Xinyu Huang

High-Performance Energy Storage and Conversion Materials Derived from a Single Metal–Organic Framework/Graphene Aerogel Composite

Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon-graphene composite electrode (denoted as C/NG-A) displayed exceptional capacitance and rate capability in a supercapacitor. Further, this method is readily applicable to creation of functional metal oxide hollow nanoparticles on the surface of other carbon materials such as graphene and carbon nanotubes, providing a good opportunity to tune their physical or chemical activities.

Nanoconfinement of phase change materials within carbon aerogels: phase transition behaviours and photo-to-thermal energy storage

We systematically investigated the thermal energy storage properties and host–guest interactions in a phase change composite based on octadecanol/carbon aerogels. Due to the nanoconfinement effect induced by the carbon aerogels, the loaded active materials show distinct phase transition behaviour to the free octadecanol, in which the solid-to-solid and solid-to-liquid phase change processes occurred at a lower temperature and the interval between these two processes became larger.

Alkylated phase change composites for thermal energy storage based on surface-modified silica aerogels

We alkylated silica aerogels to make them hydrophobic for effective impregnation and storage of a phase change material (PCM). As a result of this surface modification treatment, the aerogel scaffold exhibited an average increase of 20.9–34.7% in the PCM uptake with an improved thermal energy storage capacity and stability. For the light to thermal energy conversion experiments, we carbonized the treated aerogels and observed that they readily attained temperatures above the melting point of the PCM. Therefore, the carbonized PCM-impregnated scaffold possesses enhanced thermal energy storage and release property via a phase change response in the encapsulated PCM.

MOF-derived α-NiS nanorods on graphene as an electrode for high-energy-density supercapacitors

Hierarchically porous electrodes made of electrochemically active materials and conductive additives may display synergistic effects originating from the interactions between the constituent phases, and this approach has been adopted for optimizing the performances of many electrode materials. Here we report our findings in design, fabrication, and characterization of a hierarchically porous hybrid electrode composed of α-NiS nanorods decorated on reduced graphene oxide (rGO) (denoted as R-NiS/rGO), derived from water-refluxed metal–organic frameworks/rGO (Ni-MOF-74/rGO) templates. Microanalyses reveal that the as-synthesized α-NiS nanorods have abundant (101) and (110) surfaces on the edges, which exhibit a strong affinity for OH− in KOH electrolyte, as confirmed by density functional theory-based calculations. The results suggest that the MOF-derived α-NiS nanorods with highly exposed active surfaces are favorable for fast redox reactions in a basic electrolyte. Besides, the presence of rGO in the hybrid electrode greatly enhances the electronic conductivity, providing efficient current collection for fast energy storage. Indeed, when tested in a supercapacitor with a three-electrode configuration in 2 M KOH electrolyte, the R-NiS/rGO hybrid electrode exhibits a capacity of 744 C g−1 at 1 A g−1 and 600 C g−1 at 50 A g−1, indicating remarkable rate performance, while maintaining more than 89% of the initial capacity after 20 000 cycles. Moreover, when coupled with a nitrogen-doped graphene aerogel (C/NG-A) negative electrode, the hybrid supercapacitor (R-NiS/rGO/electrolyte/C/NG-A) achieved an ultra-high energy density of 93 W h kg−1 at a power density of 962 W kg−1, while still retaining an energy density of 54 W h kg−1 at an elevated working power of 46 034 W kg−1.

Nanoconfined phase change materials for thermal energy applications

Phase change materials (PCMs) have been extensively characterized as constant temperature latent heat thermal energy storage (TES) materials. Nevertheless, the widespread utilization of PCMs is limited due to the flow of liquid PCMs during melting, phase separation, supercooling and low heat transfer rate. In order to overcome these inherent problems and to improve thermo-physical properties, the confinement of PCMs at the nanoscale has been identified as a versatile strategy, which ensures the encapsulation of PCMs in much smaller nano-containers. Such strategies including core–shell, longitudinal, interfacial and porous confinement have been widely presented in recent years to efficiently encapsulate PCMs in nanospaces and are presenting attractive ways to enhance thermal performance. This review summarizes the recent advancement and critical issues of nanoconfinement technologies of PCMs from the point of view of material design. In addition, the potential applications of nanoconfined PCMs in diverse fields, including energy conversion and storage, thermal rectification and temperature controlled drug delivery systems, are presented in detail. Finally, the major drawbacks associated with nanoconfined PCMs and their prospective solutions are also provided.

The Application of Carbon Materials in Latent Heat Thermal Energy Storage (LHTES)

Abstract This chapter introduces the basic know-how on applications of carbon nanomaterials in phase change materials (PCMs) for latent heat thermal energy storage. It starts with a description of the working principle of PCMs and their different classes with respect to advantages and disadvantages. Following that, the criteria that govern the selection of a material is highlighted. It then summarizes the common material problems covering supercooling, containment issues, low thermal conductivity and provides an insight into recent efforts to tackle these problems with the main focus being on carbon-based nanostructures. By the end of the chapter the improved thermal properties of PCMs enhanced by carbon nanotubes and graphene are presented in detail.

Dual-encapsulation of octadecanol in thermal/electric conductor for enhanced thermoconductivity and efficient energy storage

Owing to the high energy density of phase change materials, latent heat storage systems have been an effective strategy for the improvement of energy efficiency. The severe limitations of their extensive application are the potential leakage and low thermal conductivity. Herein, we developed a facile dual-encapsulation method to solve the abovementioned problems in the phase change composite composed of octadecanol, a high thermal/electrical conductive macroporous graphite foam and a thin waterborne polyurethane (WPU) film. After dual-encapsulation, the thermal conductivity of the composite was 20 times higher than that of pure phase change material (PCM) octadecanol. As a result, the composite exhibited a reduced supercooling degree and rapid thermal energy charging behaviors, as well as electro-to-heat conversion ability. This study gives a new perspective for the synergistic enhancement of both the thermal and electric conductivity of functional PCMs for thermal energy storage and conversion.