ACS Applied Energy Materials最新文献

Understanding the diffusion properties of constituent atoms in chalcopyrite-type Ag-containing Cu(In,Ga)Se₂-based semiconductors is important for the design of highly efficient photovoltaic devices. Herein, we experimentally evaluated the vibrational energy (Einstein frequency and temperature) of individual bonds in (Ag,Cu)InSe₂ and Ag(In,Ga)Se₂ powders using Debye–Waller factors derived from extended X-ray absorption fine structure (EXAFS) data at low temperatures. We found that the Einstein temperature and frequency increased in the order of Ag–Se < Cu–Se < In–Se < Ga–Se. This order correlates with the theoretical activation energy of atomic migration calculated for Ag(In,Ga)Se₂ and Cu(In,Ga)Se₂ with Ag or Cu defect sites. In the chalcopyrite compounds, the Ag atom is the easiest to diffuse, owing to the smallest force constant and the largest reduced mass of the Ag–Se bond. The bond length varied with the sample composition, and the force constant’s dependence on bond length further suggests that activation energy for atomic diffusion can be modulated through compositional adjustments. The low-temperature EXAFS study provides beneficial information for the design of multicomponent materials including bond length variations and Einstein frequencies of individual bonds. The Einstein frequencies could be an indicator of the atomic diffusion properties, reflecting the influence of force constant and reduced mass, to understand the elemental gradients in chalcopyrite semiconductors for highly efficient photovoltaic devices.

Considering a vertical cylindrical vessel filled with LaNi₅, this study investigated the effect of cyclic hydrogen ab/desorption on the swelling pressure, i.e., the mechanical pressure exerted by LaNi₅ on the vessel, its packing fraction distribution, and the relationship between the swelling pressure and local packing fraction. The swelling pressure tended to increase close to the bottom of the vessel with increasing number of hydrogen ab/desorption cycles. In addition, it converged with the number of hydrogen ab/desorption cycles and did not increase after the 20th cycle. The packing fraction of the LaNi₅ bed was denser and closer to the bottom of the vessel. The packing fraction near the bottom increased with increasing number of hydrogen ab/desorption cycles. Almost no swelling pressure developed during the first hydrogen absorption although the packing fractions were high in some regions. Conversely, after cyclic hydrogen ab/desorption, the swelling pressure developed and increased exponentially with increasing local packing fraction. The swelling pressure appeared only in the LaNi₅ bed region where the local packing fraction exceeded 0.61 during hydrogen absorption. The obtained results are essential for preventing the deformation of LaNi₅ vessels for safe hydrogen storage.

Atomistic molecular dynamics (MD) simulations were undertaken on polymerized ionic liquids (polyILs) consisting of a poly(methyl methacrylate) (PMMA)-based backbone with attached imidazolium cations through a series of linkers and mobile anions: TFSI^–, PF₆^–, BF₄^–, and Br^–. Ionic correlations and the mechanisms of ion transport in these polyILs were systematically investigated to understand the effects of side chain flexibility coupled with specific interactions. The simulations revealed that the linker length has only a minimal effect on cation–anion interactions particularly when compared to the change with the anion. An increase in the linker length enhances the anion diffusivity to a varying extent for the different anions arising from significant increases in diffusive motion but a lesser reduction in ion hopping. Specifically, the small anions exhibit large increases in the anion diffusivity when the linker length is increased since the rigid “cage” appears to be strongly softened by increasing side chain flexibility, suggesting a size-dependent effect. Dynamical heterogeneity in the anion mobility further confirms the softening effect of the long linkers. Moreover, only a small fraction of the anions was observed to travel farther than the characteristic distance determined by the self-part of the van Hove function within the characteristic time of the strongest heterogeneity. Fast anions exhibit dominant interchain hopping associated with more cations from more chains compared with the slow anions. The string-like cooperative motion was observed in these fast anions and the string length decreases as the linker length increases. More importantly, distinct anion–anion correlation suppresses the conductivity in a barycentric reference frame, while this correlation enhances the conductivity within a polycation-fixed reference frame. The cage escape seems to serve as the primary ion transport rate-controlling mechanism in these systems. These findings may lead to interesting implications for the design of polyILs with enhanced ionic conductivity for electrochemical applications.

The electrochemical performance of ceramic–metal composite (cermet) electrodes in solid oxide cells (SOCs) is correlated to the ionic conductivity of the ion-conducting phase. This study explores the effect of replacing the 8 mol % yttria-stabilized zirconia (YSZ) in the fuel electrode of state-of-the-art SOCs with 10 mol % scandia and 1 mol % ceria-stabilized zirconia (10SSZ). The electrochemical behavior of electrodes with a 56:44 wt % (NiO:YSZ/10SSZ) ratio, symmetrically screen-printed on YSZ pellets and sintered at 1400 °C for 5 h, is investigated. The area-specific resistance (ASR) in Ar/3% H₂ between 800 and 700 °C for Ni–10SSZ is found to be much higher compared to the conventional Ni–YSZ under these conditions, even though the ionic conductivity of scandia-stabilized zirconia (SSZ) is greater than that of YSZ. Increasing the initial NiO content in NiO–10SSZ from 56 to 65 wt % also did not improve the electrochemical performance relative to Ni–YSZ. Based on scanning electron microscopy (SEM) analysis, we attribute the poor performance of Ni–10SSZ to the detachment and contact loss between Ni and 10SSZ particles. The transmission electron microscopy (TEM) analysis reveals scandium segregation at the NiO grain boundaries after sintering NiO–10SSZ at 1400 °C in air, which may contribute toward such detachment.

Sodium-ion batteries (SIBs) are a potential alternative to lithium-ion batteries (LIBs), owing to their low cost and sustainability. However, developing a promising anode for sodium-ion batteries remains challenging due to the large size of Na⁺ ions and the significant volume expansion during Na⁺ insertion reactions. Polyoxometalates (POMs) can host cations on the surface and between POM clusters rather than intercalating into the crystal structure, offering their potential as an anode material for SIBs. Herein, we report a vanadium-based POM, i.e., Na₆PV₃W₉O₄₀ (PVW), stabilized on a cobalt-based metal–organic framework (CoATP), as an effective anode material for SIBs. Electrostatic interactions between CoATP and PVW are enabled by developing cationic groups (−NH₃⁺) on the surface of CoATP. The resulting PVW@CoATP exhibits a continuous layer-by-layer interconnected architecture with intimate PVW/CoATP contact. The layered arrangement provides insertion sites and ensures complete exposure of PVW clusters for redox reactions. XPS analysis indicates that apart from the simultaneous reduction of V⁵⁺ to V⁴⁺ and of W⁶⁺ to W⁴⁺, the cobalt of CoATP reduces from Co³⁺ to Co²⁺ during discharge, which demonstrates that the nanospheres of CoATP not only provide a 3D surface for the layered arrangement of PVW clusters but also synergistically enhance the performance due to the involvement of Co in the redox process. Consequently, the PVW@CoATP composite exhibits promising performance as an anode material for sodium-ion batteries, including a high reversible capacity of 413 mAh g^–1 and long-term cycling with 84% retention after 1000 cycles. This work paves a new pathway for the MOF-supported layered growth of POM, which shows promising structural prospects in energy storage applications.

Nickel–cobalt layered double hydroxide (NiCo-LDH) shows great potential as an electrode material for various applications; however, single NiCo-LDH layered electrode materials are poorly stabilized and prone to agglomeration, which hampers ion transport. In this study, three-dimensional composite electrode materials with high specific surface area and abundant redox active sites were prepared by loading spherical CoSe₂ on the surface of nickel foam and realizing the in situ growth of NiCo-LDH nanosheets derived from ZIF-67 on the Ni@CoSe₂ skeleton. The results show that the CoSe₂@NiCo-LDH electrode achieves an area-specific capacitance of 6.06 F cm^–2 at a current density of 6 mA cm^–2. Compared with CoSe₂ and NiCo-LDH, CoSe₂@NiCo-LDH electrodes have a 0.265 eV narrow bandgap. It is demonstrated that the composite heterojunction of CoSe₂ and NiCo-LDH enhances the electrical conductivity, and the built-in electric field triggered by efficient electron migration promotes the conductivity and electrochemical activity of the electrode materials. The charge density distribution and density of states further confirm that the interaction between CoSe₂ and NiCo-LDH heterojunctions mainly relies on the hybridization of d orbitals of Co atoms, Ni atoms, and p orbitals of Se atoms, which facilitates charge transport and ion diffusion. Molecular dynamics simulations show that the composite exhibits excellent ion adsorption capacity in KOH electrolyte. An asymmetric supercapacitor assembled from this electrode with activated carbon exhibits an area capacitance of 0.51 F cm^–2 to 0.33 F cm^–2 over a current density range of 6 mA cm^–2 to 20 mA cm^–2, with an 0.183 mWh cm^–2 energy density and 40 mW cm^–2 power density, and retained 97.82% of its initial capacitance over 5000 cycles.

The transition to a hydrogen-based economy necessitates the development of safe, cost-effective hydrogen storage media at an industrial scale. The equiatomic intermetallic titanium-iron (TiFe) alloy is a prime candidate for stationary hydrogen applications due to its high volumetric storage density, nontoxicity, and safety attributes. However, the conventional synthesis of TiFe alloy relies on high purity titanium and iron metal feedstocks, which must first be extracted from their respective ores before being alloyed in equiatomic ratio. This is a complex, multistep process posing environmental and economic challenges associated with the extraction of metallurgical-grade titanium. Here, we propose an alternate straightforward synthesis pathway for TiFe alloy through the direct calciothermic reduction of ilmenite sand (FeTiO₃). Initial small-scale experiments have achieved a maximum TiFe yield of approximately 52 wt %, with similar yields observed when scaling up to 100 g samples. The TiFe alloy produced via this pathway demonstrated a hydrogen storage capacity of approximately 0.71 wt % after activation at 65 bar, indicating that direct metallothermic reduction of ilmenite sand represents an attractive alternative production route for hydrogen storage alloys, which offers economic and sustainability advantages over the existing industrial pathway.

Sodium-ion batteries (SIBs) offer a propitious choice to lithium-ion batteries (LIBs) due to sodium’s abundance and lower cost. However, SIBs’ commercial adoption is hindered by their lower energy density and higher cathode material production costs compared to those of LIBs. This study synthesizes Na₃V₂O₂(PO₄)₂F (NVOPF) nanoparticles at room temperature using solid-state mechanochemical synthesis, followed by carbon encapsulation. Pristine NVOPF achieves an initial gravimetric discharge capacity of 100 mAh g^–1 at a 0.1 C rate and delivers 98 mAh g^–1 at a 1 C rate, retaining 80% of its capacity over 250 cycles at a 1 C rate. Incorporating high surface area carbon (HSAC) enhances the intrinsic electronic conductivity of NVOPF. The HSAC-NVOPF composite shows improved cycling stability and higher rate capability, retaining 89.9% of its initial capacity after 500 cycles at a 1 C rate and 90% after 1000 cycles at 3 C rate due to fast sodium-ion diffusion and delivering 94 mAh g^–1 at a 20 C rate. This improvement is attributed to enhanced electrochemical reversibility and Na⁺-ion reaction kinetics. Reduced voltage–polarization values (113 and 111 mV for the composite vs 162 mV and 160 mV for pristine NVOPF) and lower charge transfer resistance (113 Ω cm² compared to 224 Ω cm²) indicate improved Na⁺ ion diffusion, highlighting the potential of NVOPF cathode for promising SIBs.

High-entropy oxide (HEO) represents a promising class of electrode material systems for high-energy lithium-ion batteries (LIBs). The rock-salt-type (MgCoNiCuZn)O HEO is an attractive anode due to its obvious structure stability during long cycling. However, the inherent sluggish kinetics of the (MgCoNiCuZn)O HEO led to poor rate capability, severely restricting its further development in LIBs. Herein, hollow graphene spheres are synthesized as in situ deposited (MgCoNiCuZn)O HEO nanosized particles via a simple hydrothermal reaction following a calcination process, denoted as RHEO@TrGO. First, the hollow graphene shells have abundant defects and serve as a framework for the precipitation of nanosized HEO particles, promoting the dynamic of transformation reaction. Second, the reserved hollow of the graphene spheres acts as a “reservoir” for electrolyte storage, reducing the transportation resistance of electrolytes. Third, the conductive graphene shells also could improve the electron diffusion rate. Based on the above advantages, RHEO@TrGO displayed an initial reversible capacity of 873.55 mA h g^–1 at 50 mA g^–1 and still delivered 402.03 mA h g^–1 at 2.0 A g^–1. By comparison, the synthesized pure (MgCoNiCuZn)O HEO (noted as RHEO) without hollow graphene spheres as a template only exhibits 97.21 mA h g^–1 at 2.0 A g^–1 with a 21.5% of capacity at 50 mA g^–1. During the long cycling test, RHEO@TrGO showed a capacity increase phenomenon, reaching near 1400 mA h g^–1 after 800 cycles at 1.0 A g^–1. In addition, the morphology evolution and composition-dependent electrochemical mechanism of RHEO@TrGO were further validated by theoretical calculations. This strategy demonstrates that hollow graphene spheres are an ideal template for preparing high-performance HEO anode materials with excellent stability, providing valuable insights for the development of HEO-based energy storage applications.

In this work, sulfonated lithium-rich porous aromatic frameworks (PAF-56-SO₃Li) and poly(ether ether ketone ketone) (SFPEEKK-Li) were synthesized, introducing a large number of Li⁺ ions while retaining the electrostatic repulsion effect of the sulfonic acid group. The carbon material Super P was applied to enhance the redox kinetics. They were solution-compounded and scraped onto a PE separator to produce Janus separator LSP-PAF-56-SO₃Li with a coated layer thickness of about 1 μm, which can successfully suppress the “shuttle effect” and ensure the stability of lithium stripping and plating at high current densities. LSP-PAF-56-SO₃Li exhibited an impressive Li⁺ transfer number, reaching a maximum of 0.85, which endowed it with a substantial initial specific capacity of 1153 mA h g^–1 at a current rate of 0.5 C. The initial specific capacities reached 1053 and 955 mA h g^–1 at 1 and 2 C, respectively, and when returned to 0.2 C, the capacity can still achieve 1198 mA h g^–1 with a recovery rate of 97%. This work provided a concept that LSP-PAF-56-SO₃Li can restrain the “shuttle effect” and elevate the uniform deposition of Li⁺, which was of significance in the field of lithium–sulfur battery (LSB) separators.