Urea

About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.

Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell

Abstract: Nickel is an ideal non-noble metal anode catalyst for direct urea fuel cell (DUFC) due to its high activity. However, there exists a large overpotential toward urea electrooxidation. Herein, NiCo/C bimetallic nanoparticles were prepared with various Co contents (0, 10, 20, 30 and 40 wt%) to improve the activity. The best Co ratio was 10% in the aspect of cell performance, with a maximum power density of 1.57 mW cm−2 when 0.33 M urea was used as fuel, O2 as oxidant at 60°C. The effects of temperature and urea concentration on DUFC performance were investigated. Besides, direct urine fuel cell reaches a maximum power density of 0.19 mW cm−2 with an open circuit voltage of 0.38 V at 60°C.

Nanostructured LaNiO3 Perovskite Electrocatalyst for Enhanced Urea Oxidation

Abstract: Urea electrooxidation has attracted considerable interest as an alternative anodic reaction in the electrochemical generation of hydrogen due to both the lower electrochemical potential required to drive the reaction and also the possibility of eliminating a potentially harmful substance from wastewater during hydrogen fuel production. Nickel and nickel-containing oxides have shown activities comparable to those of precious-metal catalysts for the electrooxidation of urea in alkaline conditions. Herein, we investigate the use of nanostructured LaNiO3 perovskite supported on Vulcan carbon XC-72 as an electrocatalyst. This catalyst exhibits an exceptionally high mass activity of ca. 371 mA mgox–1 and specific activity of 2.25 A mg–1 cmox–2 for the electrooxidation of urea in 1 M KOH, demonstrating the potential applications of Ni-based perovskites for direct urea fuel cells and low-energy hydrogen production. While LaNiO3 is shown to be stable at low overpotentials, through in-depth mechanistic studies the ...

Colimitation of phytoplankton growth by nickel and nitrogen

Abstract: Axenic cultures of Thalussiosiru M;eissflogii need nickel when urea is the source of nitrogen for growth, but have no measurable Ni requirement when growing on NH,‘. This result is due to the Ni-containing enzyme, urease. which is necessary for urea catabolism in this diatom. In Ni-deficient cultures, where urea is the sole source of N, urease activity is low and growth rate is reduced. In Ni-replete cultures, urease activity is enhanced and the maximum growth rate achieved. Saturated uptake rates of Ni by urea-grown cells are faster than by NH,+-grown cells and are enhanced under Ni-limiting conditions. Ni-limited T. weiss&‘ogii cells are also N limited, even with high concentrations of urea in the medium, because they have insufficient urease activity to provide adequate N for growth. In these cultures, maximum growth rates are thus obtained by supplying either Ni or NH,+. These results demonstrate colimitation of T. M;eissflogjii growth by Ni and N under laboratory conditions and provide an archetypal example of a trace metal and macronutrient interaction that may be applicable to other nutrients.