Lei Liu,Zijian Zhou,Changqing Wang,Jie Xu,Hongqiang Xia,Guozhang Chang,Xiaowei Liu,Minghou Xu
Co 3 O 4 has been regarded as one of the most promising materials for redox energy storage due to its high theoretical conversion and complete redox reversibility. However, when undergoing charge-discharge cycles at high temperature, the material becomes sintered. The reversibility of the cobaltous oxides highly deteriorates, and the reoxidation reaction rate notably decreases. In addition, the obvious thermal hysteresis in the redox reaction process also limits the energy storage performance of the material. In this work, Co 3 O 4 with different micro-nanostructured morphologies is synthesized to evaluate its thermochemical energy storage performance. The capacity of the synthesized and commercial Co 3 O 4 is tested by thermogravimetric analysis (TGA). The fresh and recycled oxides are well characterized. Results suggest that all samples show complete reversibility, and the conversion decreases slightly after 30 cycles. The synthesized samples show better performance, especially cubic Co 3 O 4 . The reoxidation rate of the commercial sample is approximately 150 μmol/min/g, but that of the cubic sample is approximately 300-200 μmol/min/g in the first five cycles. The oxidation rate of the cubic sample decreases and finally remains at about 180 μmol/min/g from the 5th cycle to the 30th cycle. After 5 charge-discharge cycles, the commercial Co 3 O 4 is severely sintered, while the cubic oxides are only slightly sintered. After 30 redox cycles, the morphology of commercial oxides completely changed, while that of the cubic oxide retains the approximate shape of a cube. Moreover, the thermal hysteresis values of the commercial and cubic Co 3 O 4 are 24.7°C and 10.1°C, respectively, suggesting that the energy loss of cubic oxides is much smaller. The higher exothermic temperature of the cubic Co 3 O 4 redox process also indicates that it can supply high-grade thermal energy.
Lee et al. report that the compound LK-99, with a chemical formula of Pb 10-x Cu x (PO 4 ) 6 O (0.9 < x < 1.1), exhibits room temperature superconductivity under ambient pressure. In this study, we investigated the transport and magnetic properties of pure Cu 2 S and LK-99 containing Cu 2 S. We observed a sharp superconducting-like transition and a thermal hysteresis behavior in the resistivity and magnetic susceptibility. However, we did not observe zero resistivity below the transition temperature. We argue that the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by the first-order structural phase transition of Cu 2 S at around 385 K, from the hexagonal structure phase at high temperature to the monoclinic structure phase at low temperature.
Multifunctional response materials exhibit potential applications in sensors and optoelectronic devices; however, successfully targeting such materials remains a significant challenge. In this study, we synthesized two zero-dimensional hybrids: (C6H16N)2MnBr1.53Cl2.47 (1, C6H16N = trimethyl propyl ammonium) and (C7H18N)2MnBr1.40Cl2.60 (2, C7H18N = trimethyl butyl ammonium). These compounds were formed by combining pseudoglobular organic ammonium cations with the highly emissive [MnX4]2– (X = Br or Cl) anion. Both compounds undergo order–disorder structural phase transitions, exhibiting thermal hysteresis: 1 at 331 K (heating)/326 K (cooling) and 2 at 383 K/373 K and 445 K/428 K (heating/cooling), respectively. These transitions result in a switchable dielectric behavior. At ambient conditions, both compounds emit the bright characteristic luminescence of the [MnX4]2– anion, with photoluminescence quantum yields (PLQY) of 88.71% for 1 and 94.59% for 2. However, they exhibit thermal quenching at elevated temperatures (∼420 K for 1 and ∼460 K for 2). Near their phase transition temperatures, both compounds also show switchable luminescent properties. Collectively, 1 and 2 represent rare examples of materials exhibiting dual-switchable dielectric and luminescence responses.
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