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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]

Herein, we present a high-temperature self-assembly strategy that directly allows the transformation of adsorbed Pt(NH3)42+ and Fe3+ sources into structurally ordered face-centered tetragonal (fct)-PtFe alloy NPs (2.6 ± 0.2 nm) by integrating reduction and phase transformation. The small-size and ordered atomic arrangement of the fct-PtFe alloy NPs, together with their robust NC protective shell, make these NPs exhibit excellent catalytic activity and stability for the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

A high-performance 3D hierarchical porous metal-free N-doped carbon catalyst toward the oxygen reduction reaction (ORR) in acidic medium was successfully synthesized by employing ZnO as a mesoporous template and NaCl as both a macroporous template and a structure protective agent. The resultant improved active site density and diffusion efficiency lead to a superior ORR activity with a half-wave potential high up to 0.755 V in 0.1 M HClO4. [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]

• Solid Pt NPs can be converted into multi-hollow PtCo alloys by annealing a NaCl-sealed Pt/C@polydopamine-Co2+ system. • NaCl act as a sealed nanoreactor to provide key conditions for nanoscale Kirkendall migration between Pt and Co atoms. • Rigid NaCl can prevent fast PDA loss and serious NPs sintering, ensuring highly active specific surface area of products. • The water-removability of NaCl makes the present synthesis a facile and green method. • The obtained h-PtCo@NC affords much higher specific and mass activity for ORR than commercial Pt/C. A thermal activated Kirkendall mitigation between Pt and Co atoms can happen within a NaCl-sealed Pt/C@polydopamine-Co2+ system, leading to form multi-hollow PtCo NPs without serious sintering. [Display omitted] Hollow-structuring of Pt-based nanoparticles (NPs) is among the most effective strategies for reducing Pt utilization whilst maintaining good performance for oxygen reduction reaction (ORR). This work presents a NaCl-sealed annealing strategy to directly convert solid Pt NPs into multi-hollow PtCo alloys with a Pt-rich surface. By annealing a NaCl-sealed Pt/C@polydopamine-Co2+ system, the essential conditions for forming hollow Pt alloys can be easily equipped and a thermal activated nanoscale Kirkendall mitigation between Pt and Co atoms can consequently let inner solid Pt accomplish alloying and hollow-structuring. Serious sintering of NPs during thermal annealing can be efficiently avoided owing to the protection of outer rigid NaCl. The whole procedures is template-free and the final catalysts can be easily released from NaCl by just water washing, making the present synthesis a facile, green and versatile method. The final obtained multi-hollow PtCo NPs featured with a nitrogen-doped carbon coating afford much enhanced ORR activity and stability than benchmark commercial Pt/C. [ABSTRACT FROM AUTHOR]

Developing efficient, stable and non-precious metal alternatives to platinum-based catalysts for oxygen reduction reaction (ORR) is significant for many energy conversion devices. Herein, we report a phytic acid-assisted self-templating strategy to fabricate N–P–Fe-tridoped carbon with a hierarchical porosity. The resultant unique structures and well-designed heteroatoms-doping condition impart final catalysts with enhanced mass transfer ability and abundant available active-sites, ensuring high performance in catalyzing ORR. Impressively, the half wave potential of the optimal catalyst is 0.926 V (vs. RHE), which is 40 mV higher than the state-of-art platinum-based catalyst and better than most reported ORR catalysts. Significantly, when applied to a primary Zn–O 2 battery, our catalyst comprehensively outperforms the commercial Pt/C catalyst whether on power density or specific capacity. • The P-Fe-NC catalyst was fabricated by a self-templating strategy. • Doping condition was well-designed through a facile coordination strategy. • Superior ORR and Zn–O 2 battery performance than precious metal catalysts. [ABSTRACT FROM AUTHOR]

Metal-nitrogen doped carbon catalysts (M-N/C) with abundantly accessible M-N x sites, particularly single metal atom M-N/C (SAM-N/C), have been developed as a substitute for expensive Pt-based catalysts. These catalysts are used to increase the efficiency of otherwise sluggish oxygen reduction reactions (ORR) and hydrogen evolution reactions (HER). However, although the agglomerated metal nanoparticles are usually easy to form, they are very difficult to remove due to the protective surface-coating carbon layers, a factor that significantly hampers SAM-N/C fabrication. Herein, we report a one-step pyrolysis approach to successfully fabricate single cobalt atom Co-N/C (SACo-N/C) by using a Co2+-SCN- coordination compound as the metal precursor. Thanks to the decomposition of Co2+-SCN- compound at lower temperature than that of carbon layer deposition, Co-rich particles grow up to larger ones before carbon layers formation. Even though encapsulated by the carbon layers, it is difficult for the large Co-rich particle to be completely sealed. And thus, it makes the Co atoms possible to escape from incomplete carbon layer, to coordinate with nitrogen atoms, and to form SACo-N/C catalysts. This SACo-N/C exhibits excellent performances for both ORR (half-wave potential of 0.878 V) and HER (overpotential at 10 mA/cm2 of 178 mV), and is thus a potential replacement for Pt-based catalysts. When SACo-N/C is integrated into a Zn-O 2 battery, battery with high open-circuit voltage (1.536 V) has high peak power density (266 mW/cm2) and large gravimetric energy density (755 mA h/g Zn) at current densities of 100 mA/cm2. Thus, we believe that this strategy may offer a new direction for the effective generation of SAM-N/C catalysts. [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]