Performance Of Li-O2 Batteries Research Articles

Highly Active Transition Metal Dichalcogenides As Bifunctional Electrocatalysts for Li-Oxygen Batteries

Lithium-air (Li-O2) batteries -comprising of an air (O2) cathode and a lithium anode- are able to deliver significantly higher amounts of theoretical energy densities compared to conventional Li-ion batteries. Therefore, these batteries have been extensively investigated lately to become the practical substitution for Li-ion batteries especially in transportation and electric vehicles. Performance of a Li-O2 battery is fundamentally governed by two main reactions occurring at the cathode: oxygen reduction reaction (ORR) during discharge and oxygen evolution reaction (OER) during charge. In order to improve the performance of Li-O2 batteries, seeking a bifunctional catalyst which operates favorably in both ORR and OER reactions, is a challenging issue. The role of various materials has been investigated in OER-ORR reduction in both aprotic and non-aprotic media, including: noble metals, metal oxides, transition metals, transition metal carbides, and etc. Among these catalysts, transition metal dichalcogenides (TMDCs) such as MoS2 indicated a superior performance towards a bifunctional catalytic activity for ORR and OER in aprotic electrolytes. Herein we report for the first time the catalytic activity of a number of novel two dimensional TMDCs with transition metals of groups V-IX and the three heavier chalcogens (S, Se, Te) in ORR-OER in an aprotic medium with Li salt. We have synthesized these materials via chemical vapor transport (CVT) and the nanoflakes accompanied by different characterization techniques such as: Raman, XPS, UPS, DLS, AFM and etc. We performed cyclic voltammetry experiements to comparatively study the TMDCs catalytic activity in ORR-OER reactions, their turnover frequency and so on. These catalysts outperformed all of the reported catalysts in aprotic media with Li salts during ORR and OER. A number of them exhibited an excellent bifunctional behavior such as: NbS2, VS2 and VSe2. Density functional theory (DFT) calculations were also performed on a number of these catalysts in order to understand their catalytic activity during ORR and OER in ionic liquid electrolyte. We believe these materials possess great potential to enhance the catalytic activity in core electrochemical reactions especially in Li-O2 battery applications.

Oxygen Reduction Reactions in Low-Viscosity Ionic Liquids Based on Phosphonium Cations

There is high expectation for the lithium-oxygen (Li-O2) battery due to its high energy density because the cathodic active material is O2 in the air. The oxygen reduction reaction (ORR) at the cathode is of great importance, and it is strongly influenced by types of electrolytes. In particular, mass transport of oxygen molecules and its parameter, i. e. the solubility and the diffusion coefficient, are important for high performance of Li-O2 battery. Ionic liquids (ILs) have drawn attentions as an electrolyte for Li-O2 battery, because of their unique properties like incombustibility, low vapor pressure, good ionic conductivity and wide electrochemical potential window [1]. Major ILs used for such electrochemical devices include imidazolium, pyridinium, quaternary ammonium, pyrrolidinium and piperidinium derivatives. On the other hand, phosphonium ILs have the remarkable features such as their chemical and thermal stabilities, and lower viscosity, compared to the ammonium counterparts [2]. Therefore, we focused on the phosphonium ILs. Recently, much lower viscosity was reported that based on small phosphonium cation such as triethylalkylphosphonium cation or tri-n-butylalkylphosphonium cation [2,3]. All electrochemical measurements such as cyclic voltammetry (CV) and potential-step chronoamperometry (CA) were performed using a three electrode type electrochemical cell at 25oC. A glassy carbon (GC) disk electrode (d = 1 mm) or a carbon fiber (CF) microdisk electrode (d = 33 μm) were used as the working electrode. Counter electrode and reference electrode were Pt wire and Ag+/Ag in 0.1 M Ag-OTf / EMI-TFSA , respectively. CAs were performed on the CF microdisk electrode to estimate the solubility and the diffusion coefficient of oxygen in the ILs, individually, by the micro-electrode technique [4]. Two typical groups which consisted of triethylalkyl or tri-n-butylalkyl phosphonium cation were observed in the solubility correlated with molar volume. Moreover, two linear relationship between the diffusion coefficient and the viscosity of ILs were observed. In addition, the diffusion coefficients were correlated to occupied molar volumes which were calculated by the oxygen solubility in each IL. These result suggested that diffusion coefficient was not only affected the viscosity but also diffusion path originated from the cation structure. [1] A. Khan, C. Zhao, ACS sustainable Chem. Eng. 4, 506 (2016) [2] K. Tsunashima, M. Sugiya, Electrochem. Commun. 9, 2353 (2007) [3] K. Tsunashima, M. Sugiya, Electrochemistry, (2007), in press. [4] J. Maruyama, M. Inaba, T. Morita, Z. Ogumi, J. Electroanal. Chem. 504, 208 (2001)

Tuning oxygen non-stoichiometric surface via defect engineering to promote the catalysis activity of Co3O4 in Li-O2 batteries

The performance of Li-O2 battery is governed by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics. Adjusting the surface property of catalysts via defect engineering will inaugurate a new complexion on developing efficient oxygen electrodes. In this work, a novel strategy of creating rich oxygen vacancy in Co3O4 is developed via cerium incorporation. The oxygen vacancy in Ce-Co3O4 not only promotes charge migration due to the formation of unsaturated coordination sites where electrons become delocalized but also acts as active site to anchor O2 and Li2O2 thereby leading to synergic enhancement of ORR and OER kinetics. The low overpotential (0.9 V), large specific capacity (8250 mAh g−1) and extended cycling life of the Ce-Co3O4 based Li-O2 battery experimentally confirm its superior bifunctional catalytic activity. This relationship between surface properties and catalytic activity established by defect engineering can serve as an innovative strategy for guiding the further development of high performance electrode materials for Li-O2 batteries in the foreseeable future.

Nitrogen-doped graphene derived from polyaniline/graphene oxide composites with improved capacity and cyclic performance of Li-O2 battery

Nitrogen-doped graphene (NGO) was synthesized by the pyrolysis of precursor polyaniline/graphene oxide composites, where the nitrogen content of the NGO was dependent on the loading amount of polyaniline. The Li-O2 cell with the NGO cathode exhibits a higher full-discharge capacity and longer cycle life than the one with the graphene oxide cathode. SEM and Raman analyses indicate that film-like Li2O2 product is formed on the NGO cathode in battery discharging following a surface-pathway mode, due to the adsorption of soluble intermediates by the nitrogen-containing species of the NGO cathode according to rotating ring disk electrode analysis, which effectively lowers the charge potential of Li-O2 cells and alleviates the corrosion of Li anode. The simple synthesis of NGO with good catalytic performance and electric conductance is prospective to be applied on Li-O2 batteries at low cost.

High rate and long cycle life in Li-O2 batteries with highly efficient catalytic cathode configured with Co3O4 nanoflower

The reaction mechanism of non-aqueous Li-O2 batteries is based on the deposition and decomposition of Li2O2. The polarization of Li-O2 batteries can be rapidly increased by operation under a high rate condition, resulting in the early capacity fade of the cells. Therefore, a well-designed catalyst with a unique structure and excellent catalytic ability is an important way to boost the round-trip performance of Li-O2 batteries, especially under high current density. In this work, a unique nanoflower structure assembled with Co3O4 nanosheets is synthesized by using 2-methylimidazole (2-MIM) as a structural directing agent. X-ray photoelectron spectroscopy (XPS) and Raman spectra reveal abundant oxygen vacancies on the surface of the Co3O4 nanoflower, which are beneficial for oxygen reduction and evolution reactions and long round-trip lifetime. Density functional theory results demonstrate that Co3O4 catalyst with oxygen vacancies could promote the wetting of Li2O2 on substrate and formation of a Li2O2 nanofilm, thereby boosting the discharge capacity of Li-O2 batteries. On account of the synergistic effect of abundant oxygen vacancies, the unique structure, and excellent oxygen evolution reaction, Co3O4 nanoflower-based cells could deliver ultralong lifetime of 276 and 248 cycles with a discharge capacity of 1000 mAh g−1 under charge/discharge current densities of 0.5 A g−1 and 1 A g−1, respectively. This study has shed light on a new strategy for catalyst preparation for long lifetime Li-O2 batteries.

Mesoporous Mn2O3 rods as a highly efficient catalyst for Li-O2 battery

Li-O2 batteries are considered as one of the future candidates for electrochemical power sources due to their high theoretical energy density. As the dominating component affects the performance of Li-O2 batteries, O2-cathode catalyst with high efficiency, low price, facile preparation is important. Herein, polyhedral and porous Mn2O3 rods are fabricated for cathode catalysts in Li-O2 batteries via electrospinning method followed by calcination. The Mn2O3 catalyst possesses a three-dimensional porous structure, which can offer good catalytic activity, expose plenty of active sites and improve the diffusion of electrolyte and O2. When employed as the cathode catalyst, the Li-O2 batteries show enhanced initial discharge capacity of 9701 mA h g−1 at a current density of 200 mA g−1, superior rate capacity and good cycling stability within 160 cycles at the capacity of 500 mA h g−1. These enhanced performances demonstrate a facile method to fabricate Mn2O3 with unique structure as a promising catalytic material for Li-O2 batteries.

Pt Nanorods-Decorated Macroporous Carbon Nanofiber Free-Standing Cathodes for High-Performance Li-O2 Battery

Controlling the pore structure of cathodes has a strong influence on the performance of Li-O2 battery. In the present study, macroporous carbon nanofiber (MCNF) mats are successfully fabricated through an electrospinning and templating methods using cross-linked polystyrene particles. Additionally, Pt nanorods are grown on the surface of the MCNF (PtNR-MCNF) as catalysts for Li/O2 reactions. As-prepared PtNR-MCNF has interconnected macropores along the MCNF interior and abundant surface openings. Those macropores are also connected to larger pores between individual MCNF through the orifices on the MCNF surface, rendering a hierarchical porous structure. Owing to the highly porous structure, Li-O2 cells using the PtNR-MCNF cathodes achieved a specific capacity of approximately 7,000 mAh/gc and even more at a current density of 200 mA/gc. In particular, the Li-O2 cell using the PtNR-MCNF cathode exhibited higher electrochemical performance in terms of rate capability, energy efficiency, and cycle stability. This study demonstrates that the growth of PtNRs resulted in the formation of poorly crystalized Li2O2, which significantly reduced the overpotentials, both during the discharge and the charge. Additionally, it contributed to the considerably prolonged cycle life of the Li-O2 cell using the PtNR-MCNF (468 cycles) compared to the cell using the MCNF cathode (272 cycles) with a limiting capacity of 1,000 mAh/gc at a current density of 500 mA/gc.

Mixed spinel and perovskite phased LaSrNiO nanoparticles as cathode catalyst for non-aqueous lithium-oxygen batteries

LaSrNiO nanoparticles with different doping amount of strontium are synthesized through sol-gel method accompanied by high-temperature calcination. With the increase of Sr content, the crystal structure of samples changes from perovskite to spinel phase that promote both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) property. As a cathode catalyst for Li-O2 battery, LaSrNiO nanoparticles show a capacity performance of 9000 mAh·g−1 and significantly enhanced cyclability. The improved battery performance with Sr-doped nanoparticles can be ascribed to the high surface area of Sr-doped LaSrNiO nanoparticles combined with mixed spinel and perovskite phased structure which facilitate specific capacity and OER performance obviously. This research work is believed to shed light on a new thought to boost the performance of Li-O2 battery.

Ultralong Cycle Life Li-O2 Battery Enabled by a MOF-Derived Ruthenium-Carbon Composite Catalyst with a Durable Regenerative Surface.

The cycling performance of Li-O2 batteries (LOBs), which is an important parameter determining the practical use of this advanced energy technology with ultrahigh energy density, is strongly affected by the nature of the oxygen electrocatalyst. As a good oxygen electrode, it should possess good activity for both the oxygen evolution reaction and the oxygen reduction reaction and superior stability under operating conditions. During the past, oxygen electrodes for LOBs were generally fabricated by loading noble metal nanoparticles on the surface of a porous carbon support. However, the nanoparticles could easily lose contact with the carbon support during the reversible liquid-gas-solid reactions that involve lithium ions, oxygen gas, and Li2O2. Herein, we reported a novel Ru-metal-organic framework (MOF)-derived carbon composite, characterized by stereoscopic Ru nanoparticle distribution within the carbon matrix, as an alternative oxygen catalyst of LOBs, enabling superior operational stability and favorable activity. More specifically, the battery demonstrated stable charge-discharge cycling for up to 800 times (∼107 days) at a current density of 500 mA g-1 with low discharge/charge overpotentials (∼0.2/0.7 V vs Li). A mechanism of regenerative surface was further proposed to explain the excellent cycling stability of the LOBs through the use of the Ru-MOF-C catalyst. These encouraging results imply an accessible solution to address issues related to the oxygen catalyst for the realization of practical LOBs.

Bifunctional perovskite electrocatalyst and PVDF/PET/PVDF separator integrated split test cell for high performance Li-O2 battery

In this work, we have studied the electrochemical performance of split test cell based Li-O2 battery using PVDF/PET/PVDF nanofiber non-woven membrane and La0.5Ce0.5Fe0.5Mn0.5O3 perovskite (denoted as LCFMO) air cathode. The LCFMO air cathode is prepared by a simple wet chemical co-precipitation method and the PVDF/PET/PVDF nanofiber separator is synthesized by an electrospinning method. The as-prepared air cathode and PVDF/PET/PVDF separators are assembled in Li-O2 cell and their charge-discharge profile is evaluated at the potential window of 2–4.5 V at 100 mA g−1 with a limited capacity range of 300, 500 and 1000 mAh g−1. The result certified that the LCFMO-(Urea) catalyst based Li-O2 battery with PVDF/PET/PVDF separator showed an excellent cycling stability over 263, 147 and 120 cycles, respectively. This is due to the excellent bifunctional activity of LCFMO catalyst and high ionic transport properties of PVDF/PET/PVDF membrane. Also, the use of LiI redox mediator can effectively reduce the both charge and discharge overpotential of our Li-O2 battery system. The optimal pore size, higher porosity and good ionic conductivity of the PVDF/PET/PVDF membrane is also an essential factor for the enhanced performance of Li-O2 battery. In addition, AC impedance study evidenced that the Li-O2 battery shows much lower interfacial charge transfer resistance (i.e., lower Rct), which indicates the good electrochemical properties of our proposed materials.

Micro‑meso-macroporous FeCo-N-C derived from hierarchical bimetallic FeCo-ZIFs as cathode catalysts for enhanced Li-O2 batteries performance

Abstract Developing bifunctional catalysts that increase both the OER and ORR kinetics and transport reactants with high efficiency is desirable. Herein, micro‑meso-macroporous FeCo-N-C-X (denoted as “M-FeCo-N-C-X”, X represents Fe/Co molar ratio in bimetallic zeolite imidazole frameworks FeCo-ZIFs) catalysts derived from hierarchical M-FeCo-ZIFs-X was prepared. The micropores in M-FeCo-N-C-X have strong capability in O2 capture as well as dictate the nucleation and early-stage deposition of Li2O2, the mesopores provided a channel for the electrolyte wetting, and the macroporous structure promoted more available active sites when used as cathode for Li-O2 batteries. More importantly, M-FeCo-N-C-0.2 based cathode showed a high initial capacity (18,750 mAh g−1@0.1 A g−1), good rate capability (7900 mAh g−1@0.5 A g−1), and cycle stability up to 192 cycles. Interestingly, the FeCo-N-C-0.2 without macropores suffered relatively poorer stability with only 75 cycles, although its discharge capacity was still as high as 17,200 mAh g−1(@0.1 A g−1). The excellent performance attributed to the synergistic contribution of homogeneous Fe, Co nanoparticles and N co-doping carbon frameworks with special micro‑meso-macroporous structure. The results showed that hierarchical FeCo-N-C architectures are promising cathode catalysts for Li-O2 batteries.

Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets with the Inherent Open Active Sites as Electrocatalysts in Aprotic Li-O2 Batteries.

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have the potential to improve the performance of Li-O2 batteries with high O2 accessibility, open catalytic active sites, and large surface areas. To obtain highly efficient cathode catalysts for aprotic Li-O2 batteries, a facile ultrasonicated method has been developed to synthesize three kinds of 2D MOFs (2D Co-MOF, Ni-MOF, and Mn-MOF). Contributing from the inherent open active sites of the Mn-O framework, the discharge specific capacity of 9464 mAh g-1 is achieved with the 2D Mn-MOF cathode, higher than those of the 2D Co-MOF and Ni-MOF cathodes. During the cycling test, the 2D Mn-MOF cathode stably operates more than 200 cycles at 100 mA g-1 with a curtailed discharge capacity of 1000 mAh g-1, quite longer than those of others. According to further electrochemical analysis, we observe that the 2D Mn-MOF outperforms 2D Ni-MOF and Co-MOF due to a superior oxygen reduction reactions and oxygen evolution reactions activity, in particular, the efficient oxidation of both LiOH and Li2O2. The present study provides new insights that the 2D MOF nanosheets can be well applied as the Li-O2 cells with high energy density and long cycling life.

Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions.

The aprotic lithium-oxygen (Li-O2 ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O2 battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O2 battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O2 batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li2 O2 and the mechanisms of Li2 O2 oxidation to O2 on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O2 batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O2 batteries in the future.

3D Hollow α-MnO2 Framework as an Efficient Electrocatalyst for Lithium-Oxygen Batteries.

Lithium-oxygen (Li-O2 ) batteries are attracting more attention owing to their superior theoretical energy density compared to conventional Li-ion battery systems. With regards to the catalytically electrochemical reaction on a cathode, the electrocatalyst plays a key role in determining the performance of Li-O2 batteries. Herein, a new 3D hollow α-MnO2 framework (3D α-MnO2 ) with porous wall assembled by hierarchical α-MnO2 nanowires is prepared by a template-induced hydrothermal reaction and subsequent annealing treatment. Such a distinctive structure provides some essential properties for Li-O2 batteries including the intrinsic high catalytic activity of α-MnO2 , more catalytic active sites of hierarchical α-MnO2 nanowires on 3D framework, continuous hollow network and rich porosity for the storage of discharge product aggregations, and oxygen diffusion. As a consequence, 3D α-MnO2 achieves a high specific capacity of 8583 mA h g-1 at a current density of 100 mA g-1 , a superior rate capacity of 6311 mA h g-1 at 300 mA g-1 , and a very good cycling stability of 170 cycles at a current density of 200 mA g-1 with a fixed capacity of 1000 mA h g-1 . Importantly, the presented design strategy of 3D hollow framework in this work could be extended to other catalytic cathode design for Li-O2 batteries.

Modulating the Surface Atomic Arrangement of Perovskite LaMnO3/C Towards Superior Electrocatalytic Activity and High Performance for Li-O2 Batteries.

A composite of Lanthanum manganese oxide-carbon (LaMnO3/C) has been also synthesized by a facile electrospinning approach followed by controlled heat treatment, in which the carbon form a continuous conductive network connecting the electrocatalyst LaMnO3 nanoparticles together to facilitate good electrochemical performance. Based on a correlation between theoretical (DFT) and experimental analysis on the effect of the surface atomic arrangement, the electrocatalyst (Mn-terminated LaMnO3) with uniform Mn surface termination show favourable rechargeability, and good phase and morphology stability in lithium oxygen batteries compared to La rich surface termination. Excellent cycling performance is also demonstrated, in which the terminal voltage is higher than 2.4 V after 100 cycles at limited capacity of 1000 mAh g-1 (based on composite). Figure 1

Novel and highly efficient cathodes for Li-O2 batteries: 3D self-standing NiFe@NC-functionalized N-doped carbon nanonet derived from Prussian blue analogues/biomass composites

Traditional 3D self-standing electrodes for lithium-oxygen (Li-O2) batteries require a high cost and complex preparation process that restrict their development. Herein, discarded biomass (pomelo peel, PP) is used as raw material and in-situ grew NiFe-Prussian blue analogues on its surface. Then a novel 3D binder-free and self-standing NiFe@NC/PPC electrode is obtained through the carbonization process and directly used as a cathode in Li-O2 batteries.Compared with PPC (carbonized pomelo peel) and NiFe@NC/CP (NiFe@NC catalysts coated on carbon paper), NiFe@NC/PPC gathered the advantageous characteristics of i) efficient diffusion rates for O2/electrolyte and ii) good catalytic activity for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). The as fabricated Li-O2 batteries, with NiFe@NC/PPC as cathode, are performed a relatively high specific capacity (13.79 mAh cm−2), a long cycle life (290 cycles) at a current density of 0.1 mA cm−2. Therefore, considering the convenience of synthesis method and the inexpensive raw materials, this is a feasible way to prepare high performance and low cost cathodes for Li-O2 batteries.

Spinel NiCo2S4 as Excellent Bi-Functional Cathode Catalysts for Rechargeable Li-O2 Batteries

Developing bi-functional catalyst is an effective way to improve the kinetics of oxygen electrochemistry and promote the performance of Li-O2 batteries. In this study, spinel NiCo2S4 with urchin-like and yolk-shell morphologies were successfully synthesized and evaluated as cathode catalysts for rechargeable Li-O2 batteries. The results demonstrate both NiCo2S4 materials are catalytically active toward ORR/OER, but the urchin-like NiCo2S4 performs better with faster kinetics, higher capacity, lower polarization and longer cycle life. Moreover, cycling performance of the Li-O2 batteries with urchin-like NiCo2S4 is evidently better than the reported data in literatures for the batteries with many other transition metal sulfides.

Highly reversible Li-O2 battery induced by modulating local electronic structure via synergistic interfacial interaction between ruthenium nanoparticles and hierarchically porous carbon

The interfacial interaction between catalysts and substrates has been considered as a pivotal factor determining the activities in different applications. However, interfacial interaction-dependent catalytic activities are currently neglected in understanding oxygen involved reaction in Li-O2 battery, seriously restricting the development of high performance Li-O2 battery. Herein, Ru@hierarchically porous carbon (Ru@HPC) with well-defined interfaces are fabricated and employed as cathode in Li-O2 battery. Notably, Ru@HPC based Li-O2 battery demonstrate better performance than that based on cathode formed by simply mixing Ru nanoparticles with hierarchically porous carbon (Ru/HPC). The Ru@HPC improved performance with a large specific capacity of ~7100 mA h g−1, high round-trip efficiency of 71%, high rate capability, and excellent cyclic stability of over 125 cycles (over 40 days). Density functional theory calculations indicated that the interfacial interaction between Ru nanoparticles and carbon substrate in Ru@HPC, which triggers electron transfer from ruthenium to carbon and thus optimizes the surface adsorption energy of the reactants and intermediate, facilitates the performance improvement of Li-O2 battery. Our study for the first time reveals that the interfacial interaction between catalyst and substrate is a critical factor determining the Li-O2 battery performance and offers a promising design strategy of catalyst for Li-O2 batteries.

α-MnO2 Nanowire-Anchored Highly Oxidized Cluster as a Catalyst for Li-O2 Batteries: Superior Electrocatalytic Activity and High Functionality.

An effective chemical way to optimize the oxygen electrocatalyst and Li-O2 electrode functionalities of metal oxide can be developed by the control of chemical bond nature with the surface anchoring of highly oxidized selenate (SeO4 2- ) clusters. The bond competition between (Se6+ -O) and (Mn-O) bonds is quite effective in stabilizing Jahn-Teller-active Mn3+ state and in increasing oxygen electron density of α-MnO2 nanowire (NW). The selenate-anchored α-MnO2 NW shows excellent oxygen electrocatalytic activity and electrode performance for Li-O2 batteries, which is due to the improved charge transfer kinetics and reversible formation/decomposition of Li2 O2 . The present study underscores that the surface anchoring of highly oxidized cluster can provide a facile, effective way of improving the oxygen electrocatalyst and electrochemical performances of nanostructured metal oxide in Li-O2 cells.

Iron phthalocyanine supported on 3D nitrogen-doped graphene aerogel as an electrocatalyst for non-aqueous Li−O2 batteries

Solid electrocatalysts of iron phthalocyanine (FePc) embedded in 3D porous N-doped graphene aerogel (NGA) are designed and applied as cathode catalysts for non-aqueous lithium-oxygen (Li−O2) batteries. Two composites with different axial bonding types between FePc and NGA, including a coordinate covalent bond (FePc/NGA-c) and non-covalent π−π stacking interaction (FePc/NGA-π), are fabricated by reflux and physical mixing methods, respectively. Systematical characterizations confirmed the FePc/NGA-c composite using axial coordination between FePc and NGA substrate via the FeNC bond exhibited more thermal stability and less stack and aggregation of FePc molecules in the composite. Combining the bifunctional catalytic activity of the FePc molecule with oxygen reduction reaction/oxygen evolution reaction (ORR/OER) processes and a flexible porous 3D structure and N-doping in NGA, the electrochemical test demonstrated both FePc anchored on NGA composites display higher activity as bifunctional catalysts for O2 electrodes in Li−O2 batteries. However, the FePc/NGA-c electrode displays better electrochemical performance than the FePc/NGA-π composite due to the axial covalent connection of the FePc catalyst with NGA substrate, leading to higher electrocatalytic activity and exceptional structural durability during cycling for FePc/NGA-c. This work provides new insight into the steric effect of the coordination bond between FePc and NGA on the electrocatalytic activity of O2 electrodes. These results indicate our unique structural design of FePc/NGA-c using solid FePc axially anchored on NGA via covalent bonding is a promising cathode material for high performance of rechargeable LiO2 batteries.