Fabrication of MIL‐101(Fe) on UiO‐66 as an Electrocatalyst for Enhanced Overall Water Splitting

Abstract The water‐splitting process is an attractive avenue for manufacturing hydrogen gas (a green and renewable energy source). However, this process requires efficient and economical electrocatalysts to lessen the high energy barrier of water oxidation and hydrogen evolution reactions. MOF‐on‐MOF hybrid structures assembled by unifying two or more MOF units are being explored as electrocatalysts with promising results. In this study, a novel electrocatalyst nanostructure of an iron‐based MOF on a zirconium‐based MOF denoted as MIL‐101(Fe)/UiO‐66 was prepared by hydrothermal synthesis. MIL‐101(Fe) offers abundant active sites with higher surface area for catalytic activity, while UiO‐66 acts as a support to enhance stability and conductivity. It was observed that compared to the individual MOFs, hybrid (MIL‐101(Fe)/UiO‐66) exhibited significantly enhanced catalytic efficiency towards overall water‐splitting. This was evidenced by the higher current densities and lower overpotentials observed for the hybrid. The MIL‐101(Fe)/UiO‐66 showed an overpotential of 185 mV for HER and 290 mV for OER @ η 10 in an alkaline electrolyte solution. Moreover, it was stable for over 24 hours with a very small decrease in activity. With MIL‐101(Fe)/UiO‐66 as the cathode and anode, the unified water‐splitting cell attained a low overall required potential of 1.58 V @ η 10 demonstrating good performance of overall water splitting. It offers an appealing strategy for creating high‐performance electrocatalysts for energy‐related applications, in particular water splitting, by combining the advantages of different MOFs through facile fabrication methods.