Mo0.2Ni0.8N/CeO2 heterojunction as bifunctional electrocatalysts for overall urea-water electrolysis

Pollution-free and low-cost bifunctional catalysts are important part for hydrogen production. In this paper, composite catalysts Ni0.2Mo0.8N/CeO2-x/NF (x = n(Ce)/n(Ni)- 0.1, 0.3, 0.5) were synthesized via hydrothermal and calcination methods on foam nickel (NF). Experimental results show that the composites have better properties than CeO2/NF, Ni0.2Mo0.8N/NF and MoN/CeO2/NF. The electrochemical properties of the composites depend on the ratio of nickel and cerium. A proper proportion of nickel leads to a larger specific surface area, increased electron capacity, more active sites, and better overall performance. Among the tested composites, Ni0.2Mo0.8N/CeO2-0.3/NF exhibits the best electrochemical performance and is well-suited for catalyzing the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). For HER, the potential is −120 mV @ 100 mA cm−2. And for UOR, the UOR potential is only 1.462 V @ 100 mA cm−2. A two-electrode electrolyzer of Ni0.2Mo0.8N/CeO2-0.3/NF|| Ni0.2Mo0.8N/CeO2-0.3/NF was also built. Overall urea splitting (OUS) is 1.672 V @ 100 mA cm−2, which is 187 mV smaller than overall water splitting (OWS, 1.859 V). Therefore, Ni0.2Mo0.8N/CeO2 has potential application in hydrogen production from urea-rich wastewater electrolysis.