Electronic Tuning of Core-Shell CoNi Nanoalloy/N-Doped Few-Layer Graphene for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries

Nitrogen-Doped Carbon Cubosomes as an Efficient Electrocatalyst with High Accessibility of Internal Active Sites

Porous carbon particles (PCPs) present considerable potential for applications across a wide range of fields, particularly within the realms of energy and catalysis. The control of their overall morphologies and pore structures has remained a big challenge. Here, using metal-organic frameworks (MOFs) as the precursor and polymer cubosomes (PCs) as the template, nitrogen-doped carbon cubosomes (SP-NCs) with a single primitive bicontinuous architecture are prepared. SP-NCs inherit the high porosity of MOFs, generating a high specific surface area of 825 m2 g-1 and uniformly distributed active sites with a 5.9 at % nitrogen content. Thanks to the presence of three-dimensional continuous mesochannels that enable much higher accessibility of internal active sites over those of their porous counterparts' lack of continuous channels, SP-NCs exhibit superior electrocatalytic performance for oxygen reduction reaction with a half-wave potential of 0.87 V, situating them in the leading level of the reported carbon electrocatalysts. Serving as an air cathode catalyst of the Zn-air battery, SP-NCs exhibit excellent performance, outperforming the commercial Pt/C catalysts.

Sodium Tartrate-Assisted Synthesis of High-Purity NiFe2O4 Nano-Microrods Supported by Porous Ketjenblack Carbon for Efficient Alkaline Oxygen Evolution

Herein, a simple two-step synthetic method was developed for the synthesis of NiFe₂O₄ nano-microrods supported on Ketjenblack carbon (NiFe₂O₄/KB). A sodium tartrate-assisted hydrothermal method was employed for the synthesis of a NiFe-MOF/KB precursor, which was then pyrolyzed under N₂ at 500 °C to yield NiFe₂O₄/KB. Benefiting from the presence of high-valence Ni³⁺ and Fe³⁺, high conductivity, and a large electrochemically active surface area, NiFe₂O₄/KB delivered outstanding OER electrocatalytic performance under alkaline conditions, including a very low overpotential of 258 mV (vs RHE) at 10 mA cm^-2, a small Tafel slope of 43.01 mV dec^-1, and excellent durability in 1.0 M KOH. Density functional theory calculations verified the superior alkaline OER electrocatalytic activity of NiFe₂O₄ to IrO₂. While both catalysts possessed a similar metallic ground state, NiFe₂O₄ offered a lower energy barrier in the rate-determining OER step (*OOH → O₂) compared to IrO₂, resulting in faster OER kinetics.

Nitrogen-doped porous carbon encapsulates multivalent cobalt-nickel as oxygen reduction reaction catalyst for zinc-air battery

In this study, we present a bimetallic ion coexistence encapsulation strategy employing hexadecyl trimethyl ammonium bromide (CTAB) as a mediator to anchor cobalt-nickel (CoNi) bimetals in nitrogen-doped porous carbon cubic nanoboxes (CoNi@NC). The fully encapsulated and uniformly dispersed CoNi nanoparticles with the improved density of active sites help to accelerate the oxygen reduction reaction (ORR) kinetics and provide an efficient charge/mass transport environment. Zinc-air battery (ZAB) equipped CoNi@NC as cathode exhibits an open-circuit voltage of 1.45 V, a specific capacity of 870.0 mAh g^-1, and a power density of 168.8 mW cm^-2. Moreover, the two CoNi@NC-based ZABs in series display a stable discharge specific capacity of 783.0 mAh g^-1, as well as a large peak power density of 387.9 mW cm^-2. This work provides an effective way to tune the dispersion of nanoparticles to boost active sites in nitrogen-doped carbon structure, and enhance the ORR activity of bimetallic catalysts.

Metal-organic framework-derived advanced oxygen electrocatalysts as air-cathodes for Zn-air batteries: recent trends and future perspectives

Electrochemical energy storage devices with stable performance, high power output, and energy density are urgently needed to meet the global energy demand. Among the different electrochemical energy storage devices, batteries have become the most promising energy technologies and ranked as a highly investigated research subject. Recently, metal-air batteries especially Zn-air batteries (ZABs) have attracted enormous scientific interest in the electrochemical community due to their ease of operation, sustainability, environmental friendliness, and high efficiency. The oxygen electrocatalytic reactions [oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)] are the two fundamental reactions for the development of ZABs. Noble metal-based electrocatalysts are widely considered as the benchmark for oxygen electrocatalysis, but their practical application in rechargeable ZAB is hindered due to several shortcomings. Thus, to replace noble metal-based catalysts, a wide range of transition-metal-based materials and heteroatom-doped metal-free carbon materials has been extensively investigated as oxygen electrocatalysts for ZABs. Recently, metal-organic frameworks (MOFs) with unique structural flexibility and uniformly dispersed active sites have become attractive precursors for the synthesis of a large variety of advanced functional materials. Herein, we summarize the recent progress of MOF-derived oxygen electrocatalysts (MOF-derived carbon nanomaterials, MOF-derived alloys/nanoparticles, and MOF-derived single-atom electrocatalysts) for ZABs. Specifically, we highlight MOF-derived single-atom electrocatalysts owing to the wide exploration of these emerging materials in electrocatalysis. The influence of the active sites, structural/compositional design, and porosity of MOF-derived advanced materials on the oxygen electrocatalytic performances is also discussed. Finally, the existing challenges and prospects of MOF-derived electrocatalysts in ZABs are briefly highlighted.

Nanostructure Engineering and Electronic Modulation of a PtNi Alloy Catalyst for Enhanced Oxygen Reduction Electrocatalysis in Zinc-Air Batteries

PtNi nanoalloys have demonstrated electrocatalysis superior to that of benchmark Pt/C catalysts for the oxygen reduction reaction (ORR), yet the underlying mechanisms remain underexplored. Herein, a PtNi/NC catalyst comprising PtNi nanoparticles (∼5.2 nm in size) dispersed on N-doped carbon frameworks was prepared using a simple pyrolysis strategy. Benefiting from the individual components and a hierarchical structure, the PtNi/NC catalyst exhibited outstanding ORR activity and stability (E_1/2 = 0.82 V vs RHE and 8 mV negative shift after 20000 cycles), outperforming a commercial 20 wt % Pt/C catalyst (E_1/2 = 0.81 V and 32 mV negative shift). A prototype zinc-air battery constructed using PtNi/NC as the air electrode catalyst achieved highly enhanced electrochemical performance, outperforming a battery constructed using Pt/C as the ORR catalyst. Density functional theory calculations revealed that the improved ORR activity of the PtNi nanoalloys originated from charge redistribution with a suitable metal d-band center to promote the formation of the ORR intermediates.