Suppressing Cation Migration and Reducing Particle Cracks in a Layered Fe-Based Cathode for Advanced Sodium-Ion Batteries.

Sodium-ion batteries have huge potential in large-scale energy storage applications. Layered Fe-based oxides are one of the desirable cathode materials due to abundance in the earth crust and high activity in electrochemical processes. However, Fe-ion migration to Na layers is one of the major hurdles leading to irreversible structural degradation. Herein, it is revealed that distinct Fe-ion migration in cycling NaFeO2 (NFO) should be mainly responsible for the strong local lattice strain and resulting particle cracks, all of which results in the deterioration of electrochemical performance. More importantly, a strategy of Ru doping could effectively suppress the Fe-ion migration and then reduce the local lattice strain and the particle cracks, finally to greatly enhance the sodium storage performance. Atomic-scale characterization shows that NFO electrode after cycling presents the intense lattice strain locally, accompanied by the remarkable particle cracks. Whereas, Ru-doped NFO electrode maintains the well-ordered layered structure by inhibiting the Fe-O distortion, so as to eliminate the resulting side effect. As a result, Ru-doped NFO could greatly improve the comprehensive electrochemical performance by delivering a reversible capacity of 120 mA h g-1 , about 80% capacity retention after 100 cycles. The findings provide new insights for designing high-performance electrodes for sodium-ion batteries.

Concave Pd-Pt Core-Shell Nanocrystals with Ultrathin Pt Shell Feature and Enhanced Catalytic Performance.

One-pot creation of unique concave Pd-Pt core-shell polyhedra has been developed for the first time using an efficient approach. Due to the concave feature and ultrathin Pt shell, the created Pd-Pt core-shell polyhedra exhibit enhanced catalytic performance in both the electrooxidation of methanol and hydrogenation of nitrobenzene, as compared with commercial Pt black and Pd black catalysts.

Phase and Interface Engineering of Platinum-Nickel Nanowires for Efficient Electrochemical Hydrogen Evolution.

The design of high-performance electrocatalysts for the alkaline hydrogen evolution reaction (HER) is highly desirable for the development of alkaline water electrolysis. Phase- and interface-engineered platinum-nickel nanowires (Pt-Ni NWs) are highly efficient electrocatalysts for alkaline HER. The phase and interface engineering is achieved by simply annealing the pristine Pt-Ni NWs under a controlled atmosphere. Impressively, the newly generated nanomaterials exhibit superior activity for the alkaline HER, outperforming the pristine Pt-Ni NWs and commercial Pt/C, and also represent the best alkaline HER catalysts to date. The enhanced HER activities are attributed to the superior phase and interface structures in the engineered Pt-Ni NWs.

Ordered PdCu-Based Nanoparticles as Bifunctional Oxygen-Reduction and Ethanol-Oxidation Electrocatalysts.

The development of superior non-platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen-reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu-based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol-oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni.

Lattice-Strained Metallic Aerogels as Efficient and Anti-Poisoning Electrocatalysts for Oxygen Reduction Reaction.

Lattice strain engineering optimizes the interaction between the catalytic surface and adsorbed molecules. This is done by adjusting the electron and geometric structure of the metal site to achieve high electrochemical performance, but, to date, it has been rarely reported on anti-poisoned oxygen reduction reaction (ORR). Herein, lattice-strained Pd@PdBiCo quasi core-shell metallic aerogels (MAs) were designed by "one-pot and two-step" method for anti-poisoned ORR. Pd@PdBiCo MAs/C maintain their original activity (1.034 A mgPd -1 ) in electrolytes with CH3 OH and CO at 0.85 V vs. reversible hydrogen electrode (RHE), outperforming the commercial Pd/C (0.156 A mgPd -1 ), Pd MAs/C (0.351 A mgPd -1 ), and PdBiCo MAs/C (0.227 A mgPd -1 ). Moreover, Pd@PdBiCo MAs/C also show high stability and anti-poisoning with negligible activity decay after 8000 cycles in 0.1 m KOH+0.3 m CH3 OH. These results of X-ray photoelectron spectroscopy, CO stripping, and diffuses reflectance FTIR spectroscopy reveal that the tensile strain and strong interaction between different elements of Pd@PdBiCo MAs/C effectively optimize the electronic structure to promote O2 adsorption and activation, while suppressing CH3 OH oxidation and CO adsorption, leading to high ORR activity and anti-poisoning property. This work inspires the rational design of MAs in fuel cells and beyond.

3D Noble-Metal Nanostructures Approaching Atomic Efficiency and Atomic Density Limits.

Noble metals have been widely used in catalysis, however, the scarcity and high cost of noble metal motivate researchers to balance the atomic efficiency and atomic density, which is formidably challenging. This article proposes a robust strategy for fabricating 3D amorphous noble metal-based oxides with simultaneous enhancement on atomic efficiency and density with the assistance of atomic channels, where the atomic utilization increases from 18.2% to 59.4%. The unique properties of amorphous bimetallic oxides and formation of atomic channels have been evidenced by detailed experimental characterizations and theoretical simulations. Moreover, the universality of the current strategy is validated by other binary oxides. When Cu2IrOx with atomic channels (Cu2IrOx-AE) is used as catalyst for oxygen evolution reaction (OER), the mass activity and turnover frequency value of Cu2IrOx-AE are 1-2 orders of magnitude higher than CuO/IrO2 and Cu2IrOx without atomic channels, largely outperforming the reported OER catalysts. Theoretical calculations reveal that the formation of atomic channels leads to various Ir sites, on which the proton of adsorbed *OH can transfer to adjacent O atoms of [IrO6]. This work may attract immediate interest of researchers in material science, chemistry, catalysis, and beyond.

PtNi/PtIn-Skin Fishbone-Like Nanowires Boost Alkaline Hydrogen Oxidation Catalysis.

The development of high-performance platinum (Pt)-based electrocatalysts for the hydrogen oxidation reaction (HOR) is highly desirable for hydrogen fuel cells, but it is limited by the sluggish kinetics and severe carbon monoxide (CO) poisoning in alkaline medium. Herein, we explore a class of facet-selected Pt-nickel-indium fishbone-like nanowires (PtNiIn FNWs) featuring high-index facets (HIFs) of Pt3In skin as efficient alkaline HOR catalysts. Impressively, the optimized Pt66Ni6In28 FNWs show the highest mass and specific activities of 4.02 A mgPt-1 and 6.56 mA cm-2, 2.0/2.1 and 13.9/15.6 times larger than those of commercial PtRu/C and commercial Pt/C, respectively, along with a competitive CO-tolerance ability. Specifically, they exhibit only 6.0% current density decay after 10000 s of operation and 25.7% activity loss after 2000 s in the presence of 1000 ppm of CO. Moreover, an isotope experiment and density functional theory (DFT) calculations further prove that the unique structure and synergy among Pt, Ni, and In endow these Pt66Ni6In28 FNWs with an optimized hydrogen binding energy (HBE) and an advantageous hydroxide binding energy (OHBE), giving them excellent alkaline HOR properties. The combined construction of surface-skin and HIFs in PtNiIn FNWs will offer an available method to realize the potential applications of advanced non-PtRu-based catalysts in fuel cells and beyond.

Mo-doped PdCu nanoparticles as high-performance catalysts for oxygen reduction reactions.

The instability of palladium-based binary alloys hinders their wide application in the oxygen reduction processes. Here, we prepared Mo-doped PdCu nanoparticles with controllable dopant content and valence. Further research has revealed that Mo, particularly Mo5+, may effectively suppress the oxidation of Pd and Cu, optimize the oxygen binding of Pd, and increase catalytic activity and stability. In particular, Mo-PdCu-1/C with the highest Mo5+ content shows the best oxygen reduction reaction (ORR) mass activity (1.20 A mg-1Pd), which is 4.8 times higher than that of PdCu/C. It also exhibits outstanding stability, retaining 80.8% of the original mass activity after 20 000 cycles. This study clearly explains the mechanism by which Mo doping affects the performance and provides a reference for further optimization of catalyst performance for fuel cell industrialization.

A high-stability biphasic layered cathode for sodium-ion batteries.

A novel biphasic layered Na0.62Ni0.33Mn0.62Sb0.05O2 cathode is introduced which can be easily synthesized via a solid-state reaction method. Compared with its monophasic counterpart Na0.67Ni0.33Mn0.67O2, biphasic Na0.62Ni0.33Mn0.62Sb0.05O2 displays a smoother (dis)charge profile, superior rate capability along with splendid cycling performance. Structural and kinetic studies respectively demonstrate extremely small volume strain and rapid charge transfer during the electrochemical process.

Improving the structural and cyclic stabilities of P2-type Na0.67MnO2 cathode material via Cu and Ti co-substitution for sodium ion batteries.

An air-stable Na0.67Mn0.7Cu0.15Ti0.15O2 (NMCT) has been synthesized using a solid-state method. It displays a reversible capacity of 170 mA h g-1 and a capacity retention of 82.5% after 300 cycles. NMCT also exhibits good structural stability upon electrochemical de/intercalation processes as observed by operando XRD. And the result shows that the unit-cell volume change of NMCT during the whole process of Na+ de/intercalation is only 3.2%. These data indicate that NMCT is a promising cathode material for sodium ion batteries (SIBs).

Ni-Doped Layered Manganese Oxide as a Stable Cathode for Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) are one of the promising alternatives to lithium-ion batteries (LIBs). Layered potassium manganese oxides are more attractive as cathodes for PIBs due to their high capacity, low cost, and simple synthesis method but suffer from the Jahn-Teller effect of Mn3+ in material synthesis. Here, a layered P3-type K0.67Mn0.83Ni0.17O2 material with a suppressed Jahn-Teller effect was successfully synthesized. K0.67Mn0.83Ni0.17O2 delivers a specific capacity of 122 mAh g-1 at 20 mA g-1 in the first discharge, superior rate performance, and good cycling stability (75% capacity retention cycled at a high rate of 500 mA g-1 after 200 cycles). Besides, the K ion diffusion coefficient of the K0.67Mn0.83Ni0.17O2 electrode can reach 10-11 cm2 s-1, which are larger than the Ni-free electrode. The X-ray diffraction and electron diffraction analyses demonstrate that appropriate nickel could suppress the Jahn-Teller effect and reduce the structural deterioration, resulting in more migration pathways for K ions, thus enhancing the rate capability and cycling performance. These results provide a strategy to develop high-performance cathode materials for PIBs and deepen the understanding of structural deterioration in layered manganese-based oxides.

P2-Type Layered Na0.75Ni1/3Ru1/6Mn1/2O2 Cathode Material with Excellent Rate Performance for Sodium-Ion Batteries.

Layered oxides acting as sodium hosts have attracted extensive attention due to their structural flexibility and large theoretical capacity. However, the diffusion of Na ions always presents sluggish kinetics due to the larger ionic radius sand mass of Na compared to Li. Herein, we report a P2-type layered cathode material, namely, Na0.75Ni1/3Ru1/6Mn1/2O2 with superfast ion transport, where the Na+ diffusion coefficient is calculated mainly in the region of 10-10 to 10-11 cm2 s-1 during the charge and discharge process. The electrochemical tests also show that this cathode material exhibits a high capacity of 161.5 mAh g-1, excellent rate performance (when the rate increases from 0.2C-10C, the capacity retention is 74%), and outstanding cyclic performance (maintaining 79.5% for 500 cycles even at a high rate of 10C). Our findings provide new insights for the design of the open framework for fast transport of Na and promote the high-power performance of sodium-ion batteries (SIBs).

A Superlattice-Stabilized Layered Oxide Cathode for Sodium-Ion Batteries.

Sodium-ion batteries are in high demand for large-scale energy storage applications. Although it is the most prevalent cathode, layered oxide is associated with significant undesirable characteristics, such as multiple plateaus in the charge-discharge profiles, and cation migration during repeated cycling of Na-ions insertion and extraction, which results in sluggish kinetics, capacity loss, and structural deterioration. Here, a new strategy, i.e., the manipulation of transition-metal ordering in layered oxides, is proposed to show a prolonged charge-discharge plateau and cation-migration-free structural evolution. The results demonstrate that the transition-metal ordering with a honeycomb-type superlattice can adjust the crystal lattice and suppress cation migration by modifying the crystal strain to realize a large reversible capacity and excellent cycling performance, which are not characteristics of the widely used common layered oxides. These findings can provide new insight that can be used to improve the design of high-performance electrode materials for secondary-ion batteries.

Sodium Alginate Enabled Advanced Layered Manganese-Based Cathode for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising candidates applied to large-scale energy storage systems owing to abundant sodium resources and high economic efficiency. Layered manganese-based oxides as a prevailing cathode for sodium-ion batteries have been extensively studied, where doping or coating has been demonstrated to improve the electrochemical performance. However, the binder that tends to be the popular poly(vinylidene difluoride), is revealed to generate swellability upon cycling, leading to electrode material cracks and disconnection with current collectors. For the above issues, in this work, environmentally friendly sodium alginate is utilized as the aqueous binder in a conventional layered transition-metal oxide cathode P2-Na2/3MnO2 for SIBs. Through credible comparative experiments, sodium alginate is testified to play an essential role in suppressing cracks on the surface of materials, preventing surge in charge-transfer resistance and restraining detachment between electrode and current collector. Therefore, sodium alginate is proved to be an ideal binder to match with P2-Na2/3MnO2, where some issues existed before, as a promising cathode material with excellent performance and low cost. This study displays that improving battery performance by exploring suitable binder systems can equal or even exceed the performance improvement through modification of the material itself, and this perspective of enhancement should not be ignored.

A New Type of Li-Rich Rock-Salt Oxide Li2 Ni1/3 Ru2/3 O3 with Reversible Anionic Redox Chemistry.

Li-rich oxide cathodes are of prime importance for the development of high-energy lithium-ion batteries (LIBs). Li-rich layered oxides, however, always undergo irreversible structural evolution, leading to inevitable capacity and voltage decay during cycling. Meanwhile, Li-rich cation-disordered rock-salt oxides usually exhibit sluggish kinetics and inferior cycling stability, despite their firm structure and stable voltage output. Herein, a new Li-rich rock-salt oxide Li2 Ni1/3 Ru2/3 O3 with Fd-3m space group, where partial cation-ordering arrangement exists in cationic sites, is reported. Results demonstrate that a cathode fabricated from Li2 Ni1/3 Ru2/3 O3 delivers a large capacity, outstanding rate capability as well as good cycling performance with negligible voltage decay, in contrast to the common cations disordered oxides with space group Fm-3m. First principle calculations also indicate that rock-salt oxide with space group Fd-3m possesses oxygen activity potential at the state of delithiation, and good kinetics with more 0-TM (TM = transition metals) percolation networks. In situ Raman results confirm the reversible anionic redox chemistry, confirming O2- /O- evolution during cycles in Li-rich rock-salt cathode for the first time. These findings open up the opportunity to design high-performance oxide cathodes and promote the development of high-energy LIBs.

Enhanced K-ion kinetics in a layered cathode for potassium ion batteries.

A layered cathode for K-ion storage was achieved using electrochemical ion-exchange. It delivers a large specific capacity, superior rate performance and excellent cycling performance. Interestingly, it was found from the GITT results that the K ion diffusion coefficients were above 10-12 cm2 s-1, comparable with that of Na-ion in the layered structure.

Suppressed the High-Voltage Phase Transition of P2-Type Oxide Cathode for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs), using the resourceful Mn-based materials as cathodes, have been considered as promising candidates for large-scale energy-storage applications. However, the representative P2-type Mn-based layered oxide cathode usually suffers from a limited specific capacity and a poor cycle life in Na-ion intercalation and deintercalation processes because of the unavoidable phase transition at a high voltage. Herein, we developed Ru-substituted P2-Na0.6MnO2 as a promising sodium host with a high reversible capacity and cycle life. The multiple characterization investigations reveal that Ru substitution could improve the electronic and ionic conductions and particularly suppress the phase transition of P2-OP4, resulting in the extension of the single-phase reaction region. Ru substitution not only enhances the specific capacity (209.3 mA h g-1) but also improves the rate capability (∼100 mA h g-1 at 50 C) and cycling stability. This work may open a new avenue for designing and fabricating SIBs by using Mn-based cathodes with high capacity and stability.

Manganese-Based Na-Rich Materials Boost Anionic Redox in High-Performance Layered Cathodes for Sodium-Ion Batteries.

To improve the energy and power density of Na-ion batteries, an increasing number of researchers have focused their attention on activation of the anionic redox process. Although several materials have been proposed, few studies have focused on the Na-rich materials compared with Li-rich materials. A key aspect is sufficient utilization of anionic species. Herein, a comprehensive study of Mn-based Na1.2 Mn0.4 Ir0.4 O2 (NMI) O3-type Na-rich materials is presented, which involves both cationic and anionic contributions during the redox process. The single-cation redox step relies on the Mn3+ /Mn4+ , whereas Ir atoms build a strong covalent bond with O and effectively suppress the O2 release. In situ Raman, ex situ X-ray photoelectron spectroscopy, and soft-X-ray absorption spectroscopy are employed to unequivocally confirm the reversibility of O2 2- species formation and suggest a high degree of anionic reaction in this NMI Na-rich material. In operando X-ray diffraction study discloses the asymmetric structure evolution between the initial and subsequent cycles, which also explains the effect of the charge compensation mechanism on the electrochemical performance. The research provides a novel insight on Na-rich materials and a new perspective in materials design towards future applications.

Amorphous P2S5/C Composite as High-Performance Anode Materials for Sodium-Ion Batteries.

We show a general method for achieving high-performance sodium storage materials via transforming crystalline P2S5 to amorphous P2S5 adhered to carbon matrix. The amorphous P2S5/C composite shows unique structural characteristics differing from the crystalline, which is identified by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM) and so on. The amorphous P2S5/C composite exhibits a safe average potential of 0.82 V, a reversible capacity of 400 mA h g-1, a remarkable capacity retention of 89.4% over 4000 cycles as well as good rate capability. Our findings open up opportunities to design of advanced anodes for room-temperature sodium-ion batteries.

Exploring a high capacity O3-type cathode for sodium-ion batteries and its structural evolution during an electrochemical process.

An O3-layered oxide of NaFe0.25Mn0.25Ni0.25Ti0.25O2 was successfully synthesized. When serving as a cathode during sodium-ion cell operation, it exhibits excellent electrochemical performance. The operando XRD result reveals a reversible O3 → O3 + P3 → O1 + P3 phase transformation of NaFe0.25Mn0.25Ni0.25Ti0.25O2 during an electrochemical process.