Heterogeneous nanocarbon materials for oxygen reduction reaction

Abstract

Heterogeneous nanocarbon materials are being increasingly investigated and deployed in numerous new technologies and devices for sustainable energy conversion and storage. Nanocarbons often consist of fullerene, graphene and carbon nanotubes. Their derivatives include quantum dots, nanofibres, nanoribbons, nanospheres/capsules and other nanostructured morphologies. The heterogeneous forms of these nanocarbons stem from the implantation of alien atoms into the aromatic carbon lattice or the covalent grafting of functional groups onto the carbon basal plane or edge sites. Heterogeneous nanocarbons have shown remarkable advantages in solar cells, water splitting, supercapacitors, lithium ion batteries and catalysis. This review focuses on recent progress in the experimental and computational studies of the roles of heteroatoms in heterogeneous nanocarbons for electrocatalytic oxygen reduction reaction (ORR). Critical perspectives are devoted to the ambiguous phenomena in this emerging research area. The long standing debate about the active sites is discussed with an emphasis on more rational development of advanced nanocarbon-based electrocatalysts for ORR. Broader contextThe emerging demand for next generation renewable and sustainable energy conversion technologies requires diverse catalytic and electrochemical methods and reactors. In terms of energy density, metal-air batteries exhibit the greatest promise for delivering compact energy by reducing oxygen from the air and oxidizing the implanted metal electrodes. Compared with metal oxidation, the kinetics of oxygen reduction is rather slow and inhibits the overall power capability of these promising devices. Platinum is the most active electrocatalyst for oxygen reduction and its high cost is urging the development of non-noble oxygen reduction electrocatalysts. Metal-free heterogeneous carbon nanotubes and many other nanocarbons have been increasingly studied in recent years. It has been greatly expected that by modifying the heteroatoms in nanostructured carbon materials their electrocatalytic activity towards oxygen reduction can be potentially increased to approaching that of platinum. However, many fundamental issues, particularly the specic functions of the heteroatoms in the oxygen reduction reaction on heterogeneous nanocarbons, are unclear. We expect to address some of these questions in this review and to propose some ideas for future research.

An Oxygen Reduction Study of Graphene-Based Nanomaterials of Different Origin

“…As can be seen from Figure 9 and Figure S5, the dependence of reduction current on the electrode rotation rate exists leading to an increased current density values. In addition, the RDE voltammetry curves on graphene-based electrodes exhibit two reduction waves consistent with the literature [44]. Moreover, the value of n is between two and three in case of GC/Graphene1 and GC/rGO, but even higher in case of GC/Graphene2 and GC/GO at higher potentials (see Figure 9 and Figure S5).…”

“…According to the literature, depending on the origin of graphene (CVD)-grown graphene, rGO, etc.) these materials exhibit different electrochemical properties towards various redox probes (including O 2 ) [24,[40][41][42][43][44]. For example, high-quality graphene (e.g., CVD-grown graphene) is inactive towards the ORR because of the exposure of mainly defect-free basal plane surface [45].…”

N-doped crumpled graphene: bottom-up synthesis and its superior oxygen reduction performance

“…More importantly, curve-fitting of the high-resolution XPS N1s peaks (Fig. S9c) indicates up to~68.9 at.% N in the form of graphitic N, which was reported to be one of the most active catalytic N sites for ORR and could also improve the overall conductivity [16,[47][48][49]. The curve-fitted XPS C1s spectrum of the CrG-900 is given in Fig.…”

The New Graphene Family Materials: Synthesis and Applications in Oxygen Reduction Reaction

“…In recent years, two-dimensional (2D) graphene-based materials have emerged as new types of electrocatalysts due to their excellent conductivity, high specific surface area (SSA) and tailorable surface chemistry, as summarized in previous excellent reviews [4,8,11,12]. Although the large SSA and high electrical conductivity of pristine graphene are supposed to be useful for the electrocatalysis process, in practice, with the strong van der Waals interactions and π-π stacking between graphene layers, the 2D graphene nanosheets could easily restack and aggregate, which significantly diminish …”

“…However, the development and wide-spread commercialization of fuel cells are largely hampered by the Pt-based catalysts due to their high cost, limited resources and CO poising sensitivity. Therefore, developing low-cost and high-performance alternatives, such as non-precious metal and metal-free electrocatalysts, to replace the expensive Pt-based catalysts has become the hot topic in the fuel cell community [8][9][10].…”