Revealing the factors affecting the textural properties of Ni-doped carbon xerogels produced via resorcinol-formaldehyde polycondensation

Abstract

In the present work, a series of Ni-doped carbon xerogels were prepared via resorcinol-formaldehyde polycondensation and subsequent pyrolysis of organic xerogels. As found, introducing nickel acetate into the resorcinol-formaldehyde gels does not lead to the reduction of Ni or the formation of large Ni particles. Due to the even distribution of acetate ions in the organic xerogel matrix, their decomposition occurs at a temperature of ~520 °C, when the matrix is almost disintegrated. This gives additional amounts of carbon oxides, which are released at this temperature and affect the porous structure. Carbon xerogel containing 2.5 wt% Ni possesses the lowest density (0.54 g/cm³) and the largest pore volume (1.62 cm³/g). Compared with pure carbon xerogel, this sample retains high values of the external (278 m²/g) and total (783 m²/g) specific surface areas and does not undergo graphitization. It is worth noting that pH has little effect on the porous structure of carbon xerogel doped with a low amount of nickel. Contrarily, varying the concentration of resorcinol and formaldehyde in the solution allows obtaining Ni-doped carbon xerogels with tunable pore radius ranging from 16 to 200 nm and density in the range of 0.27–0.80 g/cm³. On the other hand, the textural properties of the xerogel matrix were found to influence the agglomeration process of nickel particles during the pyrolysis stage. In the case of mesoporous and macroporous xerogels, the agglomeration of Ni particles is hindered due to the texture limitations or the blockage of small nickel particles inside the matrix.

Graphical Abstract