A General Electrodeposition Strategy for Fabricating Ultrathin Nickel Cobalt Phosphate Nanosheets with Ultrahigh Capacity and Rate Performance

Transition-metal phosphates/phosphides possess promising theoretical electrochemical characteristics and exhibit great potential in advanced supercapacitors. Unfortunately, limited by the processing techniques and overall structure, their specific capacity and rate performance are still unsatisfactory. Herein, we report the fabrication of transition-metal phosphate electrodes with an ultrathin sheetlike array structure by one-step electrodeposition at room temperature. As a proof-of-concept, a transition-metal phosphate member of NiCo(HPO4)2·3H2O with an ultrathin nanosheet structure (thickness ∼2.3 nm) was synthesized and investigated. The as-prepared NiCo(HPO4)2·3H2O electrode showcases an ultrahigh specific capacity of 1768.5 C g-1 at 2 A g-1 (the highest value for transition-metal phosphates/phosphides reported to date), superb rate performance of 1144.8 C g-1 at 100 A g-1, and excellent electrochemical stability. Moreover, the transition-metal phosphate nanosheet array can be uniformly deposited on various conductive substrates, demonstrating the generality of our strategy. Therefore, this simple electrodeposition strategy provides an opportunity to fabricate ultrathin transition-metal phosphate nanosheet materials that can be used for energy storage/conversion, electrocatalysis, and other electrochemical energy-related devices.