Nickel hydroxide is used as active material in nickel based batteries and capacitors. It has two phases which are alpha and beta, since alpha nickel hydroxide has higher capacity it attracts scientists attention. Although it has promising performance, low utilization and poor stability hinder commercialization of alpha nickel hydroxide. The most common strategy to improve stability is to dope nickel hydroxide with cobalt or aluminum. Aluminum is more prominent due to its lower price and environmental concern. Besides the stability, it is well known that discharge capacity of nickel hydroxide decreases with increasing amount of both aluminum and cobalt. Although capacity is decrasing, number of electrons which is involved in the reaction does not change with increasing amount of dopant. At the same molar doping levels, although aluminum doped samples had higher active mass (nickel) content, they had lower gravimetric capacity than cobalt doped samples. Therefore, it is not convenient to explain capacity loss by only decreasing amount of active mass.

Since cobalt doping raises differences between oxygen evolution potential and oxidation potential of nickel hydroxide, it enhances chargeability of nickel hydroxide but the cyclic voltammetry results showed that higher cobalt doping causes decrease in cell voltage and energy density of battery. The results showed that higher amount of aluminum must be doped to improve stability and relatively small amount of cobalt must be used to improve chargeability of alpha nickel hydroxide. Therefore, both aluminum and cobalt are effective in improving stability but cobalt is advantageous at low doping level, as it is reported in the literature.