Ultralow-content Pt nanodots/Ni3Fe nanoparticles: interlayer nanoconfinement synthesis and overall water splitting.

Minimizing precious metal loading into electrocatalysts for water splitting is vital to promoting hydrogen energy technology toward practical applications. Low-content loading of precious-metal electrocatalysts is achieved by decorating precious metal nanostructures on co-electrocatalysts typically via surface confinement. Here, an electrocatalyst of ultralow-content Pt nanodots (0.71 wt%)/Ni3Fe nanoparticles on reduced oxidation graphene (Pt/Ni3Fe/rGO) is constructed for overall water splitting by pyrolyzing a single-source precursor PtCl63- guest-intercalated MgNiFe-layered double hydroxide (MgNiFe-LDH) host via a distinctive interlayer confinement. Consequently, Pt/Ni3Fe/rGO demonstrates attractive overpotentials of 240 and 76 mV at 10 mA cm-2 for the oxygen and hydrogen evolution reactions (OER and HER), respectively, outperforming those of its /Ni3Fe/rGO counterpart. Moreover, the Pt/Ni3Fe/rGO∥Pt/Ni3Fe/rGO electrolyzer generates a current density of 10 mA cm-2 at 1.55 V, with a retention of 92.4% after 50 h. Furthermore, the measured specific activity and low transfer resistance, as well as the density functional theory (DFT) calculations, indicate that the active Pt/Ni3Fe in Pt/Ni3Fe/rGO can optimize the adsorption/desorption of reaction intermediates and thus boost OER/HER kinetics, all of which lead to enhanced performance. The results demonstrate that such an interlayer confinement-based synthesis strategy can allow for the design of cost-effective precious nanodots as potential electrocatalysts.

Bismuth-doping boosting Na+ diffusion kinetics of layered oxide cathode with radially oriented {010} active lattice facet for sodium-ion batteries.

O3-type layered oxide cathodes (NaxTMO2) for sodium-ion batteries (SIBs) have attracted significant attention as one of the most promising potential candidates for practical energy storage applications. The poor Na+ diffusion kinetics is, however, one of the major obstacles to advancing large-scale practical application. Herein, we report bismuth-doped O3-NaNi0.5Mn0.5O2 (NMB) microspheres consisting of unique primary nanoplatelets with the radially oriented {010} active lattice facets. The NMB combines the advantages of the oriented and exposed electrochemical active planes for direct paths of Na+ diffusion, and the thick primary nanoplatelets for less surface parasitic reactions with the electrolyte. Consequently, the NMB cathode exhibits a long-term stability with an excellent capacity retention of 72.5% at 1C after 300 cycles and an enhanced rate capability at a 0.1C to 10C rate (1C = 240 mA g-1). Furthermore, the enhancement is elucidated by the small volume change, thin cathode-electrolyte-interphase (CEI) layer, and rapid Na+ diffusion kinetics. In particular, the radial orientation-based Bi-doping strategy is demonstrated to be effective at boosting electrochemical performance in other layered oxides (such as Bi-doped NaNi0.45Mn0.45Ti0.1O2 and NaNi1/3Fe1/3Mn1/3O2). The results provide a promising strategy of utilizing the advantages of the oriented active facets of primary platelets and secondary particles to develop high-rate layered oxide cathodes for SIBs.

Soft-Rigid Heterostructures with Functional Cation Vacancies for Fast-Charging and High-Capacity Sodium Storage.

Optimizing charge transfer and alleviating volume expansion in electrode materials are critical to maximize electrochemical performance for energy-storage systems. Herein, an atomically thin soft-rigid Co9 S8 @MoS2 core-shell heterostructure with dual cation vacancies at the atomic interface is constructed as a promising anode for high-performance sodium-ion batteries. The dual cation vacancies involving VCo and VMo in the heterostructure and the soft MoS2 shell afford ionic pathways for rapid charge transfer, as well as the rigid Co9 S8 core acting as the dominant active component and resisting structural deformation during charge-discharge. Electrochemical testing and theoretical calculations demonstrate both excellent Na+ -transfer kinetics and pseudocapacitive behavior. Consequently, the soft-rigid heterostructure delivers extraordinary sodium-storage performance (389.7 mA h g-1 after 500 cycles at 5.0 A g-1 ), superior to those of the single-phase counterparts: the assembled Na3 V2 (PO4 )3 ||d-Co9 S8 @MoS2 /S-Gr full cell achieves an energy density of 235.5 Wh kg-1 at 0.5 C. This finding opens up a unique strategy of soft-rigid heterostructure and broadens the horizons of material design in energy storage and conversion.

MoS2/SnS/CoS Heterostructures on Graphene: Lattice-Confinement Synthesis and Boosted Sodium Storage.

The development of high-efficiency multi-component composite anode nanomaterials for sodium-ion batteries (SIBs) is critical for advancing the further practical application. Numerous multi-component nanomaterials are constructed typically via confinement strategies of surface templating or three-dimensional encapsulation. Herein, a composite of heterostructural multiple sulfides (MoS2/SnS/CoS) well-dispersed on graphene is prepared as an anode nanomaterial for SIBs, via a distinctive lattice confinement effect of a ternary CoMoSn-layered double-hydroxide (CoMoSn-LDH) precursor. Electrochemical testing demonstrates that the composite delivers a high-reversible capacity (627.6 mA h g-1 after 100 cycles at 0.1 A g-1) and high rate capacity of 304.9 mA h g-1 after 1000 cycles at 5.0 A g-1, outperforming those of the counterparts of single-, bi- and mixed sulfides. Furthermore, the enhancement is elucidated experimentally by the dominant capacitive contribution and low charge-transfer resistance. The precursor-based lattice confinement strategy could be effective for constructing uniform composites as anode nanomaterials for electrochemical energy storage.

Facile and template-free fabrication of hierarchical coral spheres for acetone gas sensors.

In this paper, highly dispersed hierarchical coral spheres of CeO2/ZnO have been constructed through a facile template-free hydrothermal strategy, followed by an annealing treatment. The resulting coral spheres exhibit enhanced activity for acetone sensing compared with CeO2 or ZnO as well as excellent cyclability and long-term stability. At the optimum working temperature of 245 °C, by controlling the ratio of Ce/Zn, the highest response of the coral spheres towards 100 ppm acetone is up to 145, which is about 5.5 times that of ZnO coral spheres. The significantly improved gas sensing activity may be ascribed to the well-dispersed and assembled CeO2 nanoparticles on the surface of ZnO coral spheres and the heterojunctions between CeO2 and ZnO, which produced abundant oxygen vacancies in the CeO2/ZnO coral spheres.

Cu/Ti co-doping boosting P2-type Fe/Mn-based layered oxide cathodes for high-performance sodium storage.

Environmentally friendly P2-type layered iron manganese oxides appear to be one of the most potential cathode materials for sodium-ion batteries (SIBs). However, their practical application is hindered by the unfavorable phase transitions, dissolution of transition metals, and poor air stability. One effective strategy by either single-cation doping or high-cost Li involved co-doping is used to alleviate the problems. Here, low-cost Cu/Ti co-doping is introduced to boost P2-Na0.7Cu0.2Fe0.2Mn0.5Ti0.1O2 as an air and electrochemical stable cathode material for SIBs. The resulting electrode delivers an initial capacity of 130 mAh g-1 at 0.1C within 2.0-4.2 V, a reversible discharge capacity of 61.0 mAh g-1 at a high rate of 5C and a capacity retention ratio exceeding 71.1% after 300 cycles. In particular, the co-doped crystal structure is well-maintained after 1 month of exposure to air, and even 3 days of soaking in water. Furthermore, the enhancement is elucidated by the effectively mitigated P2-Z and the completely suppressed P2-P'2 phase transitions, the decreased volume variation proved by in-situ X-ray diffraction (XRD), as well as the lowered transition-metal dissolution evidenced by inductively coupled plasma optical emission spectrometer (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The low-lost Cu/Ti doping strategy could thus be effective for designing and preparing environmentally friendly and high-performance cathode materials for SIBs.

A low-content CeOx dually promoted Ni3Fe@CNT electrocatalyst for overall water splitting.

Rational construction of low-cost and high-performance electrocatalysts for water splitting is crucial for the advancement of renewable hydrogen fuel. Hybridizing heterojunctions or noble metals is one typical strategy used to boost the electrocatalytic performance for either the oxygen evolution reaction (OER) or hydrogen evolution reaction (HER). Here, low-content CeOx (3.74 wt%) is introduced into Ni3Fe nanoparticle-encapsulated carbon nanotubes (Ni3Fe@CNTs/CeOx), with both the OER and HER activities boosted, as a bifunctional electrocatalyst for overall water splitting. The composite is derived by pyrolyzing a mixture of melamine/ternary NiFeCe-layered double hydroxide. The composite electrocatalyst requires low overpotentials of 195 and 125 mV at 10 mA cm-2 in 1.0 M KOH, respectively, which are superior to those of Ni3Fe@CNTs/NF (313 and 139 mV) and CeOx/NF (345 and 129 mV), and in particular, OER overpotentials of 320 and 370 mV at 50 and 100 mA cm-2, respectively. Moreover, the composite-assembled electrolyzer for overall water splitting requires a current density of 10 mA cm-2 at a decent cell voltage of 1.641 V. Furthermore, the enhancement is elucidated by the synergistic effect: the dual role of CeOx in boosting the OER and HER, the highly conductive carbonaceous CNTs, large electrochemically active surface area and low charge-transfer resistance. The results can offer an effective route for designing and preparing low-cost and high-efficiency electrocatalysts for electrocatalytic water splitting.

O3-Type Na0.95Ni0.40Fe0.15Mn0.3Ti0.15O2 Cathode Materials with Enhanced Storage Stability for High-Energy Na-Ion Batteries.

O3-type layered oxides with high initial sodium content are promising cathode candidates for Na-ion batteries. However, affected by the undesired transition metal slab sliding and reaction with H2O/CO2, their further application is typically hindered by unsatisfactory cycling stability upon charging to high voltage and poor storage stability under humid air. Herein, we demonstrate a Fe/Ti cosubstitution strategy to simultaneously enhance the electrochemical performance and storage stability of pristine O3-NaNi0.5Mn0.5O2 cathode material, via employing high redox potential and inactive stabilized dopants. The resultant Fe/Ti cosubstituted Na0.95Ni0.40Fe0.15Mn0.3Ti0.15O2 undergoes highly reversible O3-P3-OP2 phase transitions with a small cell volume change of 2.8%, instead of complex O3-O'3-P3-P'3-P3'-O1 phase transitions in NaNi0.5Mn0.5O2. Consequently, the cathode displays a high specific capacity of 161.6 mAh g-1 with an average working voltage of 3.28 V and 81.8% capacity retention after 200 cycles at 5C. Furthermore, the cathode material remains very stable after exposure to air for 7 days and even after soaking in water for 1 h, owing to the prohibition of sodium losing by elevating redox potential and contracting sodium layer spacing. This work proposes an effective method to enhance the electrochemical performance and storage stability of O3-type layered oxide cathodes and promises advancing Na-ion batteries toward large-scale industrialization.

Low-content SnO2 nanodots on N-doped graphene: lattice-confinement preparation and high-performance lithium/sodium storage.

Rational construction of nanosized anode nanomaterials is crucial to enhance the electrochemical performance of lithium-/sodium-ion batteries (LIBs/SIBs). Various anode nanoparticles are created mainly via templating surface confinement, or encapsulation within precursors (such as metal-organic frameworks). Herein, low-content SnO2 nanodots on N-doped reduced graphene oxide (SnO2@N-rGO) were prepared as anode nanomaterials for LIBs and SIBs, via a distinctive lattice confinement of a CoAlSn-layered double hydroxide (CoAlSn-LDH) precursor. The SnO2@N-rGO composite exhibits the advantagous features of low-content (17.9 wt%) and uniform SnO2 nanodots (3.0 ± 0.5 nm) resulting from the lattice confinement of the Co and Al species to the surrounded Sn within the same crystalline layer, and high-content conductive rGO. The SnO2@N-rGO composite delivers a highly reversible capacity of 1146.2 mA h g-1 after 100 cycles at 0.1 A g-1 for LIBs, and 387 mA h g-1 after 100 cycles at 0.1 A g-1 for SIBs, outperforming N-rGO. Furthermore, the dominant capacitive contribution and the rapid electronic and ionic transfer, as well as small volume variation, all give rise to the enhancement. Precursor-based lattice confinement could thus be an effective strategy for designing and preparing uniform nanodots as anode nanomaterials for electrochemical energy storage.

Ion Substitution Strategy of Manganese-Based Layered Oxide Cathodes for Advanced and Low-Cost Sodium Ion Batteries.

Sodium ion batteries (SIBs) have recently been promising in the large-scale electric energy storage system, due to the low cost, abundant sodium resources. Mn-based layered oxide cathode materials have been widely investigated, because of the high theoretical specific capacity, low cost, and abundant reserves. However, their development is limited by the problems of Jahn-Teller distortion, Na+ /vacancy ordering, complex phase transitions, and irreversible anionic redox during cycling. Ion substitution strategy is one simple and effective way to regulate the crystal structure and boost sodium-storage performances of Mn-based cathode materials. In this review, we summarize the progress and mechanism of ion-substituted Mn-based oxides, establish a composition-crystal structure-electrochemical performance relationship, and also offer perspectives for guiding the design of high-performance Mn-based oxides for SIBs.

NiS2 nanodots on N,S-doped graphene synthesized via interlayer confinement for enhanced lithium-/sodium-ion storage.

Rational design of high-capacity nanosized composites as anode nanomaterials is crucial to boosting electrochemical performances towards large-scale application for lithium- and sodium-ion batteries (LIBs and SIBs). The small sizes and homogeneous dimensional size distributions are achieved typically by either the surface confinement on the underlying supports, or the encapsulation confinement within the precursors (such as metal-organic frameworks). Herein, we report the ultrasmall NiS2 nanodots on reduced graphene oxide (NiS2/N,S-rGO) synthesized via interlayer confinement as anode nanomaterials for LIBs and SIBs. The composite is synthesized by pyrolyzing a host/guest precursor of sodium dodecyl sulfate ion/[NiEDTA]2- anions co-intercalated MgAl-layered double hydroxide LDH host, without additional sulfur source. The host/guest-derived interlayer nanoconfinement enables the composite to integrate the advantageous features: low-content active NiS2 nanodots (11.0 wt%) with a mean size of 3.8 ± 0.5 nm, high-content N,S-rGO (89.0 wt%), as well as a large specific surface area and mesopore size distribution. The composite used as anode nanomaterial exhibits reversible capacities of 801.2 mAh g-1 after 100 cycles at 100 mA g-1 for LIBs, and 207.7 mAh g-1 after 200 cycles at 0.1 A g-1 for SIBs, which are greatly higher than those of the pristine N,S-rGO without NiS2 nanodots. The enhancement is experimentally supported by the low charge transfer resistance, high capacitive-controlled contribution, and good structural stability. Our guest/host-based interlayer nanoconfinement can promise an effective synthesis strategy for designing various nanosized anodes for electrochemical energy storage.

O3-Type Na2/3Ni1/3Ti2/3O2 Layered Oxide as a Stable and High-Rate Anode Material for Sodium Storage.

Sodium-ion batteries (SIBs) are currently the most promising candidates for large-scale energy storage devices owing to their low cost and abundant resources. Titanium-based layered oxides have attracted widespread attention as promising anode materials due to delivering a safe potential of about 0.7 V (vs Na+/Na) and a small volume contraction during cycles; P2-type Ti-based layered oxides are typically reported, due to the challenging synthesis of the O3-type counterpart resulting from the high percentage of unstable Ti3+. Herein, we report an anomalous O3-Na2/3Ni1/3Ti2/3O2 layered oxide as an ultrastable and high-rate anode material for SIBs. The anode material delivers a reversible capacity of 112 mA h g-1 after 300 cycles at 0.1 C, a good capacity retention rate of 91% after 1400 cycles at 2 C, and, in particular, a capacity of 52 mA h g-1 even at a high rate of 20 C (1780 mA g-1). Furthermore, the in situ X-ray diffraction monitoring reveals no phase transitions and almost zero strain both underlie the good long-cycle stability. The measured high apparent Na+ diffusion coefficient (2.06 × 10-10 cm2 s-1) and the low migration energy barrier (0.59 eV) from density functional theory calculations are responsible for the superior rate capability. Our results promise advanced high-performance O3-type Ti-based layered oxides as promising anode materials toward application for SIBs.

Cation-Disordered O3-Na0.8Ni0.6Sb0.4O2 Cathode for High-Voltage Sodium-Ion Batteries.

O3-type sodium-layered oxides (such as antimony-based O3 structures) have been suggested as one of the most fascinating cathode materials for sodium-ion batteries (SIBs). Honeycomb-ordered antimony-based O3 structures, however, unsatisfactorily exhibit complex phase transitions and sluggish Na+ kinetics during cycling. Herein, we prepared a completely cationic-disordered O3-type Na0.8Ni0.6Sb0.4O2 compound by composition regulation for SIBs. Surprisingly, the measured redox potentials for typical O3-P3 phase transition are located at 3.4 V. Operando X-ray diffraction confirms a reversible phase transition process from the O3 to P3 structure accompanied with a very small volume change (1.0%) upon sodium extraction and insertion. The low activation barrier energy of 400 meV and the fast Na+ migration of 10-11 cm2·s-1 are further obtained by first-principles calculations and galvanostatic intermittent titration technique, respectively. As a result, the O3-Na0.8Ni0.6Sb0.4O2 cathode displays a reversible capacity of 106 mA h g-1 at 0.1C (12 mA g-1), smooth charge-discharge curves, and a high average working voltage of 3.5 V during battery cycling. The results highlight the importance of searching for a new O3-type structure with cation-disordering and high working voltage for realizing high energy SIBs.

P3/O3 Integrated Layered Oxide as High-Power and Long-Life Cathode toward Na-Ion Batteries.

Low-cost and stable sodium-layered oxides (such as P2- and O3-phases) are suggested as highly promising cathode materials for Na-ion batteries (NIBs). Biphasic hybridization, mainly involving P2/O3 and P2/P3 biphases, is typically used to boost their electrochemical performances. Herein, a P3/O3 intergrown layered oxide (Na2/3 Ni1/3 Mn1/3 Ti1/3 O2 ) as high-rate and long-life cathode for NIBs via tuning the amounts of Ti substitution in Na2/3 Ni1/3 Mn2/3- x Tix O2 (x = 0, 1/6, 1/3, 2/3) is demonstrated. The X-ray diffraction (XRD) Rietveld refinement and aberration-corrected scanning transmission electron microscopy show the co-existence of P3 and O3 phases, and density functional theory calculation corroborates the appearance of the anomalous O3 phase at the Ti substitution amount of 1/3. The P3/O3 biphasic cathode delivers an unexpected rate capability (≈88.7% of the initial capacity at a high rate of 5 C) and cycling stability (≈68.7% capacity retention after 2000 cycles at 1 C), superior to those of the sing phases P3-Na2/3 Ni1/3 Mn2/3 O2 , P3-Na2/3 Ni1/3 Mn1/2 Ti1/6 O2 , and O3-Na2/3 Ni1/3 Ti2/3 O2 . The highly reversible structural evolution of the P3/O3 integrated cathode observed by ex situ XRD, ex situ X-ray absorption spectra, and the rapid Na+ diffusion kinetics, underpin the enhancement. These results show the important role of P3/O3 biphasic hybridization in designing and engineering layered oxide cathodes for NIBs.

IrCo alloy nanoparticles supported on N-doped carbon for hydrogen evolution electrocatalysis in acidic and alkaline electrolytes.

Designing efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is of great importance to advance water splitting technology towards practical applications. Herein, we report the preparation of IrCo nanoparticles supported on nitrogen-doped carbon (IrCo/NC) as a HER electrocatalyst in acidic and alkaline electrolytes. The IrCo/NC composite is obtained by pyrolyzing an Ir-doped Co(OH)2 precursor on g-C3N4, and is endowed with N-doped carbon and uniform IrCo alloy nanoparticles via a crystal confinement resulting from the Ir-doping into the Co(OH)2 layer. Electrocatalytic analysis shows that the IrCo/NC electrode requires low overpotentials of 32 mV at 10 mA cm-2 in 0.5 M H2SO4 and 33 mV in 1 M KOH, which are superior to those of the Co/NC and IrCo alloys that are free of Ir-doping or N-doped carbon. The results provide a strategy for designing and preparing active noble-transition bimetallic alloy electrocatalysts as efficient HER catalysts.

An in situ phosphorization strategy towards doped Co2P scaffolded within echinus-like carbon for overall water splitting.

Eco-environmental synthesis of non-expensive electrocatalysts such as transition-metal phosphides (TMPs) is critical to advancing renewable hydrogen fuel. TMP nanostructures prepared typically by introducing additional conventional phosphorus sources are suggested as promising durable and low-cost electrocatalysts. Herein, an eco-efficient guest/host precursor-based synthesis route is demonstrated to prepare doped Co2P scaffolded within echinus-like carbon ((M0.2Co0.8)2P@C, M = Fe and Ni) as electrocatalysts for overall water splitting. (Fe0.2Co0.8)2P@C is derived by directly pyrolyzing a precursor of sodium dodecyl phosphate-intercalated CoFe-layered double hydroxide (CoFe-LDH), without introducing any additional phosphorus source. Electrocatalytic testing shows that (Fe0.2Co0.8)2P@C requires overpotentials of 290 and 130 mV at a current density of 10 mA cm-2 for oxygen and hydrogen evolution reactions (OER and HER) in an alkaline electrolyte, respectively. Furthermore, a different (Ni0.2Co0.8)2P@C composite, obtained only by altering a NiCo-LDH host, exhibits better electrocatalytic activities than those of Fe-doped (Fe0.2Co0.8)2P@C. In particular, the (No0.2Co0.8)2P@C||(Ni0.2Co0.8)2P@C electrolyzer affords a current density of 10 mA cm-2 at a decent voltage of 1.62 V for overall water splitting. Electron energy-loss spectroscopy (EELS) observations show the oxyhydroxide layer formed on the surface, and density functional theory (DFT) calculations reveal that Fe-/Ni-doping lowers the Gibbs free energy barrier for the OER and the HER, both underpinning the enhancements.

Air-Stable and High-Voltage Layered P3-Type Cathode for Sodium-Ion Full Battery.

The development of highly efficient and stable cathodes for sodium-ion batteries (SIBs) is strategically critical to achieving large-scale electrical energy storage. Creating air-stable and high-voltage layered cathodes for sodium-ion full batteries still remains a challenge. Herein, we describe a rational design and preparation of a stable P3-Na2/3Ni1/4Mg1/12Mn2/3O2 cathode. The cathode displays a satisfactory working voltage of 3.6 V and excellent cyclic stability over 100 cycles at a 1 C rate without obvious capacity fading. The results of ex situ X-ray diffraction (XRD) demonstrate that the P3-type structure is well retained even when charged to 4.4 V. Furthermore, the structural characterization by XRD Rietveld refinement, scanning electron microscopy, and electrochemical testing certifies that the cathode maintains its structure commendably even when soaked in water for 12 h. In particular, the P3- Na2/3Ni1/4Mg1/12Mn2/3O2∥hard carbon full battery exhibits a desired competitively high voltage of 3.45 V and an attractive energy density of up to 412.2 W h kg-1 based on the cathode. The comprehensive results achieved by the specially designed strategy provide guidance toward the exploration of stable cathodes in the application of SIBs as modern energy-storage devices.

Correction: NiS2 nanodotted carnation-like CoS2 for enhanced electrocatalytic water splitting.

Correction for 'NiS2 nanodotted carnation-like CoS2 for enhanced electrocatalytic water splitting' by Weili Xin et al., Chem. Commun., 2019, 55, 3781-3784.

NiS2 nanodotted carnation-like CoS2 for enhanced electrocatalytic water splitting.

Combining ultrasmall NiS2 nanodots with three-dimensional carnation-like CoS2 microstructures is demonstrated to be able to enhance the electrocatalytic activities for both the oxygen and hydrogen evolution reactions, leading to efficient overall alkaline water splitting.

Bimetallic sulfide nanoparticles confined by dual-carbon nanostructures as anodes for lithium-/sodium-ion batteries.

Bimetallic sulfide ((Ni0.3Co0.7)9S8) nanoparticles confined by dual-carbon nanostructures are prepared by pyrolyzing a mixture of surfactant-intercalated layered double hydroxide and melamine, and deliver a highly reversible capacity and decent rate capability as anode nanomaterials for lithium- and sodium-ion batteries.