NiFe-Based Semi-MOF Embedded by Sulfide Particles Reconstructed a Three-Layer Sandwich Structure for Alkaline Overall Water Splitting

A metal–organic framework (MOF) embedded by transition metal sulfide (TMS) particles is one of the promising electrocatalyst candidates for overall water splitting (OWS) due to the large surface area and abundant active sites from the MOF precursor, as well as the tunable electronic structure and higher intrinsic conductivity of TMS. More importantly, its self-restructuring under alkaline conditions will lead to the chemical composition and phase evolution of the catalyst surface, which is the source of its further enhanced catalytic activity. A semi-MOF (labeled as Co@Ni/Fe-MS/MOF) with MOF as the semisacrificial template and a TMS particle as the guest was designed by exercisable and universal heteroatomic Co doping and partial vulcanization. The TMS/MOF heterostructure establishes an ideal bridge for electron transfer. Simultaneously, the dopant Co and the synergistic effect of multiple metal sites also effectively regulate the charge environment around the catalytic sites, which jointly improve the adsorption/desorption kinetics of the reaction intermediates. As a result, Co@Ni/Fe-MS/MOF exhibits a distinguished overpotential (η10 = 229 mV for OER, η10 = 174 mV for HER) and Tafel slope (52.37/114.35 mV dec–1 for OER/HER), as well as unrivaled long-term durability (80 h for OWS). Moreover, the two-electrode Co@Ni/Fe-MS/MOF ∥ Co@Ni/Fe-MS/MOF cell illustrates a small cell voltage of 1.54 V to achieve a power of 10 mA cm–2. Impressively, this superior OER property comes from the three-layer sandwich structure restructured by the hybrid semi-MOFs in the alkaline environment as the true active sites. This work aspired to regulate the electronic structure of the catalyst, induce synergistic effects, and shed light on the preparation of hybrid semi-MOF materials by heterogeneous interface engineering, doping engineering, and phase evolution.