Room-Temperature Electrochemical Conversion of Metal–Organic Frameworks into Porous Amorphous Metal Sulfides with Tailored Composition and Hydrogen Evolution Activity

The conversion of metal–organic frameworks (MOFs) into inorganic nanomaterials is considered as an attractive means to produce highly efficient electrocatalysts for alternative-energy related applications. Yet, traditionally employed MOF-conversion conditions (e.g., pyrolysis) commonly involve multiple complex high-temperature reaction processes, which often make it challenging to control the composition, pore structure, and active-sites of the MOF-derived catalysts. Herein, a general, simple, room-temperature method is presented for a controlled electrochemical conversion of MOF (EC-MOF) films into porous, amorphous metal sulfides (a-MS_x). Detailed X-ray photoelectron spectroscopy analysis and control over independent EC-MOF parameters (e.g., scan-rate and potential window) enable to gain insights on the MOF-conversion mechanisms, and in turn to fine-tune the porosity and composition of the obtained MS_x. As a result, a highly active amorphous cobalt sulfide (a-CoS_x) electrocatalyst can be designed for hydrogen evolution reaction in neutral pH. Furthermore, the adjustable nature of the EC-MOF method allows to draw conclusions about the correlation between the concentration of catalytically active species (S^2-₂ sites) and the hydrogen evolution properties of the a-CoS_x. Given the method's generality and the diversity of available MOF structures, EC-MOF provides a compelling platform for a rational design of a wide variety of active electrocatalytic materials.