Design and Facile Synthesis of Highly Efficient and Durable Bifunctional Oxygen Electrocatalyst Fe-Nx/C Nanocages for Rechargeable Zinc-Air Batteries

Hetero-Diatomic CoN4-NiN4 Site Pairs with Long-Range Coupling as Efficient Bifunctional Catalyst for Rechargeable Zn-Air Batteries

In this study, Co/Ni-NC catalyst with hetero-diatomic Co/Ni active sites dispersed on nitrogen-doped carbon matrix is synthesized via the controlled pyrolysis of ZIF-8 containing Co2+ and Ni2+ compounds. Experimental characterizations and theoretical calculations reveal that Co and Ni are atomically and uniformly dispersed in pairs of CoN4-NiN4 with an intersite distance ≈0.41 nm, and there is long-range d-d coupling between Co and Ni with more electron delocalization for higher bifunctional activity. Besides, the in situ grown carbon nanotubes at the edges of the catalyst particles allow high electronic conductivity for electrocatalysis process. Electrochemical evaluations demonstrate the superior ORR and OER bifunctionality of Co/Ni-NC catalyst with a narrow potential gap of only 0.691 V and long-term durability, significantly prevailing over the single-atom Co-NC and Ni-NC catalysts and the benchmark Pt/C and RuO2 catalysts. Co/Ni-NC catalyzed Zn-air batteries achieve a high specific capacity of 771 mAh g-1 and a long continuous operation period up to 340 h with a small voltage gap of ≈0.65 V, also much superior to Pt/C-RuO2.

Immobilization of ferrocene and its derivatives within metal-organic frameworks with high loadings toward efficient oxygen evolution reaction

The use of an appropriate preparation route is the key to immobilize active molecules into a host matrix with high loadings and stability. Herein, we demonstrate a simple and general strategy to immobilize ferrocene and its derivatives into ZIF-8 with high loadings of up to 4.3% Fe content. The unique host pore structure allows for the stabilization of guest molecules and effectively prevents their leaching. As a result, the obtained electrocatalysts exhibit competitive oxygen evolution reaction (OER) catalytic performance. Optimized Fc-CHO/ZIF-8 requires only a low overpotential of 238 mV to achieve 10 mA cm-2, along with a relatively small Tafel slope of 44.4 mV dec-1. This performance is superior to that of commercial IrO2, suggesting its potential application in electrochemical energy conversion.

Bimetallic-Coordinated Covalent Triazine Framework-Derived FeNi Alloy Nanoparticle-Decorated Coral-Like Nanocarbons for Oxygen Electrocatalysis

It is highly desirable to fabricate transition bimetallic alloy-embedded porous nanocarbons with a unique nanoarchitecture for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in rechargeable zinc-air batteries. In this work, we introduce a template-assisted in situ alloying synthesis of FeNi alloy nanoparticle-decorated coral-like nanocarbons (FeNi-CNCs) as efficient OER/ORR dual-functional electrocatalysts. The present materials are produced through polycondensation of a covalent triazine framework (CTF), the coordination of Ni and Fe ions, and sequential pyrolytic treatment. Through the pyrolysis process, the nanolamellar FeNi-CTF precursors can be facilely converted into FeNi alloy nanoparticle-decorated nanocarbons. These nanocarbons possess a distinctive three-dimensional (3D) coral-like nanostructure, which is favorable for the transport of oxygen and the diffusion of electrolyte. As a result, FeNi-CNC-800 with the highest efficiency exhibited remarkable electrocatalytic performance and great durability. Additionally, it also can be assembled into rechargeable zinc-air batteries that can be assembled in both liquid and solid forms, offering a superior peak power density, large specific capacity, and outstanding reusability during charging/discharging cycles (e.g., 5160 charging-and-discharging cycles at 10 mA cm-2 for the liquid forms). These traits make it a highly promising option in the burgeoning field of wearable energy conversion.

Fe-N-C catalysts decorated with oxygen vacancies-rich CeOx to increase oxygen reduction performance for Zn-air batteries

Platinum group metal (PGM)-free catalysts represented by nitrogen and iron co-doped carbon (Fe-N-C) catalysts are desirable and critical for metal-air batteries, but challenges still exist in performance and stability. Here, cerium oxides (CeO_x) are incorporated into a two-dimensional Fe-N-C catalyst (FeNC-Ce-950) via a host-guest strategy. The Ce⁴⁺/Ce³⁺ redox system creates a large number of oxygen vacancies for rapid O₂ adsorption to accelerate the kinetics of oxygen reduction reaction (ORR). Consequently, the as-synthesized FeNC-Ce-950 catalyst exhibits a half-wave potential (E_1/2) of 0.921 V and negligible decay (<2 mV for ΔE_1/2) after 5,000 accelerated durability cycles, significantly outperforming most of ORR catalysts reported in recent years and precious metal counterparts. When applied in a zinc-air battery, it demonstrates a peak power density of 175 mW cm^-2 and a specific capacity of 757 mAh g_Zn^-1. This study also provides a reference for the exploration of Fe-N-C catalysts decorated with variable valence metal oxides.

Nanoreactor of Fe, N Co-Doped Hollow Carbon Spheres for Oxygen Reduction Catalysis

A simple template strategy was applied to prepare a Fe, N co-doped hollow carbon (Fe-NHC) nanoreactor for the oxygen reduction reaction (ORR) by coating Fe nanoparticles (Fe-NPs) with polydopamine (PDA), followed by high temperature pyrolysis and acid-leaching. With this method, Fe-NPs were used as both the template and the metal precursor, so that the nanoreactors can preserve the original spherical morphology and embed Fe single atoms on the inner walls. The carbonized PDA contained abundant N content, offering an ideal coordination environment for Fe atoms. By regulating the mass ratio of Fe-NPs and PDA, an optimal sample with a carbon layer thickness of 12 nm (Fe-NHC-3) was obtained. The hollow spherical structure of the nanoreactors and the atomically dispersed Fe were verified by various physical characterizations. As a result, Fe-NHC-3 performed well in ORR tests under alkaline conditions, with high catalytic activity, durability, and methanol resistance, demonstrating that the as-fabricated materials have the potential to be applied in the cathodic catalysis of fuel cells.

Fe, Ni-modified ZIF-8 as a tensive precursor to derive N-doped carbon as Na and Li-ion batteries anodes

Carbon materials derived from metal-organic frameworks have attracted increasing attention as anodes for energy storage. In this study, Fe, Ni-doped ZIF-8 is carbonized at high temperature to obtain bimetallic Fe and Ni modified tension -relaxed carbon (FeNi@trC). Fe and Ni have opposite structural modification effects when the metal ions are doped into the ZIF-8 dodecahedron. The obtained carbon material maintains the regular dodecahedron morphology, which means the relaxation of tension and strong thermal stability during annealing. Moreover, the presence of nickel enhances the carbonization degree and electrochemical stability of FeNi@trC, while the calcination of the tensive ZIF-8 precursor offers more defect sites. The discharge capacities of FeNi@trC materials are stable at 182.9 mAh·g^-1and 567.9 mAh·g^-1for sodium-ion batterie (SIB) and lithium-ion batterie (LIB) at 0.05 A·g^-1. Compared with the current density of 0.05 A·g^-1, the discharge capacity of SIB and LIB attenuates by 29.4% and 55.9% at 1 A·g^-1, respectively, and the FeNi@trC shows good performance stability in the following cycles.