Mesoporous Single-Atom-Doped Graphene–Carbon Nanotube Hybrid: Synthesis and Tunable Electrocatalytic Activity for Oxygen Evolution and Reduction Reactions

Abstract

Mesoporous heteroatom-doped carbon-based nanomaterials are very promising as catalysts for electrochemical energy conversion and storage. We have developed a one-step catalytic chemical vapor deposition method to grow a highly graphitized graphene nanoflake (GF)−carbon nanotube (CNT) hybrid material doped simultaneously with single atoms of N, Co, and Mo (N−Co−Mo− GF/CNT). This high-surface-area material has a mesoporous structure, which facilitates oxygen mass transfer within the catalyst film, and exhibits a high electrocatalytic activity and stability in oxygen reduction and evolution reactions (ORR and OER) in alkaline media. We have shown that in this metal (M)−N−C catalyst, M (Co, Mo)−C centers are the main sites responsible for OER, while, for ORR, both M and N−C centers synergistically serve as the active sites. We systematically investigated tuning of the ORR and OER activity of the porous catalyst depending on the choice of the underlying substrate. The ORR kinetic current and OER activity for N−Co−Mo−GF/CNT were significantly enhanced when the catalyst was deposited onto a Ni substrate, resulting in an advanced electrocatalytic performance compared to the best bifunctional ORR/OER catalysts reported so far. Using a developed scanning electrochemical microscopy analysis method, we demonstrated that the higher OER reactivity on Ni was attributable to the formation of underlying catalyst/Ni interfacial sites, which are accessible due to the porous, electrolyte-permeable structure of the catalyst.

A Freestanding 3D Heterostructure Film Stitched by MOF‐Derived Carbon Nanotube Microsphere Superstructure and Reduced Graphene Oxide Sheets: A Superior Multifunctional Electrode for Overall Water Splitting and Zn–Air Batteries

“…[ 13 ] Among plenty of conductive supports, CNT and graphene, which are reported to possess the properties of high surface area, excellent electrical conductivity, good mechanical strength and flexibility, have attracted significant attention as an excellent candidate for portable and flexible electrode materials. [ 14 ] However, the restacking and aggregation of CNT and graphene during electrode fabrication process normally reduces the specific surface area and results in limited improvement in performance, and it is difficult to selectively control the composition of the freestanding electrode. [ 15 ] Therefore, a practical and direct scheme is required for ZABs and water splitting to synthesize an efficient multifunctional freestanding 3D CNT and graphene electrode free of a support, which is rather difficult and requires innovative material design.…”

One‐dimensional nanomaterial supported metal single‐atom electrocatalysts: Synthesis, characterization, and applications

“…After acid leaching, the single atom doped hybrid catalyst was obtained, which exhibited high activity and stability for catalyzing ORR and OER in alkaline media. [56] In fact, some post-thermal treatments (e.g., nitrogenization and phosphorization) can be considered as CVD methods. As for the ALD technique, it can be used to design and synthesize catalysts with controllable composition, size and active center at the atomic scale, which is ideal for the elucidation of catalytic mechanism and understanding of structure-activity relationship.…”

“…They found that the choice of the underlying substrate played a crucial role in tuning the ORR and OER activities of the porous catalyst. [56] In addition to bifunctional activities for the ORR and OER, 1D nanomaterial supported MSACs have also been reported to exhibit excellent electrocatalytic performance for OER and HER. Very recently, Luo et al reported a double protecting strategy to disperse Ir single atoms onto Fe nanoparticles and embed IrFe nanoparticles into nitrogendoped carbon nanotubes (Ir-SA@Fe@NCNT) as a bifunctional electrocatalyst for the OER, HER and overall water splitting.…”

Local probe investigation of electrocatalytic activity

“…189 Even though carbon nanotubes are generally acknowledged for their high conductivity, their resistance can further be decreased by more than 50% if they form hybrids with graphene, due to enhanced effectiveness of charge tunneling. 190 Lately, such a hybrid electrocatalyst based on graphene nano-akes (GFs) and carbon nanotubes (CNTs) doped with heteroatoms such as N, Co and Mo (N-Co-Mo-GF/CNT) was studied for its ORR and OER activity by Tavakkoli et al 51 The OER catalytic activity was investigated by means of SECM in SG/TC mode in alkaline media on two different substrates, namely nickel (Ni) and glassy carbon (GC). When GC was used, the tip response (increase of ORR current) was almost simultaneous with the oxygen generation (OER onset potential), compared to the Ni substrate in which case the tip response was delayed (Fig.…”