Potassium-Hydrogen Hybrid Ion Alkaline Battery: A New Rechargeable Aqueous Battery Combined a K Storage Cathode and an Electrochemical Hydrogen Storage Anode.

A rechargeable aqueous hybrid ion alkaline battery, using a proton and a potassium ion as charge carriers for the anode and cathode, respectively, is proposed in this study by using well-developed potassium nickel hexacyanoferrate as the cathode material and mesoporous carbon sheets as the anode material, respectively. The constructed battery operates in a concentrated KOH solution, in which the energy storage mechanism for potassium nickel hexacyanoferrate involves the redox reaction of Fe/Fe associated with potassium ion insertion/extraction and the redox reaction of Ni(OH)/NiOOH. The mechanism for the carbon anode is electrochemical hydrogen storage. The cathode made of potassium nickel hexacyanoferrate exhibits both an ultrahigh capacity of 232.7 mAh g under 100 mA g and a consistent performance of 214 mAh g at 2000 mA g (with a capacity retention of 92.8% after 200 cycles). The mesoporous carbon sheet anode exhibits a capacity of 87.6 mAh·g at 100 mA g with a good rate and cyclic performance. The full cell provides an operational voltage of 1.55 V, a capacity of 93.6 mAh g at 100 mA g, and 82.4% capacity retention after 1000 cycles at 2000 mA g along with a low self-discharge rate. The investigation and discussion about the energy storage mechanisms for both electrode materials are also provided.