Ru ^III Incorporation in Ni-Layered Double Hydroxide Nanosheets Improves Electrochemical Hydrogen Evolution by Seawater Splitting

As fresh sources of water are limited, the use of seawater for the electrochemical HER is highly desired. However, the performance and stability of transition-metal-based electrocatalysts for HER in saline water are not up to the mark. Herein, we demonstrate self-supported hydroxide–organic framework (HOF)-derived RuNi-layered double hydroxide (RuNi-LDH) nanosheets for seawater HER. The introduction of 4d metal Ru in Ni-HOF-derived LDH was found to be prominent in modulating the electronic structure of the catalyst, leading to an improved catalytic activity and stability compared to the 3d metal-incorporated FeNi-LDH. Interestingly, the self-supported RuNi-LDH displayed an impressive performance, delivering a current density of −10 mA cm –2 at overpotentials of 48 and 66 mV in alkaline fresh water and seawater, respectively. The low potential difference (Δ E = 18 mV) between the freshwater and alkaline seawater HER makes RuNi-LDH a unique catalyst for saline-water HER. Notably, RuNi-LDH exhibited outstanding stability, maintaining continuous HER performance for 4 days in seawater with a negligible decay in the current density. In contrast, FeNi-LDH lost its activity within 20 h.