Mildly sulfurized metal-organic frameworks-derived nickel sulfide heterostructures as bifunctional catalysts for efficient water/seawater electrolysis.

The rational design of bifunctional electrocatalysts that simultaneously exhibit exceptional catalytic activity and retain the inherent merits of metal-organic frameworks (MOFs) for overall water electrolysis still presents a critical scientific challenge. Herein, we demonstrate the construction of nanoflower-like heterostructures composed of NiFe-TDC and NiS (denoted as NiS@NiFe-TDC) on nickel foam substrates through a simple and mild room-temperature sulfurization strategy, serving as highly active dual-functional electrocatalysts for overall freshwater and seawater splitting. The as-prepared NiS@NiFe-TDC-60 achieves 10 mA cm current density with the overpotentials of 81 and 244 mV in alkaline solution for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Moreover, it also exhibits the remarkable catalytic performance in alkaline seawater, with HER and OER overpotentials as low as 98 and 267 mV at 10 mA cm. Additionally, the assembled electrolysis cell with NiS@NiFe-TDC-60 as both electrodes was able to operate continuously for at least 100 h at 10 mA cm with the voltages of 1.55 and 1.67 V in 1.0 M KOH and alkaline seawater, respectively, which demonstrated the excellent long-term durability. The outstanding catalytic activity of catalysts is attributed to the synergistic interplay between the heterointerface engineering and nanoflower-like architecture, which significantly boosts the catalytic efficiency, electrical conductivity and electron transfer kinetics. The paper offers innovative insights into rational engineering of MOF-derived bifunctional electrocatalysts through a rapid and facile synthetic strategy.