Abstract
Urea oxidation reaction (UOR) has received a high level of recent interest since electrochemical oxidation of urea can remediate harmful nitrogen compounds in wastewater and accomplish hydrogen fuel production simultaneously. Thus, urea is considered to be potential hydrogen energy source that is inherently safe for fuel cell applications. However, the catalytic reaction suffers from slow kinetics due to six electron transfer in UOR. In this work, β phase NiS is successfully prepared through facile hydrothermal reaction, in which diethanolamine (DEA) was added as chelating agent leading to 3D nanoflower morphology. The crystal structure, surface morphology, and chemical bonding of the β−NiS were characterized by X–ray diffraction (XRD), scanning electron microscope (SEM), and X−ray photoelectron spectroscopy (XPS), respectively. The UOR performance of NiS was evaluated by means of linear sweep voltammetry (LSV), Tafel analysis, electrochemical impedance spectroscopy (EIS), chronoamperometry, and chronopotentiometry in 1 M KOH electrolyte containing 0.33 M urea. Compared to the Ni(OH)2 counterpart, NiS exhibits lower onset potential, increased current responses, faster kinetics of urea oxidation, lower charge transfer resistance, and higher urea diffusion coefficient, leading to the enhanced catalytic performance toward UOR. Moreover, the developed NiS catalyst exhibits superior stability and tolerance towards urea electro−oxidation in 10,000 s test.
Highlights
Urea is considered a promising hydrogen storage carrier on account of its outstanding energy density (16.9 MJ L−1 ), which is even higher than that of compressed (5.6 MJ L−1 ) or liquid hydrogen (10.1 MJ L−1 ) [1]
The results indicate the facile transport of urea in NiS catalyst, which is in line with the higher current responses observed from the linear sweep voltammetry (LSV) (Figure 4b)
The nanoflower NiS demonstrates lower of DEA chelating agent, leading to nanoflower morphology that allows abundant electrochemical onset potential, increased current responses, faster kinetics of urea oxidation, lower charge transfer active sites of NiS exposed to urea in the electrolyte
Summary
Urea is considered a promising hydrogen storage carrier on account of its outstanding energy density (16.9 MJ L−1 ), which is even higher than that of compressed (5.6 MJ L−1 ) or liquid hydrogen (10.1 MJ L−1 ) [1]. Urea is considered to be a potential hydrogen source, slow kinetics due to six electron transfer in UOR has been a major restriction. This greatly limits the power performance of DUFCs at room temperature [6]. The enhanced UOR catalytic activity is ascribed to the high conductivity of the catalyst (3.19 × 103 S m−1 at room temperature). The obtained electrode exhibits enhanced UOR performance with the stable catalytic performance over 8 h in the electrolyte containing 1 M NaOH and 0.33 M urea. FOR PEER REVIEW high electrical of β−NiS of 10 renders good electron transport pathways in the electrode. 3Thus, the enhanced UOR performance of nanoflower β−NiS is achieved
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