| Summary: | Abstract The efficiency of many clean technologies, such as urea fuel cells, hydrogen production from urea‐containing water splitting, and sewage treatment, and so forth, is restricted due to the sluggish kinetics of the urea oxygen reaction (UOR). Mo‐doped Ni‐based catalysts are excellent for UOR because of the synergistic effect between Ni and Mo. However, such applications have indeed been hampered by a lack of mechanistic comprehension. Here, we fabricate Mo‐Ni(OH)2 nanosheets for efficient UOR electrocatalysis with activity at least twice higher than Ni(OH)2 nanosheets. Various in situ characterizations including Raman, differential electrochemical mass spectrometry and Fourier transform infrared spectroscopy reveals that the doping of Mo lowers the onset potential required for Ni2+/Ni3+ conversion and promotes the coupling of the N–N bond inside the molecule and the fracture of the double bond between C and O in the urea molecule. In addition, an entirely flexible direct urea fuel cell with the Mo‐Ni(OH)2 electrocatalyst delivers a maximum output power density of 0.78 mW cm−2 and complete flexibility for the first time. Our research significantly promotes the mechanistic understanding of UOR electrocatalysis and its applications.
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