Empowering the Nickel Iron Oxyhydroxide through a Heterostructure Cocatalyst for Superior Alkaline and Saline Water Reduction

Hydrogen production using an electrochemical cell might be an alternative to conventional fuel systems (i.e., fossil fuels). The NiFe-layered hydroxide (NiFeOxHy) is one of the most popular electrocatalysts for water-splitting applications. However, its electrochemical activity is limited in the hydrogen evolution reaction (HER) because of its minimal active sites and modest charge transfer rates. To overcome the limitations in NiFeOxHy, silver sulfide (Ag2S) and graphitic carbon nitride (g-C3N4) were added as heterostructure cocatalysts. The heterostructure cocatalyst (Ag2S/g-C3N4) addition in NiFeOxHy is found to improve the electrochemical double layer capacitance (EDLC) seven times greater than that of pristine NiFeOxHy. The addition of the heterostructure cocatalyst in the NiFeOxHy sample enables hydrogen production with a minimum overpotential of η10 = 43 mV and Tafel slope of 131 mV/dec in saline water conditions. X-ray photoelectron spectroscopy reveals that the heterostructure cocatalyst effectively donates electrons to NiFeOxHy, which enhance the resultant charge transfer ability of the electrocatalyst. In addition, the density functional theoretical (DFT) analysis suggests that the exposed sulfur (S) sites within the Ag2S/g-C3N4 heterostructure cocatalyst serve as the prominent catalytic center for H* interactions. This study highlights the alteration of charge transfer dynamics in NiFeOxHy via heterostructure cocatalyst addition as an effective way to facilitate enhanced alkaline and saline water reduction.