Oxygen vacancies in α-Ni(OH)2 porous nanoflowers promote urea oxidation

Urea oxidation reaction (UOR) is a promising substitution of oxygen evolution reaction (OER) in overall water splitting technology because of the lower theoretical potential; thereby, a win-win benefit is achieved due to the simultaneous hydrogen generation and water purification . The efficient UOR catalysis substantially depends on the exposed active sites and mass transfer resistance, especially at high current density to meet the requirement of industrial water splitting technology. In this work, we have synthesized α-Ni(OH) 2 porous nanoflowers (α-Ni(OH) 2 –PNF) using ZIF-67 as template. Ascribing to the Kirkendall effect , nanopores are created on α-Ni(OH) 2 nanosheets benefiting for the formation of abundant oxygen vacancies as well as drop-off in mass transfer resistance during UOR catalysis. Meanwhile, the binding strength between active site and CO 2 , rate-determining step of UOR, is weakened by oxygen vacancies; as a result, only 1.477 V vs. RHE is demanded for α-Ni(OH) 2 –PNF to catalyze UOR with 100 mA cm −2 , 67 mV lower than α-Ni(OH) 2 nanosheets. Besides, an exceptional stability is also achieved for α-Ni(OH) 2 –PNF with negligible degradation during 20 h catalysis.