In Situ Decorated Ni Metallic Layer with CoS₂-Layered Thin Films via a Layer-by-Layer Strategy Using Pulsed Laser...

The catalytic activity of 3d-transition-metal-based electrocatalysts has exhibited considerable enhancements in electrocatalytic water splitting via pioneering modulations in the active sites. To overcome the energy loss because of the mechanic steps involved in a complex oxygen evolution reaction (OER), the electrode surface with only a few layers would be an advantage over multilayers for the ease of the electrolyte interaction and gas evolution. Here, for the first time, thin films of CoS₂ are prepared on a carbon cloth via a pulsed laser deposition (PLD) technique via layer-by-layer deposition of Ni that tend to give Ni-CoS₂ thin films. Based on varying the ablation of metallic Ni followed by CoS₂ as a layer-by-layer assembly using PLD, three catalysts, namely, Ni5-CoS₂, Ni10-CoS₂, and Ni15-CoS₂, were prepared. In OER, to achieve a benchmarking current density of 10 mA cm^-2 in 1 M KOH, Ni10-CoS₂ required a lesser overpotential of 304 mV, whereas others, namely, Ni5-CoS₂, Ni15-CoS₂, and CoS₂, required overpotentials of 328, 336, and 373 mV, respectively, to attain the same current density. The charge transfer kinetics associated with all of the catalysts were analyzed, and the corresponding Tafel slope values for Ni5-CoS₂ and Ni10-CoS₂ were 75 and 98 mV/dec, respectively, ensuring the facile transfer of electrons at the interface. The assistance of metallic Ni sites also ensured stability for long-term applications. These findings will give a way for other earth-abundant catalysts for the increased electrocatalytic activity toward energy needs in future.