Abstract
This work demonstrates the chemical synthesis of two-dimensional nanoflakes of mesoporous nickel/nickel (II) hydroxide (Ni/Ni(OH)2-NFs) using double templates of surfactant self-assembled thin-film and foam of hydrogen bubbles produced by sodium borohydride reducing agent. Physicochemical characterizations show the formation of amorphous mesoporous 2D nanoflakes with a Ni/Ni(OH)2 structure and a high specific surface area (165 m2/g). Electrochemical studies show that the electrocatalytic activity of Ni/Ni(OH)2 nanoflakes towards methanol oxidation in alkaline solution is significantly enhanced in comparison with that of parent bare-Ni(OH)2 deposited from surfactant-free solution. Cyclic voltammetry shows that the methanol oxidation mass activity of Ni/Ni(OH)2-NFs reaches 545 A/cm2 gcat at 0.6 V vs. Ag/AgCl, which is more than five times higher than that of bare-Ni(OH)2. Moreover, Ni/Ni(OH)2-NFs reveal less charge transfer resistance (10.4 Ω), stable oxidation current density (625 A/cm2 gcat at 0.7 V vs. Ag/AgCl), and resistance to the adsorption of reaction intermediates and products during three hours of constant-potential methanol oxidation electrolysis in alkaline solution. The high-performance electrocatalytic activity of Ni/Ni(OH)2 nanoflakes is mainly derived from efficient charge transfer due to the high specific surface area of the 2D mesoporous architecture of the nanoflakes, as well as the mass transport of methanol to Ni2+/Ni3+ active sites throughout the catalyst layer.
Highlights
Introduction published maps and institutional affilMethanol is regarded as an attractive fuel to feed direct methanol fuel cells (DMFCs) because of the advantages of high energy density, reduced CO2 emission, low operating temperature, and ease of storage and transport [1–3]
Nickel ions confined within the interstitial aqueous domain of the surfactant template were chemically precipitated by NaBH4 to instantaneously produce hydrogen gas, which exfoliated and fragmented the confined deposited catalyst layers in the form of nanoflakes
This work investigated a novel foam synthesis approach using Ni/Ni(OH)2 nanoflakes prepared via double templates of surfactant liquid crystal thin film and hydrogen bubbles induced by sodium borohydride reducing agent
Summary
Methanol is regarded as an attractive fuel to feed direct methanol fuel cells (DMFCs) because of the advantages of high energy density, reduced CO2 emission, low operating temperature, and ease of storage and transport [1–3]. The DMFC suffers from several challenges that limit its performance in commercial markets due to the high price of platinum catalyst and the slow kinetics of the methanol oxidation reaction (MOR) as a result of catalyst surface poisoning [1,4–7]. It is necessary to develop low-cost, non-noble, and efficient transition-metal electrocatalysts to improve electrocatalytic activity and durability for MOR [8–10]. Engineering the electrocatalyst architectures, for nickel-based materials at the nanometer scale, shape, facets, and composition, significantly boosts catalytic activity for the oxidation of small organic molecules [4,11,12]. Nickel-based nanostructured electrocatalysts such as Ni/Ni(OH)2 [13], Ni(OH)2 -NiCoO4 [14], and NiO iations
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