Hydrogen Generation From Sodium Borohydride Solution With Cobalt Catalyst Supported On Corn Stalk Activated Carbon Prepared Using A One-Step Approach

With the deterioration of non-renewable natural resources and the increasing awareness of environmental pollution by the emission of greenhouse gases, hydrogen has received the attention of the researchers working in this field. Hydrogen is deemed as 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 its application as PEMFC. Sodium borohydride (NaBH4) has been most extensively studied due to its combined advantages of high hydrogen ability (with a theoretical value of 10.8 wt.%), low reaction initiating temperature and environmentally benign hydrolysis product.The key factor for the hydrolysis process of NaBH4 is the catalyst, Thus far, much attention has focused on non-noble metal catalyst. Among them, Co-based catalysts are primarily considered as good candidates because of their good catalytic activities, low cost, and recyclability. As is known to all, it is believed that the structures and catalytic activities of Co-based catalysts are largely related to the preparation methods. Therefore, this paper is to develop a Co-based catalyst to accelerate hydrogen production process from hydrolysis of NaBH4 which exhibits good performance, low cost. A one-step approach was proposed based on the impregnation-chemical reduction method, which combined the activation process of activated carbon with the high temperature calcination process of the catalyst. As expected, such approach reduces the unit operation and save the roasting process energy consumption. On the other hand, it enhance the interaction between the carrier and active component, to improve the activity of catalyst. The main results follow as below:1 The catalytic activity of Co catalyst supported on corn stalk activated carbon prepared using a one-step approach was investigated. The optimized operating conditions of one-step approach were included carbonization and activation technique, and cycle stability of the catalyst was investigated. It demonstrates that the optimal conditions for preparing catalyst are carbonization for 1 hour at 400 ℃ and activation for 2 hours at 800 ℃. The maximum rate of hydrogen generation using the Co-based catalyst is 2952 mL·min-1·g-1, and the catalyst maintains 51% initial activity after 11 cycles.2 The effects of additives on the catalysts were comprehensively explored. The main findings are as follows. (1) The average rate of hydrogen generation with the introducing of Fe and Mn was 1784 mL·min-1·g-1, especially the Co-Mn/AC catalyst up to 3040 mL·min-1·g-1. (2) The agglomeration phenomenon of catalyst could be inhibited effectively, the active component enter pore canal of activated carbon. (3) The characteristic peak offset to low-angle with the introducing of Fe, and Fe dissolves into Co, the lattice distortion occurred, resulting in the change of lattice constant. (4) The grain size of catalyst tends to be relatively small with the introducing of Mn, which result in larger surface atomic ratio and higher specific surface area.3 The parameters influencing the hydrogen generation process are also examined, with the activation energy of 50.2 kJ·mol-1. The kinetic rate equation is expressed as r=Ae-50200/(RT)[catalyst]0.48[NaOH]0.49[NaBH4]1.16 when the concentration of NaBH4 is less than 10 wt.% and r=Ae-50200/(RT)[catalyst]0.48[NaOH]0.49[NaBH4]-0.66 over 10 wt.%.