Construction of Ultrathin Cobalt-Based Nanosheet Arrays on Titanium Mesh as Asymmetric Electrodes for Overall Water Splitting

Developing highly efficient and stable electrocatalysts is the key to realize hydrogen production from industrial electrolytic water. In this study, we constructed Co(OH)2 and CoP ultrathin nanosheet arrays on titanium mesh using electrodeposition and phosphating processes. In alkaline conditions, the Co(OH)2/Ti-2.0 needed overpotentials of 414 and 457 mV to achieve 500 and 1000 mA cm–2 for oxygen evolution reaction. Mechanism research showed that CoOOH formed by pre-oxidation of Co(OH)2 was the actual active substance. After low-temperature phosphorization of Co(OH)2, CoP nanosheets generated abundant defects and increased reactive sites, and CoP/Ti-2.0 exhibited high activity in the all-pH hydrogen evolution reaction (overpotentials of 106, 116, and 131 mV in acidic, alkaline, and neutral solutions at 10 mA cm–2, respectively). Density functional theory calculations showed the free energy of hydrogen adsorption of CoP. As efficient electrode materials, the Co(OH)2 and CoP ultrathin nanosheet arrays on Ti mesh can be assembled to an alkaline electrolyzer, which required only 1.530 V to drive 50 mA cm–2 for overall water splitting with strong durability.