Constructing Ni/NiS Heteronanoparticle-Embedded Metal–Organic Framework-Derived Nanosheets for Enhanced Water-Splitting Catalysis

Electrocatalytic water splitting is an emerging technique to produce sustainable hydrogen energy. However, it is still challengeable to fabricate a stable, efficient, and cost-effective electrocatalyst that can overcome the sluggish reaction kinetics of water electrolysis. In order to reduce the energy barrier, for the first time, metal–organic framework (MOF)-derived nickel (Ni) and nickel sulfide (NiS) heteronanoparticle-embedded semi-MOFs are prepared by a partial sulfurization strategy. These semi-MOF electrocatalysts inherit the advantages associated with MOF architecture and nanoparticles, unlike the traditional OER catalysts such as pristine MOFs or completely pyrolyzed MOFs. Due to the unique nanoarchitecture fabricated by Ni/NiS heteronanoparticles within semi-MOF nanosheets and a carbon nanotube (CNT) network (Ni-M@C-130), it displays exceptional bifunctional activity over the other transition metal-based electrocatalysts ever reported. It requires very small overpotentials for both oxygen evolution reaction (OER; η10 = 244 mV) and hydrogen evolution reaction (HER; η10 = 123 mV), with low Tafel slopes of 47.2 and 50.8 mV/dec, respectively. Furthermore, it exhibits overpotential as low as 1.565 V (η10) on nickel foam (1 mg/cm2) substrates for overall water splitting. The outstanding catalytic performance of Ni-M@C-130 is attributed to the combined benefits of MOF nanosheets, synergistic interactions, and improved electrical conductivity and mechanical stability. This study describes the advantages of partial sulfurization of CNT-integrated MOFs in attaining electrochemically active heteronanoparticles within MOF nanosheets to accomplish improved bifunctional activity.