Recent advancements in MOF-based catalysts for applications in electrochemical and photoelectrochemical water splitting: A review

A significant interest in the exploration of clean and renewable alternative energy resources has been observed in recent years to combat environmental pollution and energy shortages for a sustainable future. In this regard, hydrogen is clean, energy-rich fuel with unlimited potential. It can be produced via water-splitting process using the most abundant resources on earth, that is, water and solar/electrical energy. Metal-organic frameworks (MOFs) are a category of porous crystalline materials with well-organized structures and unique catalytic, optical, and electrical properties. MOFs and MOF-derived materials have proved to be excellent catalysts for water-splitting both by electrochemical and photoelectrochemical (PEC) routes. Furthermore, photochemical and electrochemical capabilities of these MOFs can be fine-tuned to maximize their performance by modification in the bandgap, surface area, current density, electrochemical active surface area, and overpotential, through tailoring of the organic ligands and/or metal centers. A number of works have been dedicated to this quest resulting in promising and very effective results. Such as for photoelectrocatalysis, a composite nanorod array of TiO₂/Co-MOF acting as photoanode achieved one of the highest photocurrent densities of 2.93 mA/cm² at 1.23 V (vs reverse hydrogen electrode [RHE]). In another study, MOF-derived Co₃C-3/TiO₂ photoanode attained the photocurrent density of 2.6 mA/cm² at 1.23 V vs RHE. For electrocatalysis, Fe₂O₃/Ni-MOF-74 exhibited oxygen evolution reaction overpotential of 264 mV to reach 10 mA/cm² of current density with a low Tafel plot of 48 mV/dec. Another novel material derived from MOF, MoO₂-PC-rGO displayed a Tafel Plot of 41 mV/dec. Even though this field is in its infancy phase, it is attracting increased attention for promising results suggesting extraordinary potential for practical applications. Focus of this review article is on the overview of the development of MOFs for application in electrocatalytic and photoelectrocatalytic water-splitting for hydrogen production. This review intends to provide a timely reference and insight for the advancement in catalysts based on MOFs for practical electrochemical and PEC water-splitting in a clear and comprehensive manner. Starting with the brief introduction, fundamentals, factors affecting catalytic efficiency and evaluation parameters of water-splitting are summarized followed by synthesis strategies and recent progress made by MOF-based catalysts for PEC and electrochemical water-splitting.