ACS Applied Energy Materials最新文献

Elemental substitution is well-known to benefit hydrogen storage in the intermetallic compound TiFe; however, the impact of these substituents on the native and passivating surface oxide has not been well-established. Here, we perform density functional theory calculations on several characteristic oxides that are likely to form on exposed TiFe surfaces, specifically, TiO₂, FeO, TiFeO₃, and Ti₄Fe₂O. In TiO₂ and TiFeO₃, additional acceptor species substituting for Ti can increase the solubility of protonic hydrogen (H_i⁺), likely enhancing hydrogen permeation of the oxide layer. In FeO, few dopants will act as acceptors, and hydrogen will incorporate as substitutional H_O⁺, which is likely to be less mobile and will hinder hydrogen permeation. Finally, we find that Ti₄Fe₂O, which is thermodynamically metastable, may be stabilized by defects under O-poor conditions, although the presence of certain substitutional elements can destabilize it. In general, Mn, V, and Cr are among the best substituents for enhancing hydrogenation through the oxide layer. Our results help to explain what features make additional elements particularly effective for enabling reversible hydrogen storage in TiFe, and they can guide further technological development of high-performing TiFe-based alloys for future energy applications.

This work reports a multifunctional interfacial engineering strategy using Bi₂O₂S nanosheets and a Co-Pi catalyst to enhance the photoelectrochemical (PEC) water oxidation performance of ZnFe₂O₄ photoanodes in a neutral electrolyte. Although ZnFe₂O₄ possesses suitable band-edge positions, chemical stability, and visible-light absorption, its PEC activity is severely limited by surface recombination and sluggish charge transport. By integrating low-band gap Bi₂O₂S nanosheets as a light-harvesting, surface-passivating, and hole-transport layer, and coupling them with a Co-Pi cocatalyst, the optimized ZnFe₂O₄/Bi₂O₂S/Co-Pi photoanode delivers a photocurrent density of 0.34 mA cm^–2 at 1.23 V_RHE, representing an approximately 10-fold enhancement over pristine ZnFe₂O₄. A cathodic shift of ∼180 mV in the onset potential and an applied bias photon-to-current efficiency exceeding 0.5% are also achieved under neutral pH conditions. Mechanistic investigations reveal that Bi₂O₂S effectively passivates oxygen-vacancy-related surface states and forms a favorable type-II heterojunction with ZnFe₂O₄, leading to Fermi-level depinning, enhanced interfacial band bending, and improved photogenerated charge separation. The Co-Pi cocatalyst further accelerates interfacial hole injection and oxygen evolution reaction kinetics, resulting in a charge-transfer efficiency of ∼63% and reduced interfacial resistance. Overall, this study demonstrates that multifunctional Bi₂O₂S nanosheets, combined with an earth-abundant cocatalyst, provide an effective route to improving the efficiency and stability of spinel ferrite photoanodes for solar fuel generation in neutral aqueous environments.

A catalyst of the oxygen reduction reaction (ORR) containing as few precious metals as possible is one of the key factors for the large-scale application of fuel cells, and researchers continue to explore special catalyst structures and mechanisms to meet this requirement. We report here a catalyst named NCM⊂PtCo/C with its catalytic PtCo particles surrounded by a nitrogen–carbon matrix (NCM) as the external interface capable of enriching oxygen. The PtCo nanoparticles are confined by the NCM to a size as small as ∼2.39 nm, even after thermal treatment at high temperatures. As the reactant–catalyst interface, the electron-rich NCM layer can modulate active centers in multiple aspects, including channels for electrons and protons. Meanwhile, the NCM interface layer strongly adsorbs and holds large amounts of oxygen, causing the equivalent oxygen partial pressure in the vicinity of PtCo centers to measure ∼5 times higher than that around flowing gas, oxygen, or air. As a result, the catalyst shows a 1.5 or 2.4 times higher promotion of ORR activity compared with PtCo/C on the basis of the mass or area of Pt, respectively. The membrane electrode assembly employing the NCM⊂PtCo/C cathode catalyst achieves a peak power density of 1.6 W cm^–2 at an ultralow Pt loading of 0.06 mg_Pt cm^–2, significantly outperforming PtCo/C. The role of the interface with oxygen enrichment in boosting the MEA performance is verified by direct quantitative evidence. Moreover, the NCM interface imparts exceptional resistance to methanol poisoning to the catalyst. We think the catalyst is highly useful for fuel cells, and the work also opens up an effective approach of developing catalysts that are practically applicable for other processes.

The achievement of carbon neutrality requires not only reducing CO₂ emissions but also developing strategies for its effective utilization. In this study, we explored the feasibility of employing carbonate ions, captured in alkaline solutions via direct air capture (DAC) based on chemical absorption, as charge carriers in electrochemical energy storage devices. Layered double hydroxides (LDHs) were selected as the host materials for CO₃^2– storage, and the influence of their constituent metal elements on the insertion–extraction behavior of carbonate anions was systematically investigated. Cyclic voltammetry in a model electrolyte of 1 mol kg^–1 K₂CO₃ (pH 12.1) revealed no electrochemical activity from MgAl-LDH, whereas MnAl- and NiAl-LDH exhibited redox responses associated with anion insertion–extraction. Although NiAl-LDH was expected to undergo redox reactions, these did not proceed within the potential window of the electrolyte. Comparison with HCO₃^– and OH^– indicated that the intercalating species was predominantly CO₃^2– anions. Galvanostatic charge–discharge measurements demonstrated that structurally optimized MnAl-LDH, with well-developed anion storage sites, delivered initial charge and discharge capacities of 288 and 248 mA h g^–1, respectively. XRD and XPS analyses confirmed the reversible interlayer expansion–contraction and the Mn^3+/2+ redox process accompanying CO₃^2– insertion–deinsertion. While the capacity decreases to 90 mA h g^–1 after 20 cycles, this issue may be alleviated through compositional tuning and by enhancing the oxidative decomposition resistance of the electrolyte. Electrochemical impedance spectroscopy revealed no significant difference in activation energy between CO₃^2– and OH^– insertion. Importantly, the electrochemical control of CO₃^2– release, which is otherwise stabilized and scarcely exchangeable once incorporated into LDH interlayers, suggests promising applicability in ion-exchange processes, such as the removal of hazardous anions.

We report the layer-by-layer growth of poly(ethylenimine) (PEI) that has been modified with sulfamate functionalities (S-PEI) using Zr⁴⁺-complexation interlayer linking chemistry. We have also deposited adlayers of graphene oxide (GO) that have been modified to possess sulfate functionalities (S-GO), onto the S-PEI layers. The multilayer assemblies are formed with sulfamate/sulfate and sulfate/sulfate (S-PEI + S-GO) interlayer linking chemistry. In all cases the adlayer thickness is consistent with predictions based on van der Waals volume and/or molecular mechanics calculations. X-ray photoelectron spectroscopy (XPS) is used to characterize the Zr/S stoichiometry in the multilayer assembly. The utility of these hybrid multilayer structures is demonstrated in a Proton Exchange Membrane (PEM) fuel cell, where they are shown to reduce H₂ gas crossover by 15% with only a 12 nm thick layer.

Redox-Targeting Flow Batteries (RTFBs) are promising alternatives to classical vanadium-based batteries for large-scale and stationary energy storage. Typically, RTFBs are marked by higher energy densities thanks to the addition of solid boosters within aqueous systems, taking care to limit the use of critical raw materials. This work subsequently investigates the case of sodium titanium phosphate (NTP, NaTi₂(PO₄)₃, 132.8 mAh/g) as a potential booster material for the negolyte side of aqueous RTFBs. Pure NTP and carbon-coated NTP (C-NTP) particles were synthesized and characterized by various techniques (X-ray, TEM, TGA, Raman). So-obtained NTP and C-NTP particles were found to be suitable for creating innovative porous composite boosters formed as centimeter-sized granules by dry processing. Porous composite granules with an open porosity of 65% and 50 wt % of immobilized NTP or C-NTP were successfully produced by an extrusion–dissolution process using a regular PVDF binder and PEO as a porogen agent. Subsequently, intensive electrochemical tests were performed using an innovative dual-mediator reaction system (Fe-Tiron and 2,7-AQDS). High NTP reactivity, with booster utilization rates of up to 84% of its theoretical capacity, can be achieved under flow conditions, with an increase in volumetric capacity by a factor of 1.5, from 4 Ah L^–1 to 6 Ah L^–1. The mediator concentration (10 – 100 mM) and the mediator/booster ratio (0.5 – 1) play key roles in NTP reactivity. The fundamental work also highlights the benefit of C-NTP, allowing higher reactivity at low mediator concentrations. The study consequently validates the potential of NTP as an interesting booster material in future RTFB applications, with its scalable extrusion–dissolution technique to create innovative porous booster granules.

NaSICON electrolytes, such as Na_1+xZr₂(SiO₄)_x(PO₄)_3–x (NZSP), constitute promising candidates for solid-state battery (SSB) development. Research on such fast superionic conductors has primarily focused on two key phenomena acting specifically on Na⁺ ion migration: (i) the Na-concentration-driven modulation effect and (ii) the incidence of substitution. While numerous experimental and computational studies have established the fundamental role of concerted migration in ionic conduction, the precise influence of bottleneck size along with its dependence on NaSICON composition remains elusive. In view of participating in this research field and following an experimentally tested strategy, suggesting that the migration bottleneck can be expanded by partially substituting diffusing Na⁺ ions with larger-radius alkali elements, we investigated the impact of the introduction of such point defects (i.e. K⁺ or Cs⁺ replacing Na⁺) on structural and Na⁺ diffusion aspects in the NZSP crystal structure. A proof of concept of the interest linked to this unconventional doping approach has been searched for. Theoretical investigations relying on density functional theory (DFT) and subsequent kinetic Monte Carlo simulations were involved to unravel interrelations between the ionic radius of the substituting ion and bottleneck sizes, structural changes, diffusion pathways, and ionic conductivity features. Apart from an opening of the bottleneck along the migration path as a common feature, a clear differentiation between both kinds of substituents was evidenced on various aspects, K-NZSP outperforming the undoped counterpart and effectively enabling the maximization of ionic conductivity in these envisaged NaSICON-type matrices. Furthermore, the identification─emerging from this study─of a critical bottleneck size in such systems may contribute to provide a further key clue and lead to well thought-out crystal chemical engineering of improved materials for this research area.

Phase change materials (PCMs) hold considerable potential for efficient thermal management in reducing heat radiation, providing thermal comfort, and improving thermal protection. However, their practical application has been significantly hindered by various issues, such as leakage, low thermal conductivity, and brittleness. This study addresses these challenges by constructing a porous composite scaffold with melamine foam (MF) as a template and vapor-grown carbon fiber (VGCF) as a highly thermally conductive medium. VGCF was first uniformly dispersed by using polyvinylpyrrolidone (PVP) as a dispersant and then incorporated into the MF matrix to construct a three-dimensional (3D) thermally conductive network throughout the scaffold (PCF/MF_x), which was subsequently utilized to encapsulate the thermal storage unit of polyethylene glycol (PEG). The resultant phase change composite (PEG–PCF/MF_0.7) exhibited enhanced thermal conductivity, which was 2.57 times that of the control sample without VGCF (PEG-MF). It also demonstrated outstanding photothermal conversion capability and exceptional thermal energy storage performance with a high latent heat of 140.0 J·g^–1 and an enthalpy efficiency exceeding 93%. The integration of PEG–PCF/MF_0.7 into the glove extended thermal protection time by 352% in the oven test, proving its significant potential for thermal protection application in firefighting gloves.

Direct laser interference patterning (DLIP) with nanosecond laser pulses at 355 nm was employed to microstructure nickel Watts (Ni-Watts) electrodes with a periodic channel-like structure, aiming to enhance their performance toward the hydrogen evolution reaction (HER) in alkaline media. This technique enables the treatment of large surface areas with high reproducibility without significantly altering the chemical composition of the material. Electrochemical characterization at 30 °C in 2 M KOH revealed that the introduction of microchannels increases the catalytic activity for HER by increasing the current density up to 23% at −1.5 V versus SCE without affecting the kinetic and thermodynamic properties of the material. Although electrochemical impedance spectroscopy indicated no significant changes in the active surface area (roughness factor close to 1), this improvement is attributed to favorable modifications in bubble dynamics; Ni-Watts electrodes displayed multiple nucleation zones and smaller maximum bubble diameters, while Ni electrodes with 5 μm microchannels exhibited fewer nucleation sites and larger bubbles. These results demonstrate that DLIP structuring offers a promising strategy to optimize HER efficiency without requiring changes in material composition.