Phase change materials for thermal energy storage

In order to void environmental pollution and an energy shortage, the application of clean and renewable energy, such as solar, instead of fossil fuel is foreseen as a prospective issue. It is urgent and important to develop and optimize various energy storage and conversion technologies and materials aimed at utilization of different clean energy sources. Metal–organic frameworks (MOFs), a new class of porous crystalline materials, act as an outstanding candidate in this field based on their high surface areas, controllable structures and excellent electrochemical properties. Here, selected recent and significant advances in the development of MOFs for clean energy applications are reviewed, and special emphases are shown to the applications of MOFs as platforms for hydrogen production and storage, fuel cells, Li-ion rechargeable batteries, supercapacitors and solar cells.

Metal–organic frameworks as platforms for clean energy

In the search for future energy supplies, the application of hydrogen as an energy carrier is seen as a prospective issue. However, the implementation of a hydrogen economy is suffering from several unsolved problems. Particularly challenging is the storage of appropriate amounts of hydrogen. In this context one of the promising hydrogen storage techniques relies on liquid-phase chemical hydrogen storage materials, in particular, aqueous sodium borohydride, ammonia borane, hydrazine, hydrazine borane and formic acid. The use of these materials in hydrogen storage provides high gravimetric and volumetric hydrogen densities, low potential risk, and low capital investment because it is largely compatible with the current transport infrastructure. In this review, we survey the research progresses in hydrogen generation from these liquid-phase chemical hydrogen storage materials and their regeneration.

Liquid-phase chemical hydrogen storage materials

The search for hydrogen storage materials capable of efficiently storing hydrogen in a compact and lightweight package is one of the most difficult challenges for the upcoming hydrogen economy. Liquid chemical hydrides with high gravimetric and volumetric hydrogen densities have the potential to overcome the challenges associated with hydrogen storage. Moreover, the liquid-phase nature of these hydrogen storage systems provides significant advantages of easy recharging, and the availability of the current liquid fuel infrastructure for recharging. In this review, we briefly survey the research progress in the development of diverse liquid-phase chemical hydrogen storage materials, including organic and inorganic chemical hydrides, with emphases on the syntheses of active catalysts for catalytic hydrogen generation and storage. Moreover, the advantages and drawbacks of each storage system are discussed.

Liquid organic and inorganic chemical hydrides for high-capacity hydrogen storage

In recent years, energy conservation and environmental protection have become most important issues for humanity. Phase change materials (PCMs) for thermal energy storage can solve the issues of energy and environment to a certain extent, as PCMs can increase the efficiency and sustainability of energy. PCMs possess large latent heat, and they store and release energy at a constant temperature during the phase change process. Thereby PCMs have gained a wide range of applications in various fields, such as buildings, solar energy systems, power systems and military industry. However, low thermal conductivity of PCMs leads to low heat transfer rate, thus, numerous studies have been carried out to improve thermal conductivity of PCMs. The main purpose of this paper is to review the methods for enhancing thermal conductivity of PCMs, which include adding additives with high thermal conductivity and encapsulating phase change materials. It is found that addition of thermal conductivity enhancement fillers is a more effective method to improve thermal conductivity of PCMs, where carbon-based material additives possess a more promising application prospect. Finally, the applications of PCMs in solar energy system, buildings, cooling system, textiles and heat recovery system are also analyzed.

Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage

Shape-stabilized phase change materials based on polyethylene glycol/porous carbon composite: The influence of the pore structure of the carbon materials

Preparation and characterization of polyethylene glycol/active carbon composites as shape-stabilized phase change materials

Graphene oxide (GO) sheets were introduced to stabilize the melted polyethylene glycol (PEG) during the solid–liquid phase change process, which can be used as a smart heat storage system. The structural properties and phase change behaviors of the PEG–GO composites were comprehensively investigated as a function of the PEG content by means of various characterization techniques. The highest stabilized PEG content is 90 wt% in the composites, resulting in a heat storage capacity of 156.9 J g−1, 93.9% of the phase change enthalpy of pure PEG. Notably, GO has much stronger impact on lowering of the phase change temperature of PEG compared with some other porous carbon materials (activated carbon and ordered mesoporous carbon) due to the unique thin layer structure of GO. Because of the high heat storage capacity and the moderate phase change temperature, the PEG–GO composite is a promising heat energy storage candidate at mild temperature.

Wei Li

Papers

Shape-stabilized phase change materials based on polyethylene glycol/porous carbon composite: The influence of the pore structure of the carbon materials

Preparation and characterization of polyethylene glycol/active carbon composites as shape-stabilized phase change materials

Graphene oxide stabilized polyethylene glycol for heat storage

A highly efficient Co (0) catalyst derived from metal-organic framework for the hydrolysis of ammonia borane

One step preparation of a high performance Ge-C nanocomposite anode for lithium ion batteries by tandem plasma reactions.