Strong magnetic anisotropy in low-dimensional magnets leads to a significant rotating magnetocaloric effect, presenting new opportunities for the exploration of more efficient and streamlined refrigeration systems. In this study, we have successfully synthesized a series of centimeter-scale rare-earth-containing fluorocarbonates, K 4 RE 2 (CO 3 ) 3 F 4 ( RE = Ce, Pr, Nd, Sm, Eu, Tb, and Dy) through a supercritical hydrothermal method, featuring unique RE 2 O 12 F 4 magnetic dimers. The above materials' fundamental magnetism has been systematically investigated, and no long-range magnetic transitions were captured above 1.8 K. Based on the low-temperature specific heat results, the long-range magnetic ordering was found around 0.84 K and 0.97 K for K 4 Tb 2 (CO 3 ) 3 F 4 and K 4 Dy 2 (CO 3 ) 3 F 4 , respectively. Furthermore, the anisotropic magnetism of K 4 Tb 2 (CO 3 ) 3 F 4 and K 4 Dy 2 (CO 3 ) 3 F 4 reveals significant magneto-crystalline anisotropy, with the magnetic field ( B ) aligned along the RE 2 O 12 F 4 magnetic dimer, which acts as the easy magnetic axis. The maximum rotating field entropy change, − Δ S R max for K 4 Tb 2 (CO 3 ) 3 F 4 reaches approximately 9 J kg -1 K -1 around 17 K, while for K 4 Dy 2 (CO 3 ) 3 F 4 , it is approximately 5.5 J kg -1 K -1 near 11 K, both under a 7 T field applied along the c -axis. These findings highlight the potential of these compounds for magnetic refrigeration applications through a rotating crystallographic direction.
Yongchao Tang,Xuejin Li,Haiming Lv,Dong Xie,Wenlong Wang,Chunyi Zhi,Hongfei Li
In aqueous alkaline Zn batteries (AZBs), the Co 3+ /Co 4+ redox pair offers a higher voltage plateau than its Co 2+ /Co 3+ counterpart. However, related studies are scarce, due to two challenges: the Co 3+ /Co 4+ redox pair is more difficult to activate than Co 2+ /Co 3+ ; once activated, the Co 3+ /Co 4+ redox pair is unstable, owing to the rapid reduction of surplus Co 3+ to Co 2+ . Herein, CoSe 2− x is employed as a cathode material in AZBs. Electrochemical analysis recognizes the principal contributions of the Co 3+ /Co 4+ redox pair to the capacity and voltage plateau. Mechanistic studies reveal that CoSe 2− x initially undergoes a phase transformation to derived Co x O y Se z , which has not been observed in other Zn//cobalt oxide batteries. The Se doping effect is conducive to sustaining abundant and stable Co 3+ species in Co x O y Se z . As a result, the battery achieves a 10 000-cycle ultralong lifespan with 0.02% cycle −1 capacity decay, a 1.9-V voltage plateau, and an immense areal specific capacity compared to its low-valence oxide counterparts. When used in a quasi-solid-state electrolyte, as-assembled AZB delivers 4200 cycles and excellent tailorability, a promising result for wearable applications. The presented effective strategy for obtaining long-cyclability cathodes via a phase transformation-induced heteroatom doping effect may promote high-valence metal species mediation toward highly stable electrodes.
Song Cheng,Yutao Liu,Xinyi Liu,Changqing Zhu,Jingyang Luo,Jiashun Cao,Fuqiang Liu
Electro-assisted activation of peroxymonosulfate (EA-PMS) by transition metals oxides (TMOs) has been extensively studied for the removal of organic pollutants. Despite TMOs possess considerable activity and affinity to PMS, their poor bulk conductivity still limits the electron exchange during the TM δ/δ+1 redox cycle, especially the efficient reduction of TM δ+1 via cathodic process. In this study, carbon felt loaded with modified Co 3 O 4 nanosheets (Co@FCF) was fabricated and applied as the flow-through electrode of EA-PMS process, where the Co 3 O 4 nanosheets were embedded with numerous metallic Ni particles encapsulated within carbon layers (Ni@C). Driven by weak electric current, continuous electrons can be supplied to the bulk Co 3 O 4 from the electron-rich Ni@C nanoparticles, resulting in accelerated Co 3+ /Co 2+ cycle, enhanced production of SO 4 ·− and improved energy utilization efficiency. Electrochemical tests along with density functional theory calculations indicate that the unique structure of Co@FCF played essential role in the enhanced performance.
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