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Transition metal and heteroatom co-doped carbon nanomaterials (TM-H-C) are considered to be the most promising candidates to replace the expensive platinum-based catalysts for oxygen reduction reactions (ORR). Herein, we report a semi-closed molten salt-assisted one-step strategy for fabricating N-P-Fe-tridoped porous carbon nanotube (CNT) catalysts by using the evaporation of ZnCl2 and the catalysis of iron ions to control the heteroatoms doping process and CNT formation. The resultant densely packed porous CNT structure imparts final catalysts with an enhanced mass transfer ability for electron and ORR-involved species, ensuring a high performance in catalyzing the ORR. Significantly, the optimal catalysts show a half-wave potential of 0.89 V (vs. RHE), which is better than commercial platinum-based catalysts and most reported TM-H-C ORR catalysts. Impressively, when applied to a primary inc-oxygen (Zn–O2) battery, the synthesized catalyst comprehensively outperforms the state-of-the-art platinum-based catalyst in both its maximum power density and specific capacity. [ABSTRACT FROM AUTHOR]

Atomically dispersed Zn–N–C nanomaterials are promising platinum‐free catalysts for the oxygen reduction reaction (ORR). However, the fabrication of Zn–N–C catalysts with a high Zn loading remains a formidable challenge owing to the high volatility of the Zn precursor during high‐temperature annealing. Herein, we report that an atomically dispersed Zn–N–C catalyst with an ultrahigh Zn loading of 9.33 wt % could be successfully prepared by simply adopting a very low annealing rate of 1° min−1. The Zn–N–C catalyst exhibited comparable ORR activity to that of Fe–N–C catalysts, and significantly better ORR stability than Fe–N–C catalysts in both acidic and alkaline media. Further experiments and DFT calculations demonstrated that the Zn–N–C catalyst was less susceptible to protonation than the corresponding Fe–N–C catalyst in an acidic medium. DFT calculations revealed that the Zn–N4 structure is more electrochemically stable than the Fe–N4 structure during the ORR process. [ABSTRACT FROM AUTHOR]

Abstract Studies indicated that the existing carbon supported Pt-based nanoalloys may exhibit instability and lose activity under acidic conditions due to particle aggregation, leaching/dissolution of the non-precious metals and carbon corrosion, which impeded the practical use of these nanomaterials for fuel cell electrocatalysts. This work presents a polyaniline (PANI)-confined space annealing strategy to efficiently promote the stability and activity of solution phase synthesized PtNi nanoparticles. By virtue of an in situ formed PANI coating layer, PtNi NPs can be developed to be more stable and active at thermal annealing process without serious agglomeration. Simultaneously, high temperature forces the carbonization of PANI, featuring the final obtained PtNi NPs with a nitrogen-doped carbon (NC) coating layer. XPS analysis attributed the enhanced catalytic performance of as-constructed PtNi/C@NC composite to the unique electronic interaction between Pt atoms and NC outer layer, which is beneficial for stabilizing PtNi NPs under fuel cell working condition. Graphical abstract Image 1 Highlights • PANI-confined space annealing makes solution phase synthesized PtNi NPs to be more stable and active. • The in situ polymerized PANI shell renders PtNi NPs with highly resistance toward sintering. • An electronic interaction between PANI-derived NC layer and Pt creates a stabilizing effect against Pt oxidation/dissolution. [ABSTRACT FROM AUTHOR]

Abstract: Fe‐based electrocatalysts are elegant due to their better performance towards the oxygen reduction reaction. Nevertheless, they commonly contain different moieties, for example Fe‐Nx, Fe, Fe3C and N‐doped carbon, primarily the debatable assistance of these components towards ORR electrocatalysis, specifically for intermediate peroxide reduction reactions (PRR). In this paper, to explore the role of Fe‐Nx centres for PRR, a Fe‐N‐C electrocatalyst rooted in nitrogen‐doped carbon nanotubes with mesoporous structures was synthesized from a Fe/Zn‐dicyanoimidazolate framework. The use of dicyanoimidazole coordinated with iron can introduce the Fe‐Nx active sites as well as directional N‐doped carbon nanotubes, which is good for enhancing electronic conductance of the catalyst. The attained electrocatalyst shows tremendous enactment to ORR, being comparable to the activity of Pt/C in acidic and better in alkaline electrolytes. This study also reveals that Fe‐Nx active centres are responsible for less H2O2 production. Though the Fe‐Nx moieties and Fe3C/Fe particles encapsulated N‐doped carbon, both are active centres for ORR, however, Fe‐Nx sites are more active than others for peroxide reduction reaction. These perceptions suggest rational methodologies for more active and consequently further durable Fe‐N‐C catalysts. [ABSTRACT FROM AUTHOR]

Abstract Presently, the practical application of Fe/N/C catalysts as replacements of Pt for oxygen reduction reaction is still limited by insufficient activity. Herein, we demonstrate a novel design for such catalyst. On one hand, the obtained Fe/N/C SiO 2 ZnCl 2 catalyst owns high densities of well-exposed active-sites derived from three-dimensional well-balanced macro-, meso-, and microporous structures constructed by adopting ZnCl 2 salt and SiO 2 microspheres as combined templates. On the other hand, simulation reveals that a high loading of catalyst in cathode catalyst layer would not benefit cell performance and fast oxygen reduction reaction process occurs only inside a limited thickness of catalyst layer. Particularly, the Fe/N/C SiO 2 ZnCl 2 shows a maximal output power density as high as 480 mW cm−2 at an ultra-low loading of 0.5 mg cm−2. This study firstly exhibits that development of catalysts with high-density active sites and construct of ultra-thin catalyst layer are of great significance for improving the performance of fuel cell. Highlights • Fe/N/C SiO 2 ZnCl 2 was synthesized using ZnCl 2 templating and silica templating. • Fe/N/C SiO 2 ZnCl 2 shows superior ORR activity in both alkaline and acidic medium. • The P max of Fe/N/C SiO 2 ZnCl 2 is as high as 480 mW cm−2 at a 0.5 mg cm−2 loading. [ABSTRACT FROM AUTHOR]

• Cross-linked multi-atom Pt anchored on a Zn, Fe and N co-doped carbon catalyst is prepared. • The MAC-Pt/ZnFe -N- C catalyst shows 100 % exposure of surface Pt atoms. • The MAC-Pt/ZnFe -N- C catalyst exhibits remarkable catalytic activity and stability for the oxygen reduction reaction. • A fuel cell assembled by this catalyst delivers a maximal power output of 1.02 W cm−2 at 0.035 mg Pt cm−2 at the cathode. Although single-atom catalysts (SACs) are drawing wide attention because they offer properties that differ from those of conventional nanoparticle (NP)-based catalysts, the lack of neighboring metal centers to cooperate in catalysis limits their actual application in many important chemical processes. Here, we report the synthesis of multi-atom Pt catalyst that consists of cross-linked Pt-Pt metal centers stabilized by atomically dispersed ZnFe -N- C support through Pt-N bonds. XAFS analysis reveals that each Pt atom in the multi-atom Pt catalyst coordinates with ∼2.6 N atoms and ∼4.3 Pt atoms. This novel catalyst combines the merits of SACs and NPs, resulting in 100 % exposure of surface Pt atoms and excellent stability and fuel cell performance. With an ultralow Pt loading of 0.035 mg cm−2 at the cathode, the fuel cell delivers a 1.02 W cm-2 maximal power output. DFT calculations revealed that the strongly coupled Pt-N bond is critical for stabilizing the cross-linked Pt. [ABSTRACT FROM AUTHOR]