Catalysts For Hydrogen Generation From Hydrolysis Of NaBH₄ And Related Studies

Fuel cell is an energy-conversion device which can directly convert the chemical energy into electric energy at high efficiency. It is not limited by the Carnot cycle, and is highly efficient, easy to operate, friendly to the environment. Therefore, it is considered to be the fourth power generation method following the hydrodynamic, thermal and nuclear power. However, the inconvenience of supplying the fuel of PEMFC and the low efficiency of the electrode catalysts hinder the application of PEMFC dramatically.Hydrogen is considered to be an ideal power source in the future, which can provide both heat energy through combustion and electricity via fuel cells. However, the inconvenience of the storage and transportation hinders the application of it in PEMFC. Chemical hydrides are widely used in the field of hydrogen storage. Compared with other technologies, these chemical hydrides can store hydrogen at much milder ambient, room temperature and relatively low pressure, so they have attracted increasing interest. Among these hydrides, NaBH4 has become the most prominent one because of its high hydrogen content, high stability, environmentally friendly, convenient transportation and high-purity hydrogen. So the application of NaBH4 as the hydrogen source for the fuel cells has been widely explored by researchers.The catalyst is the key factor to the hydrolysis of NaBH4 solution. The focus of this paper is to prepare the catalysts which have high catalytic activity, long durability and low cost for the hydrogen generation from hydrolysis of NaBH4 solution.First, supported Ru/C catalysts were prepared by the impregnation method with different reductants and reductive pH value. It is found that the catalyst whose reductant is NaBH4 and the pH value is 10 has the longest durability. Then the catalyst with the longest durability was used to study the kinetics of NaBH4 hydrolysis. A series of hydrolysis experiments were conducted by changing many factors, such as the reaction temperature, the amount of catalysts, the shapes of catalysts, the concentration of NaOH and NaBH4. The overall activation energies obtained by different reaction temperatures with the powder Ru/C catalysts and the spherical Ru/C catalysts are 50.74 kJ/mol and 52.12 kJ/mol, respectively. The effect of the amount of powder catalysts on hydrogen generation (HG) rate is similar to that of the spherical catalysts, which means that the hydrolysis of NaBH4 is a first order reaction with respect to the amount of Ru/C catalysts regardless of the shapes of catalysts. The impact of NaOH concentration with two catalysts shows the same trend, which reflects that the NaOH has a negative effect on HG rate with Ru/C catalysts. Varying the concentration of NaBH4, the changing trends of HG rate are completely different with two Ru/C catalysts. When the concentration of NaBHH4 is within the scope of 1 wt%-15 wt%, HG rate of the powder Ru/C catalysts decreases monotonically while that of the spherical Ru/C catalysts increases first and then decreases. This is mainly due to the competition between mass and heat transfer in the Ru/C catalysts.In order to reduce the cost of catalyst, non-precious metal was used as the catalysts. In this paper, Co-base catalysts were prepared for hydrogen generation from hydrolysis of NaBH4 solution. First, the preparation conditions of supported Co catalyst were optimized and then the kinetics of hydrolysis of NaBH4 with this catalyst was studied. After that, the transition metal doped Co catalysts were prepared, and the selected metals are Ni and Fe. Among the catalysts, Co-Fe catalyst has the highest activity.The anode catalysts for direct methanol fuel cell (DMFC) are also discussed. The impregnation method was applied to prepare the Pt-Ru catalysts. The properties of the catalysts prepared with different carrier, reductant and impregnated medium were studied in detail. The catalyst prepared with the carbon aerogels as the carrier, the metal precursor impregnated in CH3COOH and the NaBH4 as the reductant has the highest electrocatalytic activity. The peak current density of methanol oxidation gets to 38.24 mA/cm2.