Rare Metals最新文献

Abstract

Despite the great leap forward perovskite solar cells (PSCs) have achieved in power conversion efficiency, the device instability remains one of the major problems plaguing its commercialization. Dopant-free hole transport material (HTM) has been widely studied as an important strategy to improve the stability of PSCs due to its avoidance of moisture-sensitive dopants and cumbersome doping process. In this work, a series of dopant-free HTMs L1F, L2F and L3F based on D-A-π-A-D configuration were synthesized through two steps of reaction. L3F presents a high glass transition temperature of 180 °C and thermal decomposition temperature of 448 °C. Notably, electron paramagnetic resonance signals of L1F, L2F and L3F powders indicate the open-shell quinoidal diradical resonance structure in their aggregation state due to aggregation-induced radical effect. All these HTMs present higher hole mobility than dopant-free Spiro-OMeTAD, and the dopant-free L3F-based PSC device achieves the highest power conversion efficiency of 17.6% among them. In addition, due to the high hydrophobic properties of L1F, L2F and L3F, the perovskite films spin-coated with these HTMs exhibit higher humidity stability than doped Spiro-OMeTAD. These results demonstrate a promising design strategy for high glass transition temperature dopant-free hole transport material. The open-shell quinoid-radical organic semiconductors are not rational candidates for dopant-free HTMs for PSC devices.

Graphic abstract

Ultrathin Li-rich Li–Cu binary alloy has become a competitive anode material for Li metal batteries of high energy density. However, due to the poor-lithiophilicity of the single skeleton structure of Li–Cu alloy, it has limitations in inducing Li nucleation and improving electrochemical performance. Hence, we introduced Ag species to Li–Cu alloy to form a 30 μm thick Li-rich Li–Cu–Ag ternary alloy (LCA) anode, with Li–Ag infinite solid solution as the active phase, and Cu-based finite solid solutions as three-dimensional (3D) skeleton. Such nano-wire networks with LiCu₄ and Cu_xAg_y finite solid solution phases were prepared through a facile melt coating technique, where Ag element can act as lithiophilic specie to enhance the lithiophilicity of built-in skeleton, and regulate the deposition behavior of Li effectively. Notably, the formation of Cu_xAg_y solid solution can strengthen the structural stability of the skeleton, ensuring the geometrical integrity of Li anode, even at the fully delithiated state. Meanwhile, the Li–Ag infinite solid solution phase can promote the Li plating/stripping reversibility of the LCA anode with an improved coulombic efficiency (CE). The synergistic effect between infinite and finite solid solutions could render an enhanced electrochemical performance of Li metal batteries. The LCA|LCA symmetric cells showed a long lifespan of over 600 h with stable polarization voltage of 40 mV, in 1 mA·cm⁻²/1 mAh·cm⁻². In addition, the full cells matching our ultrathin LCA anode with 17.2 mg·cm⁻² mass loading of LiFePO₄ cathode, can continuously operate beyond 110 cycles at 0.5C, with a high capacity retention of 91.5%.Kindly check and confirm the edit made in the article title.OK

Graphical abstract

Abstract

High-entropy perovskite ferroelectric materials have attracted significant attention due to their remarkably low remnant polarizations and narrow hysteresis. Thus, these materials offer high-energy density and efficiency, making them suitable for energy storage applications. Despite significant advancements in experimental research, understanding of the properties associated with structure remains incomplete. This study aims to study the structural, electric, and mechanical performances at various scales of the high-entropy (Na_0.2Bi_0.2Ca_0.2Sr_0.2Ba_0.2)TiO₃ (NBCSB) material. The results of first-principles calculations indicated that the pseudo-intralayer distortion was obviously smaller compared to the interlayer distortion. Among the various bonds, Bi–O, Ca–O, and Na–O experienced the greatest displacement. Similarly, the hybridization between O 2p and Ti 3d states with Bi 6p states was particularly strong, affecting both the ferroelectric polarization and relaxor behavior. The NBCSB materials produced using a typical solid-state process demonstrated exceptional performance in energy storage with a recoverable density of 1.53 J·cm⁻³ and a high efficiency of 89% when subjected to a small electric field of 120 kV·cm⁻¹. In addition, these ceramics displayed a remarkable hardness of around 7.23 GPa. NBCSB ceramics exhibited exceptional relaxation characteristics with minimal hysteresis and low remanent polarization due to its nanoscale high dynamic polarization configuration with diverse symmetries (rhombohedral, tetragonal, and cubic) resulting from randomly dispersed A-site ions. The excellent mechanical property is related to the dislocation-blocking effect, solid solution strengthening effect, and domain boundary effect. The findings of this study offer a comprehensive and novel perspective on A-site disordered high-entropy relaxor ferroelectric ceramics.

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The development of stable and highly efficient multifunctional electrocatalysts for the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the efficient conversion and storage of renewable energy. The significant advantages of single-atom catalysts, such as strong metal slab interactions, unsaturated coordination and efficient atomic utilization, have opened new avenues for designing multifunctional catalysts. Herein, based on density functional theory, a single atom doped PdPX system was designed as a multifunctional electrocatalyst, which demonstrated the synergistic effect between defects and transition metal atoms and led to enhanced catalytic performance. The results showed that PdPS/PdPSe with P/X vacancy, PdPTe with P/Pd vacancy and Co/Rh/Ir@PdPX exhibited promising HER activity. Co@PdPS(Se), with an overpotential of 0.56(0.44) V, was predicted to be a promising OER catalyst. Moreover, Rh(Ir)@PdPS(Se) catalysts exhibited efficient catalytic properties for ORR. Besides, Co@PdPS(Se), Rh(Ir)@PdPS^V(S), Co@PdPSe^V(Se) and Ir@PdPS^V(S)−1 exihibited multifunctional catalytic performance with moderate overpotential. Next, the origin of catalytic activity was revealed by using the crystal orbital Hamilton populations theory. For a strong adsorption system, proper filling of the anti-bonding state can increase the energy of the system, weaken the adsorption strength, and facilitate the desorption of intermediates. Conversely, augmenting bonding states can enhance its adsorption capacity. These findings provide theoretical guidance for the design and fabrication of novel multifunctional electrocatalysts in terms of filling of bonding-state.

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Highly active and robust electrocatalysts for methanol oxidation reaction (MOR) are of great significance to the commercial availability of alkaline direct methanol fuel cells (ADMFC). Pd-based nanostructures have received considerable attention in ADMFCs among non-platinum catalysts due to their high activity and tolerance against CO poisoning, which is strongly determined by their composition and structure. Herein, a one-spot hydrothermal method to synthesize Cu-doped Pd₇Te₃ ultrathin nanowires was proposed. The density functional theory calculations show that the Cu doping simultaneously facilitates the desorption of CO^* and adsorption of OH, which refreshes the active sites quickly and thus enhances the electroactivity for MOR. Benefiting from their ultrathin architecture and the modified bonding and anti-bonding d states of Pd, Cu-doped Pd₇Te₃ nanowires show about twofold and threefold mass activity promotion and enhanced durability for MOR when compared to the pure Pd₇Te₃ nanowires and commercial Pd/C catalysts. This work not only provides a simple one-step synthesis strategy for Pd-based nanowire catalysts, but also helps to inspire the catalyst design in ADMFC.

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High-lead solder joints are still playing an indispensable role in military and space applications. Nevertheless, in-depth characterization of high-lead solder joints and the underlying degradation mechanisms remain unexplored. This research first performed aging tests on Sn10Pb90 solder joints, the shear strength at room and elevated temperatures gradually reduced, and the resistance increased. Here, a two-layered Ni–Sn intermetallic compound (IMC) structure was identified using transmission electron microscopy (TEM), which could be attributed to the change of Sn content in the solder. Moreover, the internal annealing twin of a Sn particle was discovered, which could be attributed to creeping induced by thermal expansion coefficient (CTE) difference between Sn and Pb. Detailed analysis of partial and whole annealing twins was conducted through high-resolution TEM (HRTEM). Finally, four degradation mechanisms were proposed. Thickening of the IMC layer would result in increased brittleness and resistivity. For particle coarsening, apart from diminishing the ductility and toughness of the solder joint, it would also accelerate the creeping rate by weakening the phase boundary strength. Regarding voids and cracks induced by phase boundary sliding, wedge-shaped cracking and pore-shaped cracking were discovered and their formation was analyzed. Most importantly, the consumption of Sn resulted in a depletion of wettable layer, leading to the formation of Pb streams and isolated IMC islands, also known as the spalling and delamination of IMCs. Pb diffusion followed a spiral path, which was mutually influenced by orientation misfit and concentration gradient. A technique to prevent cracking was proposed. This research is expected to provide significant technical references for high-lead solder joints.

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The magnetic properties of Ho₆MnBi₂ and Ho₆FeBi₂ crystals are investigated by means of density functional theory. These materials are currently an active subject of research in the context of magnetic refrigeration applications since they exhibit a remarkable magnetocaloric effect. In this work, the equation of state, density of states and magnetic moments are calculated and compared with previous experimental results for these materials. Also, the Curie temperatures for the paramagnetic to ferromagnetic phase transition observed in these systems are calculated from first principles. All the calculated quantities are in reasonable agreement with experimental data, which suggests that density functional theory could provide a reliable framework to theoretically investigate the magnetic properties of intermetallic ternary compounds.

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Enhancing the ductility of internally oxidized AgMg alloys has posed a longstanding challenge. A new method to achieve simultaneous hardening and toughening of AgMgNi alloys is presented by means of internal oxidation. The influence of Ni content on the internal oxidation process and the mechanical behavior of AgMgNi alloys is systematically investigated. It is found that Ni addition induces grain refinement by forming nanoscale Ni particles, which act as heterogeneous nucleation sites and inhibit grain growth during internal oxidation. This enhances the plasticity and toughness of the alloys via the Hall–Petch effect. The alloys exhibit a conductivity of ~ 42 MS·m⁻¹ and surface hardness of ~ HV 125, which are insensitive to the variation of Ni content within 0 wt%–2 wt%. The optimal range of Ni content for achieving the best combination of hardness, strength and toughness is 0.15 wt%–0.3 wt%, corresponding to alloys with a tensile strength above 300 MPa and a toughness surpassing 3300 MJ·m⁻³. Higher Ni contents reduce the internal oxidation depth (from about 340.6 to about 238.4 μm) and the tensile strength (from about 342.1 to about 230.1 MPa) of the alloys by generating micrometer-sized Ni-rich particles in the matrix, which consume oxygen, obstruct some of the oxygen diffusion channels and impede the oxidation front advancement. The non-oxidized region, which does not benefit from oxidation strengthening, diminishes the overall strength of the alloy. These results reveal the crucial role of Ni in regulating the internal oxidation dynamics and microstructure evolution of AgMgNi alloys, and suggest a novel approach for designing high-performance alloys with concurrent hardening and toughening.

Graphical abstract

To efficiently diminish the Pt consumption while concurrently enhancing the anodic reaction kinetics, a straightforward synthesis for PtPdAg nanotrees (NTs) with exceedingly low Pt content is presented, utilizing the galvanic replacement reaction between the initially prepared PdAg NTs and Pt ions. Due to the multilevel porous tree-like structure and the incorporation of low amounts of Pt, the electrocatalytic activity and stability of PtPdAg NTs are markedly enhanced, achieving 1.65 and 1.69 A·mg⁻¹_Pt + Pd for the anodic reactions of formic acid oxidation (FAOR) and methanol oxidation (MOR) within DLFCs, surpassing the performance of PdAg NTs, as well as that of commercial Pt and Pd black. Density functional theory (DFT) calculations reveal that the addition of low amounts of Pt leads to an increase in the d-band center of PtPdAg NTs and lower the CO_ads adsorption energy to −1.23 eV, enhancing the anti-CO toxicity properties optimally. This approach offers an effective means for designing low Pt catalysts as exceptional anodic electrocatalysts for direct liquid fuel cells.

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