2.1. Materials
The Ni foams with different pore sizes (35, 75, and 110 PPI) were purchased from Kunshan Ansu Electronic Materials Business. CoCl2ยท6H2O, NaBH4, KOH, NaOH, acetone, and HCl were purchased from Chron Chemicals (Chengdu, China). All reagents used in experiments are analytical grade and used as received without further purification. All deionized water (DI) is treated with nitrogen to remove dissolved oxygen prior to use.