Heterostructural Coupling of Phase-Modulated NiMoO<sub>4</sub> with NiCo<sub>2</sub>O<sub>4</sub> for Enhanced Urea Electro-Oxidation
Ming Yang, Zirui Liu, Fei Liu, Jie Gan, Yanping Lv, Jun Zhang, Hao Wu
Abstract
Developing catalysts with high efficiency and low cost for the urea oxidation reaction (UOR) is attractive but challenging. Herein, relying on the high catalytic activity of Ni, low overpotential of Co, and superior antipoisoning resistance of Mo, a NiMoO 4 –NiCo 2 O 4 p–p heterojunction is constructed via a hydrothermal strategy followed by calcination. Interestingly, phase transformation of β-NiMoO 4 to α-NiMoO 4 occurs when a heterojunction is generated. The unique structure of NiMoO 4 –NiCo 2 O 4 enables faster charge transfer capability, greater active site availability, lower impedance, and reduced activation energy. Thus, a much better catalytic performance for the UOR is triggered when employing NiMoO 4 –NiCo 2 O 4 as a catalyst. A specific current density of 1306 mA cm –2 mg –1 (at 0.6 V vs Hg/HgO) is achieved for NiMoO 4 –NiCo 2 O 4, which is much larger than that for NiMoO 4 and NiCo 2 O 4 . Potential-dependent impedance analyses unveil that Ni 3+ should be active sites and both indirect and direct urea oxidation paths should be accelerated on NiMoO 4 –NiCo 2 O 4 . Phase transformation of β-NiMoO 4 to α-NiMoO 4 is vital. Making the energy bands of NiCo 2 O 4 and NiMoO 4 match better, promoting Ni 3+ formation, facilitating active sites exposure, and reducing alkalinity to enhance antipoisoning capacity all make sense. This work stresses the importance of crystal phases in developing heterojunctions with high catalytic performance.