关键词: Ni-Fe-B合金, 电沉积, 催化, 石墨化, 碳纤维毡, 导电性

Abstract: Graphite fiber felt is a key component of proton exchange membrane fuel cells, namely the substrate of the gas diffusion layer, and its good performance is a prerequisite for ensuring the stable operation of the battery. Ensuring the excellent conductivity and chemical stability of graphite fiber felt requires high-temperature graphitization treatment, but the extremely high energy consumption leads to a significant increase in the preparation cost of graphite felt, and the degree of graphitization cannot be rapidly improved, which is not conducive to the improvement of product performance. At present, catalytic graphitization is one of the main methods to reduce energy consumption and improve the degree of graphitization.
Metal or B is commonly used to catalyze the graphitization of carbon materials. Transition metals, due to the special electronic configuration of the d-layer, are prone to receiving electrons from carbon, thereby dissolving carbon. At this time, carbon-carbon bonds will be broken by metal catalysts at the interface between disordered carbon and metal, and then carbon will dissolve in solid or molten metal, precipitating graphite carbon. Metal alloys composed of Fe3+and Ni2+ions can significantly reduce the graphitization temperature. At high temperatures, transition metals Ni and Fe are selected as precursors for graphitization catalysts.
B can accelerate the graphitization of carbon materials. During the catalytic graphitization process, it can replace the carbon atoms in the hexagonal carbon ring or insert itself into the gaps of the graphite layer, catalyzing the continuous growth of graphite carbon. The catalytic performance of B based catalysts is not sensitive to the particle size of the catalyst and the type of carbon used, which has prominent advantages for metal based catalysts. Although B doping methods have been used for the catalytic graphitization of carbon, with most studies on the catalytic graphitization of carbon by B alone or B with single metals, there is relatively little research on B and alloys. Therefore, this paper introduces B and Ni-Fe alloys with catalytic graphitization properties during the graphitization process of carbon fiber felt.
The present study utilized the electrodeposition method to prepare Ni-Fe-B alloy and investigated the effects of B and the alloy on catalytic graphitization of carbon fiber felt. After heat treatment, the influence of different FeSO4·7H2O mass concentrations in Ni-Fe-B alloy on the structure and properties of carbon fibers was studied. The results showed that when carbon fiber felt was electrodeposited in an electrolyte with a FeSO4·7H2O mass concentration of 100 g/L and subsequently heat treated, the graphitization rate could reach up to 90.77%, while the surface resistivity decreased from 1.99 mΩ·cm to 0.82 mΩ·cm, a decline of 58.69%. This indicates that Ni-Fe-B alloy can catalyze graphitization of carbon fiber felt at high temperatures (2,400 ℃), successfully transforming disordered carbon fibers into ordered graphite fibers.

Key words:  Ni-Fe-B alloy, electrodeposition, catalyst, graphitization, carbon fiber felt, conductivity