Constructing Hierarchical Wire-on-Sheet Nanoarrays in Phase-Regulated Cerium-Doped Nickel Hydroxide for Promoted Urea Electro-oxidation

Abstract

Electrocatalytic urea oxidation reaction (UOR) is a key half-reaction in assembling the direct urea fuel cells (DUFCs) to generate electricity, or constructing a urea electrolyzer to convert electricity to clean hydrogen energy. However, the sluggish six-electron transfer process of UOR significantly limits the reaction kinetics, thereby restricting the development of the aforementioned energy conversion techniques. Herein, we highlighted a high-performance UOR catalyst based on the hierarchical wire-on-sheet Ni(OH) 2 nanoarrays with optimal cerium doping and controllable phase regulation. The local Ni 3+ species and the unique wire-on-sheet morphology of the α-Ni(OH) 2 nanoarray catalyst guarantee fast formation of high-valence species for UOR catalysis, and the Ce doping further optimizes the electronic structure, therefore resulting in greatly enhanced UOR behavior synergistically. This work may provide a universal structural optimization strategy for designing advanced UOR electrocatalysts.

Co(OH)2 Nanosheets Array Doped by Cu2+ Ions with Optimal Electronic Structure for Urea‐Assisted Electrolytic Hydrogen Generation

“…The UOR catalytic performances of Cu 6.2% −Co(OH) 2 was also evaluated in other urea concentrations of 0.1 and 0.5 M. The Cu 6.2% −Co(OH) 2 electrode drave 100 mA cm −2 at a potential of 1.442 V in 1 M KOH with 0.1 M urea, whereas 1.392 V in 1 M KOH with 0.5 M urea (Figure S5). Obviously, the best UOR performance of Cu 6.2% −Co(OH) 2 can be obtained in 1.0 M KOH with 0.33 M urea, which were consistent with the result on Ce‐doped α‐Ni(OH) 2 [1] . The increased UOR catalytic activity of the catalyst with increasing the urea concentration from 0.1 to 0.33 M can be attributed to the diffusion‐controlled reaction mechanism; whereas the decreased UOR catalytic activity with further increasing the urea concentration to 0.5 M was possibly due to the fact that the covered active sites on the catalyst's surface by excessive urea and its oxidation intermediates led to the local deficiency of OH − ions, thus decreasing the oxidation rate of urea [40] …”

“…Hydrogen has been considered as one of the most captivating substitute energy carriers for conventional fuels due to its high energy density and eco‐friendly characteristics [1,2] . Water electrolysis is a sustainable and promising route for commercial hydrogen production [3] .…”

Preferential Microstructure Design of Two‐Dimensional Electrocatalysts for Boosted Oxygen Evolution Reaction

“…Hence, the local Ni 3+ ions can be easily stabilized via intercalating the anions with the opposite charges. During the fabrication of the hierarchical α‐Ni(OH) 2 wire‐on‐sheet nanoarrays, urea is a key reactant which could form NH 3 in situ and subsequently lead to the partial coordination etching of the as‐formed α‐Ni(OH) 2 nanosheets, therefore finally resulting in the 1D‐2D‐3D hierarchical nanoarrays . Detailed structural analyses indicate that the wire‐on‐sheet nanostructure is single‐crystalline with abundant surface nanowires on the ultrathin 2D layer.…”

“…Detailed structural analyses indicate that the wire‐on‐sheet nanostructure is single‐crystalline with abundant surface nanowires on the ultrathin 2D layer. Besides, by modifying the metal precursors, controllable elemental doping can be readily achieved, and the as‐obtained Cu, Fe and Ce doped catalysts exhibit remarkable performance on electro‐oxidation reactions such as OER and the urea oxidation reaction . Similarly, 2D nanosheets grown on 1D nanoarrays were also reported, for which the 1D charge transport pathway and the highly exposed surface sites could effectively boost the OER process .…”

Defective NiFe2O4 Nanoparticles for Efficient Urea Electro‐oxidation

“…Amongt he reported methods, electrochemicalu rea oxidation has attracted much attentiona sa ne ffective and controllable method. [6] Currently,many kinds of catalysts have been developedb yr esearchers, such as oxidesa nd hydroxides, [7][8][9][10][11][12][13][14][15][16][17] non-oxides, [18,19] metals and alloys. [4,20] In particular,N i-based catalysts, as non-precious ande arth-abundant materials, have been widely studied and made great progress.…”