Herein, we report synthesis of Co3V2O8 nanoparticles for an electrocatalyst of seawater batteries. The cell using Co3V2O8 achieves a higher voltage efficiency of ∼76% than ∼72% of the cell without catalyst. In addition, the Co3V2O8 shows a good rate capability with reduced voltage gaps and an increased power density of ∼5.9 mW cm−2. This cell is stable over 20 cycles for 400 h with reduced voltage gap of ∼0.95 V. These findings are attributed to the facilitated redox kinetics of the clustered Co3V2O8 nanoparticles arising from the optimal metalOH bond strength and large surface area.