Insights into the synergistic effect between nickel and molybdenum for catalyzing urea electrooxidation

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 Ni 2+ /Ni 3+ 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.

Facile electrolysis-solvothermal synthesis of NiOx/graphene for enhanced ethanol oxidation to acetate

“…The interplanar distances of 0.24 and 0.34 nm are consistent with the lattice of Ni(OH) 2 and match well with the (422) and (131) planes. 22 The element mapping demonstrates that Ni, O, C, and O were all evenly distributed throughout the nanosheets (Fig. 1d-h).…”

Catalytic Urea Electrooxidation on Nickel-Metal Hydroxide Foams For Use in A Simplified Dialysis Device

“…The addition of nickel and other metals into nickel hydroxide has been shown to increase the electrode activity by altering the electronic structure and by expanding the electrochemically active surface area. [39][40][41][42][43][44][45][46][47][48] The inclusion of chromium oxide into nickel has been shown to depress the density of states at the Fermi level of the d-band of nickel, thereby weakening the Ni-O urea bond and decreasing the energy for adsorption. 49 The inclusion of Mo into the nickel hydroxide films causes Ni to complete the Ni(OH) 2 /NiOOH transition at lower onset potentials.…”