Synthesis of Cu-doped Ni-B amorphous alloy catalyst and its catalytic performance for BH4- oxidation

Searching for non-precious metal anode catalysts with high catalytic activity and low cost is essential for direct borohydride fuel cells (DBFC). The Ni-B alloys with crystalline states prepared by physical methods commonly exhibit high B content (NiB₄, NiB₆, etc.). This work first prepared four kinds of amorphous Ni-B alloy with low boron content by the chemical reduction method. The composition of Ni-B alloy is critical to its performance. Cu is doped in the Ni-B alloy in a suitable proportion to improve the catalytic activity further. The crystal structure, microstructure, and composition information of Ni-B and Ni-B-Cu alloys were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selective area electronic diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-optical emission spectrometer (ICP-OES) tests. The results show that the Ni-B and Ni-B-Cu alloys are amorphous nanoparticles with particle sizes of about 70 and 50 nm, respectively. The electrocatalytic oxidation BH₄⁻ performance of Ni-B and Ni-B-Cu was studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). It was shown that Ni-B and Ni-B-Cu alloy catalysts have good catalytic activity for BH₄⁻ oxidation reaction, and Cu doping improves the catalytic activity of the Ni-B alloy for borohydride oxidation reaction (BOR). In addition, it is found that the maximum power density (79.124 mW·cm⁻²) of the direct borohydride fuel cell using Ni-B-Cu/NF (NF: nickel foam) as an anode electrode is significantly higher than that of the Ni-B/NF electrode (21.063 mW·cm⁻²). The Ni-B and Ni-B-Cu alloys with low boron content can be used as potential anode catalyst materials for DBFC.