High-Valent Ni Species Induced by Inactive MoO₂ for Efficient Urea Oxidation Reaction

Abstract

The microenvironment tuning of Ni species, a promising non-precious catalyst, is significant in the energy and environmentally relevant urea electro-oxidation reaction (UOR). Herein, we found that the high-valent Ni species induced by the inactive MoO2 in mixed nanocrystals of NiO/MoO2 were effective for urea oxidation. The redox interaction of MoO2 and NiO revealed by the spectroscopic analysis well supported the formation of high-valent Ni species and the changes in the surface chemical state. High catalytic activity and stability for urea oxidation were observed by a series of electrochemical measures compared to the counterpart catalysts of MoO2 and NiO. The optimal NiO/MoO2 hybrid catalyst showed a UOR activity of 73.1 mA cm–2 at 1.50 V, which was about 12-fold that of the NiO catalyst. In addition, largely improved catalytic kinetics and catalytic stability for UOR were also demonstrated. Because of the inactive activity of MoO2 and the low performance of NiO, the largely improved preference can be affirmatively attributed to the efficient catalytic synergism of NiO/MoO2 in the mixed nanocrystals. The current finding clarifies the catalytic promotion effect of the inactive Mo species on Ni-based catalysts for urea oxidation, which would be instructive for Ni/Mo-relevant catalyst development.

Modulating the Electronic Structure of Ni/NiO Nanocomposite with High‐Valence Mo Doping for Energy‐Saving Hydrogen Production via Boosting Urea Oxidation Kinetics

“…[ 27 ] This suggests that the oxidized state of Ni 3+ serves as the active site, participating in the urea oxidation process, which is consistent with the proposed indirect electrochemical–chemical mechanism. [ 53 ] As displayed in Figure 5c, the histogram of the driving overpotential attains various current densities at 10, 50, 100, and 200 mA cm −2 . Based on an intuitive observation, the overpotential required for UOR is smaller than that needed for OER at all current densities.…”

Phase Segregation in Cu0.5Ni0.5 Alloy Boosting Urea‐Assisted Hydrogen Production in Alkaline Media

“…As a result, such alloys often exhibit poor UOR catalytic activity. [ 42 ] Considering the above issues, we prefer constructing a Ni‐based alloy electrocatalyst in a metastable state. The as‐synthesized electrocatalyst will be able to become more stable during HER due to the applied reduction potential and to get unstable or even undergo partial phase segregation during UOR due to the applied oxidation potential, which can result in the rapid formation of a large amount of NiOOH active species.…”

“…As a result, such alloys often exhibit poor UOR catalytic activity. [42] Considering the above issues, we prefer constructing a Ni-based Coupling urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is promising for energy-efficient hydrogen production. However, developing cheap and highly active bifunctional electrocatalysts for overall urea electrolysis remains challenging.…”

Beneficial Synergistic Intermetallic Effect in ZnCo2O4 for Enhancing the Limonene Oxidation Catalysis

“…Transitional metal oxides are promising candidate catalysts in various catalytic reactions due to their storage abundance, component variety, variable oxidation states, high stability, and adjustable geometric/electronic structure. − As one of the most studied transitional metal oxides, spinel Co 3 O 4 stands out owing to its good redox capability, facile oxygen mobility, and relatively weak Co–O bond strength. − Partially substituting Co in the Co 3 O 4 lattice with a second metal is a common strategy to achieve the performance enhancement via synergistic catalysis when single Co 3 O 4 cannot meet all the requirements. Especially, well-defined bimetallic ACo 2 O 4 spinels (A = Ni, Cu, Mg, etc.…”