| In the twenty-first century, hydrogen is a kind of green and clean energy to solve the problems of the fossil energy crisis and environmental pollution. Moreover, hydrogen as the carrier of the renewable energy could solve the problem of energy storage and effectively reuce the emission of carbon dioxide. Safe and efficient hydrogen storage materials play a key role in the the development of “hydrogen economy”. Ammonia borane(NH3BH3, AB) is regarded as a promising chemical hydrogen storage material due to its high hydrogen content(19.6 wt%),nontoxicity and high stability in aqeous. Hydrogen can be released from AB through thermolysis, methanolysis and hydrolysis. The thermal decomposition of AB usually produces byproducts at high temperature and the cost of the methanolysis is high, while the hydrolysis of AB can proceed at room temperature in the presence of proper catalysts. Therefore, searching for a sutiable catalyst has attracted a great attention.Although noble metals exhibit high catalytic activity for the hydrolysis of ammonia borane, the high cost and scarce resources hinder their practical applications. It's an inevitable trend to explore non-noble metal catalyst systems. Among non-noble metal catalysts(Fe, Co, Ni and Cu), Co nanoparticles exhibit superior performance under the same condition. Non-noble metals can be available for the hydrolysis of AB owing to their low-cost and abudance. Metal catalysts can be usually prepared via physical method, chemical reduction such as electro-deposition, thermal reduction at high temperature, solution chemical reduction method and so on. Among them, the last two methods are more facile. In this article, we report the synthesis of Co-based catalysts for the hydrolysis of AB.1. Cu Co catalysts with different ratios of Cu and Co have been synthesized using Na BH4 as reducing agent. Among them, Cu0.2Co0.8 catalyst shows the best catalytic performance for the hydrolysis of AB, displaying a hydrogen generation rate of 1364 m L min-1 g-1. In order to further improve its catalytic activity, porous carbon is applied to disperse Cu0.2Co0.8 nanoparticles.The results show that Cu0.2Co0.8 nanoparticles with the mean size of 8 nm are homogeneously anchored on porous carbon(denoted as Cu0.2Co0.8/HPC). 32.3 wt% Cu0.2Co0.8/HPC exhibits better catalytic performance, displaying a max hydrogen generation rate of 2960 m L min-1 g-1 and an activation energy of 41.7 k J/mol, remaining 45.3% of its original catalytic activity after 4 cycles.2. Co@N-C nanocomposites have been prepared by thermal reduction of Co(salen) at high temperature in Ar atmosphere. The structure and performance of Co@N-C prepared at different temperature have been characterized. Co nanoparticles(~9 nm) in Co@N-C-600 and Co@N-C-700 nanocomposites are homogeneously embedded in porous N-doped carbon, while Co nanoparticles suffer from serious aggregation at 800 ?. Co@N-C-700 exhibits the best catalytic activity, displaying a max hydrogen generation rate of 2075 m L min-1 g-1 and an activation energy of 31.0 k J/mol. In particular, Co@N-C-700 catalyst remains 97.2% of its initial catalytic activity.In summary, Co0.2Co0.8/HPC catalyst and Co@N-C nanocomposites have been prepared by solution chemical reduction method and thermal reduction at high temperature, respectively, resulting in well distributed metal nanoparticles on porous carbon. These methods are low-cost and more facile, which is beneficial for the practical application of Co-based catalysts. |
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