The mechanism and conditions for the phase transformations from α-Fe₂O₃ to Fe₃O₄ and Fe₃O₄ to γ-Fe₂O₃ nanoparticles have been investigated by the thermal analysis method. The morphologies and structures of various nanoparticles after annealing in H₂ : Ar at 294 °C and in an O₂ atmosphere at 302 °C have been examined and characterized. Finally, we confirmed that the monodisperse, porous and magnetic γ-Fe₂O₃ nanoparticles could be obtained by annealing the α-Fe₂O₃ nanoparticles synthesized by the hydrothermal route.

Binder-free layered graphene/polyaniline composite supercapacitor film was prepared by an environmentally friendly route. It exhibited 384 F g ⁻¹ at 0.5 A g ⁻¹ and 84% capacitance retention over 1000 cycles.

Nickel oxide (NiO) is a promising candidate for future electrochromic supercapacitors due to its pronounced electrical properties and low cost. Unfortunately, the weak interaction between NiO films and conductive substrates results in poor cycling stability. In addition, the long color-switching time and low capacitance by the small lattice spacing in dense NiO impede its practical applications seriously. Herein, a hierarchical porous NiO film/ITO glass bifunctional electrode has been prepared via the solvothermal and subsequent calcination process of growing MOF-74 in situ on ITO, which shows outstanding cycle reversibility, excellent capacitance, high coloration efficiency and short color-switching time. Because of the strong binding force between the NiO film and substrate, and large surface areas with a hierarchical porous structure which are beneficial to the ion transport, the NiO film demonstrates perfect capacitive and electrochromic properties. As a bifunctional electrode, the NiO film shows a specific capacitance of 2.08 F cm⁻² at 1 mA cm⁻², large optical modulation of 41.08% and about 86% of optical modulation retention after 10 000 cycles. Furthermore, we assembled a bifunctional device whose energy condition can be roughly estimated according to the color state of the device. This finding can provide us with a new application of MOFs in the dual device of electrochromic supercapacitors.

Adaptive infrared (IR) electrochromic devices driven by electrical energy have considerable potential use in intelligent IR thermal management application in the future. Polyaniline (PANI) is regarded as an ideal material for IR electrochromic devices due to its intrinsic IR electrochromic properties. However, despite extensive study focusing on improving the IR electrochromic properties of PANI, few experiments have been performed for in-depth study of the IR electrochromic mechanism of PANI or to improve its variable IR emissivity efficiency. Herein, an HClO₄-doped PANI porous film with excellent IR regulation ability was fabricated via in situ electrochemical deposition on an Au/microporous substrate, and the IR electrochromic mechanism of the PANI film was further elucidated. A combination of Raman spectra, UV-vis spectra, XPS analyses, transmittance curves and emittance curves of the PANI porous film in distinct conjugation states and corresponding dedoping states confirms that the most direct and critical factors for realizing the emissivity modulation of PANI films are the formation and the elimination of polarons and bipolarons delocalized on PANI chains. The key factor to achieve large amplitude emissivity modulation of PANI films is fully and effectively regulating the transformations between the various states of PANI. In addition, an IR electrochromic device was fabricated through assembly with HClO₄-doped PANI porous films. The device can realize modulation of the emittance variation from 0.735 to 0.316 (Δε = 0.419) and of the radiation energy variation from 273.503 to 117.661 W m⁻² (ΔP = 155.842 W m⁻²) in the wavelength range of 2.5 to 25 μm. Furthermore, the device assembled with nanoporous PE possesses lower α(s) and excellent IR control capability. Also, this study shows that the device can change its color by electrical control in a thermal imaging system; these demonstrations suggest its potential for the future development of intelligent IR thermal management applications.