Co Nanoparticles Encapsulated in N‐Doped Carbon Nanotubes Grafted CNTs as Electrocatalysts for Enhanced Oxygen Reduction Reaction

Abstract

The exploration of high‐efficiency and inexpensive electrocatalysts for oxygen reduction reaction (ORR) is of critical significance for renewable energy conversion. Herein, an in situ catalytic transformation strategy toward a unique hierarchical nanostructure is reported. In the architecture, Co nanoparticles encapsulated at the tip of bamboo‐like N‐doped carbon nanotubes (NCNTs) are grafted on N‐doped polypyrrole‐derived CNTs. Thanks to the smart design of unique 3D architecture, the NPCN@Co‐NCNTs catalyst displays an extraordinary ORR activity in 0.1 m KOH solution (the onset and half‐wave potentials are 0.96 and 0.90 V vs RHE, respectively), which is similar to commercial Pt/C catalyst (0.99 and 0.88 V vs RHE, respectively). Meanwhile, the catalyst shows the low Tafel slope of 78 mV dec−1 and long‐time stability. Experimental and theoretical results verify that the improved ORR performance is mainly related to the existence of Co nanoparticles protected by pyridinic‐N‐doped carbon, which lowers the theoretical overpotential of ORR. Density functional theory calculations reveal that Pyridinic‐NCCo site is the reactive site with the lowest overpotential for ORR (0.57 V). These results unambiguously indicate that the NPCN@Co‐NCNTs represent a low‐cost yet high‐efficiency electrocatalyst for the electrocatalytic ORR.

l-Alanine-Assisted Synthesis of a Hierarchically Porous Co@N–C/N-Ketjenblack Carbon Catalyst for Oxygen Reduction in Zn–Air Batteries

“…31 As described above, the presence of pyridinic-N and graphitic-N species in the carbon support is expected to be highly beneficial for ORR electrocatalysis, lowering the onset potential and increasing the limiting diffusion current density. 20,33 Figure 2e compares the surface N speciation for Co@N−C/N−KB, Co@N−C/ N−KB(NL), and Co/N−KB. The relative N speciation in the three catalysts is presented graphically in Figure 2f.…”

“…Ideally, Co-based N–C catalysts for ZABs should be based around cheap and readily available carbonaceous sources. The Co-active materials in Co-based N–C catalysts include metallic Co, oxides, nitrides, chalcogenides, or their composites . Metallic Co nanoparticles offer promise as “Pt-like catalysts” due to their abundant d electrons and good charge transfer ability, which act to enhance ORR kinetics .…”

“…Further, pyridinic-N sites can anchor Co atoms to form Co-N x /C active sites. , As a result, the catalytic ORR current density can be enhanced and the ORR onset potential ( E onset ) shifts positively. Wang et al demonstrated that Co nanoparticles protected by pyridinic-N-doped carbon offered a low ORR overpotential . Alternatively, graphitic-N species can also affect ORR by optimizing the electronic configuration of C atoms to facilitate O 2 adsorption and promote the four-electron ORR, thereby increasing the limiting current density for catalyzing ORR. , Very recently, Wei et al established that an abundance of graphitic-N was beneficial for boosting the performance of Co nanoparticle-based electrocatalysts towards ORR .…”

Design and Performance Enhancement of Cobalt-Encapsulated Nitrogen-Doped Carbon Nanofiber Electrocatalyst through Ionic Liquid Modification for Efficient Oxygen Reduction

“…In view of this, an efficient and durable catalyst with a rigid structure, resistant to degradation, is essential for reliable operation. Among metal-free catalysts, defect-rich nitrogen-doped carbon nanotubes (NCNTs) or nanofibers (NCNFs), owing to their robust morphology with modified electronic structure, can offer ORR activity with enhanced durability. − Recent investigations have also revealed that the catalytic activity of carbon structures can be enhanced through the encapsulation of metal nanoparticles, leading to the modification of its electronic structure. − Thus, the ORR activity of NCNFs can also be increased through the encapsulation of suitable metals such as Fe, Co, etc. − However, in all the above cases, the ORR activity of the nonprecious metal-based catalysts has been demonstrated in an alkaline medium with very few reports on the behavior of the catalysts in the acidic medium.…”

Activated carbon supported Fe–Cu–NC as an efficient cathode catalyst for a microbial fuel cell

“…5,6 Oxygen (O 2 ) is the ideal electron acceptor in the cathode of MFCs because of its availability, sustainability, and high redox potential. 7–10 However, the sluggish kinetics of the oxygen reduction reaction (ORR) and a great loss of overpotential, which generally results in 300–400 mV loss 11 and hampers the electron transfer, directly reduce the output power of MFCs and finally limit the application of MFCs as an emerging energy source. 12,13 Therefore, it is highly desirable to search for high-performance catalysts to improve the performance of the cathodes in MFCs.…”