Enhancing Oxygen Evolution Reaction Activity through Linker Functionalization in Manganese-Based Metal-Organic Frameworks (Mn-MOFs)

Developing efficient and durable electrocatalysts for oxygen evolution reaction (OER) remains a critical bottleneck for economic and large-scale production of green hydrogen. Metal-organic frameworks (MOFs) with their unique structural tunability, redox properties, and high surface area have emerged as promising candidates for the OER process. In this work, a presentation on how linker functionalization in rather unexplored manganese-based MOFs leads to enhanced OER activity is given. A series of manganese-based MOFs in rarely reported MIL-88B structure (Mn-MIL-88-X) is synthesized using functionalized linkers [X = NH₂, NO₂, Br]. The objective is to modulate the electronic structure and hydrophilicity of the MOFs leading to enhanced OER activity. Among functionalized MOFs, Mn-MIL-88-NH₂ shows remarkable performance, requiring only 260 mV of overpotential to reach a current density of 10 mA cm⁻² and a small Tafel slope of 73 mV dec⁻¹. The improvement in OER activity of Mn-MIL-88-NH₂ is ascribed to the higher oxidation states of manganese (Mn³⁺/Mn⁴⁺) and the presence of the amino group (-NH₂) as confirmed through X-ray photoelectron spectroscopy (XPS). This work paves the way for the designing and exploring of mixed-valence state metal-based MOFs as advanced electrode materials for electrocatalysis.