ACS Materials Letters最新文献

Multinary sulfides represent a significant family of semiconductors because of their low cost and promising performance, yet controlling their composition is challenging. CuFeS₂ thin films are particularly attractive because of their great potential in thermoelectricity and photovoltaics. Herein we reveal the newest finding that Zn promotes the cation ordering and stabilizes the chalcopyrite CuFeS₂ film, preventing the reverse transformation to wurtzite with a random distribution of Cu–Fe at high temperature. The thermoelectric properties of chalcopyrite thin films are investigated as a function of Zn content, resulting in an optimized power factor of 0.168 mW/m·K² at room temperature, outperforming any CuFeS₂ thin films ever reported. For the first time, synchrotron-based in situ X-ray diffraction and X-ray absorption fine structure confirm the phase transition, offering insights into the isomeric structure of CuFeS₂ and the role of Zn. The in-depth understanding of cation-ordering and phase transformation between CuFeS₂ polymorphs might impact the multinary sulfide film fabrication and improvement in efficiency of renewable energy applications.

The alkaline hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are crucial for achieving high efficiency in anion-exchange membrane water electrolyzers and fuel cells. While Pt is highly active for HER/HOR at low pH, its activity decreases ∼200-fold under alkaline conditions due to stronger hydrogen binding. Manipulating the local environment around the electrode is an effective but underexplored strategy in hydrogen electrocatalysis. In this study, we prepared nanohybrid electrocatalysts comprising Pt nanoparticles and Mo oxides (Pt-MoO_x). Pt-MoO_x exhibited a 2.6-fold increase in alkaline HER/HOR activity compared to that of Pt black. It demonstrated a low overpotential of 65 mV at −10 mA cm^–2, with stability for 3 days. The enhanced reaction kinetics were attributed to the decreased hydrogen binding strength by MoO_x and stabilized local environment resulting from H+/H₂O exchange equilibria by the acidic Mo−OH species. This work provides an alternative design strategy for fine-tuning electrosorption properties.

Transition-metal oxides (TMOs) are promising anode materials for safe and fast-charging batteries, but their high operating potentials limit energy density. Here, we develop a strategy to suppress the operating potential of the disordered rock salt (DRS) Li₃V₂O₅ (LVO) anode by ∼10% to 0.54 V via Mg doping. Density functional theory (DFT) calculations attribute this voltage reduction to increased site energy of Li ions because of Mg doping, with minimal impact on Li migration barriers. Mg-doped LVO retains over 95% of its capacity over 1000 cycles at a rate of 5 C. Full cells with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode demonstrate the expected increase in cell voltage and energy density while retaining 91% of their capacity over 250 cycles at 5 C. Our findings show that Mg doping provides a promising pathway for designing fast-charging, long-cycle-life anode materials with enhanced energy density.

Electrically conductive polyaniline (PANI) is ubiquitously applied in energy storage devices using its three oxidation states and reversible doping and dedoping processes. However, the chemical stability of the most oxidized state, the pernigraniline base, has gained considerably less interest than its emeraldine base counterpart. By utilizing the phenyl-capped aniline tetramer (TANI) as a model of PANI, this work examines the heterophase reductions of the pernigraniline base. Through UV–vis spectroscopy and electrochemical methods, we provide both a quantitative and qualitative analysis, demonstrating the dependence of the reduction rate on acidity, as corroborated with cyclic voltammograms and open circuit potential measurements. Solid state reactions reveal that reduction can be achieved via ball milling with a solid acid, the piezoelectric material BaTiO₃, and cadmium metal pieces. This behavior was also applied to thin films, enabling the patterning via a responsive and irreversible vapor reduction.

This study explores the challenging heteroepitaxial growth of wurtzite AlN on monoclinic β-Ga₂O₃(-201) using plasma-assisted molecular beam epitaxy. By optimizing various nucleation and growth conditions, particularly the Al/N flux ratio, we achieve optimal surface morphology and structural quality. Substrate nitridation growth under N-rich conditions is found to favor the formation of smooth AlN with a sharp nitride/oxide heterointerface, whereas Al-rich conditions lead to the formation of rougher AlN textured along the <0001> direction but with highly twisted grains. Comprehensive structural analyses show the growth of a high-quality AlN(0001) layer with a homogeneous Al polarity on β-Ga₂O₃(-201), exhibiting an epitaxial relationship of AlN[2-1-10] // β-Ga₂O₃[020]. The present findings, supported by theoretical calculations reporting the formation of a two-dimensional electron gas with a charge interface density higher than 10¹³ cm^–2, open important perspectives for the development of next generation power electronic devices made of ultrawide band gap semiconductors.

In this work, we describe a solid-state polymer electrolyte (SPE)-based electrolyte-gated organic field-effect transistors (EGOFETs) consisting of a thiol–ene-assisted photo-cross-linked nitrile butadiene rubber (NBR) network embedded with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte. The photocurable SPE film can be patterned with different dimensions by photolithography and exhibits excellent electronic properties and crucial synaptic behavior. The photocurable NBR/LiTFSI EGOFET exhibits a high transconductance of 11.9 mS and a high on/off ratio of 10⁵ at a scan rate of 40 mV/s. Due to the strongly polarized nature of the photo-cross-linked NBR network and Li-ion diffusion, the NBR/LiTFSI device exhibits a significant current hysteresis, enabling synaptic-like learning and memory behavior. The NBR/LiTFSI device demonstrates a DNN of 91.9% handwritten digit recognition accuracy. This work demonstrates the potential of the solid-state NBR/LiTFSI EGOFET in creating highly efficient and low-energy neuromorphic devices.

In this work, we describe a solid-state polymer electrolyte (SPE)-based electrolyte-gated organic field-effect transistors (EGOFETs) consisting of a thiol-ene-assisted photo-cross-linked nitrile butadiene rubber (NBR) network embedded with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte. The photocurable SPE film can be patterned with different dimensions by photolithography and exhibits excellent electronic properties and crucial synaptic behavior. The photocurable NBR/LiTFSI EGOFET exhibits a high transconductance of 11.9 mS and a high on/off ratio of 10⁵ at a scan rate of 40 mV/s. Due to the strongly polarized nature of the photo-cross-linked NBR network and Li-ion diffusion, the NBR/LiTFSI device exhibits a significant current hysteresis, enabling synaptic-like learning and memory behavior. The NBR/LiTFSI device demonstrates a DNN of 91.9% handwritten digit recognition accuracy. This work demonstrates the potential of the solid-state NBR/LiTFSI EGOFET in creating highly efficient and low-energy neuromorphic devices.

A major challenge in developing smart micromachines that can mimic natural microorganisms is their ability to adapt to changing environments. This study presents a matchstick-shaped microrotor consisting of a TiO₂ head and a SiO₂ tail, with one side coated by PtO. The TiO₂ head provides photochemical propulsion under UV light, while the PtO coating provides chemical propulsion in H₂O₂. The microrotor rotates because of its asymmetric structure and uneven propulsion forces. Notably, under stronger UV light, the rotor orbits in tighter circles as the photochemical engine counteracts the chemical engine, with the two engines located on opposite sides of the center of mass. Additionally, microrotors with shorter SiO₂ tails moved in smaller circles and were more sensitive to changes in light intensity.

In this study, strain-induced cracks and a lead-rich impurity phase (CsPb₂Br₅) have been detected at the buried interface of the two-step prepared CsPbBr₃ films. To solve this problem, a sacrificing layer (CsAc) was introduced before the deposition of the PbBr₂ precursors. This provides enough cesium precursors for the afterward CsPbBr₃ growth. Besides, the CsAc sacrificing layer brings more holes in the prepared PbBr₂ films, which benefits the volume expansion during the PbBr₂ to CsPbBr₃ conversion. Thus, residual strain released films can be expected. With the assistance of the CsAc sacrificing layer, the performance of our CsPbBr₃ devices can be improved from 7.70% (control) to 10.07% (6% CsAc assisted) with enhanced stability. Finally, we introduce a sacrificing layer assisted strategy for preparing strain released and phase pure CsPbBr₃ films, and this strategy might also be applicable to other types of PSCs.

The limited affinity of horseradish peroxidase (HRP) for H₂O₂ makes it unsuitable for identifying situations containing trace amounts of H₂O₂. Herein, a set of regulation schemes for Fe, Co-MOF was proposed to develop a substitute for HRP. Regarding H₂O₂ adsorption, solvent engineering allowed the MIL framework to expose the (101) crystal plane with the highest density of Lewis acid sites, and the unsaturated center of the ligand generated by the Co sites on the 1D metal–oxygen chain facilitates the adsorption of H₂O₂ in sub-nanochannels. Regarding H₂O₂ reduction, ligand amination engineering created electron donor regions. Hydrogenation engineering increased the number of Fe²⁺ as catalytic centers, and the synergy between in situ modified tiny AuNPs and them reduced the activation energy of the peroxidase-like reaction. Ultimately, the affinity of Fe, Co-MOF for H₂O₂ was increased by 70 times compared with HRP. As a proof-of-concept, it was used to detect isoniazid, a typical antituberculosis drug, in human urine samples.