Ex-situ X-ray Photoelectron Spectroscopy Research Articles

In-situ synthesis of two-dimensional sheet-like MoO2/NPC@rGO as advanced anode for alkali metal ion batteries

MoO2 anode displays excellent potential in the alkali ion batteries owing to its large capacity, high conductivity and stability. However, exploiting the stable and high performance MoO2 anode endowed with triple roles for the storage of lithium/sodium/potassium ions is still a challenge. Herein, a two-dimensional sheet-like MoO2/NPC@rGO composites were in-situ synthesized and utilized as anode materials for alkali metal ion batteries. Applied as an anode in lithium ion batteries (LIBs), superior cycling capability and rate performance were obtained, which kept a large reversible capacity of 1233.1 mAh/g in the 200th cycle at 100 mA/g. Impressively, it displayed superior long cycling performance over 1000 cycles with a 249.5 mAh/g capacity at a high current density of 10 A/g. Simultaneously, MoO2/NPC@rGO displayed enhanced electrochemical performance both in sodium and potassium ion batteries (NIBs/KIBs). Furthermore, the ex-situ X-ray photoelectron spectroscopy results verified the reversible reaction during Li+ insertion-extraction process. The improved energy storage properties were attributed to the typical two dimensional structure and synergistic effects between various constituents, which suppressed the volume change, created more active sites, increased the conductivity and facilitated reaction kinetics. More significantly, our design provides a simple and green route to synthesize transition metal oxide anode and promote their applications in energy storage devices.

Kinetically optimized copper sulfide cathodes for rechargeable magnesium batteries

Copper sulfides have been recognized as one of the most promising cathode materials for rechargeable magnesium batteries due to their large theoretical capacity and unique conversion-type mechanism. However, the solid-state diffusion of bivalent Mg2+ ions in CuS host lattice is subjected to huge electrostatic interaction and thus sluggish kinetics. Herein, anion substitution strategy and crystal engineering are reported to regulate electrochemical reaction kinetics and reinforce magnesium storage performances of tubular CuS cathodes. Benefitting from anion substitution and crystal facet regulation, the lattice well-exposed Se-substituted CuS nanotube cathodes demonstrate excellent magnesium storage capacity (372.9 mAh g−1 at 100 mA g−1), remarkable cycling stability (1600 cycles at 2.0 A g−1), and a good rate capability (112.4 mAh g−1 at 2.0 A g−1). Electrochemical kinetics investigation further suggests that anionic Se-substitution and crystal facet regulation can significantly optimize electrochemical reaction kinetics and accelerate diffusion rate of Mg2+ ions. Ex-situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations reveal the conversion reaction mechanism of Se-substituted CuS cathodes. These novel findings provide an effective approach to construct high-performance cathode materials for rechargeable magnesium batteries and hold great promise for development of other new battery systems.

Enhancement of Lithium-Mediated Ammonia Synthesis By Addition of Oxygen

Ammonia is one of the most produced chemicals worldwide and is currently synthesized by the Haber-Bosch process, which is a thermally catalyzed method that requires high pressures and temperatures. These harsh conditions, in addition to the prerequisite steam reforming process, leads to about 1 % of the annual energy consumption and 1.4 % of the global CO2 emission. One way to mitigate some of the Haber-Bosch process is to produce ammonia electrochemically, utilizing renewable energy sources.The electrochemical synthesis of ammonia faces several big issues. One being the selectivity, since the more facile hydrogen evolution reaction (HER) will always dominate over the nitrogen reduction reaction (NRR), and another issue being the activity, given that the nitrogen triple bond is very stable and therefore hard to split. Hence, most often the reported ammonia contents are in the low ppm regime, which makes it very susceptible to contaminations both from the gas stream (NH3 and NOx impurities) and the system itself (catalyst, cell, chemicals, nitrile gloves, etc.). To avoid misleading results, several protocols have been published on how to correctly perform NRR experiments [1, 2]. One of these confirm that only the Li-mediated ammonia synthesis (LiMeAS) is currently able to produce ammonia electrochemically [3]. The actual mechanism is not fully understood, but it is generally believed that the first step is Li plating from a Li salt containing non-aqueous electrolyte. The very reactive Li will then react with N2 solvated in the electrolyte to form Li3N, which is believed to hydrolyze to ammonia when in contact with a proton source. The currently highest archived faradaic efficiency (FE) is at 69 % at 20 bar N2 pressure when applying an ionic liquid as a proton shuttle [4].In this work, we achieved up to 79 % FE at 20 bar N2 by the addition of 0.8 mol. % O2 in the reaction atmosphere. The positive effect of O2 is a very counterintuitive observation, since the original work by Tsuneto et al. [5] showed that the use of synthetic air significantly hindered the reaction, as it was postulated that O2 inhibits the reaction due to LiO2 formation and/or leading primarily to the oxygen reduction reaction (ORR). We will present experimental results obtained at 10 and 20 bar with varying O2 contents, which were measured accurately by a mass spectrometer probing the atmosphere just above the electrolyte inside the pressure vessel. By combining experimental observations with theoretical modelling, we conclude that the unexpectedly beneficial role of small O2 concentrations has a positive influences the solid electrolyte interface (SEI), which is of great importance in our system. Additional ex-situ X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS) measurements were conducted without exposure to air and moisture, to analyze the SEI layer and deposition after electrochemistry. We believe that this study will not only be beneficial for industrializing the LiMeAS, but will also bring us a step further in understanding the complex mechanism behind this process.[1] S. Z. Andersen et al., "A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements," Nature, vol. 570, pp. 504-508, 2019.[2] H. Iriawan et al., "Methods for nitrogen activation by reduction and oxidation," Nature Reviews Methods Primers, vol. 1, no. 1, pp. 1-26, 2021.[3] J. Choi et al., "Identification and elimination of false positives in electrochemical nitrogen reduction studies," Nature communications, vol. 11, no. 1, pp. 1-10, 2020.[4] B. H. Suryanto et al., "Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle," Science, vol. 372, no. 6547, pp. 1187-1191, 2021.[5] A. Tsuneto, A. Kudo, and T. Sakata, "Lithium-mediated electrochemical reduction of high pressure N2 to NH3," Journal of Electroanalytical Chemistry, vol. 367, no. 1-2, pp. 183-188, 1994.

Stabilizing solid electrolyte/Li interface via polymer-in-salt artificial protection layer for high-rate and stable lithium metal batteries

Solid electrolytes are fundamental for next-generation solid-state Li-metal batteries that promise high energy density and safety. However, various solid electrolytes suffer from chemical/electrochemical instability against Li metal and poor interfacial contact with electrodes. Herein, a polymer-in-salt (PiS) artificial protection layer composed of fluoropolymer in highly-concentrated lithium salt (labeled as PiSPL) is introduced to address these problems using NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) as a typical solid electrolyte. The resulted PiSPL layer exhibits small thickness (10 μm), good chemical/electrochemical stability, and excellent ionic conductivity (0.5 and 1.8 mS cm−1 at 25 and 60 °C, respectively). These properties endow the LATP/Li interface with improved contact, favorable Li+ diffusion, and, most importantly, inhibited interfacial reactions, which is examined using ex-situ X-ray photoelectron spectroscopy and electrochemical analyses and morphological observations. Consequently, Li||LATP@PiSPL||Li symmetric cells can deliver small overpotentials at various current densities and long lifetime at 0.16 mA cm−2 over 400 h. On the contrary, the same configuration cells with LATP die after only 50 h. Moreover, the LiFePO4||LATP@PiSPL||Li solid-state full cells exhibit excellent rate capability (124.0 mA h g−1 at 2.0C) and cyclability (148.9 and 140.6 mA h g−1 after 200 cycles at 0.2C and 300 cycles at 1.0C, respectively). The PiS strategy represents a general and effective approach to stabilize various solid electrolyte/Li interfaces to push solid-state Li-metal batteries forward.

Unravelling Li+ Intercalation Mechanism and Cathode Electrolyte Interphase of Na3 V2 (PO4 )3 and Na3 (VOPO4 )2 F Cathode as Robust Framework Towards High-Performance Lithium-Ion Batteries.

Although lithium-ion batteries (LIBs) are promising towards high energy density and superior safety energy storage systems (ESS), severe depletion of Li reserve cannot meet the ever-growing demand for LIBs due to the uneven distribution and limited amount of Li resource. Li-free polyanionic cathodes, such as Na3 V2 (PO4 )3 (NVP) and Na3 (VOPO4 )2 F (NVOPF), show intriguing electrochemical performances with prospective future for LIBs due to their appropriate crystallographic sites, robust host structure, and abundant Na resource. In this work, NVP and NVOPF were systematically investigated as cathodes for LIBs using different voltage windows of 2.5-4.3, 2.0-4.3, and 1.5-4.8 V, along with their electrochemical mechanisms, cathode electrolyte interphase properties, and electrode morphologies for comparison. Ex-situ X-ray diffraction, ex-situ X-ray photoelectron spectroscopy, and post-mortem scanning electron microscopy revealed that their mechanisms shifted from a predominant Na+ intercalation/deintercalation in the first charging/discharging to a mixed Li+ /Na+ intercalation/deintercalation at the subsequent cycling. Due to the residual Na+ acting as pillar in the structure, NVP and NVPF could serve as robust host framework, providing appropriate crystallographic sites for repeated Li+ /Na+ intercalation/deintercalation. NVP electrode delivered a higher discharge capacity of 107.6 mAh g-1 with superior capacity retention of 84.3 % after 1000 cycles (2.5-4.3 V, 100 mA g-1 ) than NVOPF electrode (97.3 mAh g-1 , 68.8 %). Electrode polarization and kinetic analysis manifested one energetically similar and two energetically nonequivalent crystallographic Na sites within the R c and I4/mmm polyanionic structure of NVP and NVOPF. This work comprehensively demonstrates the feasibility and prospect of sodium-based NVP and NVOPF polyanions serving as advanced Li-free cathodes for LIBs, which provides novel insights into seeking Li-free candidates as prospective cathodes for LIBs towards a more sustainable society and a cost-effective battery manufacturing system.

Microwave-assisted hydrothermal synthesis of three-dimensional NbOPO4-reduced graphene oxide-carbon nanotube composite for high performance sodium-ion battery anode

Sodium-ion batteries (SIBs) have aroused more and more academic and industrial interest due to their decent electrochemical performance and the cost-effectiveness of sodium (Na) resource. However, fabricating an appropriate anode material with high specific capacity, long-term cycle stability and superior rate capability remains a great challenge. Here, we adopt an efficient microwave-assisted hydrothermal method to prepare layered niobium oxyphosphate (NbOPO4) nanosheets, which grows on the single-walled carbon nanotubes (SWCNT) and reduced graphene oxide (rGO) (NbOPO4-rGO-SWCNT). Benefiting from three-dimensional hierarchical architecture combining NbOPO4 nanosheets with rGO-SWCNT framework with excellent electrical conductivity, NbOPO4-rGO-SWCNT electrode delivers a higher reversible specific capacity (323.2 mAh g−1 at 0.1 A g−1) and superior rate capability (147.9 mAh g−1 at 5 A g−1) than that of NbOPO4 (143.1/43.5 mAh g−1). Ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements further reveal the electrochemical mechanism that reversible reaction between niobium phosphate (NbPO4) and niobium (Nb) occurs after the initial intercalation-conversion reaction, which contributes to the stable reversibility and high-rate capability in the following cycling. This work not only indicates that NbOPO4-rGO-SWCNT can act as a desirable anode material for SIBs, but also provide new insights to material design for niobium oxyphosphate composite.

Advantageous Al-ion intercalation in Mo15S19 nanosheets for aqueous symmetric supercapacitors

This work reports the anchoring of Mo15S19 nanosheets on conductive carbon cloth (CC) using a simple hydrothermal reaction. Based on the specific capacitance data for Mo15S19/CC electrode in 1 M AlCl3, 1 M MgCl2, 3 M LiCl, 1 M KCl, 1 M LiCl and 1 M NaCl electrolytes, the highest value (400 F g−1) obtained for aluminum chloride is attributed to the fast redox reactions with short diffusion path. This is supported by the decrease in the acidity of the electrolyte and reduction in the relative intensity of the Raman peaks between A1g and E1/2g for the Al3+ intercalated Mo15S19 nanosheets. Moreover, ex-situ X-ray photoelectron spectroscopy displays the reduction of Mo4+ to Mo3+ for Mo15S19 nanosheets, confirming a charge compensation mechanism via Al3+ intercalation. Furthermore, an aqueous Al-ion capacitor is fabricated based on Mo15S19/CC positive/negative electrodes and 1 M AlCl3 electrolyte for efficient energy storage. The device delivers a long cycling lifespan with over 90.1% capacitance retention over 10,500 cycles at 10 A g−1. This work provides the possibility of aqueous capacitors based on trivalent Al-ion as a guest and offers a new direction for the future development of metal-ion capacitors.

Improved and stable triazine-based covalent organic framework for lithium storage

Covalent organic frameworks (COFs) have attracted widespread attention for gas storage, separation, catalysis, and sensors applications. We report a simple, inexpensive, and abundant aromatic nitrile 1,4-dicyanobenzene (1,4-DCB) as a lithium-ion battery anode material through the synthesis of a DCB triazine-based covalent organic framework (DCB-COF) under ionic thermal conditions. An investigation of the lithium storage mechanism of the active groups in the DCB-COF by in-situ Fourier-transform infrared spectroscopy, ex-situ X-ray photoelectron spectroscopy, and density functional theory calculations demonstrates that DCB-COF had a high initial capacity of 2100 mAh g−1, and good structural and cycling stability. This work provides an effective strategy for the subsequent fabrication of novel COF electrode materials.

Surface optimized P2-Na2/3Ni1/3Mn2/3O2 cathode material via conductive Al-doped ZnO for boosting sodium storage

Layered transition-metal oxides have been potential as high-performance cathode materials for sodium-ion batteries (SIBs), however, suffer from the undesirable side reactions between cathode/electrolyte interface during cycling. One improvement strategy by surface coatings is typically used, but at the compromise of lowering ion transport kinetics and poor rate capability. Herein, we report a surface optimized high-rate P2-Na2/3Ni1/3Mn2/3O2 cathode material for SIBs via a highly conductive Al-doped ZnO (AZO). By tuning the calcination temperatures, the optimized cathode material coated with 1 wt% AZO at 500 °C exhibits decent cycling and rate performances (66.2 mAh g−1 with a capacity retention of 82.6% at 5C after 500 cycles). Electrochemical kinetics analysis demonstrates that the NM@AZO-500 exhibits a high Na+ diffusion coefficient and a low charge-transfer resistance, and in-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) reveal that the AZO coating effectively relieves the lattice stress during cycles and inhibits undesirable side reaction; all of which give rise to the observed enhancement. The result promises an effective surface optimized route for high-performance cathode materials for SIBs by coating highly conductive oxide.

Regulating the transformation behavior of nickel iron metal–organic frameworks through a dual-ligand strategy for enhanced oxygen evolution reaction performance

Two-dimensional (2D) 2,6-naphalene dicarboxylic acid-based nickel iron metal–organic frameworks (NiFe-NDC MOFs) have been widely deemed as promising electrocatalysts by virtue of their adorable specific surface area and the highly-exposed reactive metal centers. However, the practical performance of the pristine NiFe-NDC MOFs is far from satisfaction towards the electrocatalytic water oxidation for the sluggish ion-transport. Herein, we report a co-coordination approach to afford dual-ligand NiFe electrocatalysts (NiFe-NDCxBDC1-x) with striking oxygen evolution reaction (OER) performance. Except for the 2,6-naphalene dicarboxylic acid (NDC), 1,4-terephthalic acid (BDC) is adopted as the co-coordination ligand to tune the electronic and structural configuration of the catalysts via the unique ligand processability of the MOFs. The optimal NiFe-NDC0.9BDC0.1 displays a superior performance for OER catalysis with an overpotential of 295 mV when current density arrives at 10 mA cm−2 and the Tafel slope is 69.4 mV dec-1, as well as excellent stability in alkaline media. In-situ Raman and ex-situ X-ray photoelectron spectroscopy further indicates that introduction of BDC ligands not only strengthen the interaction between Ni and Fe atoms, but also facilitate the deeper conversion from MOF to active NiOOH species, especially the higher proportion of β-NiOOH species which can greatly promote the OER performance.

Polyaniline nanoarrays/carbon cloth as binder-free and flexible cathode for magnesium ion batteries

• The reversible storage of Mg 2+ in PANI at non-aqueous MIBs was first proved. • The binder-free flexible cathode was prepared by simple in-situ polymerization. • The CC stabilized the structure and improved conductivity of the cathode. • The double-ion storage mechanism provides capacity for the PANI/CC. • The capacity retention of 97.25% was obtained after 1500 cycles at 1 A g −1 . Magnesium ion batteries (MIBs) attracted much attention in recently years due to the advantages of high theoretical capacity and low cost. However, the strong polarization effect of Mg 2+ cause slow diffusion rate, hindering the development of MIBs. Herein, we designed and synthesized a binder-free polyaniline array/carbon cloth (PANI/CC) as cathode for MIBs. Given the benefit of improved electrical conductivity and alleviated agglomeration, the cathode exhibits enhanced electrochemical performance compared with the pure polyaniline cathode in MIBs. The PANI/CC cathode displays the highest specific capacity of 219 mA h g −1 at 200 mA g −1 and the capacity retention of 97.25% after over 1500 cycles at 1 A g −1 . Then, the reversible redox transformation between quinone rings and benzene rings during charging and discharging process was demonstrated by the ex-situ X-ray photoelectron spectroscopy (XPS) and ex-situ Raman spectra. In addition, PANI/CC shows an initial capacity of 75 mA h g −1 at 50 mA g −1 in PANI/CC //Mg(TFSI) 2 // MNTO full cell. Our work demonstrates that PANI/CC is a promising cathode for MIBs, which may offer new insight for the development for high-performance MIBs.

A new Li2Mn3O7 cathode for aqueous Zn-Ion battery with high specific capacity and long cycle life based on the realization of the reversible Li+ and H+ co-extraction/insertion

• Li 2 Mn 3 O 7 is firstly reported as the new cathode for aqueous Zn-ion battery. • Complex storage mechanism is discussed by In-situ XRD and ex-situ XPS. • Excellent performance is related to reversible Li + /H + co-extraction/insertion. • Dynamic mechanism of electrode and reason of capacity variation were pointed. Aqueous Zn-ion batteries (ZIBs) are expected to be used for practical energy storage and grid-scale applications because of their low-cost, high-safety and environmental friendliness. However, it is still a major challenge to achieve a suitable cathode for ZIBs with a high energy density and long cycle life. Herein, we reported a new cathode Li 2 Mn 3 O 7 for aqueous ZIBs and have studied in detail the role of Li + as electrolyte additives in further improving electrochemical performance. The Li + in the additive-contained electrolyte itself not only facilitates the reversible extraction/insertion of Li + in Li 2 Mn 3 O 7 but also effectively reduce the decomposition effect of Li 2 Mn 3 O 7 caused by the charge process through the re-insertion of Li + in subsequent discharge process and thus realizes the reversible deintercalation/intercalation of H + . Owing to the realization of the reversible Li + and H + co-extraction/insertion caused by the use of Li + additive, the Li 2 Mn 3 O 7 electrode exhibits a high reversible specific capacity of 242 mAh g −1 with nearly 100% coulombic efficiency at 200 mA g −1 current density. In particular, due to the enhanced capacitive contribution, Li 2 Mn 3 O 7 electrode presented an impressive life span at high current density 2 A g −1 , and after 1000 cycles, a stable specific capacity greater than 100 mAh g −1 can be maintained, which is significantly better than that of manganese oxide-based cathode materials in ZIBs. Furthermore, by In-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS), we discuss in detail the complex energy storage mechanism of Li 2 Mn 3 O 7 as cathode material for ZIBs with electrolyte containing Li + additive for the first time. Based on the high specific capacity and big current life span, aqueous ZIBs with Li 2 Mn 3 O 7 exbibit a great potential for large scale electrical energy storage.

Heterogeneous interface in hollow ferroferric oxide/ iron phosphide@carbon spheres towards enhanced Li storage

Heterogeneous interface and structural engineering play important roles for electrochemical performance of lithium-ion batteries. Herein, heterostructures of hollow Fe3O4/FeP spheres coated with carbon shell (H-Fe3O4/FeP@C) are designed to enhance lithium storage performance. As bifunctional anode materials, the H-Fe3O4/FeP@C spheres show the good rate performance with 458.4 mAh g−1 at 5 A g−1 and long-cyclic performance (630.2 mAh g−1 at 2.0 A g−1 after 1000 cycles). Density functional theory calculations demonstrate that the heterogeneous interfaces from (311) plane of Fe3O4 and (002) plane of FeP possess high charge density and distinct metallic character, which can improve the conductivity, increase the adsorption energy, provide more active sites and reduce the transfer barrier of ions and electrons. Besides, hollow structure of H-Fe3O4/FeP@C not only alleviates the volume expansion during lithiation/delithiation process but also shortens the diffusion distance of Li ions. In addition, the ex-situ X-ray diffraction and X-ray photoelectron spectroscopy are used to reveal the electrochemical Li storage mechanisms of H-Fe3O4/FeP@C. This work provides a novel route for design and preparation of Fe-based heterostructures for various energy storage systems in the future.

Ion-induced secondary electron emission of oxidized nickel and copper studied in beam experiments

Ion-induced secondary electron emission at a target surface is an essential mechanism for laboratory plasmas, i.e. magnetron sputtering discharges. Electron emission, however, is strongly affected by the target condition itself such as oxidation. Data of oxidized targets, however, are very sparse and prone to significant systematic errors, because they were often determined by modeling the complex behavior of the plasma. Thus, it is difficult to isolate the process of ion-induced electron emission from all other plasma-surface-interactions. By utilizing ion beams, the complex plasma environment is avoided and electron yields are determined with higher accuracy. In this study, ion-induced secondary electron emission coefficients (SEECs) of clean, untreated (air-exposed), and intentionally oxidized copper and nickel surfaces were investigated in such a particle beam experiment. Pristine and oxidized metal foils were exposed to beams of singly charged argon ions with energies of 0.2 keV - 10 keV. After the ion beam treatment, the surface conditions were analyzed by ex-situ x-ray photoelectron spectroscopy measurements. Further, a model for the electron emission of a partly oxidized surface is presented, which is in agreement with the experimental data. It was found, that oxidized and untreated/air-exposed surfaces do not show the same SEEC: for intentionally oxidized targets, the electron yields were smaller by a factor of 2 than for untreated/air-exposed surfaces. SEECs of oxides were found to be between the values for clean and for untreated metal surfaces. Further, the SEEC was at maximum for untreated/air-exposed surfaces and at minimum for clean surfaces; the electron yields of untreated/air-exposed and clean surfaces were in agreement with values reported in the literature.

The spinel MnFe2O4 grown in biomass-derived porous carbons materials for high-performance cathode materials of aqueous zinc-ion batteries

Here a novel composite material that is described by the MnFe2O4 with spinel structure in-situ grown on the biomass-derived amorphous porous carbon (PC@MFO) is proposed as a cathode material for aqueous zinc-ion batteries (AZIBs). This electrode has an excellent initial discharge capacity of 168 mA h g−1 at 0.3 A g−1 and superior cycle stability with capacity retention rate of 92% over 900 cycles even at a high rate of 1 A g−1. The excellent charge/discharge performance of PC@MFO electrode is attributed to some beneficial synergistic effects including increasing good electrode conductivity and high ion transmission speed and more reactive points and avoiding the rapid collapse of the structure of the MnFe2O4 electrode produced by the introduction of mesoporous carbon, which promotes and stabilizes charge/discharge reaction of multivalent redox (Mn2+/Mn4+, Fe2+/Fe3+). The rapid electrochemical kinetic behavior of the PC@MFO electrode is also analyzed by cyclic voltammetry, where the kinetic process of electrochemical reaction involving the diffusion control faraday process and capacitance control behavior is revealed and the capacitance contribution rate of about 88.19% is attained. Moreover, the galvanostatic intermittent titration technique (GITT) also explains that this PC@MFO electrode has a high Zn2+ ion diffusion capacity and the diffusion coefficient can reach 10−14~10−10 cm2 s−1. In addition, the reaction mechanism and structural evolution of this electrode is also studied by ex-situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction test (XRD) from different cycle stages. XPS and XRD reveal the strong deintercalation ability of Zn2+ ions in the highly stable MFO which grows in biomass-derived porous carbon. The present result implies that such a PC@MFO composite material could be a promising cathode material for AZIBs.

Metal-organic framework derived cobalt phosphide nanoparticles encapsulated within hierarchical hollow carbon superstructure for stable sodium storage

Metal-organic framework (MOF) derivatives with controllable morphology, porosity, and high specific area are considered as potential anodes for sodium-ion batteries (SIBs). However, the poor conductivity and sluggish diffusion kinetics of Na+ of MOF-derived materials result in rapid capacity decline and inferior rate capability. Herein, a hierarchical hollow superstructure composed of CoP nanoparticles anchored on the N-doped carbon polyhedral frameworks with the epitaxial growth of carbon nanotubes (CoP@N-HP/CT), is prepared by MOF coating, and subsequent carbonization − oxidation − phosphorization strategy. Owing to the elaborate hierarchical hollow superstructure, the CoP@N-HP/CT composites achieve long cycling stability (over 2500 cycles), and good rate capability as SIBs anodes. The remarkable electrochemical performance of the CoP@N-HP/CT hybrids is attributed to their high capacitive contribution and fast sodium ion diffusion rate. Furthermore, the sodium storage behaviors of the CoP@N-HP/CT are revealed by ex-situ X-ray photoelectron spectroscopy and transmission electron microscope techniques. Thus, the well-designed hierarchical hollow CoP@N-HP/CT superstructure gives an insight into the superior anodes for sodium storage.

Facile synthesis of KVPO4F/reduced graphene oxide hybrid as a high-performance cathode material for potassium-ion batteries

Potassium-ion batteries (PIBs) as a substitute for lithium-ion batteries have aroused widespread attention and have been rapidly developed. In the positive electrode materials, polyanionic compound has a high working voltage and large reversible capacity on account of its distinct framework and the strong inducing effect of the anionic group. Herein, a KVPO4F/reduced graphene oxide (KVPF/rGO) hybrid was fabricated via a simple multi-step approach as the polyanionic cathode material for PIBs. Profiting from the small size of KVPF nanoparticles and their uniform distribution in the rGO framework, the as-synthesized KVPF/rGO hybrid manifests a large discharge capacity of 103.2 mAh g−1 with an outstanding energy density of 436.5 Wh kg−1. Through rGO decoration, the hybrid also demonstrates remarkable rate and cycling properties. By employing ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, the potassium storage mechanism of KVPF was clearly revealed. The facile preparation procedure and superior properties endow it great application prospects in large-scale energy storage.

Unlocking the energy storage potential of polypyrrole via electrochemical graphene oxide for high performance zinc-ion hybrid supercapacitors

Safe and low-cost zinc-ion hybrid supercapacitors using neutral aqueous electrolytes are promising for large scale and high power energy storage. A key challenge for Zn-ion hybrid supercapacitors is to increase their energy density without sacrificing the high power performance. Herein, we report a Zn-ion hybrid supercapacitor using a polypyrrole/electrochemical graphene oxide (PPy/EGO) composite cathode and aqueous 1 M ZnCl 2 or ZnBr 2 electrolytes. The Zn-PPy/EGO system with an operating cell voltage from 0.5 to 1.5 V exhibited high energy and high power densities of 117.7 and 72.1 Wh kg −1 at 0.34 and 12.4 kW kg −1 , respectively, outperforming the Zn-ion hybrid supercapacitors using carbon cathodes. This high performance is because of the facilitated electronic and ionic transport in the PPy/EGO composite. In brief, the EGO prepared via the electrochemical method we recently reported has good structure integrity and is easily reduced; the porous PPy/EGO composite from co-electrodeposition benefits fast ion diffusion in pores; the small, monovalent halides anions in the zinc halides electrolytes are highly mobile in bulk PPy for fast solid-phase anion insertion/de-insertion. Electrochemical characterization and ex-situ X-ray photoelectron spectroscopy confirmed the anion-dominated charge storage mechanism of PPy/EGO cathode in Zn-PPy/EGO system. • PPy/EGO composite electrodes were prepared by one-step co-electrodeposition. • Mildly oxidized EGO with less disrupted structure benefits electron conduction. • Porous structure of PPy/EGO composite electrode facilitate ion diffusion. • Zn-PPy/EGO system using ZnCl 2 or ZnBr 2 electrolyte show record high performance.

Selectivity in atomically precise etching: Thermal atomic layer etching of a CoFeB alloy and its protection by MgO

• Atomic layer etching (ALE) has been demonstrated for CoFeB alloy. • This ALE process maintains the atomic concentration on the alloy surface. • This ALE process maintains a nearly atomically smooth surface. • The process of ALE is demonstrated to stop by MgO. The central unit in an integrated memory device is a magnetic tunnel junction (MTJ) consisting of two ferromagnetic layers, often using complex alloys such as CoFeB, separated by an insulating barrier such as MgO. Atomic level precision is required to fabricate miniaturized devices, and atomic layer etching (ALE) is one of the most promising methods to do this. However, at the nanoscale, it is imperative to maintain the concentration of each element in an alloy during etching, and it is important to not affect the insulating barrier, i.e. the etching process should stop at MgO. Here we use thermal dry etching of CoFeB alloy thin films with sequential doses of chlorine and 2,4-pentanedione (acetylacetone, acacH). Patterned samples are modified with atomic level precision, and the process is completely selective to the removal of CoFeB alloy in ALE regime without changing the alloy composition and without etching MgO that is used as a protecting layer. The etching process was investigated by comparing the film thickness on a patterned surface before and after ALE process using atomic force microscopy (AFM). The viable key features of the reaction mechanism were proposed by detection of key desorbing fragments during a heating ramp via temperature-programmed desorption (TPD) experiments. Ex-situ X-ray photoelectron spectroscopy (XPS) was performed to characterize the surface during ALE process.

Double‐shell and yolk‐shell structured ZnSe ‐carbon nanospheres as anode materials for high‐performance potassium‐ion batteries

Transition-metal chalcogenides are prospective anode materials for potassium-ion batteries. Herein, crystalline ZnSe nanocrystal-loaded hollow carbon nanospheres (ZnSe-HC) are synthesized by infiltration of zinc nitrate and selenium dioxide into hollow carbon nanospheres and subsequent selenization. The electrochemical reaction mechanism of ZnSe with K-ion is systematically examined by ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy. Two samples with distinctive nanostructures, which are double-shelled hollow structure and yolk-shelled structure, can be fabricated by controlling the selenization temperature, and their K-ion storage performances are compared. The double-shelled ZnSe-HC, which is prepared at a lower temperature, exhibits superior cycling and rate performances to those of the yolk-shelled ZnSe-HC. For double-shelled ZnSe-HC, small ZnSe nanocrystals embedded in the carbon shell and dispersed over the inner carbon shell contribute to the structural stability and fast kinetics during repeated cycles. As a result, the double-shelled ZnSe-HC exhibits a stable cycling performance (400 mA h g−1 at 0.1 A g−1 after 100 cycles) and excellent rate capability (240 mA h g−1 at 3.0 A g−1).