Cobalt powders and porous cobalt particles prepared by co-reduction of hydrazine and sodium phosphate and its formation mechanism

Abstract Co particles and macroporous Co particles of various shapes were synthesized from the inorganic salt of cobalt (CoCl 2 ·6H 2 O) using a liquid phase co-reduction process in which hydrazine (N 2 H 4 ) and sodium hypophosphite (NaH 2 PO 2 ) were used as reducing agents. The reduction efficiency of individual reducing agents (N 2 H 4 , NaH 2 PO 2 ) and the N 2 H 4  + NaH 2 PO 2 co-reduction system for synthesizing phase pure Co powder is investigated and comparable data are presented. Various size and shapes (spherical and dendrite) of Co particles were obtained by controlling the N 2 H 4 and NaH 2 PO 2 molar ratio. Creating a hydrothermal condition of the co-reduction system (N 2 H 4  + NaH 2 PO 2 ) enabled the formation of the porous structure of Co particles. The prepared porous structure of Co consisted of different sizes of cavities with bonded Co particles, and the surface of the Co frame was covered with many flake-shaped particles. The size of Co monolith was controllable with the reaction temperature and time. The formation mechanism of Co powder and porous Co monolith was discussed.