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Research Article Issue
In situ generated layered NiFe-LDH/MOF heterostructure nanosheet arrays with abundant defects for efficient alkaline and seawater oxidation
Nano Research 2023, 16 (7): 8945-8952
Published: 26 April 2023
Downloads:109

As the main limiting step of overall water splitting, oxygen evolution reaction (OER) is urgent to be enhanced by developing efficient catalysts to promote the process of electrolytic water. Based on theoretical analysis, the Ni-metal-organic framework (Ni-MOF) and NiFe-layered double hydroxide (NiFe-LDH) (NiFe-LDH/MOF) heterostructure can optimize the energy barrier of the OER process and decrease the adsorption energy of oxygen-containing intermediates, effectively accelerating the OER kinetics. Accordingly, layered NiFe-LDH/MOF heterostructures are in situ constructed through a facile two-step reaction process, with substantial oxygen defects and lattice defects that further improve the catalytic performance. As a result, only 208 and 275 mV OER overpotentials are needed for NiFe-LDH/MOF to drive the current densities of 20 and 100 mA·cm−2 in 1 M KOH solutions, and even maintain catalytic stability of 100 h at 20 mA·cm−2. When applied to seawater oxidation, only 235 and 307 mV OER overpotentials are required to achieve the current densities of 20 and 100 mA·cm−2, respectively, with almost no attenuation for 100 h stability test at 20 mA·cm−2, all better than commercial RuO2. This work provides the theoretical and experimental basis and a new idea for efficiently driving fresh water and seawater cracking by heterostructure and defect coupling design toward catalysts.

Research Article Issue
Atomically dispersed dual Fe centers on nitrogen-doped bamboo-like carbon nanotubes for efficient oxygen reduction
Nano Research 2022, 15 (3): 1966-1972
Published: 18 September 2021
Downloads:39

Interfacial atomic configuration between dual-metal active species and nitrogen-carbon substrates is of great importance for improving the intrinsic activity of catalysts toward oxygen reduction reaction (ORR). Thus, from the atomic-scale engineering we develop a high intrinsic activity ORR catalyst in terms of incorporating atomically dispersed dual Fe centers (single Fe atoms and ultra-small Fe atomic clusters) into bamboo-like N-doped carbon nanotubes. Benefiting from atomically dispersed dual-Fe centers on the atomic interface of Fe-Nx/carbon nanotubes, the fabricated dual Fe centers catalyst exhibits an extremely high ORR activity (Eonset = 1.006 V; E1/2 = 0.90 V), beyond state-of-the-art Pt/C. Remarkably, this catalyst also shows a superior kinetic current density of 19.690 mA·cm−2, which is 7 times that of state-of-the-art Pt/C. Additionally, based on the excellent catalyst, the primary Zn-air battery reveals a high power density up to 137 mW·cm−2 and sufficient potential cycling stability (at least 25 h). Undoubtedly, given the unique structure–activity relationship of dual-Fe active species and metal-nitrogen-carbon substrates, the catalyst will show great prospects in highly efficient electrochemical energy conversion devices.

Research Article Issue
Tuning the dual-active sites of ZIF-67 derived porous nanomaterials for boosting oxygen catalysis and rechargeable Zn-air batteries
Nano Research 2021, 14 (7): 2353-2362
Published: 05 July 2021
Downloads:49

The rational control of the active site of metal-organic frameworks (MOFs) derived nanomaterials is essential to build efficient bifunctional oxygen reduction/evolution reaction (ORR/OER) catalysts. Accordingly, through designing and constructing a Co3O4-Co heterostructure embedded in Co, N co-doped carbon polyhedra derived (Co3O4-Co@NC) from the in-situ compositions of ZIF-67 and cobalt nanocrystals synthesized by the strategy of in-situ NaBH4 reduction, the dual-active site (Co3O4-Co and Co-Nx) is synchronously realized in a MOFs derived nanomaterials. The formed Co3O4-Co@NC shows excellent bifunctional electrocatalytic activity with ultra-small potential gap (ΔE = Ej=10 (OER) - E1/2 (ORR)) of 0.72 V, which surpasses the commercial Pt/C and RuO2 catalysts. The theory calculation results reveal that the excellent bifunctional electrocatalytic activity can be attributed to the charge redistribution of Co of Co-Nx induced by the synergistic effects of well-tuned active sites of Co3O4-Co nanoparticle and Co-Nx, thus optimizing the rate-determining step of the desorption of O2* intermediate in ORR and OH* intermediate in OER. The rechargeable Zn-air batteries with our bifunctional catalysts exhibit superior performance as well as high cycling stability. This simple-effective optimization strategy offers prospects for tuning the active site of MOF derived bifunctional catalyst in electrochemical energy devices.

Research Article Issue
Defects enriched hollow porous Co-N-doped carbons embedded with ultrafine CoFe/Co nanoparticles as bifunctional oxygen electrocatalyst for rechargeable flexible solid zinc-air batteries
Nano Research 2021, 14 (3): 868-878
Published: 01 March 2021
Downloads:85

The construction and design of highly efficient and inexpensive bifunctional oxygen electrocatalysts substitute for noble-metal- based catalysts is highly desirable for the development of rechargeable Zn-air battery (ZAB). In this work, a bifunctional oxygen electrocatalysts of based on ultrafine CoFe alloy (4-5 nm) dispersed in defects enriched hollow porous Co-N-doped carbons, made by annealing SiO2 coated zeolitic imidazolate framework-67 (ZIF-67) encapsulated Fe ions. The hollow porous structure not only exposed the active sites inside ZIF-67, but also provided efficient charge and mass transfer. The strong synergetic coupling among high-density CoFe alloys and Co-Nx sites in Co, N-doped carbon species ensures high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. First-principles simulations reveal that the synergistic promotion effect between CoFe alloy and Co-N site effectively reduced the formation energy of from O* to OH*. The optimized CoFe-Co@PNC exhibits outstanding electrocatalytic stability and activity with the overpotential of only 320 mV for OER at 10 mA·cm−2 and the half-wave potential of 0.887 V for ORR, outperforming that of most recent reported bifunctional electrocatalysts. A rechargeable ZAB constructed with CoFe-Co@PNC as the air cathode displays long-term cyclability for over 200 h and high power density (152.8 mW·cm−2). Flexible solid-state ZAB with our CoFe-Co@PNC as the air cathode possesses a high open circuit potential (OCP) up to 1.46 V as well as good bending flexibility. This universal structure design provides an attractive and instructive model for the application of nanomaterials derived from MOF in the field of sustainable flexible energy applications device.

Research Article Issue
ZIF-8/LiFePO4 derived Fe-N-P Co-doped carbon nanotube encapsulated Fe2P nanoparticles for efficient oxygen reduction and Zn-air batteries
Nano Research 2020, 13 (3): 818-823
Published: 26 February 2020
Downloads:25

Iron-based oxygen reduction reaction (ORR) catalysts have been the focus of research, and iron sources play an important role for the preparation of efficient ORR catalysts. Here, we successfully use LiFePO4 as ideal sources of Fe and P to construct the heteroatom doped Fe-based carbon materials. The obtained Fe-N-P co-doped coral-like carbon nanotube arrays encapsulated Fe2P catalyst (C-ZIF/LFP) shows very high half-wave potential of 0.88 V in alkaline electrolytes toward ORR, superior to Pt/C (0.85 V), and also presents a high half-wave potential of 0.74 V in acidic electrolytes, comparable to Pt/C (0.8 V). When further applied into a home-made Zn-air battery as cathode, a peak power density of 140 mW·cm-2 is reached, exceeds commercial Pt/C (110 mW·cm-2). Besides, it also presents exceptional durability and methanol resistance compared with Pt/C. Noticeably, the preparation method of such a high-performance catalyst is simple and easy to optimize, suitable for the large-scale production. What’s more, it opens up a more sustainable development scenario to reduce the hazardous wastes such as LiFePO4 by directly using them for preparing high-performance ORR catalysts.

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