Highly active and durable catalysts play a key role in clean energy technologies. However, the high cost, low reserves, and poor stability of noble‐metal‐based catalysts have hindered the large‐scale development of renewable energy. Owing to their low cost, earth abundance, high activity, and excellent stability, carbon‐based metal‐free catalysts (CMFCs) are promising alternatives to precious‐metal‐based catalysts. Although many synthetic methods based on solution, surface/interface, solid state, and noncovalent chemistries have been developed for producing numerous CMFCs with diverse structures and functionalities, there is still a lack of effective approaches to precisely control the structures of active sites. Therefore, novel chemical approaches are needed for the development of highly active and durable CMFCs that are capable of replacing precious‐metal catalysts for large‐scale applications. Herein, a comprehensive and critical review on chemical approaches to CMFCs is given by summarizing important advancements, current challenges, and future perspectives in this emerging field. Through such a critical review, our understanding of CMFCs and the associated synthetic processes will be significantly increased.
Atomically
dispersed metal–nitrogen–carbon (M–N–C)
catalysts have emerged as the promising alternative to replace platinum-based
catalysts for oxygen reduction reaction (ORR) in proton exchange membrane
fuel cells (PEMFCs). However, their practical applications are restricted
by the relatively low intrinsic activity, low utilization rate, and
poor stability of atomic metal sites. Herein, we propose a simple
but efficient strategy to synthesize a geometrically deformed single
Fe site catalyst (d-SA-FeNC) by trace NaCl-coating-assisted
pyrolysis of Fe-containing zeolitic imidazolate frameworks. Benefiting
from the significantly exposed Fe-N4 active sites and enhanced
mass transport by the hierarchically porous structure, the newly developed
catalysts exhibit improved ORR performance in acidic media. Remarkably,
the as-constructed membrane electrode assemblies achieve high peak
power densities of 0.904 and 0.502 W cm–2 in H2–O2 and H2–air PEMFCs
even at a low catalyst loading of 1 mg cm–2, respectively,
revealing ultrahigh mass activity density. Both experimental and theoretical
results reveal that the enhanced intrinsic activity is attributed
to the synergy of deformed Fe-N4 moieties and the surrounding
graphitic N dopant. In addition, the locally increased graphitization
of the carbon matrix can efficiently reduce carbon corrosion, thereby
promoting catalyst stability. This work provides useful guidance for
the development of highly efficient ORR catalysts for PEMFCs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.