ACS Materials Letters最新文献

Enhancing the dissymmetry factor (g_lum) is crucial for circularly polarized luminescence (CPL) applications. Herein, we present an innovative strategy achieving an ultrastrong |g_lum| of 1.73. This is accomplished through the synergistic effect of coassembly of the CPL-emitting ternary liquid crystal (T-N*-LC, |g_lum| = 0.47) and the selective reflection (λ = 590 nm) of the polymer cholesteric liquid crystal (CLC) within a composite system. Unlike the mismatched chirality combination (|g_lum| = 1.42, ΔFL = 57%), the matched combination demonstrates an ultrastrong CPL signal with a |g_lum| of 1.73 and a low ΔFL of 50% when the CPL direction of the T-N*-LC agrees with the CLC film’s chirality. Furthermore, we alter the matching degree of the composite system by applying a direct-current (DC) electric field to realize the CPL switch. This study paves the way for developing outstanding CPL-active display materials through synergistic amplification of g_lum.

Bioelectronics based on regular hydrogels containing conductive components severely suffer from inferior structural compatibility, impaired signal accuracy, and fatigue failure under harsh environments, thus constraining their multifunctionalities. To address the issues of additive agglomeration and phase separation within the polymer matrix, assembly of amphiphilic nanosheets at oil/water interfaces for costabilization is innovatively proposed. The critically dispersed graphene nanosheets, assisted by ionic liquid (IL) graft-exfoliation, can be chemically integrated into swelling-resistant polymeric networks through ultrasonic-induced gelation. Additionally, the synergistic effect between dimethyl sulfoxide (DMSO)/H₂O binary solvents and charged polar terminal groups weakens the hydrogen bonding within water molecules, enabling the organohydrogel with reliable environmental tolerance and long-lasting moisture retention. Owing to its high mechanical stretchability, satisfactory sensitivity, and exceptional photothermal conversion behavior, the fast prepared organohydrogel is fabricated into an all-climate wearable sensor for daily activities detection and temperature sensing, which lays the groundwork for human–machine interaction and thermosensation-based actuation.

Developing highly efficient oxygen evolution reaction (OER) electrocatalysts based on earth-abundant elements is critical to improve the efficiency of water electrolysis, but it remains a challenge. Herein, an amorphous ternary oxides composites FeNiCoO_x/CoO_x with rich oxygen vacancies are developed through a low-cost wet chemical deposition strategy toward this challenge. Benefiting from the synergistic effect of multimetal atom interaction and high exposure of active sites caused by oxygen vacancies and amorphous structure, the as-developed FeNiCoO_x/CoO_x electrocatalyst exhibits an exceptional catalytic performance with a low overpotential of only 221 mV at a current density of 100 mA cm^–2 and negligible performance degradation over 240 h. Furthermore, the FeNiCoO_x/CoO_x-assembled anion exchange membrane water electrolyzer (AEMWE) can achieve a high current density of 1 A cm^–2 at a low voltage of 1.765 V, demonstrating its great potential for practical application.

Perovskite oxides are promising electrocatalysts due to their rich composition, facile synthesis, and favorable stability under oxidizing conditions. Despite extensive research on doping strategies, the impact of cation nonstoichiometry on electrocatalytic performance is less understood. Here, we reveal that A-site cation nonstoichiometry significantly influences the phase evolution of Ba_x(Co, Fe, Zr, Y)O_3−δ, transitioning from a single cubic perovskite (x = 1) to a nanocomposite comprising a major cubic perovskite phase and a minor hexagonal swedenborgite phase (0.80 ≤ x ≤ 0.95). The nanocomposite with a nominal chemical composition of Ba_0.80Co_0.7Fe_0.1Zr_0.1Y_0.1O_3−δ showed markedly enhanced electrocatalytic performance for the oxygen evolution reaction (OER) in alkaline solutions due to the synergistic effect of the two strongly interacting phases, promoting a lattice-oxygen-participating OER pathway. Further optimizing cation nonstoichiometry allowed the design of nanocomposites with controlled phase concentrations. The optimal candidate, with an increased content of the swedenborgite phase, demonstrated further boosted OER performance.

Rather than supplying electrical power from a photovoltaic cell to a separate water electrolyzer, photoelectrochemical (PEC) water-splitting studies attempt to integrate key components into a single device for solar-driven hydrogen production. Despite the compact device architecture enhancing the cost-efficiency of solar-driven hydrogen production, the realization of PEC technology remains challenging. In this review, we focus on the physical properties of earth-abundant metal oxides and the choice of device architecture as key considerations for constructing a PEC device for practical hydrogen production. We introduce previous studies on BiVO₄ to elaborate on various methods for facilitating the transport of charge carriers through metal oxides and their interface with an electrolyte. Furthermore, we discuss how the choice of PEC device structures affects the electrical and ionic charge transport and the usage of precious elements. Based on this discussion, we highlight a wireless monolithic tandem PEC device made up of earth-abundant elements and expatiate on practical aspects regarding the preparation and operation of such PEC devices.

The formation of a charge density wave (CDW) in 2D materials caused by Peierls instability is a controversial topic. This study investigates the extensively debated role of Fermi surface nesting in causing the CDW state in 2H-NbSe₂ materials. Four NbSe₂ structures are identified on the basis of the characteristics in scanning tunneling microscopy images and first-principles simulations. The calculations reveal that an energetically favored filled phase corresponds to Peierls’ description with fully opened gaps at the CDW Brillouin zone boundary, resulting in a drop at the Fermi level in the density of states and scanning tunneling spectroscopy spectra. The electronic susceptibility and phonon instability indicate that the Fermi surface nesting is triggered by two nesting vectors, whereas the involvement of only one nesting vector leads to a so-called stripe phase. This comprehensive study demonstrates that the filled phase of NbSe₂ can be categorized as a Peierls instability-induced CDW in two-dimensional systems.

We achieved improved photoelectrochemical (PEC) efficiency by inducing strain through substitutional Al³⁺ doping in hematite, followed by codoping with Ti⁴⁺. The substitution of Al³⁺ for Fe³⁺ induces local strain within the lattice, reducing interionic distances and thereby enhancing the charge carrier transport properties. However, theoretical findings revealed initially unfavorable formation energy when Al³⁺ is doped into hematite, leading to significant lattice distortion due to size mismatch and thus limiting PEC activity. Co-doping Al³⁺ with Ti⁴⁺ in Fe₂O₃ restored the lattice symmetry by alleviating strain, resulting in a favorable formation energy. Additionally, Ti⁴⁺ contributes excess electrons, further increasing the electrical conductivity. By leveraging formation energy control through Ti doping, our optimized Al:Ti–Fe₂O₃ with a cocatalyst exhibited a photocurrent density of 4.00 mA cm^–2 at 1.23 V_RHE, representing a 6.5-fold improvement over Fe₂O₃ alone. Our study proposes an approach for utilizing Al³⁺ as a codopant in Fe₂O₃, which can potentially be extended to other codoped systems.

Herein, a p–n junction composed of cobalt-based metal–organic frameworks (Co-MOFs) and Fe₂O₃ has been designed to provide a strong built-in electric field (B-IEF) to enhance electron transport and facilitate intermediate adsorption of oxygen during the oxygen evolution reaction. Meanwhile, partial sulfurization surface modulation is envisioned to achieve a switchable phase transformation, and the B-IEF has been further broadened to 1.535 V. The Co-MOF@Fe₂O₃–S bearing partial sulfurization delivered a lower overpotential of 300 mV at 50 mA cm^–2, a modest Tafel slope of 83.8 mV dec^–1, and remarkable long-term stability. Density functional theory calculations and in situ Raman analysis have indicated charge redistribution, accelerated electron transfer and OH^– ion diffusion, and the modest adsorption/desorption energy of oxygen-containing intermediates. This interfacial p–n heterojunction and sulfurization treatment without losing the microstructure lays the foundation for the production of clean energy.

Research on electrochemical water splitting has experienced significant growth in interest in transition metal borides, carbides, pnictides, and chalcogenides, owing to their notable catalytic performance. These materials, collectively called X-ides, are often considered promising electrocatalysts for the oxygen evolution reaction (OER). However, under the strongly oxidizing conditions of the OER, transition metal X-ides often act as precatalysts, undergoing in situ reconstruction to a different, catalytically active phase. Discrepancies exist in the literature, with some studies claiming the absence of such transformations. Building upon previous efforts to elucidate catalytic performance trends in the community, this Perspective discusses a more nuanced approach to X-ide research, emphasizing the need to reassess our understanding of their chemical stability and the significance of the in situ reconstruction process. By discussing the role of experimental and computational databases, we present strategies for predicting X-ide stability and stress the importance of thorough experimental validation. Moreover, we highlight the use of machine learning to extract meaningful insights from these data and urge the community to adopt a standardized, systematic reporting of X-ide performance. Finally, we provide strategic guidelines and directions to advance transition metal X-ide research, ultimately enhancing their future application for a sustainable hydrogen economy.

Oxygen reduction reaction (ORR), involving either a two-electron (2e^–) pathway or a four-electron (4e^–) pathway, is an important reaction in energy conversion and storage systems. It is well-known that metal–nitrogen–carbon (M–N–C) catalysts, as emerging state-of-the-art electrocatalysts, are applied to fuel cells via the 4e^– pathway (e.g., Fe–N–C) while generating hydrogen peroxide via the 2e^– pathway (e.g., Co–N–C). However, the effects of the MN_x and C–N species on the catalytic activity of ORR require thorough clarification. Especially, the real active sites of the M–N–C configuration are a long-standing conundrum. In this review, the latest advanced M–N–C catalysts were categorized according to the ORR pathways and MN_x moieties. Then, the effects of coordination atoms, N-coordinated structures, and pH on the activity of the M–N–C catalysts were discussed. The detection and quantification of the active sites of M–N–C catalysts by in situ Raman spectroscopy and electrochemical techniques were summarized. Finally, the opportunities and challenges for the M–N–C catalysts with efficient activity were highlighted.