Synergistic two-dimensional metal sulfide heterostructures from ZIF-67: A promising catalyst for efficient overall water splitting

The morphology of nanomaterials plays a significant role in electrocatalytic water splitting. Metal–organic frameworks (MOFs) offer several advantages, including high porosity, large specific surface area, adjustable structure and various morphologies. Among the various MOFs, zeolitic imidazolate framework-67 (ZIF-67) is a cobalt-based MOF that can produce carbon-containing metal sulfides through appropriate sulfurization and annealing processes. Since the control of the morphology of nanostructured electrocatalysts plays a crucial role in optimizing catalytic activity, in this study, we synthesized rhombic dodecahedral, cubic, and plate-shaped ZIF-67 nanocrystals and utilized them as templates to fabricate Co3S4@CoMoS3 nanomaterials with various morphologies. These materials were characterized and subjected to electrochemical tests to evaluate their performance in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrocatalytic water splitting. The electrochemical measurements revealed that the plate-shaped Co3S4@CoMoS3–P exhibited the low overpotential for OER at 20 mA cm−2, with a value of 200 mV and a Tafel slope of 173 mV dec−1. Similarly, for HER at 10 mA cm−2, it showed an overpotential of 240 mV and a Tafel slope of 93 mV dec−1. Moreover, in the water splitting setup employing a dual electrode configuration, the plate-shaped Co3S4@CoMoS3–P achieved a voltage of 1.61 V at 20 mA cm−2, outperforming a commercial electrode combination (10% Pt/C//RuO2) in terms of water-splitting efficiency.