Synthesis of Ni(OH) _2 nanostructures by the hydrothermal treatment in the presence of guanidine carbonate and their electrochemical properties

摘要

Nanostructure control of β-Ni(OH) _2 was attempted by adopting hydrothermal treatment for the high specific surface area (high-SSA) β-Ni(OH) _2 in the presence of guanidine carbonate. β-Ni(OH) _2 nanosheets-linked structures could be synthesized from high-SSA β-Ni(OH) _2 owing to the strong effects of guanidine carbonate for keeping or enlarging SSA during hydrothermal treatment. The discharging capacities of the high-SSA sample showed the highest capacity above 80 % at 0.2C. However, the capacities were decreased with decreasing SSA of the β-Ni(OH) _2 prepared. It was also found that, at lower SSA, charging/discharging rates below 1C did not affect the discharging capacity, i.e., the almost same capacities for 0.2C and 1C. Cyclic voltammetry revealed that the electrochemical reactions for the charging/discharging were considered to be reversible and smooth at various scanning rates. The rate-determining step of the electrochemical reaction is considered to be regulated by the diffusion of the active species involved for the lower SSA samples. However, for the higher SSA sample (280 m ~2 g (-1)) obtained at 200 °C in the presence of 1.0 × 10 ~(-1) mol L ~(-1) guanidine carbonate strongly indicates the effects of the rate of surface reaction or electronic conductivity on rate-determining step of charging/discharging of the material.