| Fuel cell is a new kind of device that can convert chemical energy in fuels into electrical power directly. Direct borohydride fuel cells (DBFCs) with alkaline aqueous solution of NaBH4 as fuel have some special advantages, such as very stable, non combustible of the solid sodium borohydride (NaBH4) so that easy to storage and transport, higher theory cell voltage and capacity. The electro-oxidation reaction of BH4 is an eight electrons transfer process theoretically. However, owing to the H-of the BH4 have a special structure with 1S2 makes the excessive electron very unstable and easy to lose, so the direct electro-oxidation and hydrolysis reaction occur at the same time in most case, which will undoubtedly reduce the fuel utilization rate. Therefore, developing an anode catalyst, in favor of direct electro-oxidation reaction and not conducive to the hydrolysis reaction, has a very vital significance.In the first place, a series of carbon-supported Cu-Pd nanoparticles of core-shell structure (Cu@Pd/C) with different proportion are successfully prepared using a two-step reduction method. Physical and electrochemical properties of the as-prepared catalysts are investigated by XRD, TEM, EDS, CV, CP, CA and fuel cell test. The results show that the Cu@Pd/C nanoparticles are spherical, adopt a core-shell structure, and the particle size is about 9 nm. In addition, some of the particles exhibit certain reunion phenomenon. The electrochemical active surface area (ECSA) of Cu@Pd/C is bigger than single metal Pd/C, and shows better electrocatalytic performances. However, different proportion of Cu-Pd nanoparticles show different catalytic performance, especially the Cu1@Pd1/C attains a power density of 40 mW cm-2 when used as anode catalyst of DBHFC at 20℃.In the second place, we also prepared Ni@Au/C nanoparticles with different proportion by unite the inverse microemulsion method with the two-step reduction method. Physical and electrochemical results are shown as follows:the Ni@Au/C nanoparticles are formed a core-shell structure and exhibit a well dispersion, and the particle size is approximately 10 nm. As the Au shell becomes more and more thinner, the catalytic performance of Ni@Au/C for the first increased and then decreased. The ECSA for Au/C, Ni1@Au2/C, Ni1@Au1/C and Ni2@Au1/C are calculated as 161 cm2 mg-1,348.1 cm2 mg-1,815.7 cm2 mg-1 and 402.4 cm2 mg-1. Ni1@Au1/C catalyst achieves the largest ECSA and also the best stability, and the number of electrons transfered is calculated as 6.6 based on the al oxidation peak in CV experiment. Moreover, DBHFC fabricated using Ni1@Au1/C as anode catalyst and Pt mesh (1cm × 1cm) as cathode electrode attains a maximum power density of 74 mW cm-2 at 20℃, which is 3 times higher than Au/C in the same conditions.In this paper, the prepared catalyst of core-shell structure shows a better catalytic capabilities than that single metal for BH4 electro-oxidation, the improvement of catalytic performance may be due to electronic effect and geometric effect of the special core-shell structure. On the one hand, the core metal may have a suitable induced effect to d-orbit electrons of the shell metal when have an appropriate shell thickness, and thus, makes BH4 has a more suitable adsorption capacity on metal atoms of shell, then makes the process of BH4 adsorption and it’s products desorption occurs more easily. In this paper, the as-prepared Cu1@Pd1/C or Ni1@Au1/C nanoparticles exhibit a better catalytic activity, this may have some relations with its microscopic structure, the 3-4 layer Pd or Au atoms of shell. On the other hand, the higher catalytic ability of Cu1@Pd1/C and Ni1@Au1/C catalysts may also have some relations with their larger ECSA. |
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