Application Of Metal-air Batteries Research Articles

3D honeycombed cobalt, nitrogen co-doped carbon nanosheets via hypersaline-protected pyrolysis towards efficient oxygen reduction

The broad application of metal-air batteries and fuel cells have been greatly limited due to their slow kinetics of oxygen electrodes involving the oxygen reduction reaction (ORR), and therefore the development of high-efficient, low-cost and high-reserve ORR electrocatalysts is of great significance. Herein, a hypersaline-protected pyrolysis strategy is presented for preparing 3D honeycombed cobalt, nitrogen co-doped carbon nanosheets (Co/N-CNS) by using eco-friendly biomass as a carbon and nitrogen source. During the hypersaline-protected pyrolysis, the pyridinic nitrogen-rich biomass facilitates the formation of highly active Co/N active sites among the resultant Co/N-CNS, while the templating-washing-drying cyclic utilization of salts creates honeycombed pore structures among the Co/N-CNS. Due to the structural features of honeycombed pores and uniform distributed active sites, the Co/N-CNS catalyst offers excellent ORR activity, high durability and methanol-tolerant performance in an alkaline electrolyte. As a demonstration, a primary Zn-air battery using the Co/N-CNS cathode delivers a high power density and excellent operating stability beyond that of commercial Pt/C cathode.

Co-Doped LaMnO3 Perovskite Structure Nanoparticles as a Bifunctional Electrocatalysts for Oxygen Reduction/Evolution Reactions

Current paper, we have examined lanthanum manganese cobalt (LaMn1-xCoxO3) perovskite nanoparticles synthesized by utilizing the sol-gel process and following calcinated at 450 °C for 1h and 900 °C for 7h, respectively. The fabricated alloys show single-phase perovskite structure is an order of LaMn1-xCoxO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1). The synthesized LaMn1-xCoxO3 perovskite oxide nanoparticles have the crystal structure, and powder morphology properties were investigated by X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM), respectively. The perovskite structure has been shown to be particularly effective for the catalytic reactions of ORR and OER in alkaline medium. The merged valance transition metal oxides are bifunctional electrocatalysts which give rise to potential candidates, the electrochemical functioning of the LaMn1-xCoxO3 catalyst was entirely investigated. All compounds of ORR polarization curves show that the four-electron pathway, which results in Koutecky-Levich is compatible with these perovskite structures. Current work, we describe B-site extend adding of Co ratio into perovskite structure is an appropriate strategy to increase ORR and OER electrocatalytic performance for application in metal-air batteries.

Elucidation of Active Sites on S, N Codoped Carbon Cubes Embedding Co–Fe Carbides toward Reversible Oxygen Conversion in High‐Performance Zinc–Air Batteries

The development of high-performance but low-cost catalysts for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of central importance for realizing the prevailing application of metal-air batteries. Herein a facile route is devised to synthesize S, N codoped carbon cubes embedding Co-Fe carbides by pyrolyzing the Co-Fe Prussian blue analogues (PBA) coated with methionine. Via the strong metal-sulfur interaction, the methionine coating provides a robust sheath to restrain the cubic morphology of PBA upon pyrolysis, which is proved highly beneficial for promoting the specific surface area and active sites exposure, leading to remarkable bifunctionality of ORR and OER comparable to the benchmarks of Pt/C and RuO2 . Further elaborative investigations on the activity origin and postelectrolytic composition unravel that for ORR the high activity is mainly contributed by the S, N codoped carbon shell with the inactive carbide phase converting into carbonate hydroxides. For OER, the embedded Co-Fe carbides transform in situ into layered (hydr)oxides, serving as the actual active sites for promoting water oxidation. Zn-air batteries employing the developed hollow structure as the air cathode catalyst demonstrate superb rechargeability, energy efficiency, as well as portability.

Hollow La0.5Sr0.5MnO3 nanospheres as an electrocatalyst for the oxygen reduction reaction in alkaline media

Hollow perovskite oxide La0·5Sr0·5MnO3 nanospheres are synthesized by using carbon spheres as template in the presence of citric acid. Among the samples investigated in this work, the one obtained at a sintering temperature of 700 °C exhibits the highest catalytic activity in the oxygen reduction reaction (ORR) in an alkaline electrolyte. The electrochemical measurement data shows that the sample has a positive onset potential (0.860 V) and a high limiting current density (6.48 mA cm−2). Furthermore, the catalyst shows a high selectivity towards methanol and a better stability than a commercial Pt/C catalyst. The hollow La0·5Sr0·5MnO3 nanoshperes described in this manuscript hold a great promise for applications in metal-air batteries and alkaline fuel cells.

Robust MOF-253-derived N-doped carbon confinement of Pt single nanocrystal electrocatalysts for oxygen evolution reaction

Although carbon-supported platinum (Pt/C) is still considered the most active electrocatalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), its applications in metal-air batteries as a cathode catalyst, or for oxygen generation via water splitting electrolysis as an anode catalyst is mainly constrained by the insufficient kinetic activity and stability in the oxygen evolution reaction (OER). Here, MOF-253-derived nitrogen-doped carbon (N/C)-confined Pt single nanocrystals (Pt@N/C) have been synthesized and shown to be efficient catalysts for the OER. Even with low Pt mass loading of 6.1 wt% (Pt@N/C-10), the catalyst exhibits greatly improved activity and long-time stability as an efficient OER catalyst. Such high catalytic performance is attributed to the core-shell structure relationship, in which the active N-doped-C shell not only provides a protective shield to avoid rapid Pt nanocrystal oxidation at high potentials and inhibits the Pt migration and agglomeration, but also improves the conductivity and charge transfer kinetics.

Defect Engineering on Electrode Materials for Rechargeable Batteries.

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Short-range amorphous carbon nanosheets for oxygen reduction electrocatalysis.

Selectively creating active sites that can work well in different media as much as possible remains an open challenge for the widespread application of sustainable metal air batteries and fuel cells. Herein, short-range amorphous nitrogen-doped carbon nanosheets (NCS) coupled with partially graphitized porous carbon architecture were reported, and were prepared via flexible salt-assisted calcination strategy and followed by a simple cleaning process. The short-range amorphous structure not only significantly promotes the exposure of electrochemically active sites of carbon defects with less protonation in acidic medium, but also maintains the structural stability and electron conduction of the NCS. This unique structure endows the NCS (0.832 V) with efficient ORR electrocatalytic performance with a high half-wave potential (E1/2) comparable to that of commercial Pt/C (0.837 V) in alkaline electrolyte and an impressive E1/2 of 0.64 V in harsh acidic medium, making it outstanding among the reported analogous metal-free carbon electrocatalysts. In addition, the NCS manifests robust stability for ORR electrocatalysis with little change in the catalytic activity after accelerated stability tests. This work will provide a feasible inspiration to the construction of carbon nanomaterials with high active site density for efficient energy conversion-related electrochemical reactions.

Recent Advances in Single-Atom Electrocatalysts for Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) plays significant roles in electrochemical energy storage and conversion systems as well as clean synthesis of fine chemicals. However, the ORR process shows sluggish kinetics and requires platinum-group noble metal catalysts to accelerate the reaction. The high cost, rare reservation, and unsatisfied durability significantly impede large-scale commercialization of platinum-based catalysts. Single-atom electrocatalysts (SAECs) featuring with well-defined structure, high intrinsic activity, and maximum atom efficiency have emerged as a novel field in electrocatalytic science since it is promising to substitute expensive platinum-group noble metal catalysts. However, finely fabricating SAECs with uniform and highly dense active sites, fully maximizing the utilization efficiency of active sites, and maintaining the atomically isolated sites as single-atom centers under harsh electrocatalytic conditions remain urgent challenges. In this review, we summarized recent advances of SAECs in synthesis, characterization, oxygen reduction reaction (ORR) performance, and applications in ORR-related H2O2 production, metal-air batteries, and low-temperature fuel cells. Relevant progress on tailoring the coordination structure of isolated metal centers by doping other metals or ligands, enriching the concentration of single-atom sites by increasing metal loadings, and engineering the porosity and electronic structure of the support by optimizing the mass and electron transport are also reviewed. Moreover, general strategies to synthesize SAECs with high metal loadings on practical scale are highlighted, the deep learning algorithm for rational design of SAECs is introduced, and theoretical understanding of active-site structures of SAECs is discussed as well. Perspectives on future directions and remaining challenges of SAECs are presented.

A theoretical study of atomically dispersed MN4/C (M = Fe or Mn) as a high-activity catalyst for the oxygen reduction reaction.

Carbon-based, non-noble metal catalysts for the oxygen reduction reaction (ORR) are crucial for the large-scale application of metal-air batteries and fuel cells. Density functional theory calculations were performed to explore the potential of atomically dispersed MN4/C (M = Fe or Mn) as an ORR catalyst in an acidic electrolyte and the ORR mechanism on MN4/C was systematically studied. The results indicated MN4 as the active site of MN4/C and a four-electron OOH transformation pathway as the preferred ORR mechanism on the MN4/C surface. The Gibbs free energy diagram showed that the rate-determining step of the FeN4/C and MnN4/C catalysts is the formation of the second H2O molecule and OOH*, respectively. FeN4/C exhibited higher thermodynamic limiting potential (0.79 V) and, thus, higher ORR activity than MnN4/C (0.52 V) in an acidic environment; its excellent catalytic performance is due to the nice electron structure and adsorption properties of the FeN4 site. Therefore, this work demonstrates that atomically dispersed MN4/C is a promising catalyst for the ORR.

Nitrogen-Doped Porous Carbon Derived from Biomass Used as Trifunctional Electrocatalyst toward Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions

Tremendous developments in energy storage and conversion technologies urges researchers to develop inexpensive, greatly efficient, durable and metal-free electrocatalysts for tri-functional electrochemical reactions, namely oxygen reduction reactions (ORRs), oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs). In these regards, this present study focuses upon the synthesis of porous carbon (PC) or N-doped porous carbon (N-PC) acquired from golden shower pods biomass (GSB) via solvent-free synthesis. Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies confirmed the doping of nitrogen in N-PC. In addition, morphological analysis via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) provide evidence of the sheet-like porous structure of N-PC. ORR results from N-PC show the four-electron pathway (average n = 3.6) for ORRs with a Tafel slope of 86 mV dec−1 and a half-wave potential of 0.76 V. For OERs and HERs, N-PC@Ni shows better overpotential values of 314 and 179 mV at 10 mA cm−2, and its corresponding Tafel slopes are 132 and 98 mV dec−1, respectively. The chronopotentiometry curve of N-PC@Ni reveals better stability toward OER and HER at 50 mA cm−2 for 8 h. These consequences provide new pathways to fabricate efficient electrocatalysts of metal-free heteroatom-doped porous carbon from bio-waste/biomass for energy application in water splitting and metal air batteries.

Transition Metal Oxide-Based Perovskite Structures as a Bifunctional Oxygen Electrocatalysts: Fe Doped LaCoO3 Nanoparticles

In this report, we have investigated lanthanum cobalt iron (LaCo1-xFexO3) perovskite nanoparticles synthesized by combining metallic nitrates, deionized water, and citric acid by using sol-gel method and subsequently calcinated at 400 °C for 1h and 900 °C for 7h, respectively. The formation of single-phase perovskite structure is a series of LaCo1-xFexO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1). The crystal structure, mean particle, and morphology properties of the prepared LaCo1-xFexO3 perovskite oxide nanoparticles were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM). The perovskite structure has shown special performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity in alkaline medium. As the combined valence transition metal oxides are rising capable candidates for bifunctional electrocatalysts, the electrochemical performance of the LaCo1-xFexO3 catalyst was thoroughly investigated. Koutecky-Levich results on the ORR polarization curves of all compounds shows that the four-electron pathway is favorable on these perovskite oxides. In this paper, we report B-site Fe doping in perovskite structure is a sufficient strategy to improve ORR and OER catalytic activity for application in metal-air batteries.

NiCo2S4 spheres grown on N,S co-doped rGO with high sulfur vacancies as superior oxygen bifunctional electrocatalysts

Rational design of stable and active bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is desirable but it remains challenging. In this work, NiCo2S4 spheres grown on N,S co-doped reduced graphene oxide sheets with sulfur vacancies (Vs-NiCo2S4/N,S-rGO) have been successfully fabricated through a facile solution method with post heat-treatment. As ORR catalyst, it presents more positive half-wave potential (0.84 V), smaller Tafel slope (43.8 mV dec−1) than that of pure NiCo2S4 nanoparticles (0.59 V and 75.6 mV dec−1) and N,S-rGO (0.54 V and 113.7 mV dec−1) in 0.1 M KOH. As OER catalyst, the Vs-NiCo2S4/N,S-rGO only requires an overpotential of 340 mV to deliver a current density of 10 mA cm−2 in 0.1 M KOH. Significantly, as oxygen bifunctional electrocatalyst, the Vs-NiCo2S4/N,S-rGO provides a smaller potential difference (0.73 V) than that of pristine NiCo2S4 nanoparticles (1.11 V), N,S-rGO (1.36 V) and most non-precious electrocatalysts. The much improved electrochemical performance of the Vs-NiCo2S4/N,S-rGO for both OER and ORR in 0.1 M KOH could be ascribed to considerable high-valence Ni3+ and Co3+ in spinel-type material and sulfur vacancies, which can improve electrical conductivity and increase the exposure of metal active sites, respectively, and thereby facilitate catalytic process. This work provides a feasible strategy to develop high-efficient bifunctional electrocatalysts with promising applications in rechargeable metal-air batteries and fuel cells.

Robust assembly of urchin-like NiCo2O4/CNTs architecture as bifunctional electrocatalyst in Zn-Air batteries

Cost-effective bifunctional electrocatalysts with desirable oxygen catalytic activity to both of ORR and OER are essential to the large-scale commercial application of metal-air batteries. In this work, a robust hydrothermal assembly strategy is presented to fabricate the three-dimensional (3D) urchin-like hybrid material of acid-treated multiwall CNTs (MWCNTs) and needle-like NiCo2O4 as a cost-effective bifunctional oxygen electrocatalyst. Benefiting from the particular 3D urchin-like mesoporous structure providing rich transport channels for O2 diffusion and electrolyte infiltration and abundant active sites for charge transfer reaction, and the synergistic effect of high electrocatalytically active NiCo2O4 and high conductive MWCNTs network, the optimized NCO@20%MWCNTs composite exhibits a superior OER and ORR catalytic activity. In its practical application, an ultrahigh initial round-trip efficiency of 79.4% and long-term cycle stability (950 cycles) at 10 mA cm−2 are achieved in Zn-air battery. This simple strategy for construction of the cost-effective unique 3D porous urchin-like structure together with the improved electrochemical catalytic activity provides a great potential for material design in oxygen catalysis and metal-air batteries.

Chirality Induces the Self-Assembly To Generate a 3D Porous Spiral-like Polyhedron as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction.

The sluggish kinetics and large overpotential of the oxygen reduction reaction (ORR) severely limit the widespread production and application of metal-air batteries. Herein, a conductive three-dimensional (3D) porous spiral-like polyhedron structure composed of nitrogen-doped carbon nanosheets (L/D-SPNC) was utilized as catalysts with combination of 3D hierarchical porous properties and distinguishing intrinsic properties of two-dimensional (2D) nanosheets for ORR. The chiral template, l/d-tartaric acid, induces the self-assembly of the supramolecule and the formation of an orderly array of carbon with spiral-like surface feature on a molecular scale. The resulting L/D-SPNC exhibits a small wall thickness (2.5 nm), large specific surface area (2034.2 m2/g), and high conductivity (155.76 S/m), which indicates that the properties of 2D nanosheets building blocks are kept in 3D mode. As catalysts for ORR, the optimized L-SPNC-950-1 exhibits a more positive onset potential of 1.03 V compared with those of Pt/C (1.00 V) and a half-wave potential of 0.87 V is also comparable to those of Pt/C (0.87 V). Al-air battery discharge data demonstrate that the spiral-like structure facilitates the diffusion of the electrolyte and oxygen on a three-phase interface, causing weak polarization. Density functional theory (DFT) calculations prove that the twisted surface aggravates the differential charge distribution between C-C/C-N bonds.

Enhanced Electrocatalytic Stability of Platinum Nanoparticles Supported on Sulfur-Doped Carbon using in-situ Solution Plasma

The metal-air battery is a form of renewable energy generation technology that produces energy electrochemically and can address energy concerns in the near future. However, state-of-the-art Pt electrocatalysts often suffer from agglomeration or detachment from carbon supports under prolonged operation, eventually limiting the long-term utilization of metal-air batteries. In this work, Pt nanoparticles were deposited on sulfur-doped nanocarbon to increase its stability. We first synthesized sulfur-doped (S-doped) and pristine carbon as support materials via a plasma process, and thereafter loaded platinum (Pt) nanoparticles onto the S-doped and pristine carbon matrix. From a sintering test at 600 °C, the Pt nanoparticles supported on pristine carbon increased from 2.4 to 5.2 nm; meanwhile, the average size of Pt NPs supported on S-doped carbon only increased from 2.2 to 2.51 nm. From the electrochemical analyses, the mass activity of Pt on pristine and S-doped carbon supports decreased by 25% and 10%, respectively, after 1500 cycles. The results proposed that the sulfide C–S–C bond provided a strong platinum-S-doped carbon support interaction between the support materials and the loaded Pt nanoparticles. Thus, S-doped carbon supports can serve as a stabilizer of Pt nanoparticles to enhance their durability in the application of metal-air batteries and other electrochemical devices.

Co3O4 Nanocube -3DrGO Hybrid Structure: Efficient Non-Noble-Metal Electrocatalyst with High-Performance for Oxygen Evolution Reaction

Oxygen Evolution reaction (OER) by water splitting is one of the emerging technologies for the ongoing research in the field of sustainable, clean yet highly efficient energy generation. Electrocatalysis for OER is a key step forward towards achieving this goal and enormous efforts has been devoted recently on the development of high-performance electrocatalysts that are cost-effective, abundant as well as environmentally benign. Transition metal based non-noble electrocatalysts anchored on high-surface area, conductive carbonaceous support serves the dual purpose of being highly catalytically active as well as having excellent stability. Herein, we report the synthesis of Co3O4 nanocube -3DrGO hybrid structure as a high-performance electrocatalyst for OER applications via a facile hydrothermal synthesis technique followed by heat treatment. The unique nanocube like structure offers more active edge sites which plays an important role in its catalytic performance. The hybrid structure exhibits an overpotential of 428 mV (vs RHE) and a small tafel slope of 96.92 mV dec-1 with 100% faradaic efficiency in 1 M NaOH alkaline electrolyte. The electrode needs an overpotential of 648 mV to afford a current density of 10 mA cm-2. This offers a low-cost electrocatalytic electrode for water splitting and rechargeable metal–air battery applications. Figure 1

Modeling of Si-B-N Sheets and Derivatives as a Potential Sorbent Material for the Adsorption of Li+ Ion and CO2 Gas Molecule.

In the present exploration, a few Si–B–N derivatives are derived to adsorb Li ions and CO2 gas molecules for the potential application of metal–air batteries. The newly derived structure’s bond lengths are as follows: Si=Si, 2.2 Å; Si–B, 1.9 Å; Si–N, 1.7 Å; and B–N, 1.4 Å, consistent with the experimental results of relevant structures. The stability of the newly derived structures is examined by the atom-centered density propagation study by varying the temperature from 270 to 400 K, and no structural variations are observed throughout the dynamics. Li adsorption on the Si4B2 ring has the maximum binding energy of −3.9 eV, and the result is consistent with the previous results. The rings with the 2:1 silicon–boron ratio provide strong adsorption for Li atoms. The calculated maximum electromotive force of the newly derived sheets is 0.56 V with the maximum theoretical density of 783 Wh/kg. Similarly, the maximum adsorption of CO2 on the sheet is −0.106 eV, which is considerably higher than that on graphene and its derivatives. CO2 adsorption has been carried out in the presence of water molecules to investigate the change in CO2 adsorption with the moisture (water) content, and the results show no significant change in the adsorption of CO2 with moisture. However, water has a strong interaction with the maximum interaction energy of −0.72 eV. Further, to explore the potential ability of the sheets, each sheet’s edges are examined as hydrogen storage expedient and the surface as an artificial photosynthesis platform. The Si4B2 ring is more favorable for the adsorption of H atom with the chemisorption of −7.138 eV. Similarly, all of the major UV-absorption spectral peaks fall between 450 and 800 nm, which shows that the sheet can be used as an artificial photosynthesis platform.

Iron-Salt Thermally Emitted Strategy to Prepare Graphene-like Carbon Nanosheets with Trapped Fe Species for an Efficient Electrocatalytic Oxygen Reduction Reaction in the All-pH Range.

Earth-abundant, highly active, and durable electrocatalysts toward oxygen reduction reaction (ORR) in the all-pH range are highly required for practical application of electrochemical energy conversion technologies. Here, non-noble-metal graphene-like carbon nanosheets with trapped Fe species (Fe-N/GPC) are developed by an iron-salt thermally emitted strategy, which integrates the modulation of the electronic structure for boosted intrinsic activity with the engineering of hierarchical porosity for enriched active sites. The ORR electrocatalytic performance of Fe-N/GPC-800 achieves the half-wave potentials of 0.86 and 0.77 V with limiting current densities of 6.1 and 4.7 mA cm-2 in 0.1 M KOH and 0.1 M PBS solutions, respectively, as well as respectable stability. Furthermore, Fe-N/GPC-800 also shows considerable ORR catalytic activity in acid media accompanied by stability superior to those of Pt/C catalysts. The as-prepared Fe-N/GPC-800, as a cathodic catalyst, is assessed in a Zn-air battery test and delivers an open-circuit voltage of 1.44 V with a power density of 134 mW cm-2 as well as the outstanding durability after 350 cycles at 10 mA cm-2, demonstrating appreciable promise in application of metal-air batteries. This work provides an enabling and versatile strategy for facile and scale-up preparation of high-performance non-noble-metal electrocatalysts.

Nitrogen/sulfur dual-doped porous carbon nanofibers with Co9S8 nanoparticles encapsulated by graphitic shells: A highly active stable free-standing air electrode for rechargeable non-aqueous Li-O2 batteries and primary alkaline Al-air batteries

The rational design of economical air cathodes or electrocatalysts with high electrocatalytic activity and durability for both non-aqueous lithium-oxygen (Li-O2) and alkaline electrolyte aluminum-air (Al-air) batteries is a critical factor for promoting the practical applications. Herein, we report the fabrication of graphitic layers covered with Co9S8 nanoparticles immobilized inside N,S dual-doped hierarchical porous carbon nanofibers by a facile and one-step electrospinning method combined with a pyrolytic process. When employed as free-standing electrodes for a Li-O2 battery and an Al-air battery, the as-prepared Co9S8@G/NS-PCNFs deliver excellent battery performances and afford comparable catalytic performance as that of a 20 wt% Pt/C electrode. The results show that the superior battery performance of the Co9S8@G/NS-PCNF cathode can be attributed to the synergistic effect between the catalytic behavior of the uniformly distributed Co9S8 nanoparticles and the textural properties of the N,S dual-doped hierarchical porous carbon nanofibers. Our findings open a new direction for designing nonprecious hybrid metal sulfide carbon architectures to replace costly Pt/C electrodes and indicate their promising application in next-generation metal-air batteries.

Enhanced Bifunctional Catalytic Activity of Manganese Oxide/Perovskite Hierarchical Core-Shell Materials by Adjusting the Interface for Metal-Air Batteries.

LaMnO3 perovskite is one of the most promising catalysts for oxygen reduction reaction (ORR) in metal-air batteries and can be compared to Pt/C. However, the low catalytic activity toward oxygen evolution reaction (OER) limits its practical application in rechargeable metal-air batteries. In this work, the MnO2/La0.7Sr0.3MnO3 hierarchical core-shell composite materials with a special interface structure have been designed via the selective dissolution method. The core of La0.7Sr0.3MnO3 particles is wrapped by the porous and loose MnO2 nanoparticles. The as-prepared MnO2/La0.7Sr0.3MnO3 materials have excellent catalytic activity toward ORR/OER and are used as bifunctional oxygen electrocatalysts for metal-air batteries. Based on results of transmission electron microscopy, X-ray photoelectron spectroscopy, valence-band spectroscopy, and O2 temperature-programmed desorption analysis, we conclude that the bifunctional catalytic activity of the MnO2/La0.7Sr0.3MnO3 materials can be effectively promoted due to the specific interface structure between the La1-xSrxMnO3 core and the MnO2 shell. This can be attributed to three aspects: (a) the electronic conductivity, which is beneficial for providing the faster charge-transfer paths and kinetics at the oxide/solution interface than that of the MnO2 sample; (b) the enhancement of oxygen adsorption capacity due to surface defects (oxygen vacancies) and chemical adsorption, which is helpful to improve the reaction kinetics during the process of oxygen catalysis; and (c) the tuning of oxygen adsorption ability via the moderate Mn-O bond strength, which may be conducive to getting for obtain an enhanced Mn-O bond strength on the surfaces for ORR and a weakened Mn-O bond in the lattice for OER.