Effect of nickel on hydrogen storage behaviors of carbon aerogel hybrid

Abstract

Limited conventional energy resources and serious environmental calamities have motivated researchers to find new and efficient sources of energy. The considerable efforts devoted to this end include the development of bio-diesel, solar cells, coal liq-uefaction/gasification technologies, and fuel cells. Hydrogen is considered by many an ideal energy source owing to its renewable and clean energy characteristics. In addition, it mostly produces water, which is eco-friendly compared to the byproducts of many other energy sources [1-6]. To use hydrogen as an energy source, various hydrogen stor -age methods such as the use of metal hydrides, liquefied hydrogen, and adsorption of hydrogen in porous materials have been studied [7-14]. The adsorption of hydrogen in porous materials is particularly suitable for hydrogen storage, which is critical for suit -ably utilizing hydrogen energy, owing to the reversibility and stability of this method. To date, the wide ranging attempts to develop hydrogen storage mechanisms include studies on carbon materials [15-17], metal-organic frameworks, and zeolites [18-21]. Carbon materials offer many advantages for hydrogen storage, such as easy preparation, suitable surface functional groups, low mass density, thermal stability, and hydropho -bicity [22-24]. Carbon aerogels (CAs) in particular have been recognized as potential hydrogen storage materials because of their suitable structural properties, controllable mass densities, high specific surface areas, and mesopore volumes. However, it is neces -sary to modify the surfaces of carbon materials in order to reach the hydrogen storage capacities determined by the US Department of Energy (DOE).Carbon materials containing transition metals such as platinum, copper, vanadium, and nickel exhibit attractive hydrogen storage properties [10,22,25]. Nickel is particularly prom -ising since it is easily obtained on Earth, and it is inexpensive compared to other metals and enhances hydrogen storage properties. Improved hydrogen storage capacities have been obtained with nickel-plated porous carbon nanofibers owing to the spillover of hydrogen molecules onto the metal-carbon interfaces. In general, the presence of nickel particles on carbon materials has been shown to enhance the hydrogen storage capacity [3,9,19].In this work, CAs were chemically activated by KOH to produce well-developed pore structures and ultimately increase the hydrogen storage capacities. Nickel-loaded activated carbon aerogels (ACAs/Ni hybrid materials) with various nickel content were prepared. Ni particles were loaded onto ACAs to introduce hydrogen-favorable active sites onto the ACA surfaces and improve the hydrogen storage capacities.The CAs were prepared using resorcinol as the carbon precursor and formaldehyde as the initiator. Resorcinol (7.5 g) was dissolved in a solution of distilled water (75 mL) and formaldehyde (25 g). Sodium carbonate was then added to this solution, and the mixture was stirred for 3 h in an open container and dried for 3 h at room temperature. Subsequently, the wet gel was dried at 80°C for 48 h and then immersed in an acetone solution for 24 h without stirring. The aerogels were obtained after drying at 80°C for 24 h. Prior to use, the aerogels were carbonized in a furnace with a heating rate of 2°Cmin