Electrochemical oxidation-driven formation of nickel/nickel-based compounds on hollow carbon shells: Mechanistic insights and energy storage applications.

Hydrangea-like nickel/nickel-based compounds decorated hollow carbon shells were synthesized through low-temperature calcination and a facile electrochemical oxidation process. This three-dimensional hollow hierarchical structure ensures intimate contact between the electrically conductive nickel (Ni) substrate and uniformly distributed electrochemically active nickel-based compounds. This hierarchical structure offers abundant active sites and accessible pathways, maximizing energy storage, particularly during rapid charge-discharge cycles. With 30 min of electrochemical oxidation, the optimized Ni-compound-based electrode exhibits a specific capacity of 643 C g-1 at 1 A/g. When assembled into a nickel-zinc battery cell with a zinc foil anode, the cell demonstrates swift current responses, with full capacity recovery even after a twentyfold increase in current density, followed by a return to 1 A/g. Density functional theory computations reveal that the electrochemical oxidation, conducted for an optimized duration, results in partial oxidation of Ni(OH)2, reducing the surface adsorption energy of OH- from the electrolyte and improving charge storage capacity.