α-MnO 2 nanorods and flower-like γ-MnO 2 microspheres were synthesized by facile and mild methods to illustrate the effect of crystal structures and surface features on catalytic performance with the help of carbon monoxide (CO) oxidation. It is revealed that the flower-like γ-MnO 2 microspheres possess better catalytic oxidation performance (CO complete conversion temperature at 120 °C and long-time stability for 50 h) than α-MnO 2 nanorods, which can be attributed to the obvious differences in the chemical bonds and linking modes of [MnO 6 ] octahedra due to the different crystal structures. γ-MnO 2 possesses lower Mn−O bond strength that enables γ-MnO 2 to present a large amount of surface lattice oxygen and superior oxygen mobility. The disordered random intergrowth tunnel structure can adsorb effectively CO molecules, resulting in excellent catalytic performance for CO catalytic oxidation. In addition, the MnO 2 catalyst probably occurred via a Mars−van Krevelen mechanism for CO oxidation. This work provides an insight into the effect of crystal structures and surface property of manganese oxide on catalytic oxidation performance, which presents help for the future design of promising catalysts with excellent catalytic performance.
In electrocatalytic hydrolysis, the oxygen evolution reaction (OER) reaction involves a four-electron transfer process. The complex transfer process reduces the rate of hydrolysis. Therefore, the electrocatalyst with good OER performance is desirable for not only fundamental research but also further application. Transitionmetal electrocatalysts, as one of the alternatives to noble-metal catalysts, have abundant reserves and unique d orbital electrons. In particular, transition-metal molybdates undergo dynamic reconstruction at oxidation potentials, and the hydroxyl oxides formed after reconstruction are the main active species for oxygen-related reactions. In this work, we prepared self-supported Fe-doped NiMoO 4 •nH 2 O@NiOOH electrocatalysts by hydrothermal reaction and electrochemical oxidation. Porous NiOOH was generated on the surface of NiMoO 4 •nH 2 O by electrooxidation, and Fe doping was realized in this process. The porous structure of the surface is conducive to the penetration of the electrolyte, which can accelerate the ion transport rate. The doping of Fe was used to modulate the electronic structure and improve the electrocatalytic activity. The overpotential was only 227 mV at 10 mA/cm 2 in the 1 M KOH electrolyte. In addition, the electrocatalyst exhibited high stability at a current density of 20 mA/cm 2 .
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