Recent progress in non-noble metal-based electrocatalysts for urea-assisted electrochemical hydrogen production

Water electrolysis is known as an efficient strategy in the direction of green energy production to remove fossil fuels and generate hydrogen. On the other hand, the slow kinetics of the anodic half-reaction (OER) significantly reduces the efficiency of this system. Therefore, choosing an alternative to OER has become a new and reliable approach. Urea oxidation reaction (UOR) is considered an excellent alternative to OER due to its low required potential (0.37V), the abundance of urea sources (industrial waste and human/ animal urine), and harmless by-products (N2, CO2). Electrocatalysts based on non-noble metals such as nickel, cobalt, molybdenum, manganese, iron, and copper in electrochemical urea-assisted water splitting due to their high electrocatalytic performance and lower price than noble metals play an essential role in reducing costs and increasing the efficiency of this system. This review investigated the electrochemical water splitting reaction and its anodic and cathodic half-reactions. Then, urea, electro-oxidation of urea, methods of making catalysts, measuring parameters of electrocatalytic properties, solutions to improve performance, and types of non-noble catalysts used in this field were reviewed, and finally, challenges and solutions to improve results in the future were introduced. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.