Maximized Schottky Effect: The Ultrafine V₂O₃/Ni Heterojunctions Repeatedly Arranging on Monolayer Nanosheets for Efficient and Stable Water‐to‐Hydrogen Conversion

Abstract

electrochemical water splitting is an advocated way to meet the requirement for future fuel applications. [3] But its shortcomings, such as the considerable overpotential and sluggish anodic oxygen evolution reaction (OER) kinetics, still remain. To give rise to energy-saving H 2 production, using more readily oxidized molecules to replace the formidable OER may be a feasible solution to overcome this limitation. [4,5] Following this strategy, several molecules such as glycerol, [6] urea, [2,7] hydrazine, [8] have been recently developed. Using urea electrolysis instead of water splitting can not only offer a prospect of wastewater purification, but also change the thermodynamic potential from 1.23 to just 0.37 V. [5] However, the complex 6e − transfer process in the half-reaction causes the urea oxidation reaction (UOR) to suffer from inherent kinetic retardation. [9] Therefore, to promote the anodic urea oxidation process, highly efficient catalysts are actually required to boost the intrinsically sluggish UOR kinetics. Vanadium (V)-based electrocatalysts (such as VS 2 , [10,11] VN, [12-15] VP, [16] and V 2 O 3 [17-19]) are conducive for its application in catalysis fields, because of its more valence state diversity. Catalytic activities of the vanadium-based electrocatalyst are closely related with its electronic structure. [16] Thus, it is widely accepted that adjusting the behavior of electrons and phonons more precisely is the key to optimizing the catalyst performance. [16] Schottky heterojunction, formed at the semiconductor metal interface, could generate the built-in electric field and enhance the charge transportation as well as separation. [20-22] To balance the differences of Fermi levels between semiconductor and metal sides, charge flow would spontaneously transfer across the interface, leading to form the stable local nucleophilic/electro region. [20] Hence, preparing ingenious V-based Schottky catalyst is the proof-of-concept way to simultaneously promote the hydrogen evolution reaction (HER) and UOR activities. For example, Fu et al. reported that construction of heterointerfaces of Ni 3 NVN and Ni 2 PVP 2 can improve the HER and OER activities significantly. [16] However, most of the reported works only focus on the construction The Mott-Schottky heterojunction formed at the interface of ultrafine metallic Ni and semiconducting V 2 O 3 nanoparticles is constructed, and the heterojunctions are "knitted" into the tulle-like monolayer nanosheets on nickel foam (NF). The greatly reduced particle sizes of both Ni and V 2 O 3 on the Mott-Schottky heterojunction highly enhance the number of Schottky heterojunctions per unit area of the materials. Moreover, arranging the heterojunctions into the monolayer nanosheets makes the heterojunctions repeat and expose to the electrolyte sufficiently. The Schottky heterojunctions are like countless selfpowered charge transfer workstations embedded in the tulle-like monolayer nanosheets, promoting maximum of the materials to participate into the electron trans...

Oxygen Vacancies and Interface Engineering on Amorphous/Crystalline CrOx‐Ni3N Heterostructures toward High‐Durability and Kinetically Accelerated Water Splitting

“…The NNi bond occurs a negative shift of 0.2 eV, indicating the weak Cr−N interaction in the CrO x -Ni 3 N. The O 1s spectrum of CrO x (Figure 3e) can be fitted into three peaks, which belong to the MetalO bond in CrO x (Cr−O, 530.2 eV), oxygen vacancies (O v , 531.6 eV), and the absorbed O (533.7 eV), respectively. [22] The MetalO bond in CrO In addition, The O v content in CrO x -Ni 3 N is calculated to be 44.0%, a bit higher than that of CrO x (42.0%). The electron paramagnetic resonance (EPR) was further carried out to examine the O v content in the CrO x -Ni 3 N samples (Figure 3f).…”

Strategies for designing more efficient electrocatalysts towards the urea oxidation reaction

“…Such a novel strategy for designing advanced UOR catalysts has been adopted by other researchers. 162–164 Wang's group prepared a CoMn/CoMn 2 O 4 heterojunction catalyst on Ni foam via in situ electrochemical treatment of CoMn 2 O 4 . 63 The as-fabricated CoMn/CoMn 2 O 4 heterojunction induced electron transfer from CoMn to CoMn 2 O 4 spontaneously, resulting in the generation of electrophilic (CoMn) and nucleophilic (CoMn 2 O 4 ) regions, respectively.…”

Vanadium-Doping and Interface Engineering for Synergistically Enhanced Electrochemical Overall Water Splitting and Urea Electrolysis

“…As one of these molecules, the thermodynamic potential of the urea electro-oxidation reaction (UOR) is 0.37 V (CO­(NH 2 ) 2 + 6OH – → N 2 + CO 2 + 5H 2 O + 6e – ), much less than 1.23 V of OER. , Therefore, UOR is a thermodynamic favorable process. More importantly, urea electrolysis not only provides an approach for energy-saving hydrogen production but also offers a potential solution for purifying urine-containing wastewater. , …”

“…More importantly, urea electrolysis not only provides an approach for energy-saving hydrogen production but also offers a potential solution for purifying urine-containing wastewater. 52,59 Herein, we successfully synthesized V-doped bimetallic nitrides, namely, V-FeNi 3 N/Ni 3 N heterostructure, via a hydrothermal−nitridation protocol for electrocatalytic hydrogen production via water and urea electrolysis. The obtained product exhibited superior activities and long-term durability toward HER and OER.…”