Tailoring the density of states of Ni(OH)2 with Ni0 towards solar urea wastewater splitting.

Abstract

Solar urea wastewater splitting is capable of producing hydrogen and degrading the urea pollutant simultaneously. Nickel hydroxide (Ni(OH)2) has been recognized as an effective cocatalyst for the urea oxidation reaction (UOR). But the lack of an efficient preparation method and a suitable Ni(OH)2 based cocatalyst limits the performances of solar urea wastewater splitting. Herein, a potential-cycling method is developed with a high-purity nickel plate serving as the counter electrode and nickel source in a three-electrode configuration. Spherical Ni0-doped Ni(OH)2 nanoparticles are successfully synthesized on the surface of TiO2 nanorod arrays. The photocurrent density of TiO2/Ni0:Ni(OH)2 can reach 0.56 mA cm-2 at 1.23 VRHE in 1 M NaOH and 0.33 M CO(NH2)2 mixed electrolyte under AM1.5G illumination, which is 1.75 and 1.93 times those of TiO2/Ni(OH)2 deposited using a normal potentiostatic method with nickel salt solution and pristine TiO2, respectively. Ni0 doping can significantly decrease the charge transfer resistance and provide a more favorable distribution of density of states of Ni(OH)2 for the UOR. Furthermore, Ni0:Ni(OH)2 decorated TiO2 photoanodes exhibit good photocurrent retention during 12 h continuous testing. This work expands the preparation technique of urea catalysts and the strategy for developing highly efficient nickel-based catalysts.