Oxygen Vacancy-Rich RuO2-Co3O4 Nanohybrids as Improved Electrocatalysts for Li-O2 Batteries

Piperidine-based ionic liquid additive with electrostatic shielding and redox activity enabling advanced lithium-oxygen batteries

Here, we propose a piperidine-based ionic liquid additive. The electrostatic shielding effect of the piperidine cation (PP13+) effectively inhibits the growth of lithium dendrites. Simultaneously, the redox activity of the bromine anion synergistically reduces the overpotential. This approach significantly improves the cycling performance of lithium-oxygen batteries.

Terephthalic Acid Intercalated CoNi-LDH Materials for Improved Li-O2 Battery

CoNi-LDH (layered CoNi double hydroxides) hollow nanocages with specific morphology are obtained by Ni ion etching of ZIF-67 (Zeolitic imidazolate framework-67). The structure of the layered materials is further modified by molecular intercalation. The original interlayer anions are replaced by the ion exchange effect of terephthalic acid, which helps to increase the interlayer distance of the material. The intercalated cage-like structures not only benefit for the storage of oxygen, and the discharge product reaction, but also have more support between the material layers. The experimental results show that the excessive use of intercalation agent will affect structural stability of the intercalated CoNi-LDH. By adjusting the amount of terephthalic acid, the intercalated CoNi-LDH-2 (with 0.02 mmol terephthalic acid intercalated) is not easy to collapse after 209 cycles and shows the best electrochemical performance in Li-O2 battery.

NiCu alloys anchored Co3O4 nanowire arrays as efficient hydrogen evolution electrocatalysts in alkaline and neutral media

Robust and long-lasting non-precious metal electrocatalysts are essential to achieve sustainable hydrogen production. In this work, we synthesized Co₃O₄@NiCu by electrodepositing NiCu nanoclusters onto Co₃O₄ nanowire arrays that were formed in situ on nickel foam. The introduction of NiCu nanoclusters altered the inherent electronic structure of Co₃O₄, significantly increasing the exposure of active sites and enhancing endogenous electrocatalytic activity. Co₃O₄@NiCu exhibited overpotentials of only 20 and 73 mV, respectively, at 10 mA cm^-2 current densities in alkaline and neutral media. These values were equivalent to those of commercial Pt catalysts. Finally, the electron accumulation effect at the Co₃O₄@NiCu, along with a negative shift in the d-band center, is finally revealed by theoretical calculations. Hydrogen adsorption on consequent electron-rich Cu sites was effectively weakened, leading to a robust catalytic activity for the hydrogen evolution reaction (HER). Overall, this study proposes a practical strategy for creating efficient HER electrocatalysts in both alkaline and neutral media.

Engineering the Electronic Interaction between Atomically Dispersed Fe and RuO2 Attaining High Catalytic Activity and Durability Catalyst for Li-O2 Battery

It is significant to develop catalysts with high catalytic activity and durability to improve the electrochemical performances of lithium-oxygen batteries (LOBs). While electronic metal-support interaction (EMSI) between metal atoms and support has shown great potential in catalytic field. Hence, to effectively improve the electrochemical performance of LOBs, atomically dispersed Fe modified RuO₂ nanoparticles are designed to be loaded on hierarchical porous carbon shells (Fe_SA -RuO₂ /HPCS) based on EMSI criterion. It is revealed that the Ru-O-Fe₁ structure is formed between the atomically dispersed Fe atoms and the surrounding Ru sites through electron interaction, and this structure could act as the ultra-high activity driving force center of oxygen reduction/evolution reaction (ORR/OER). Specifically, the Ru-O-Fe₁ structure enhances the reaction kinetics of ORR to a certain extent, and optimizes the morphology of discharge products by reducing the adsorption energy of catalyst for O₂ and LiO₂ ; while during the OER process, the Ru-O-Fe₁ structure not only greatly enhances the reaction kinetics of OER, but also catalyzes the efficient decomposition of the discharge products Li₂ O₂ by the favorable electron transfer between the active sites and the discharge products. Hence, LOBs based on FeSA-RuO₂ /HPCS cathodes show an ultra-low over-potential, high discharge capacity and superior durability.

RuO2-Incorporated Co3O4 Nanoneedles Grown on Carbon Cloth as Binder-Free Integrated Cathodes for Tuning Favorable Li2O2 Formation

Developing ideal Li-O₂ batteries (LOBs) requires the discharge product to have a large quantity, have large contact area with the cathode, and not passivate the porous surface after discharge, which put forward high requirement for the design of cathodes. Herein, combining the rational structural design and high activity catalyst selection, minor amounts of RuO₂-incorporated Co₃O₄ nanoneedles grown on carbon cloth are successfully synthesized as binder-free integrated cathodes for LOBs. With this unique design, plenty of electron-ion-oxygen tri-phase reaction interface is created, the side reaction from carbon is isolated, and oxygen reduction reaction/oxygen evolution reaction (OER) kinetics are significantly facilitated. Upon discharge, film-like Li₂O₂ is observed growing on the needle surface first and eventually ball-like Li₂O₂ particles form at each tip of the needle. The cathode surface remains porous after discharge, which is beneficial to the OER and is rare in the previous reports. The battery exhibits a high specific discharge capacity (7.64 mAh cm^-2) and a long lifespan (500 h at 0.1 mA cm^-2). Even with a high current of 0.3 mA cm^-2, the battery achieves a cycling life of 200 h. In addition, punch-type LOBs are fabricated and successfully operated, suggesting that the cathode material can be utilized in ultralight, flexible electronic devices.

Interfacial Engineering of Co3 O4 /Fe2 O3 Nano-Heterostructure Toward Superior Li-O2 Batteries

A major issue with Li-O₂ batteries is their slow oxygen reduction and evolution kinetics, necessitating catalysts with high catalytic activity to improve reaction kinetics and cycle stability. Herein, a nano-heterostructured catalyst composed of Co₃ O₄ and Fe₂ O₃ (Co₃ O₄ /Fe₂ O₃ ) with a porous rod morphology is achieved through an interfacial engineering strategy by constructing Fe₂ O₃ on the Co₃ O₄ surface, which can function as a high-performance cathode in order to efficiently encourage the oxygen reduction and evolution while also reduce the battery polarization during charging and discharging. The density functional theory (DFT) calculations show the differences in charge density at the interface of nano-heterostructures, demonstrating the occurrence of an electron transfer process in the interface region of Co₃ O₄ and Fe₂ O₃ , implying a strong electronic coupling transfer, and in turn changing the electronic structure of the Co₃ O₄ . This significantly reduces the adsorption energy of LiO₂ intermediates, thereby effectively lowering the overpotential. The resultant Li-O₂ battery has larger discharge specific capacity, lower overpotential for the efficient oxygen evolution/reduction, as well as good cycling stability of 280 cycles. This work demonstrates an effective method to fabricate the nano-heterostrucutred materials with enhanced catalytic efficiency for advanced energy applications.

Interface engineering of hierarchical NiCoP/NiCoSx heterostructure arrays for efficient alkaline hydrogen evolution at large current density

The development of non-noble metal electrocatalysts with high activity and long-term stability for the hydrogen evolution reaction (HER), especially at large current density, is of great significance for industrial hydrogen production from water using renewable electricity. Constructing heterostructures with interfacial interactions is an effective strategy to improve the catalytic performance for large-current-density HER. Herein, we innovatively present a facile two-step electrodeposition method to immobilize a hierarchical NiCoP/NiCoS_x heterostructure on Ni foam (NF) for alkaline HER. The strong interfacial coupling effect between NiCoP and NiCoS_x not only offers abundant active sites for fast electrochemical reaction, but also enhances the charge transfer ability accompanied by high electrical conductivity. Consequently, the obtained self-supporting NiCoP/NiCoS_x/NF exhibits an excellent catalytic performance with low overpotentials of 68, 144 and 222 mV to deliver current densities of 10, 100 and 500 mA cm^-2 in 1 M KOH, along with good stability for more than 110 h, outperforming most of the reported non-noble metal based HER catalysts. Density functional theory (DFT) results further confirm that this bimetal phosphide/sulfide heterostructure can synergistically optimize the Gibbs free energy of H* during the HER process, thus accelerating the HER reaction kinetics. This work provides a new strategy toward the rational design of large-current-density electrocatalysts, which have great potential in practical large-scale hydrogen production.

Porous MCo2O4(M = Zn, Cu, Fe, Mn) as high efficient bi-functional catalysts for oxygen reduction and oxygen evolution reaction

High-efficiency bi-functional electrocatalysts with long-term stability are critical to the development of many kinds of fuel cells, because that the performance of battery is limited by the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, porous MCo₂O₄(M = Zn, Cu, Fe, Mn) were prepared by hydrothermal method with NH₄F and urea as surfactants. FeCo₂O₄with porous structure has more oxygen defects and the larger specific surface area than other MCo₂O₄(M = Zn, Cu, Mn), and it not onlysupplies more active sites but also avails the transmission of electrolyte and O₂in the process of ORR and OER in 0.1 M KOH aqueous solution. Porous FeCo₂O₄electrode material produces less intermediate H₂O₂, and its ORR is mainly controlled by a 4e^-reaction path. Compared with commercial Pt/C, the prepared FeCo₂O₄has comparable ORR activity and excellent OER activity. At the same time, the stability of FeCo₂O₄to ORR is significantly higher than that of commercial Pt/C. The porous FeCo₂O₄was prepared by facile synthesis procedure could be a potential promising bi-functional catalyst due to its high electrocatalytic activities and long-term stability for both the ORR and OER.

Crystal Phase Conversion on Cobalt Oxide: Stable Adsorption toward LiO2 for Film-Like Discharge Products Generation in Li-O2 Battery

Regulating the structure and morphology of discharge product is one of the key points for developing high performance Li-O₂ batteries (LOBs). In this study, the reaction mechanism of LOB is successfully controlled by the regulated fine structure of cobalt oxide through tuning the crystallization process. It is demonstrated that the cobalt oxide with lower crystallinity shows stronger affinity toward LiO₂ , inducing the growth of film-like LiO₂ on the electrode surface and inhibiting the further conversion to Li₂ O₂ . The batteries catalyzed by the lower crystallinity cobalt oxide hollow spheres which pyrolyzed from ZIF-67 at 260 °C (ZIF-67-260), go through the generation and decomposition of amorphous film-like LiO₂ , which significantly reduces the charge overpotential and improves the cycle life. By contrast, the ZIF-67 hollow spheres pyrolyzed at 320 °C (ZIF-67-320) with better crystallinity are more likely to go through the solution-mediated mechanism and induce the aggregation of discharge product, resulting in the sluggish kinetics and limited performance. The combined density functional theory data also directly support the strong relationship between the adsorption toward LiO₂ by the electrocatalyst and the battery performance. This work provides an important way for tuning the intermediate and constructing the high-performance battery system.

Cobalt Single Atom Incorporated in Ruthenium Oxide Sphere: A Robust Bifunctional Electrocatalyst for HER and OER

The development of highly active and stable bifunctional noble-metal-based electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is a crucial goal for clean and renewable energy, which still remains challenging. Herein, we report an efficient and stable catalyst comprising a Co single atom incorporated in an RuO₂ sphere for HER and OER, in which the Co single atom in the RuO₂ sphere was confirmed by XAS, AC-STEM, and DFT. This tailoring strategy uses a Co single atom to modify the electronic structures of the surrounding Ru atoms and thereby remarkably elevates the electrocatalytic activities. The catalyst requires ultralow overpotentials, 45 mV for HER and 200 mV for OER, to deliver a current density of 10 mA cm^-2 . The theoretical calculations reveal that the energy barriers for HER and OER are lowered after incorporation of a cobalt single atom.