M₃C (M: Fe, Co, Ni) Nanocrystals Encased in Graphene Nanoribbons: An Active and Stable Bifunctional Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reactions

Abstract

Transition metal carbide nanocrystalline M3C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M3C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec(-1) for Fe3C-GNRs, Co3C-GNRs, and Ni3C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M3C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm(-2) at an overpotential of 200 mV, low onset overpotential of 32, 41, and 35 mV, small Tafel slope of 46, 57, and 54 mV dec(-1) for Fe3C-GNRs, Co3C-GNRs, and Ni3C-GNRs, respectively, as well as an excellent stability in acidic media.

Nanoporous Gold Surface: An Efficient Platform for Hydrogen Evolution Reaction at Very Low Overpotential

“…As a result, enormous efforts have been devoted to finding alternative catalysts for producing hydrogen at low overpotential. For example, cobalt, [11][12][13] nickel, 14 copper [15][16][17] bimetallic catalyst, 18 transition metal carbide nanocrystals M3C (M: Fe, Co, Ni) encapsulated with vertically aligned graphene nanoribbons, 19 nitrogen and sulfur co-doped nanoporous graphene, 20 molybdenum sulfide (MoS 2 ), phosphide, carbon and noble metal-free catalysts are reported for the HER process. [21][22][23][24] Currently, nanoporous gold films (NPGF) have attracted attention for their widespread application in catalysis and in the sensors field because of their higher surface area in comparison to bulk gold electrodes, allowing superior electron transfer rate between the electrode-electrolyte interface.…”

Atomic H-Induced Mo2C Hybrid as an Active and Stable Bifunctional Electrocatalyst

“…25 Furthermore, hot-filament chemical vapor deposition (HF-CVD) is one of the most promising techniques for 4 growing high melt point carbide materials at relatively low substrate temperature, such as WC, 26 M 3 C (M:Fe,Co,Ni), 27 silicon carbide (SiC) 28 and so on. In the HF-CVD processing, the filament was heated to over 2000 o C for activation of the source gas.…”

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

“…Due to their intrinsic properties, such as abundant edges, thin walls, high surface area and excellent electrical conductivity, GNRs are extremely attractive to enhance the ORR activity [110][111][112][113][114][115][116][117][118]. In Liu's group, they used longitudinal unzipping technology to produce GNRs from CNTs [110].…”

“…All of the 3D-G can offer good catalytic properties towards ORR, and moreover, the ORR activity of 3D-G increased with the increasing number of graphene layers. The applications of GNRs can also be easily extended to other metal/metal oxides [112][113][114][115]118]. For example, combining GNRs with nanoparticles to form a hybrid is conceivable to integrate their respective merits and enhance their catalytic activity.…”

“…For example, combining GNRs with nanoparticles to form a hybrid is conceivable to integrate their respective merits and enhance their catalytic activity. A series of Fe 3 C-GNRs, Co 3 C-GNRs and Ni 3 C-GNRs have been synthesized by the hot filament CVD method [115]. Such materials show excellent electrocatalytic activity for ORR with higher current density and better durability.…”