Effect of doping Ni on microstructures and properties of CoxNi1-xHCF based seawater battery

Prussian blue analogues (PBAs) have been proven to be a kind of seawater battery cathode due to the accommodation of electrons upon the intercalation of Na+ in seawater. In the current work, Ni-doped cobalt hexacyanoferrate (CoxNi1-xHCF) was fabricated by using co-precipitation method at room temperature. Results have shown that with increasing the molar ratio of Co: Ni, the specific capacity of the cathode initially increases and then decreases. The best battery properties were obtained when the molar ratio of Co: Ni was 1:2. The specific capacity was up to 76.5 mAh·g−1 at 0.1 A g−1, the capacity retention was up to 63.5 % at a current density of 10 A g−1, and the capacity retention of 81 % was obtained after 100 cycles. The introduction of Ni2+ increases the specific surface area leading to the additional active sites for the redox reaction. At the same time, the specific capacity decreased due to the Ni doping. The enhanced electrochemical performance of CoxNi1-xHCF cathode for seawater battery was achieved by considering the synergistic effects of specific surface and elemental composition. Furthermore, seawater battery was successfully assembled by matching the Co0.86Ni0.14HCF cathode with Mg anode, which demonstrates the promising application of PBAs for seawater batteries.