Non-noble metal–organic frameworks in electrocatalytic urea-assisted hydrogen production and energy-saving regeneration

One of the unique features of urea is its non-toxicity and high hydrogen content, which makes it a very good candidate for the generation of hydrogen as a fuel. The urea oxidation reaction (UOR) is an efficient strategy involving electrolysis of urea, which allows for simultaneous energy production and treatment of urea-laden wastewater, although it faces difficulty in the transfer of six electrons with diminished reaction kinetics. To increase the efficiency of the UOR, the deployment of efficient electrocatalysts is of utmost importance. The problem is the lack of promising materials that can be used as low-cost and efficient electrocatalysts in the production of hydrogen via urea splitting. Different strategies have been recently reported for the preparation of materials to design efficient UOR catalysts. Metal organic frameworks (MOFs) have achieved extensive applications in various domains, including electrocatalysis, owing to their diverse structures, tunable properties, and high surface area. In this regard, MOFs comprising the first-row metals have garnered the attention of researchers due to their low cost and relative abundance. Herein, recent developments in the production and application of first-row transition metal-based (nickel, cobalt, and manganese) pristine MOFs and their composites with the introduction of the architectural advantages of nanoarrays and characteristics of MOFs are appraised for the UOR. Modifications to improve the performance of pristine MOFs and the corresponding hybrids are also discussed. Additionally, the current state-of-the-art strategies and future perspectives encompassing fabrication designs and compositional and structural modifications are discussed to amend the activity of MOF-based substances in the UOR. Finally, a future vision for developing pristine MOFs and their composites in electrocatalytic urea-assisted hydrogen production is described, with emphasis on the current problems and future prognoses. This is the first review dedicated to the field of non-noble metal–organic frameworks toward the development of urea oxidation electrocatalysts.