Graphene wrapped Fe7C3 nanoparticles supported on N-doped graphene nanosheets for efficient and highly methanol-tolerant oxygen reduction reaction

Well entrapped platinum-iron nanoparticles on three-dimensional nitrogen-doped ordered mesoporous carbon as highly efficient and durable catalyst for oxygen reduction and zinc-air battery

The high-performance and durable oxygen reduction reaction (ORR) catalyst on air cathode is a key component in assembly of Zn-air batteries. Herein, three-dimensional N-doped ordered mesoporous carbon (3D N-OMC) was first prepared with silica as a template via pyrolysis with assistance of dicyandiamide as a N-doping agent, combined by full adsorption of platinum (II) acetylacetonate (Pt(acac)₂) and iron (II) phthalocyanine (FePc) via π-π interactions. After further pyrolysis of the resulting mixture, many PtFe nanoparticles were efficiently incorporated in 3D N-OMC (termed as PtFe@3D N-OMC for simplicity). Control experiments were certificated the important role of the pyrolysis temperature played in this synthesis. The resultant composite synergistically combines advantages of hierarchically accessible surfaces, highly open structure, and well-dispersed PtFe particles, which endow the PtFe@3D N-OMC with onset and half-wave potentials of 0.98 and 0.86 V in alkaline media, respectively, showing appealing catalytic activity for the ORR. Most significantly, the PtFe@3D N-OMC based Zn-air battery has a high power density of 80.57 mW cm^-2 and long-term durability (220 h, 660 cycles). This work opens a new avenue for design of high-efficiency and durable ORR electrocatalysts in energy conversion and storage systems.

In situ produced Co9S8 nanoclusters/Co/Mn-S, N multi-doped 3D porous carbon derived from eriochrome black T as an effective bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Construction of high-efficiency, low cost and stable non-noble metal catalyst on air cathode is of great importance for design and assembly of rechargeable Zn-air battery. Eriochrome black T (EBT) has phenolic hydroxyl and -N=Ν- groups, which provides multiple coordination sites for metal ions. Herein, Co₉S₈ nanoclusters implanted in Co/Mn-S,N multi-doped porous carbon (Co₉S₈@Co/Mn-S,N-PC) are fabricated with the mixture (i.e. EBT, metal precursors and dicyandiamide) by a coordination regulated pyrolysis strategy. Specifically, EBT effectively chelates with the Co and Mn ions, resulting in multiple incorporation and fine modulation of the carbon electronic structures. Meanwhile, its sulfonic acid groups are reduced at such high temperature, accompanied by simultaneously embedding S element in the carbon, ultimately in situ forming Co₉S₈ nanoclusters. The Co₉S₈@Co/Mn-S,N-PC performs as an effective bifunctional oxygen catalyst, displaying a positive half-wave potential of 0.85 V and a large limiting current density of 5.89 mA cm^-2 for oxygen reduction reaction (ORR) in alkaline media, coupled with a small overpotential of 320 mV at 10 mA cm^-2 towards oxygen evolution reaction (OER), outperforming commercial Pt/C and RuO₂ catalysts, respectively. Furthermore, the assembled rechargeable Zn-air battery with Co₉S₈@Co/Mn-S,N-PC exhibits the much better charge/discharge performance and long-term durability (210 h, 630 cycles). This research opens an instructive avenue to develop high-efficient and stable bifunctional oxygen electrocatalysts in energy transformation and storage devices.

Cobalt nanoparticles/ nitrogen, sulfur-codoped ultrathin carbon nanotubes derived from metal organic frameworks as high-efficiency electrocatalyst for robust rechargeable zinc-air battery

It remains a challenge for efficient and facile synthesis of promising non-noble metal electrocatalysts with outstanding properties. This work reported a simple pyrolysis method to prepare cobalt nanoparticles/nitrogen, sulfur-codoped ultrathin carbon nanotubes (Co NPs/N,S-CNTs) with metal organic frameworks (cobalt 2-methylimidazole, ZIF-67), melamine, polyvinylpyrrolidone (PVP) and thiourea. The prepared catalyst exhibited superior catalytic activity towards oxygen reduction reaction (ORR) such as the more positive onset potential of 0.96 V, half-wave potential of 0.86 V and smaller Tafel slope of 67.9 mV dec^-1, outperforming those of commercial Pt/C. Furthermore, the Co NPs/N,S-CNTs based Zn-air battery not only showed good cycling performance, but also displayed a notable peak power density (153.8 mW cm^-2) and large open-circuit voltage (1.433 V). This study provides some valuable guidelines for synthesizing advanced electrocatalysts in renewable energy techniques.

One-step pyrolysis synthesis of nitrogen, manganese-codoped porous carbon encapsulated cobalt-iron nanoparticles with superior catalytic activity for oxygen reduction reaction

Replacing precious metal catalysts with low-price and abundant catalysts is one of urgent goals for green and sustainable energy development. It is imperative yet challenging to search low-cost, high-efficiency, and long-durability electrocatalysts for oxygen reduction reaction (ORR) in energy conversion devices. Herein, three-dimensional low-cost Co₃Fe₇ nanoparticles/nitrogen, manganese-codoped porous carbon (Co₃Fe₇/N, Mn-PC) was synthesized with the mixture of dicyandiamide, cobalt (II) tetramethoxyphenylporphyrin (Co(II)TMOPP), hemin, and manganese acetate by one-step pyrolysis and then acid etching. The resultant Co₃Fe₇/N, Mn-PC exhibited excellent durability and prominent ORR activity with more positive onset potential (E_onset, 0.98 V) and half-wave potential (E_1/2, 0.87 V) in 0.1 M KOH electrolyte, coupled with strong methanol resistance. The pyrolysis temperature and optimal balance of graphite with pyridine-nitrogen are of significance for the ORR performance. The prepared Co₃Fe₇/N, Mn-PC displayed excellent ORR performance over commercial Pt/C in the identical environment. It was ascribed to the uniform 3D architecture, Mn- and N-doping effects by finely adjusting the electronic structures, coupled with the synergistic catalytic effects of multi-compositions and multi-active sites. This work provides some constructive guidelines for preparation of low-cost and high-efficiency ORR electrocatalysts.

N-doped graphene foam obtained by microwave-assisted exfoliation of graphite

The synthesis of metal-free but electrochemically active electrode materials, which could be an important contributor to environmental protection, is the key motivation for this research approach. The progress of graphene material science in recent decades has contributed to the further development of nanotechnology and material engineering. Due to the unique properties of graphene materials, they have found many practical applications: among others, as catalysts in metal-air batteries, supercapacitors, or fuel cells. In order to create an economical and efficient material for energy production and storage applications, researchers focused on the introduction of additional heteroatoms to the graphene structure. As solutions for functionalizing pristine graphene structures are very difficult to implement, this article presents a facile method of preparing nitrogen-doped graphene foam in a microwave reactor. The influence of solvent type and microwave reactor holding time was investigated. To characterize the elemental content and structural properties of the obtained N-doped graphene materials, methods such as elemental analysis, high-resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy were used. Electrochemical activity in ORR of the obtained materials was tested using cyclic voltamperometry (CV) and linear sweep voltamperometry (LSV). The tests proved the materials’ high activity towards ORR, with the number of electrons reaching 3.46 for tested non-Pt materials, while the analogous value for the C-Pt (20 wt% loading) reference was 4.

Zinc, sulfur and nitrogen co-doped carbon from sodium chloride/zinc chloride-assisted pyrolysis of thiourea/sucrose for highly efficient oxygen reduction reaction in both acidic and alkaline media

Zn and N co-doped carbon (Zn-N-C) shows encouraging catalytic stability for oxygen reduction reaction (ORR) because of the fulfilled d orbital of Zn, but its catalytic activity is not satisfactory. Herein, hierarchically porous Zn, S and N co-doped carbon (Zn-S-N-C) with large specific surface area (2433 m² g^-1) and pore volume (3.007 cm³ g^-1) is synthesized by using NaCl/ZnCl₂-assisted pyrolysis of sucrose and thiourea. The Zn-S-N-C catalyst exhibits superior ORR activity with half-wave potentials (E_1/2) up to 0.774 V in 0.1 M HClO₄ and 0.894 V in 0.1 M KOH, good ORR stability with 19- and 4-mV loss in E_1/2 values after 10,000 potential cycles in 0.1 M HClO₄ and 0.1 M KOH, respectively, and excellent methanol tolerance. The good ORR performance of Zn-S-N-C can be attributed to its enhanced intrinsic ORR activity resulting from the formation of S, N doped carbon and ZnS in Zn-S-N-C, its hierarchically porous structure resulting from the pore-forming roles played by ZnCl₂, NaCl and thiourea, and its improved graphitization degree resulting from the added ZnCl₂ during Zn-S-N-C synthesis. This work will provide a novel strategy for the synthesis of hierarchically porous Zn, S and N co-doped carbon materials for ORR.

A novel cobalt and nitrogen co-doped mesoporous hollow carbon hemisphere as high-efficient electrocatalysts for oxygen reduction reaction

Exploring a cheap catalyst with effective activity for oxygen reduction reaction (ORR) to replace precious metal electrocatalysts has gained tremendous attention for several decades. In this study, we designed and synthesized cobalt and nitrogen supported on mesoporous hollow carbon hemisphere (Co/N/HCHs) nanocomposites by a facile and economical approach. Semisphere-shaped mesoporous hollow carbon is self-generated using silica particles as template, followed by a pyrolysis-etching process; and exhibits high electrical conductivity and high specific surface. The unique porous structure of carbon provides significant number of the abundant defective sites and shortens the mass transfer pathway, leading to a greatly enhanced electrocatalytic activity with mainly 4e^- reduction. Moreover, the synergistic effects of large electrochemically active areas and good electrical conductivity, resulting from the introduction of Co and N heteroatom, are the main reason for displaying outstanding ORR activity with a high half-wave potential of 0.8 V and the electron transfer numbers of 3.89. Furthermore, an excellent long-term stability (the current density retention of 87.0%) and superb methanol tolerance in alkaline medium are achieved. Undoubtedly, this demonstrates a potential way to strategically design the non-precious metal doped carbon catalysts for wider practical applications.

Porous carbons embedded with nitrogen-coordinated cobalt as an exceptional electrochemical catalyst for high-performance Zn–air batteries

Establish a polymer framework coordination transition metal strategy to fabricate Co/N-PCs for energy conversion and storage.