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

Abstract

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 via electrolysis of urea, that allows for simultaneous energy production and treatment of urea-laden wastewater although the process is challenged by 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 useful materials that can be used as low-cost and efficient electrocatalysts in the production of hydrogen using 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 appliances in various domains including electrocatalysis in view of 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 metals-based (Nickel, Cobalt, Manganese,..) pristine MOFs and their composites with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs have been appraised for UOR. Modifications to improve performance of pristine MOFs and the corresponding hybrids are also discussed. Additionally, the current state of art strategies and future perspectives encompassing fabrication designs and compositional and structural modifications have been discussed to amend the activity of MOF-based substances in 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 in the field of non-noble metal–organic frameworks toward urea oxidation electrocatalysts.