ACS Applied Energy Materials最新文献

Surface fluorination is an effective strategy to stabilize high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathodes against interfacial degradation, yet the role of the fluorinating agent and its decomposition pathway in governing surface speciation remains poorly understood. Here, PTFE and CYTOP are investigated as solid fluoropolymer-derived fluorinating agents for LNMO surface modification via thermal decomposition under inert atmosphere, yielding comparable surface fluorine contents of approximately 0.08 mmol g^–1 for both treatments. X-ray diffraction and Raman spectroscopy confirm that both treatments preserve the cubic spinel framework, indicating that fluorination is confined to the particle surface. XPS reveals the formation of LiF-like species, M–F bonds and manganese oxyfluoride-like environments, while EPR reveals modifications of the manganese electronic environment after treatment. Galvanostatic cycling over 100 cycles at C/10 demonstrates improved capacity retention for both fluorinated samples: all three electrodes deliver an initial discharge capacity close to 143 mAh g^–1. After 100 cycles, LNMO–PTFE retains 95% of its initial discharge capacity (136 mAh g^–1), compared to 91% for LNMO–CYTOP and 90% for pristine LNMO (∼128 mAh g^–1). TGA-MS and in situ gas-phase FTIR identify the reactive species generated during decomposition: PTFE mainly releases :CF₂, •CF, •C₂F₃ and •CF₃ fragments, whereas CYTOP produces a broader distribution of fluorinated species over a wider temperature range. These differences in decomposition chemistry directly control the nature of the fluorinated interphase and the resulting electrochemical stabilization of LNMO. This work establishes mechanistic guidelines for designing scalable fluoropolymer-based surface treatments for high-voltage cathode materials, as an alternative to reactive fluorine sources such as F₂ or XeF₂.

This study proposes an integrated thermochemical energy storage and air separation process and investigates Na-containing Ce–Mn composite oxides as candidate redox materials. The materials were prepared by coprecipitation, and the effects of coprecipitation temperature and Ce mixing ratio on their redox characteristics were evaluated under temperature-swing conditions involving reduction at 550 °C and oxidation at 350 °C. The largest redox swing of 2.5 wt % was obtained at a coprecipitation temperature of 5 °C and a Ce mixing ratio of 7.5 mol %. XRD analysis confirmed the formation of Na₀.₇MnO₂, whose presence was correlated with higher redox performance. The heat of reaction per unit oxygen exchange remained largely constant regardless of Ce loading, suggesting that Ce incorporation did not predominantly contribute as a direct oxygen storage mechanism under the investigated conditions and that Mn-based redox reactions constituted the dominant contribution to oxygen exchange. Repeated redox cycling showed a gradual decrease in redox swing, although reversible oxygen exchange was maintained throughout the investigated cycles.

The electrochemical nitrogen reduction reaction (ENRR) is an environmentally friendly and sustainable route for ammonia (NH₃) production. It offers a promising alternative to the energy-intensive Haber–Bosch process, significantly reducing its environmental impact. In this study, cobalt hydroxide nanoneedle arrays were successfully prepared on nickel foam (Co(OH)₂@NF) by a facile hydrothermal approach. The Co(OH)₂ structure was then overlayered simply by Au atoms through galvanic replacement. This process created a synergistic effect between Co and Au, which promotes N₂ activation while suppressing the competing hydrogen evolution reaction (HER). Density functional theory (DFT) calculations revealed that Au incorporation significantly modifies the electron density redistribution around adsorbed N₂ molecules, creating more favorable sites for protonation and thereby enhancing the ENRR kinetics. The replacement of Co with Au atoms increased the Faradaic efficiency (FE) from 38.2 ± 2.4% to 90.1 ± 2.3%. The NH₃ yield rate (rNH₃) nearly doubled from 0.45 µg h⁻¹ cm⁻² ± 0.02 (2.00 × 10⁻⁸ mol h⁻¹ cm⁻²) at –0.15 V vs RHE to 0.85 ± 0.06 µg h⁻¹ cm⁻² (4.98 × 10⁻⁸ mol h⁻¹ cm⁻²) at a more favorable potential of + 0.00 V vs RHE. The Co(OH)₂–Au@NF electrocatalyst can be used as a stable and effective electrocatalyst for the green synthesis of NH₃, which is, to the best of our knowledge, among the highest FE values reported for ENRR under ambient conditions, particularly considering the extremely low overpotential.

Molecule-electrode hybrid materials based on cobalt phthalocyanine (CoPc) supported on carbon nanostructures have emerged as highly effective electrocatalysts for the selective six-electron reduction of CO₂ to methanol (e-methanol). However, the strong π-stacking tendency of CoPc leads to poor solubility and hinders its uniform integration with conductive supports such as multiwalled carbon nanotubes (CNTs), limiting the controlled preparation of well-defined hybrid architectures. Here, we introduce a thermocleavable CoPc-ester precursor strategy that enables the synthesis of a highly dispersed CoPc-acid@CNT hybrid catalyst. Controlled thermal activation cleaves the solubilizing ester groups, generating insoluble CoPc-acid species that molecularly anchor onto the CNT surface. This approach promotes active site dispersion, as supported by electron microscopy, and alters the local environment of the Co-bound *CO intermediate, as indicated by a different Stark tuning response in operando IR spectroscopy relative to conventionally prepared CoPc@CNT materials. Under H-cell conditions, the optimized hybrid catalyst achieves a methanol Faradaic efficiency (FE) of 44.4 ± 0.8% at a total current density of 18.9 mA/cm², compared with 39.8 ± 2.6% at 27.1 mA/cm² for the benchmark CoPc@CNT system tested under the same conditions (mean ± standard deviation, n = 3), a modest difference of borderline statistical significance. To place these results in a broader process context, we also present a prospective techno-economic analysis (TEA) and life-cycle analysis (LCA) that combine experimentally measured product distributions and cell voltage with literature-based flow cell assumptions. The baseline TEA gives a minimum selling price of $4.16/kg for e-methanol, while a modeled target of $0.41/kg requires simultaneous improvements in current density, methanol FE, electricity cost, CO₂ conversion, electrolyzer capital cost and cell voltage beyond those demonstrated in the present H-cell system. The baseline LCA indicates a 34% reduction in carbon intensity (CI) relative to fossil-derived methanol, while near-zero CI requires high methanol FE together with renewable heat integration for methanol distillation. Collectively, these results identify thermocleavable molecular precursors as a useful strategy for controlling molecular catalyst dispersion and anchoring on conductive carbon supports, while also showing that high current density operation, catalyst layer optimization and long-term durability remain important targets for future development.

The low energy density and mismatched electrode kinetics of conventional asymmetric supercapacitors (ASCs) greatly limit their practical commercial applications. To address these problems, here, a nitrogen-doped polyacrylonitrile-derived porous carbon embedded with carbon nanotubes (N-doped PC/CNTs) is prepared using a simple and scalable blade-coating and carbonization method and used to fabricate high-performance all-carbon asymmetric supercapacitors. The N-doped PC/CNT composites deliver a large specific surface area (SSA) and high degree of graphitization. Electrochemical tests show that the PC/CNT composite displays different capacitance performances in different potential windows, achieving gravimetric capacitances of 286.3 and 178.1 F g^–1 within operating windows of –0.8 to 0 V and 0 to 0.8 V, respectively. Based on these properties, an assembled all-carbon ASC delivers a wide voltage window of 1.6 V, achieving a maximum operating window of 1.6 V, a maximum energy density of 24.4 Wh kg^–1, and maintains 15.2 Wh kg^–1 even at a high-power density of 40 kW kg^–1. Moreover, the capacitance retention remains above 90% after 20,000 cycles, showing favorable potential for advanced electrochemical energy storage.

Solid-state sodium batteries are attractive next-generation energy-storage systems, combining the safety of inorganic solid electrolytes with the resource and cost benefits of sodium-based chemistries. Among Na⁺ conductors, NaSICON-type Na₃Zr₂Si₂PO₁₂ (NZSP) is particularly promising due to its high conductivity and stability, yet its practical implementation is challenged by energy-intensive ceramic processing, typically requiring prolonged high-temperature sintering for densification. Here, spray-flame synthesis (SFS) is introduced as a scalable route to nanoparticulate NZSP precursors, offering nanometer-scale compositional homogeneity beyond conventional solid-state synthesis and greater compositional flexibility than sol–gel approaches. Rather than forming crystalline NZSP directly, SFS yields a nanostructured intermediate consisting of ∼5 nm ZrO₂ domains embedded in an amorphous Na–Si–P–O matrix, enabling NaSICON formation at ∼980 °C and densification to ∼97% within 2 h at 1140 °C. Systematic variation of the Si/P ratio and substitution of Zr⁴⁺ with Mg²⁺ or Ca²⁺ increase the Na content per formula unit, resulting in reduced lattice distortion and lower activation energies. Si-rich and Mg-substituted compositions reach conductivities up to 1.16 mS cm^–1 with activation energies of 0.299(2)–0.327(6) eV. We have discovered that macroscopic conductivity is governed not by composition alone but by the interplay of the crystal structure, phase stability, densification, and grain-boundary chemistry.

Hydrogen-assisted degradation of metals is governed by the local hydrogen population available at near-surface lattice sites and defects. However, atomistic mechanical simulations commonly employ hydrogen concentrations that are not representative of realistic exposure conditions. In this study, ReaxFF-based reactive molecular dynamics is used to translate sustained CH₄ and CH₄ + H₂O exposure on a Ni(211) surface under an accelerated closed-cell protocol at 1000–1350 K into exposure-conditioned hydrogen availability descriptors. Three independent trajectories are performed for each exposure-temperature condition to quantify the normalized Ni-associated H inventory, hydrogen partitioning between adsorbed and subsurface regions, and localization across CN-defined step and terrace regions. A key finding is a dry–wet inversion in hydrogen accessibility. Although CH₄ + H₂O exposure produces a larger normalized Ni-associated H inventory (θ_H = 0.67–0.77), 71.6–86.1% of that inventory is primarily O-bound, while less than 3.5% of the geometrically defined near-surface H population lies within the subsurface window. In contrast, CH₄-only exposure yields a smaller normalized Ni-associated H inventory (θ_H = 0.088–0.447) but substantially greater subsurface partitioning, reaching 12.3% at 1350 K. These results show that the surface with the largest normalized Ni-associated H inventory does not necessarily have the largest geometric subsurface fraction. Furthermore, CH₄ + H₂O suppresses carbon accumulation, sustains an oxygen-containing surface state, and maintains higher per-site hydrogen localization around CN-defined step regions. Additional Ni(111) and laterally doubled Ni(211) checks retain the wet-over-dry H areal-density ordering and the complementary dry-over-wet subsurface-fraction ordering at 1250 K. The resulting protocol-specific descriptors provide candidate inputs for controlled downstream simulations of hydrogen transport, trapping, and degradation.

Due to its unique electronic structure and suitable active sites, Cu is a promising catalyst for CO₂ reduction. In this study, a series of Cu_x-Ga_0.9-In_0.1 oxides was synthesized via co-precipitation by varying Cu²⁺ concentration. X-ray diffraction and X-ray photoelectron spectroscopy reveal that Cu exists as CuO, Ga forms Ga₂O₃ due to its strong oxophilicity, and a small amount of In is uniformly dispersed as In₂O₃ within the CuO lattice, forming a composite catalyst. Combined density functional theory calculations and X-ray absorption fine structure spectroscopic analyses indicate Cu as the primary active site. The introduction of Ga and In enhances electron transfer with Cu, strengthening intermediate adsorption and accelerating product conversion, thereby improving catalytic performance for the CO₂ reduction reaction. When the molar ratio of divalent to trivalent ions n(M²⁺):n(M³⁺) is 5:1, the catalyst achieves a total current density of 28.4 mA·cm^–2, a CO Faradaic efficiency of 98.54%, and good stability.

Bismuth copper oxyselenide (BiCuSeO) is a highly promising p-type thermoelectric (TE) material due to its intrinsically layered structural property. However, conventional thin-film fabrication methods, such as pulsed laser deposition and multi-step selenization, often struggle with industrial scalability, stoichiometric control, and phase purity. In this study, we report the successful fabrication of high-quality BiCuSeO thin films using a scalable, two-step reactive magnetron co-sputtering technique utilizing Bi₂Se₃ and Cu targets in an Ar/O₂ atmosphere. Thin films subjected to vacuum annealing at 350 °C exhibited a highly crystalline tetragonal P4/nmm phase, as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. X-ray photoelectron and Raman spectroscopies validated the expected chemical states and vibrational modes, while surface analysis revealed a dense, uniform, and crack-free morphology optimal for charge transport. TE evaluations up to 250 °C demonstrated a clear transition from n-type conduction in pristine Bi₂Se₃ to robust p-type transport in the quaternary films. By effectively decoupling the inverse relationship between electrical conductivity and the Seebeck coefficient, the BiCuSeO phase achieved a superior peak power factor of 1.71 mW m^–1 K^–2 at 250 °C. The power factor is approximately 1.5 folds higher than that of pristine Bi₂Se₃ and 3 folds higher than that of the intermediate BiSe–Cu films. Our findings establish reactive magnetron co-sputtering as a highly effective, industry-compatible platform for developing next-generation oxychalcogenide thin-film TE devices.

A three-dimensional nanoscale architecture originating from semiconductor manufacturing offers a powerful route to overcome ion-transport limitations in microscale electrochemical systems. Here, we report a sodium-ion microbattery array based on a coaxial γ’-V₂O₅/Pt nanotube architecture embedded within anodic aluminum oxide (AAO) nanopores, forming vertically aligned nanotubular electrodes conformally integrated with Pt nanotube current collectors. This nanoconfined geometry shortens Na⁺ diffusion pathways, enhances charge-transfer kinetics, and maintains electronic conduction across the microbattery array. The resulting device delivers a high areal capacity of 44 μAh cm^–2 (corresponding to one Na⁺ per γ’-V₂O₅) at 1/10 C, excellent rate capability up to 2 C, and exceptional cycling stability with 80% capacity retention after 720 cycles. Cyclic voltammetry analyzed by both Trasatti's and Dunn's methods reveals that 66–69% of the stored charge arises from surface-dominated processes enabled by the nanotube architecture, compared to only 17–25% in planar films. The stark performance contrast between the nanoscale nanotube geometry and micron-scale planar controls suggests a fundamental length-scale dependence of sodiation kinetics, with implications for particle size selection in conventional sodium-ion battery electrodes. These results demonstrate that semiconductor-derived 3D architectures can be directly translated to sodium-ion systems, enabling high-power, long-life microbatteries and establishing a generalizable platform for nano-ionic device engineering.