Efficient Bifunctional Oxygen Research Articles

Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zn−air Batteries Derived from Ni‐modified Prussian Blue

AbstractThe rational design and exploration of efficient, low‐cost and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the development of rechargeable metal−air batteries. Here, we report a novel approach to in‐situ synthesize Fe0.64Ni0.36 nanoalloy encapsulated in nitrogen‐doped porous carbon nanotubes (FeNi@N−CNTs) as bifunctional electrocatalyst derived from Ni‐modified Prussian blue, on which the ORR/OER can be promoted by the N−CNTs surface due to the electron modulation caused by electron transfer from the inner FeNi nanoalloy to the N−CNTs surface. The abundant wide‐size range of mesopores in N−CNTs can offer rapid mass transport channels to facilitate the catalytic reactions. In addition, the encapsulation structure endows the outer N−CNTs acting as a “shield” to prevent the inner FeNi nanoalloy from corrosion in strong basic medium. Thanks to the synergistic effect between the N−CNTs and FeNi nanoalloy, the obtained FeNi@N−CNTs exhibits excellent bifunctional oxygen catalytic activity together with outstanding performance and cycling durability in rechargeable Zn−air battery. This work will open new avenues for the development of advanced bifunctional electrocatalysts for other metal−air batteries.

MnF2 Surface Modulated Hollow Carbon Nanorods on Porous Carbon Nanofibers as Efficient Bi-Functional Oxygen Catalysis for Rechargeable Zinc-Air Batteries.

Developing highly efficient bi-functional noble-metal-free oxygen electrocatalysts with low-cost and scalable synthesis approach is challenging for zinc-air batteries (ZABs). Due to the flexible valence state of manganese, MnF2 is expected to provide efficient OER. However, its insulating properties may inhibit its OER process to a certain degree. Herein, during the process of converting the manganese source in the precursor of porous carbon nanofibers (PCNFs) to manganese fluoride, the manganese source is changed to manganese acetate, which allows PCNFs to grow a large number of hollow carbon nanorods (HCNRs). Meanwhile, manganese fluoride will transform from the aggregation state into uniformly dispersed MnF2 nanodots, thereby achieving highly efficient OER catalytic activity. Furthermore, the intrinsic ORR catalytic activity of the HCNRs/MnF2@PCNFs can be enhanced due to the charge modulation effect of MnF2 nanodots inside HCNR. In addition, the HCNRs stretched toward the liquid electrolyte can increase the capture capacity of dissolved oxygen and protect the inner MnF2, thereby enhancing the stability of HCNRs/MnF2@PCNFs for the oxygen electrocatalytic process. MnF2 surface-modulated HCNRs can strongly enhance ORR activity, and the uniformly dispersed MnF2 can also provide higher OER activity. Thus, the prepared HCNRs/MnF2@PCNFs obtain efficient bifunctional oxygen catalytic ability and high-performance rechargeable ZABs.

Directly assembling initial metal–organic framework and covalent organic polymer toward bifunctional oxygen electrocatalysts for Zn-air flow battery

Developing highly efficient bifunctional oxygen electrocatalysts is important but still remains a challenge for Zn-air flow battery. Metal-organic frameworks (MOFs) and covalent organic polymers (COPs) materials have emerged as promising alternatives to the benchmark precious metal electrocatalysts due to their designable and controllable structures at the atomic level. However, their catalytic performances are limited by the conductivity and catalytic activity using initial materials. Moreover, these materials are generally developed either as single oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts. Herein, we utilize the π-π stacking effect to directly assemble initial nanosheet FeNi-MOF and iron phthalocyanine rich COP hybrid materials toward the highly efficient bifunctional electrocatalysts via pyrolysis-free strategy. The carbon black is added to the composite as support to limit the stacking of composites and increase the conductivity. The obtained catalyst, named as NSFeNi@COPFe-C, exhibits superior catalytic performance with an ORR onset potential of 0.99 V (vs. reversible hydrogen electrode: RHE), half-wave potential of 0.9 V (vs. RHE), and the OER potential of 1.65 V at 10 mA cm−2 in alkaline electrolyte. The assembled zinc-air flow battery with NSFeNi@COPFe-C as the bifunctional oxygen electrocatalyst shows a discharge power up to 115 mW cm−2 and a long-term stability.

Co9S8-FeCoS2 Two-Phase Nanoparticles Anchored in N, S Co-Doped Honeycomb Carbon Spheres as Highly Efficient Bifunctional Oxygen Catalyst

Transition metal sulfides (TMS) are considered as candidate oxygen redox catalysts (OER/ORR) due to their high catalytic activity and reversible redox performance. The OER/ORR performance for TMS can be further improved through the multi-doped electrochemical active sites provided by the dual-metallic (Co,Fe) and dual-nonmetallic species (N,S). Herein, a Co9S8-FeCoS2 two-phase nanoparticle anchored in N, S co-doped honeycomb carbon sphere ((Co,Fe)S@N,S-HCS) is synthesized by a multistep process template method. It has been found that the (Co,Fe)S@N,S-HCS possesses a mesoporous structure with a highly graphitized carbon along with the key OER active site of Co9S8 and the major ORR active center of FeCoS2. Also, the synergistic effect of Co9S8-FeCoS2 two-phase nanoparticles can further enhance the activity of OER and ORR. The as-prepared (Co,Fe)S@N,S-HCS exhibits excellent bifunctional activity in alkaline media, with an OER overpotential as low as 310 mV at 10 mA cm−2 and good stability, which exceeds (Fe)S@N,S-HCS, (Co)S@N,S-HCS and the noble metal RuO2. Besides, the ORR activity exhibits a half-wave potential of 0.84 V, which exceed the other two single component sulfides and close to the commercial Pt/C. Therefore, this work provides a significant approach to prepare highly efficient and stable dual-TMS heteroatom modified carbon-based OER/ORR bifunctional oxygen catalyst.

Pomegranate-like structured FeNi-nanodots@FeNi LDH composite as a high performance bifunctional catalyst for oxygen electrocatalytic reactions in zinc-air batteries

An efficient bifunctional oxygen catalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for the widespread application of rechargeable zinc-air batteries (ZABs) with high energy density and low-cost electrically. Herein, we report an effective pomegranate-like structured FeNi–N–C@FeNi LDH catalyst using Zeolitic Imidazolate Framework (ZIF-8) as precursor via pyrolysis and hydrothermal reactions. The as-prepared FeNi–N–C@FeNi LDH composite, consisting of FeNi-nanodots embedded in carbon matrix and metal layered double hydroxides (LDHs) as outer layer, exhibits preferable performance toward ORR (E1/2 = 0.890V) and OER (Ej = 10 = 1.535V) compared to precious metal-based catalysts. Moreover, when being applied in ZABs, the FeNi–N–C@FeNi LDH composite displays a high open-circuit voltage of 1.497 V and a durability of up to 100 h, demonstrating its great possibility in practical application.

Densely populated trimetallic single-atoms for durable low-temperature flexible zinc-air batteries

The fundamental challenge of trimetallic single-atoms catalysts stems from the difficulty in supporting the coexistence of different metals with their unique physicochemical features. Here, the trimetallic single-atoms electrocatalyst is constructed as a model system to explore electrocatalytic ORR/OER. The tri-metal (Fe, Co, and Ni) single-atoms loaded on nitrogen-carbon framework exhibits superior ORR/OER kinetics (E1/2 = 0.927 V, Ej=10 = 1.56 V). The flexible zinc-air batteries generate excellent power density and durability (62 mW cm−2 and 200 h at −15 °C, 291.2 mW cm−2 and 250 h at room temperature). Density functional calculations confirm that the trimetallic synergy effect outperform mono- and bimetallic effects, yielding adsorption strength close to 0. This paper describes an intuitionistic descriptor where ΔEOH* displays a volcano relationship with ORR overpotential, and establishes a generalized strategy for efficient bifunctional oxygen electrocatalyst while comprehensively understanding the structure-mechanism-activity relationship.

Interface of Nickel Sulfides Optimizing Surface Reconstruction toward Efficient Bifunctional Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries

Interface of Nickel Sulfides Optimizing Surface Reconstruction toward Efficient Bifunctional Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries

Nickel Phosphonate MOF Derived N-Doped Carbon-Coated Phosphorus-Vacancies-Rich Ni2 P Particles as Efficient Bifunctional Oxygen Electrocatalyst.

The design of non-noble metal bifunctional electrocatalysts with outstanding performance and remarkable stability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most essential issues to the realization of rechargeable zinc-air battery, and transition metal phosphides (TMPs) have emerged as robust candidates for oxygen electrocatalysts. Herein, N-doped carbon-coated phosphorus-vacancies-rich Ni2 P particles (Vp -Ni2 P@NC) is proposed via simple carbonization and following Ar plasma treatment from a single nickel phosphonate metal-organic framework (MOF) without extra phosphine and nitrogen sources. The facile and rapid plasma treatment can achieve phosphorus vacancies which could modulate the electronic structure to enhance the inherent active and electrical conductivity. Meanwhile, the pyridine-N and graphitized-N produced during calcination also could provide more active sites and increase the electrical conductivity. The resultant Vp -Ni2 P@NC catalyst shows excellent bifunctional electrocatalytic activity (OER/ORR) based on synergistic effect of introducing P vacancies into Ni2 P and N-doped carbon. Vp -Ni2 P@NC catalyst shows more advantageous ΔE value (0.70 V) compared to Pt/C+RuO2 (0.73 V) and most reported catalysts. Additionally, the zinc-air bbatterie (ZAB) employing Vp -Ni2 P@NC as air cathode shows excellent performance. The maximum power density of 203.48 mW cm-2 , the cycling stability of more than 150 h at 10 mA cm-2 .

Conjugated polymerized bimetallic phthalocyanine based electrocatalyst with Fe−N4/Co−N4 dual-sites synergistic effect for zinc-air battery

The bifunctional oxygen catalyst is essential for zinc-air batteries (ZABs). Here, an efficient bifunctional oxygen catalyst, PPcFeCo/3D-G, is obtained through π-π interaction between the conjugated polymerized iron-cobalt phthalocyanine (PPcFeCo) with excellent thermal stability and three-dimensional graphene (3D-G). The bimetallic synergistic effect of PPcFeCo, verified by DFT (Density functional theory) calculation, and π-π interactions enhances the catalytic activity and durability of the PPcFeCo/3D-G. Regarding electrochemical performance, the PPcFeCo/3D-G with a high electron transfer number (3.98, @0.768 V vs. RHE) has excellent half-wave potential (E1/2 = 0.890 V vs. RHE) and exhibits outstanding reversibility (ΔE = 0.700 V, ΔE = Ej=10 − E1/2). The liquid ZAB (LZAB) employed PPcFeCo/3D-G displays a high power density (222 mW cm−2), a specific capacity (792 mA h g−1), and excellent durability (120 h). This work has guiding significance for the preparation of high-efficiency bifunctional catalysts.

Hollow Co/N-C@NiCo2O4 Spheres as Highly Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

Hollow Co/N-C@NiCo₂O₄ Spheres as Highly Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

FeNiCrCoMn High-Entropy Alloy Nanoparticles Loaded on Carbon Nanotubes as Bifunctional Oxygen Catalysts for Rechargeable Zinc-Air Batteries.

An efficient and stable bifunctional oxygen catalyst is necessary to complete the application of the rechargeable zinc-air battery. Herein, an economical and convenient process was adopted to successfully coat high-entropy alloy Fe12Ni23Cr10Co55-xMnx nanoparticles on carbon nanotubes (CNTs). In 0.1 M KOH solution, with a bifunctional oxygen overpotential (ΔE) of only 0.7 V, the catalyst Fe12Ni23Cr10Co30Mn25/CNT exhibits excellent bifunctional oxygen catalytic performance, exceeding most catalysts reported so far. In addition, the air electrode assembled with this catalyst exhibits high specific capacity (760 mA h g-1) and energy density (865.5 W h kg-1) in a liquid zinc-air battery, with a long-term cycle stability over 256 h. The density functional theory calculation points out that changing the atomic ratio of Co/Mn can change the adsorption energy of the oxygen intermediate (*OOH), which allows the ORR catalytic process to be accelerated in the alkaline environment, thereby increasing the ORR catalytic activity. This article has important implications for the progress of commercially available bifunctional oxygen catalysts and their applications in zinc-air batteries.

The Heterointerface between Fe1/NC and Selenides Boosts Reversible Oxygen Electrocatalysis

AbstractThe rational design and construction of efficient and inexpensive bifunctional oxygen electrocatalysts are highly desirable for the development of rechargeable Zn–air batteries (ZABs). Although single‐atom Fe sites anchored on N‐doped carbon catalysts (Fe1/NC) ensure high oxygen reduction reaction activity, their unitary atomically dispersed active center faces difficult condition in catalyzing oxygen evolution reaction simultaneously. Herein, a composite catalyst containing heterointerface between Fe1/NC and selenides ((Fe,Co)Se2) is constructed. The obtained (Fe,Co)Se2@Fe1/NC exhibits extremely narrow potential gap of 0.616 V and remarkable stability in alkaline media, outperforming the benchmark catalysts (Pt/C+RuO2: 0.720 V). Experimental results and density functional theory calculations reveal that heterointerface between Fe1/NC and (Fe,Co)Se2 accelerates the electron transfer and provides more moderate adsorption sites, which endow (Fe,Co)Se2@Fe1/NC with extremely high bifunctional oxygen catalytic activity. This study not only provides a superior bifunctional catalyst for ZABs, but also enriches the application of single‐atom catalysts in multifunctional energy storage and conversion devices.

Glucose‐hexamethylenetetramine‐derived Co, N Co‐doped Carbon Nanoflowers with Encapsulated Co@Co3O4 as Efficient Bifunctional Oxygen Electrocatalyst for Zinc‐air Batteries

AbstractDeveloping low‐cost, eco‐friendly, and efficient bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important issue for zinc‐air batteries. In this study, HMT‐Co/G‐700 catalyst with nanoflower structure and Co, N co‐doped carbon encapsulated Co@Co3O4 nanoparticles are synthesized from D‐glucose, hexamethylenetetramine (HMT), and Co(NO3)2. HMT is presented as the complex to uniformly disperse Co@Co3O4 nanoparticles, dope nitrogen, and create the nanoflower structure. The nanoflower structure enhances high surface area to expose the active sites. The formation of Co3O4 via mild oxidation of Co surface provides oxygen vacancies to adsorb O2. HMT‐Co/G‐700 catalyst exhibits excellent ORR electrocatalytic property, i. e. high onset potential (1.03 V), high half‐wave potential (0.83 V), low Tafel slope (85.9 mV dec−1), and superior OER activity. Especially, the HMT‐Co/G‐700 catalyst assembled rechargeable zinc‐air battery present high‐power density (111.0 mW cm−2) and long cycle life at 10 mA cm−2 (576 cycles).

Strong interaction and confine effect of manganese oxide-cobalt embedded in self-templated nitrogen-doped carbon enable ultra-stable zinc-air batteries

Developing efficient bifunctional oxygen electrocatalysts with high stability is of great significance for the implementation of rechargeable Zn–air batteries. Herein, MOC-NC bifunctional electrocatalyst with active MnO–Co components embedded in the N-doped carbon sphere is prepared by facile hydrothermal conversion and post-pyrolysis process. The strong interaction between MnO and Co, and confine effect induced by the microstructure endow the fabricated MOC-NC composite with modified electronic configuration, improved conductivity, and significantly reinforced stability. Consequently, the MOC-NC electrocatalyst exhibits good activity and ultrahigh stability for oxygen electrocatalysis. Moreover, when the catalyst was applied to the cathode electrode for the zinc-air battery, it shows excellent performance (specific capacity of 718 ​Wh kgZn−1, power density of 152.3 ​mW ​cm−2) and extraordinary long-term stability (after 200 ​h of charge and discharge cycling, the round-trip efficiency still maintains at 44%). The present work demonstrates a strategy for synthesizing ultrastable bifunctional non-precious metal electrocatalysts for oxygen electrocatalysis.

Dysprosium-induced FeN0.0324-Dy2O3 sites with efficient bifunctional oxygen electrocatalytic reactions for Zn-air batteries

Dysprosium-induced FeN0.0324-Dy2O3 sites with efficient bifunctional oxygen electrocatalytic reactions for Zn-air batteries

NaCl sealing Strategy-Assisted synthesis CoO-Co heterojunctions as efficient oxygen electrocatalysts for Zn air batteries

Developing highly efficient, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the wide popularization of rechargeable Zn-air batteries. Combining zero-dimensional metal nanoparticles with two-dimensional metal oxide nanosheets is an appealing strategy to balance performance and cost. However, the precise construction of these composites remains a great challenge, and their interaction mechanisms lack thorough study. Herein, a cobalt-oxide-based bifunctional oxygen electrocatalyst comprising a rich Co-CoO heterointerface (CoO/Co@NG) was synthesized via a NaCl sealing-assisted pyrolysis strategy. The NaCl crystals played the role of a closed nanoreactor, which facilitated the formation of a CoO-Co heterojunction. Experimental results and theoretical calculations confirmed that the ingeniously constructed heterojunction expedited the oxygen reduction reaction and oxygen evolution reaction kinetics, which is superior to Pt/C. When serving as the air electrode in an assembled liquid-state Zn-air battery, the battery shows high power density (215 mW cm−2), specific capacity (710 mAh gzn−1), and outstanding durability (720 h at 10 mA cm−2). This work provides an innovative avenue to design high-performance heterojunction electrocatalysts for perdurable Zn-air batteries.

Nitrogen-Rich Porous Carbon Nanotubes Coated Co/Mo2N Composites Derived from Metal-Organic Framework as Efficient Bifunctional Oxygen Electrocatalysts

Noble metal catalysts such as Pt/C and RuO2 are the most efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts and show excellent activity. However, their high costs, scarcity, single function, and weak durability impede their large-scale practical application. Therefore, it is paramount to design bifunctional electrocatalysts with high activity, long durability, and low cost. In this work, we used the functionalized modification and hierarchical porous structure of MOFs and adjusted the ratio of Co/Mo atoms to prepare uniformly dispersed nanospheres. The uniform porous nitrogen-doped carbon nanotubes coated with Co/Mo2N composites were obtained by trapping the volatile CNx during high-temperature pyrolysis via a vapor deposition strategy. The physical and chemical properties of the materials were analyzed by various characterization methods such as XRD, XPS, TEM, SEM, Raman, and BET. Notably, CoMoN@NCNTs-700 exhibited excellent ORR/OER bifunctional electrocatalytic activity in alkaline conditions due to the synergistic effect of porous nitrogen-doped carbon nanotubes and the unique heterostructure of Co/Mo2N. In 0.1 M KOH, its ORR half-wave potential was E1/2 = 0.78 V, with a limiting current density even reached to 5.3 mA cm−2 and its operating potential was 1.60 V at a current density of 10 mA cm−2. At the same time, CoMoN@NCNTs-700 also showed better stability and methanol resistance than the commercial catalysts. This work provides a valuable reference for the design and construction of inexpensive non-noble metal bifunctional electrocatalysts.

Edge atomic Fe sites decorated porous graphitic carbon as an efficient bifunctional oxygen catalyst for Zinc-air batteries

The development of advanced bifunctional oxygen electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) is critical to the practical application of zinc-air batteries (ZABs). Herein, a silica-assisted method is reported to integrate numerous accessible edge Fe-Nx sites into porous graphitic carbon (named Fe-N-G) for achieving highly active and robust oxygen electrocatalysis. Silica facilitates the formation of edge Fe-Nx sites and dense graphitic domains in carbon by inhibiting iron aggregation. The purification process creates a well-developed mass transfer channel for Fe-N-G. Consequently, Fe-N-G delivers a half-wave potential of 0.859 V in ORR and an overpotential of 344 mV at 10 mA cm−2 in OER. During long-term operation, the graphitic layers protect edge Fe-Nx sites from demetallation in ORR and synergize with FeOOH species endowing Fe-N-G with enhanced OER activity. Density functional theory calculations reveal that the edge Fe-Nx site is superior to the in-plane Fe-Nx site in terms of OH* dissociation in ORR and OOH* formation in OER. The constructed ZAB based on Fe-N-G cathode shows a higher peak power density of 133 mW cm−2 and more stable cycling performance than Pt/C + RuO2 counterparts. This work provides a novel strategy to obtain high-efficiency bifunctional oxygen electrocatalysts through space mediation.

Bimetallic ZIFs-derived electrospun carbon nanofiber membrane as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

The recharged zinc-air battery (ZAB) has drawn significant attention owing to increasing requirement for energy conversion and storage devices. Fabricating the efficient bifunctional oxygen catalyst using a convenient strategy is vitally important for the rechargeable ZAB. In this study, the bimetallic ZIFs-containing electrospun (ES) carbon nanofibers membrane with hierarchically porous structure was prepared by coaxial electrospinning and carbonization process, which was expected to be a bifunctional electrocatalyst for ZABs. Owing to the formed dual single-atomic sites of Co–N4 and Zn–N4, the obtained ES-Co/Zn-CNZIF exhibited the preferable performance toward oxygen reduction reaction (ORR) with E1/2 of 0.857 V and JL of 5.52 mA cm−2, which were more than Pt/C. Meanwhile, it exhibited a marked oxygen evolution reaction (OER) property with overpotential of 462 mV due to the agglomerated metallic Co nanoparticles. Furthermore, the ZAB based on the ES-Co/Zn-CNZIF carbon nanofibers membranes delivered peak power density of 215 mW cm−2, specific capacity of 802.6 mA h g−1, and exceptional cycling stability, far larger than Pt/C+RuO2-based ZABs. A solid-state ZAB based on ES-Co/Zn-CNZIF showed better flexibility and stability with different bending angles.

FeNi alloys supported on nitrogen-enriched carbon nanospheres as efficient bifunctional oxygen electrocatalyst for rechargeable Zinc-air battery

The development of high-performance transition metal catalysts to replace precious metal catalysts toward oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) reactions is essential and challenging. Rational embedding of transition metal nanoparticles (NPs) into nitrogen-enriched carbon frameworks to obtain bifunctional catalysts is a well-established approach. Here, we have successfully prepared an integrated electrocatalyst consisting of nitrogen-enriched porous carbon nanospheres and FeNi alloy NPs (P-FeNi/NC) by carbonizing the Hofmann-type FeNi metal–organic frameworks (MOFs) coated with polydopamine (PDA). Benefiting from the abundant ORR-active pyridinic-N species and OER-active FeNi alloy NPs, large surface area, and porous carbon framework, P-FeNi/NC-900 demonstrates a competitive ORR/OER activity (E1/2 = 0.85 V, Ej=10 mA cm-2 = 1.62 V). When applied as the air electrode, the discharging specific capacity normalized to the mass of consumed Zn is 817.2 mAh g−1 at 10 mA cm−2 and the corresponding maximum power density is 164 mW cm−2. Integration of nitrogen-enriched carbon framework and bimetallic alloys provides a new avenue for the rational preparation of bifunctional oxygen electrocatalysis for high-efficiency energy conversion and storage devices.