Growth mechanism of Ni on the graphite particles regulated by the OH− ionic concentration

In this work, nickel–coated graphite (C@Ni) particles with varying morphologies of Ni were prepared by electroless plating under different OH− ionic concentrations. The microstructure of resultant particles was characterized by XRD, SEM, EDS and TEM. At the OH− ionic concentration of 0.75 M, tiny thorn–like Ni particles with a length of approximately 150 nm grew on the graphite after the electroless plating. Flocculent Ni whiskers decorated with thorn–like crystals of about 50 nm in diameter were fabricated as the OH− ionic concentration was increased to 1 M. When the OH− ionic concentration was further raised to 1.5 M, the synthesized Ni whiskers consisted of the stacking quasi–spherical Ni nanoparticles in the diameter around 25 nm. Combined with the first–principles calculation, it is found that OH− ions tend to absorb on the Ni (111) plane and form the ions barrier layer against the deposition of Ni atoms. With the increasing of OH− ionic concentration, the barrier layer became denser and exhibited higher resistance toward the deposition of Ni atoms on to the Ni (111) plane. And this promoted more Ni atoms to deposit on the Ni (220) and (200) planes with lower deposition resistance, leading to the reduction of gap in the growth rate among the low–index crystal planes. The change in stacking behavior of Ni crystal also induced the variation in the electromagnetic shielding and microwave absorbing properties of C@Ni particles. The C@Ni particles with flocculent Ni whiskers exhibited desirable electromagnetic shielding and microwave absorbing properties, and the corresponding average values of electromagnetic shielding effectiveness and absorption loss were about 37 dB and 25.9 dB in the frequency range of 1 to 18 GHz, respectively.