Electrocatalytic Oxygen Research Articles

Interface engineering induced charge rearrangement boosting reversible oxygen electrocatalysis activity of heterogeneous FeCo-MnO@N-doped carbon nanobox

The advancement of bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is imperative yet challenging for the optimization of Zn-air batteries. In this study, we reported the successful incorporation of a novel Mott-Schottky catalytic site within a MnO-FeCo heterojunction into an N-doping carbon nanobox, taking into consideration the effects of the intrinsic electric field and hollow/porous support carriers for electrocatalyst design. As expected, the resulting heterogeneous catalyst exhibited an encouraging half-wave potential of 0.88 V and an impressive limiting-current density of 5.62 mA/cm2 for the ORR, as well as a minimal overpotential of 271 mV at 10 mA/cm2 for the OER, both in alkaline conditions. Furthermore, the Zn-air battery constructed with the heterojunction nanobox product displayed a decent potential gap of 0.621 V, an outstanding power density of 253 mW/cm2, a considerable specific capacity of 761 mAh/gZn, and exceptional stability, with up to 336 h of cycling charging and discharging operation. Consequently, this method of modulating the catalyst's surface charge distribution through an internal electric field at the interface and facilitating mass transport offers a novel avenue for the development of robust bifunctional oxygen catalysts.

Modulating electronic structure of interfacial Fe sites in Fe2N/CoFe2O4 nano-heterostructure for enhancing corrosion-resistance and oxygen electrocatalysis in zinc-air battery

Interface engineering can regulate electronic structure of transition-metal nitrides to promote their electrocatalytic activities. However, design of iron nitride (Fe2N)-based electrocatalytic interface with desirable properties is still challenging. Here, an in-situ nucleation strategy is developed to construct the highly-dispersed Fe2N/spinal (CoFe2O4) heterojunctions to optimize the electro-conductivity and activity. The heterostructure exhibits robust activities towards ORR (half-wave potential, 0.903 V) and OER (overpotential, 300 mV). Interfacial interactions between Fe2N and CoFe2O4 mitigate the corrosion (leaching) and severe agglomeration of active components in harsh environments to stabilize the electrocatalytic activity, maintaining the integrity of heterostructure and the sustainable exposure of active sites. Theorical calculations confirm the feasibility of incorporating Fe2N into basal plane of spinal lattice (Fe2N (002) and CoFe2O4 (400) is well matched). Modulated electronic state optimizes the adsorption/desorption strength of O-intermediates on the interfacial Fe-sites (the main active sites) of Fe2N/CoFe2O4 for both ORR and OER. Strong coupling of Fe2N and CoFe2O4 bolsters the charge-transfer across the interfaces to substantially accelerate the ORR/OER kinetics. Notably, by vital of a small potential-gap (0.634 V), it displays excellent power-density (225 mW cm−2) and cycling-stability (280 h) in zinc-air battery. This work enriches the understanding of electronic structure modulation of hetero-structured nitride/spinel-based electrocatalysts.

Bending the ORR Scaling Relations on Zirconium Oxynitride for Enhanced Oxygen Electrocatalysis

AbstractTechnologies like polymer electrolyte membrane fuel cells play an important role in environmentally friendly energy conversion. Essential for their commercialization is the development of cheap and efficient electrocatalyst for the oxygen reduction reaction (ORR). Non‐platinum group metal (PGM) based catalysts has exhibited favourable activity in acidic electrolytes. In this study, we computationally explore the catalytic sites on the (111) surface of hydrated zirconium oxynitride using periodic DFT calculations. The thermodynamically limiting step is determined to be the O2 activation step, (O2→OOH*) for the majority of the sites, hence strengthening the OOH* intermediate binding will improve ORR activity. The calculations also reveal that the determined scaling relation for GOH‐GOOH ( 3.52 eV) is comparable to the standard ORR scaling relation ( 3.2 eV) however GO*‐GOH scaling ( 2.16 eV) deviates dramatically from the typical ORR scaling relation ( ).

Tailoring the d-band electronic structure of deficient LaMn0.3Co0.7O3-δ perovskite nanofibers for boosting oxygen electrocatalysis in Zn-Air batteries

The development and design of efficient bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for rechargeable Zinc-air batteries (ZABs). Optimizing the d-band structure of active metal center in perovskite oxides is an effective method to enhance ORR/OER activity by accelerating the rate-determining step. Herein, we report a deficient method to optimize the d-band structure of Co ions in LaMn0.3Co0.7O3-δ (LMCO-2) perovskite nanofibers, which regulates the mutual effect between B-site Co ions and reactive oxygen intermediates. It is proved by experiment and theoretical calculation that the d-band center (Md) of transition metal ions in LMCO-2 is moved up and the electron filling number of eg orbital in B site is 1.01, thus leading to the reduction of Gibbs free energy required for ORR rate-determining step (OH*→H2O*) to 0.22 eV and promoting reaction proceeds. In this manner, LMCO-2 showed good bifunctional oxygen electrocatalytic activity, with a half-wave potential of 0.71 V vs. RHE. Furthermore, the high specific capacity of 811.54 mAh g−1 and power density of 326.56 mW cm−2 were obtained by using LMCO-2 as the cathode catalyst for ZABs. This study proved the feasibility of d-band structure regulation to enhance the electrocatalytic activity of perovskite oxides.

Gorgeous turn-back: Rough surface treatment strategy induces Cu-C and N-C active moieties for bifunctional oxygen electrocatalysis

Fabricating inexpensive and quality bifunctional catalysts for catalyzing oxygen reduction/evolution reactions (ORR/OER) is urgent for the wide application of zinc-air batteries (ZAB). Herein, a bifunctional catalyst, nitrogen-doped graphdiyne (Cu NPs/NGDY) with Cu-C and N-C active moieties, is fabricated through pyrolysis. Cu NPs/NGDY exhibits excellent catalytic performance towards ORR (E1/2 = 0.86 V), stability of 86.5% current retention for 24 h and OER (Ej=10 = 360 mV). Experimental results and theoretical calculations reveal the vital role of Cu-C and nitrogen doping in regulating electrocatalytic activity. Assembled with Cu NPs/NGDY as electrocatalyst, both the liquid-state and flexible ZABs exhibit high power density and barely changed gap between discharge and charge voltage with robust stability, demonstrating tremendous potential in the field of wearable-related equipment. This work develops a simple strategy to fabricate GDY -based bifunctional catalyst.

Tuning the Coordination Environment of Single‐Atom Iron Catalysts Towards Effective Nitrogen Reduction

AbstractElectrocatalytic nitrogen reduction reaction (eNRR) relies on developing efficient catalysts towards high reaction activity and selectivity. In recent years, designing single‐atom catalysts have been the research frontier in electrochemical reactions. However, compared to their widely studied applications in oxygen electrocatalysis, their potential structure‐function relationship and reaction mechanism in eNRR were less explored. Herein, single‐atom Fe−Nx−C materials were systematically analysed considering the coordination environments of single‐atom Fe. It was found that coordination environment plays a key role in determining the N2 adsorption and activation. Among the concept catalysts designed, FeCN2 and FeCN3 offer the highest eNRR activities with a suppressed side reaction (i. e., the hydrogen evolution). Moreover, the Bader charge of the single‐atom Fe and *NH adsorption energy can be the good descriptors to guide the design of eNRR catalysts. This study unravels the key role of coordination environment in tuning the reactivity of eNRR over single‐atom Fe−Nx−C materials.

Single-atom Zn with nitrogen defects on biomimetic 3D carbon nanotubes for bifunctional oxygen electrocatalysis

Single atoms catalysts (SACs) have promising development in electrocatalytic energy conversion. Nevertheless, rational design SACs with reversible oxygen electrocatalysis still remain challenge. Herein, we synthesized atomically dispersed Zn with N defect on three-dimensional (3D) biomimetic carbon nanotubes by secondary pyrolysis (Zn-N-C-2), which possesses excellent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalytic activities. The biomimetic 3D structure and unique “leaf-branch” system are beneficial to fully expose the active sites. Density functional theory (DFT) calculations show that Zn-N3-D can optimize the charge distribution and facilitate electron transfer step of OH*→O*. Zn-N-C-2 exhibits higher ORR activity than commercial Pt/C with a half-wave potential (E1/2) of 0.85 V and OER overpotential of 450 mV at 10 mA cm−2. After being assembled into the air cathode of aqueous Zn-air battery (ZAB), it demonstrates superior performances with long-term charge and discharge for more than 200 h. This work not only clarifies the controlled synthesis of N-defects Zn SACs with excellent bifunctional electrocatalyst, but also provide in-depth understanding of structural-performance relationships by regulating local microenvironments.

Mesoporous Manganese Oxides with High-Valent Mn Species and Disordered Local Structures for Efficient Oxygen Electrocatalysis.

Active and nonprecious-metal bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are vital components of clean energy conversion devices such as regenerative fuel cells and rechargeable metal-air batteries. Porous manganese oxides (MnOx) are promising electrocatalyst candidates because of their high surface area and the abundance of Mn. MnOx catalysts exhibit various oxidation states and crystal structures, which critically affect their electrocatalytic activity. These effects remain elusive mainly because the synthesis of oxidation-state-controlled porous MnOx with similar structural properties is challenging. In this work, four different mesoporous manganese oxides (m-MnOx) were synthesized and used as model catalysts to investigate the effects of local structures and Mn valence states on the activity toward oxygen electrocatalysis. The following activity trends were observed: m-Mn2O3 > m-MnO2 > m-MnO > m-Mn3O4 for the ORR and m-MnO2 > m-Mn2O3 > m-MnO ≈ m-Mn3O4 for the OER. These activity trends suggest that high-valent Mn species (Mn(III) and Mn(IV)) with disordered atomic arrangements induced by nanostructuring significantly influence electrocatalysis. In situ X-ray absorption spectroscopy was used to analyze the changes in the oxidation states under the ORR and OER conditions, which showed the surface phase transformation and generation of active species during electrocatalysis.

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.

CoNi Alloys Encapsulated in N-Doped Carbon Nanotubes for Stabilizing Oxygen Electrocatalysis in Zinc-Air Battery.

Alloy-based catalysts with high corrosion resistance and less self-aggregation are essential for oxygen reduction/evolution reactions (ORR/OER). Here, via an in situ growth strategy, NiCo alloy-inserted nitrogen-doped carbon nanotubes were assembled on a three-dimensional hollow nanosphere (NiCo@NCNTs/HN) using dicyandiamide. NiCo@NCNTs/HN exhibited better ORR activity (half-wave potential (E1/2) of 0.87 V) and stability (E1/2 shift of only -13 mV after 5000 cycles) than commercial Pt/C. NiCo@NCNTs/HN displayed a lower OER overpotential (330 mV) than RuO2 (390 mV). The NiCo@NCNTs/HN-assembled zinc-air battery exhibited high specific-capacity (847.01 mA h g-1) and cycling-stability (291 h). Synergies between NiCo alloys and NCNTs facilitated the charge transfer to promote 4e- ORR/OER kinetics. The carbon skeleton inhibited the corrosion of NiCo alloys from surface to subsurface, while inner cavities of CNTs confined particle growth and the aggregation of NiCo alloys to stabilize bifunctional activity. This provides a viable strategy for the design of alloy-based catalysts with confined grain-size and good structural/catalytic stabilities in oxygen electrocatalysis.

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.

Synergistic Effects of Phase Transition and Electron‐Spin Regulation on the Electrocatalysis Performance of Ternary Nitride (Adv. Funct. Mater. 25/2023)

Phase Transitions The synergistic effects of phase transition and electron-spin regulation boosts oxygen electrocatalysis. In article number 2300623, Junhua Hu and co-workers, report that a core shell structure of (CoxFe1−x)3N with high dispersibility is induced by an intermediate phase transition process. The moderate eg electron filling (t2g5eg1) in (Co0.17Fe0.83)3[email protected] balances the adsorption of *O2 and the hydrogenation of *OH, improving bifunctional catalytic performances.

Regulation of Atomic Fe-Spin State by Crystal Field and Magnetic Field for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

Highly-active and low-cost bifunctional electrocatalysts for oxygen reduction and evolution are essential in rechargeable metal-air batteries, and single atom catalysts with Fe-N-C are promising candidates. However, the activity still needs to be boosted, and the origination of spin-related oxygen catalytic performance is still uncertain. Herein, an effective strategy to regulate local spin state of Fe-N-C through manipulating crystal field and magnetic field is proposed. The spin state of atomic Fe can be regulated from low spin to intermediate spin and to high spin. The cavitation of dxz and dyz orbitals of high spin Fe(Ⅲ) can optimize the O2 adsorption and promote the rate-determining step (*O2 to *OOH). Benefiting from these merits, the high spin Fe-N-C electrocatalyst displays the highest oxygen electrocatalytic activities. Furthermore, the high spin Fe-N-C-based rechargeable zinc-air battery displays a high power density of 170 mW cm-2 and good stability.

Regulation of Atomic Fe‐Spin State by Crystal Field and Magnetic Field for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc‐Air Batteries

AbstractHighly‐active and low‐cost bifunctional electrocatalysts for oxygen reduction and evolution are essential in rechargeable metal‐air batteries, and single atom catalysts with Fe−N−C are promising candidates. However, the activity still needs to be boosted, and the origination of spin‐related oxygen catalytic performance is still uncertain. Herein, an effective strategy to regulate local spin state of Fe−N−C through manipulating crystal field and magnetic field is proposed. The spin state of atomic Fe can be regulated from low spin to intermediate spin and to high spin. The cavitation of dxz and dyz orbitals of high spin FeIII can optimize the O2 adsorption and promote the rate‐determining step (*O2 to *OOH). Benefiting from these merits, the high spin Fe−N−C electrocatalyst displays the highest oxygen electrocatalytic activities. Furthermore, the high spin Fe−N−C‐based rechargeable zinc‐air battery displays a high power density of 170 mW cm−2 and good stability.

Symmetric Electronic Structures of Active Sites to Boost Bifunctional Oxygen Electrocatalysis by MN4+4 Sites Directly from Initial Covalent Organic Polymers

AbstractTransition metal‐nitrogen‐carbon (M‐N‐C) catalysts with CoN4 centers have attracted great attention as a potential alternative to precious metal catalysts for bifunctional oxygen electrocatalysis. However, the asymmetric charge environment of the active site of MN4 obtained by conventional pyrolysis strategy makes the unbalanced adsorption of oxygen molecules, which restricts the activities of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a series of well‐defined quasi‐phthalocyanine conjugated 2D covalent organic polymer (COPBTC‐M) is developed with MN4+4 active sites through a pyrolysis‐free strategy. Compared to CoN4 site, the additional subcentral N4 atoms in MN4+4 site in COPBTC‐Co catalyst balance the charge environment and form a symmetric charge distribution, which changes the antibonding orbital of the active metal and regulate the oxygen species adsorption, thus improving the activity of the bifunctional oxygen electrocatalysis. In Silico screening demonstrates that cobalt has the best ORR and OER activity for COPBTC‐M with MN4+4 sites, which can be attributed to the fewer anti‐bonding orbital below the Fermi level, which weakens the oxygen species adsorption. Both theoretical and experimental results verify that the COPBTC‐Co possesses unique CoN4+4 active sites and the harmonious coordinating environment can lead to superior bifunctional oxygen catalytic activity with a high bifunctional oxygen catalytic activity (ΔE [Ej10 – E1/2] = 0.76 V), which is comparable with the benchmark Pt/C‐IrO2 pairs. Accordingly, the as‐assembled Zn–air battery exhibits a maximum power density of 157.7 mW cm −2 with stable operation for >100 cycles under an electric density of 10 mA cm −2. This study provides a characteristic understanding of the intrinsic active species toward MNx centers and could inspire new avenues for designation of advanced bifunctional electrocatalysts that catalyze ORR and OER processes simultaneously.

Atomic Structure of Mn-Doped CoFe2O4 Nanoparticles for Metal–Air Battery Applications

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode.

Surface reconstruction of SrCoO2.52 nanofibers as bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Rechargeable metal-air battery is an emerging renewable energy technology with advantages of high efficiency, zero pollution and environmental friendliness. The development of efficient and cost-effective oxygen electrocatalyst plays a key role in tackling the performance restrain of air electrode for rechargeable metal-air batteries, especially for Zn-air batteries. Herein, we reported surface reconstruction on a complex metal oxide, SrCoO2.52 (SCO) utilizing selective ion corrosion to boost its activity for O2 electrocatalysis and Zn-air batteries. Based on the difference in bond strength between Sr–O and Co–O, a selective etching of Sr cation on the surface of SCO nanofibers has been realized using a gentle wet chemical method. The selective Sr etching altered both the crystal and electronic structure of the catalyst surface, reconstructing the surface to form a cobalt-rich layer over the SCO matrix. The obtained core-shell structure significantly enhanced the activity of the SCO catalyst for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The bifunctional SCO catalyst was applied as air electrode for rechargeable Zn-air batteries, delivering a power density of 191 mW cm-2 and a stability of 500 charging-discharging cycles outperforming that of the IrO2‖Pt/C composite (180 mW cm-2 and 100 cycles). The performance enhancement was proposed to be due to the surface reconstruction increasing the exposure and approachability of the active Co sites and improving the redox ability of the Co cations. This work not only presents an efficient method of reconstructing SCO with highly active surface for oxygen electrocatalysis and Zn-air batteries, but also may arouse interest to design advanced complex metal oxides with surface-regulating potential for various electrocatalytic applications.

Simultaneously Incorporating Atomically Dispersed Co‐Nx Sites with Graphitic Carbon Layer‐Wrapped Co9S8 Nanoparticles for Oxygen Reduction in Acidic Electrolyte

AbstractA facile yet robust synthesis is reported herein to simultaneously incorporate atomically dispersed Co‐Nx sites with graphitic layer‐protected Co9S8 nanoparticles (denoted as Co SACs+Co9S8) as an efficient electrocatalyst for oxygen reduction in acidic solution. The Co SACs+Co9S8 catalyst shows low H2O2 selectivity (∼5 %) with high half‐wave potential (E1/2) of ∼0.78 VRHE in 0.5 M H2SO4. The atomic sites of the catalyst were quantified by a nitrite stripping method and the corresponding site density of the catalyst is calculated to be 3.2×1018 sites g−1. Besides, we also found the presence of a reasonable amount of Co9S8 nanoparticles is beneficial for the oxygen electrocatalysis. Finally, the catalyst was assembled into a membrane electrode assembly (MEA) for evaluating its performance under more practical conditions in proton exchange membrane fuel cell (PEMFC) system.

Ag Anchored Atomically Around Nanopores of Porous Co(OH)2 for Efficient Bifunctional Oxygen Catalysis

AbstractVarious clean energy storage and conversion systems highly depend on rational design of efficient electrocatalysts for oxygen reactions. Increasing both gas molecular diffusion and intrinsic activity is critical to boosting its efficiency for bifunctional oxygen electrocatalysis. However, controllable synthesis of catalysts that combines gas molecular diffusion and intrinsic activity remains a fundamental challenge. Herein, a two‐step synthetic strategy is adopted to fabricate a composite oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalyst (P‐Ag‐Co(OH)2), of which, atomic Ag is anchored in reactive oxygen atoms around nanopores of Co(OH)2 nanosheets. Abundant nanopores provide enough gas molecular diffusion channels, and the special Ag‐O‐Co‐OH catalytic groups around nanopores display high intrinsic catalytic activity, which jointly result in an excellent ORR/OER performance. In alkaline electrolyte, P‐Ag‐Co(OH)2 displays a high half‐wave potential (0.902 V versus RHE) for ORR, and a low overpotential (235 mV at 10 mA cm−2) for OER, which is superior to non‐noble catalysts in previous studies and Pt/C (Ir/C) catalyst. At the same time, the single‐cell zinc‐air battery is prepared with an extremely high discharge peak power density of 435 mW cm−2 and excellent discharge–charge cycle stability.

Advances in Transition-Metal-Based Dual-Atom Oxygen Electrocatalysts.

Oxygen electrocatalysis has aroused considerable interest over the past years because of the new energy technologies boom in hydrogen energy and metal-air battery. However, due to the sluggish kinetic of the four-electron transfer process in oxygen reduction reaction and oxygen evolution reaction, the electro-catalysts are urgently needed to accelerate the oxygen electrocatalysis. Benefit from the high atom utilization efficiency, unprecedentedly high catalytic activity, and selectivity, single-atom catalysts (SACs) are considered the most promising candidate to replace the traditional Pt-group-metal catalysts. Compared with SACs, the dual-atom catalysts (DACs) are attracting more attraction including higher metal loading, more versatile active sites, and excellent catalytic activity. Therefore, it is essential to explore the new universal methods approaching to the preparation, characterization, and to elucidate the catalytic mechanisms of the DACs. In this review, several general synthetic strategies and structural characterization methods of DACs are introduced and the involved oxygen catalytic mechanisms are discussed. Moreover, the state-of-the-art electrocatalytic applications including fuel cells, metal-air batteries, and water splitting have been sorted out at present. The authors hope this review has given some insights and inspiration to the researches about DACs in electro-catalysis.