Influence of nitrogen doping on the electrocatalytic activity of Ni-incorporated carbon nanofibers toward urea oxidation
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Overall, boosting the formation of the active NiOOH layer distinctly improves the electro catalytic activity of nickel-based materials. Moreover, due to the adsorption capacity, the carbonaceous supports improve the electrocatalytic activities of several function materials including nickel. In this manuscript, nitrogen doping is introduced as an effective strategy to enhance formation of the NiOOH active layer on the surface of nickel nanoparticles decorating carbon nanofibers. Typically, addition of urea to the nickel acetate/poly(vinyl alcohol)/water sol-gel leads to obtain nitrogen-doped and nickel-decorated carbon nanofibers after electrospinning the prepared solution and calcination the nanofiber mats under Ar at 750 °C. The invoked characterizations including XRD, TEM, SEM and XPS affirmed formation of smooth nitrogen-doped carbon nanofibers decorated by crystalline nickel nanoparticles. Nitrogen doping strongly enhanced the formation of NiOOH active layer on the surface of the metallic nanoparticles which distinctly improved the electrocatalytic activity toward urea oxidation. However, the electrochemical measurements indicated that the content of the urea in the initial electrospun solution should be optimized as the results showed that the best nickel surface activation as well as the maximum observed current density can be achieved when the urea content is kept at 5 wt%. Typically, the observed current densities using 1.0 M urea (in 1 M KOH) were 3.15, 29.7, 13.75, 47.55, 14.13 and 9.85 mA/cm2 for the nanofibers obtained from electrospun solutions having 0, 1, 2, 5, 7 and 9 wt% urea, respectively. Moreover, the proposed nitrogen doping strategy leads to perform a distinguish decrease in the onset potential of the urea electrooxidation which reduces the required energy for the electrolysis process.
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