(NiFeCu)₃S₂@(NiFeCu)O Core-Shelled Heterostructure Having Dual-Anion Vacancies for Stable, High-Efficiency Urea Oxidation Reaction

Abstract

In response to the need of stable high-efficiency electrocatalyst for urea oxidation reaction (UOR), a defect-rich (NiFeCu)3S2@(NiFeCu)O core-shelled heterostructure is presented. The core-shelled heterostructure consists of sulfur vacancy (Vs) in the crystalline core and oxygen vacancy (Vo) in the amorphous shell. The Vs enhances the charge transfer, and the Vo contributes to the mass transfer. The unique heterostructure requires only 1.37 and 1.38 V versus reversible hydrogen electrode at 100 and 180 mA cm–2, respectively, and exhibits outstanding cycle stability without potential decay after 12,000 cycles. The structural stability is also contributed by the in situ formation of Cu2O and CuO which was investigated via in situ Raman. The defect-rich (NiFeCu)3S2@(NiFeCu)O core-shelled heterostructure also shows excellent bifunctionality with an electrolyzer cell voltage of 1.47 V at 10 mA cm–2 and 180 h stability. This novel electrocatalyst is highly promising for hydrogen production and also wastewater treatment from urea decomposition.

Electrocatalytic urea oxidation: advances in mechanistic insights, nanocatalyst design, and applications

“…Creating oxygen defects can contribute to reducing the electron transport resistance, and promoting electron/mass transfer, thus improving the electrocatalytic reaction kinetics. 90 For example, the Co 3 O 4 nanowires with oxygen defects displayed a lower electron transport resistance of 0.0615 U than that of the initial Co 3 O 4 (0.3338 U), which plays a dominant role in enhancing catalytic performance for the UOR. 14 Additionally, effective active sites can be increased by introducing oxygen vacancies in metal oxides.…”

Modulation Strategies for the Preparation of High‐Performance Catalysts for Urea Oxidation Reaction and Their Applications

“…Of course, considering the preparation of catalysts with high UOR activity and low OER activity can also effectively prevent the competition of OER at high potentials, but the current research reports have not yet developed in this area. Jyh-Ming Ting et al reported that the presence of O vacancies can promote mass transfer, [174] tivity by jointly stabilizing important intermediates. [247] We also look forward to more novel ideas for creating dual active sites.…”

“…Jyh‐Ming Ting et al introduced S vacancies and O vacancies into the catalyst, and studied the relationship between vacancies and mass transfer and charge transfer. [ 174 ] The authors fitted the EIS data and found that with increased S vacancies, R ct gradually decreased, indicating that S vacancies can increase carrier concentration and contribute to charge transfer. On the other hand, with the increase of O vacancies, the resistance (R ads ) caused by the reaction intermediates adsorption on the electrode surface decreases, indicating that O vacancies can accelerate mass transfer.…”

“…Of course, considering the preparation of catalysts with high UOR activity and low OER activity can also effectively prevent the competition of OER at high potentials, but the current research reports have not yet developed in this area. Jyh‐Ming Ting et al reported that the presence of O vacancies can promote mass transfer, [ 174 ] so constructing catalysts rich in O vacancies may further reduce OER competition at high current densities. Jung et al compared the potential difference between UOR and OER catalysts with or without Ni doping at the current density of 100 mA cm −2 , and believed that the presence of Ni could improve the selectivity of UOR.…”

Enhancing hydrogen generation through urea electro-oxidation on a bimetallic and dual-anionic NiFeSP/NF nanostructured electrode

“…In addition to the electrochemical results, calculations based on density functional theory (DFT) showed the ease of charge transfer from cationic nuclei to anionic nuclei due to the high synergy between bimetallic oxy/phosphide, which can provide a potential of 1.42 V vs. RHE at a current density of 50 mA cm −2 in an overall urea electro-oxidation system. Sari et al 23 increased charge and mass transfer in a heterogeneous nanostructure (NiFeCu) 3 S 2 @(NiFeCu)O by utilizing two anionic vacancy defects, S and O. This in addition to disposing intermediate species and helping in breakdown of urea molecules provided a potential of 1.47 V vs. RHE at a density of 10 mA cm −2 with a long term stability of 180 h for the overall urea electro-oxidation.…”