance carbon-based and other metal-free catalysts.

Structure and facet control are considered to be effective routes to enhance catalytic performance. We successfully synthesized hollow multi-shelled structures (HoMSs) of a Co 3 O 4 dodecahedron by adopting metal−organic frameworks (MOFs) as templates and using the sequential templating approach (STA). Importantly, owing to the topological arrangement of metal atoms in MOFs, the Co 3 O 4 nanocrystals in HoMSs are assembled in the desired orientation, forming a unique shell with dominant exposure of ( 111) facets. This process is defined as "genetic inheritance" in this work. In addition, these exposed facets possess high activity for photocatalytic CO 2 reduction. Adding this to the properties inherited from HoMSs, i.e., multiple interfaces and strong solar light harvesting, these Co 3 O 4 HoMSs present high catalytic activity for CO 2 photoreduction. The catalytic activity of quadruple-shelled (QS) Co 3 O 4 HoMSs was about 5 and 3 times higher than that of Co 3 O 4 nanoparticles and Co 3 O 4 HoMSs without facet control, respectively.

Developing metal-free catalysts with high catalytic activity for oxygen evolution reaction (OER) is essentially important for energy and environment-related techniques. Compared with individual element doping, doping carbon materials with multiple heteroelements has more advantages for enhancing the OER performance. However, doped sites for the different atoms are highly uncontrollable under the reported methods, which hinder the deeper understanding on the relationship between structure and property, and also limit the enhancement of catalytic activity. Our latest research has reported a method to site-controlled introducing a new form of nitrogen atoms, i.e. sp-hybridized nitrogen (sp-N), into graphdiyne, showing its potential advantages in OER catalysis. Since the sites of sp-N atoms are defined in graphdiyne, and the doping sites for S atoms are well understood, the relative position between N and S can be further defined. It gives us a chance to understand deeply the mechanism in the N, S heteroelements doped metal-free catalyst. Experimental results present that the codoping of sp-N and S atoms brought an excellent OER performance with low overpotential and high current density owning to the effectively synergistic effect of the stereodefined heteroatoms.

As a rising star of carbon allotropes, graphynes (GYs) merely consist of sp‐ and sp2‐hybridized carbon atoms, which endow them a large conjugated network and expanded 2D porous structure. With unique topological structure, GYs display unusual semiconducting properties, especially in the aspects of charge mobility and electron transport. Among the members of the GY family, only graphdiyne (GD) can be successfully synthesized in large quantities. The advanced properties of GD make it promising in various applications. Here, the recent progress in the synthesis of GD and GD‐based composites is reviewed as well as their applications in photorelated and electrocatalytic applications. It is hoped that this Review will promote the development and applications of carbon chemistry.

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