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• A highly porous Ni-based electrocatalyst was synthesized by a sol–gel method with bubbling of gel mixture. • The Ni-based catalyst exhibited a high oxidation activity of 570 mA mg−1. • A urea fuel cell with the Ni-based anode catalyst exhibited a maximum power density of 36.4 at 70 °C. • The urea fuel cell showed a stable voltage over 3 days. A highly electroactive Ni-based catalyst for urea oxidation is prepared by a sol–gel method with bubbling of gel mixture. It is observed that the conditions for the gel formation strongly affect the morphology and electrochemical properties of the catalyst materials. As synthesized Ni-catalysts are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The Ni-based catalyst prepared at optimum conditions in the scope of this study exhibits the urea oxidation activity of 570 mA mg−1 (at 0.54 V). In a single urea/hydrogen peroxide fuel cell test, the Ni-catalyst provides maximum power densities of 19.6 and 36.4 mW cm−2 at 30 and 70 °C, respectively. Additionally, the cell catalyst shows a stable voltage for 3 days. Thus, this work suggests that a novel Ni-based catalyst derived from a facile method can be used for urea oxidation and as an efficient anode material for urea fuel cells. [ABSTRACT FROM AUTHOR]

Ni-based catalysts are considered as an efficient anode material for urea fuel cells due to the low cost and high activity in alkaline media. Herein, we demonstrate that Ni-Co bimetallic hydroxide particles with highly porous nanostructures can be synthesized using mesoporous silica nanoparticles as templates. The replicated nanostructures of the Ni-Co hydroxide samples from the mesoporous silica templates are observed. The porous Ni 0.8 Co 0.2 (OH) 2 particles exhibited considerably enhanced electro-catalytic activity for urea oxidation reaction by providing a high surface area and fast mass transport for urea oxidation reaction. It is also found that the Co-doping at 20% significantly reduce the overpotential and increase the peak current of urea oxidation reaction. A direct urea/H 2 O 2 fuel cell with the porous Ni 0.8 Co 0.2 (OH) 2 as anode material shows an excellent performance with maximum power densities of 11.2 and 25.6 mW cm−2 at 20 °C and 70 °C with 0.5 M urea in 5 M KOH, respectively. Thus, this work suggests that the highly porous Ni 0.8 Co 0. 2 (OH) 2 -derived from the mesoporous silica templates can be used for urea oxidation and as an efficient anode material for urea-based fuel cells. Image 1 • Highly porous nanostructured Ni-Co hydroxide was synthesized using silica as template. • The Ni-Co hydroxide exhibited a mesoporous structure with a high specific surface area. • The Ni-Co hydroxide featured excellent electro-catalytic activity for urea oxidation. • A urea fuel cell with Ni-Co hydroxide exhibited a maximum power density of 25.6 mW cm−2 at 70 °C. [ABSTRACT FROM AUTHOR]

Graphene aerogel‐supported manganese ferrite (MnxFe3−xO4/GAs) and reduced‐graphene oxide/manganese ferrite composite (MnFe2O4/rGO) were synthesized and studied as cathode catalysts for oxygen reduction reactions in urea/O2 fuel cells. MnFe2O4/GAs exhibited a 3D framework with a continuous macroporous structure. Among the investigated Fe/Mn ratios, the more positive oxygen reduction onset potential was observed with Fe/Mn=2/1. The half‐wave potential of MnFe2O4/GAs was considerably more positive than that of MnFe2O4/rGO and comparable with that of Pt/C, while the stability of MnFe2O4/GAs significantly higher than that of Pt/C. The best urea/O2 fuel cell performance was also observed with the MnFe2O4/GAs. The MnFe2O4/GAs exhibited an OCV of 0.713 V and a maximum power density of 1.7 mW cm−2 at 60 °C. Thus, this work shows that 3D structured graphene aerogel‐supported MnFe2O4 catalysts can be used as an efficient cathode material for alkaline fuel cells. [ABSTRACT FROM AUTHOR]

A highly porous free-standing NiCr-bimetallic catalyst is synthesized by electrospinning and carbonization and is applied as an anode in a direct urea/H 2 O 2 fuel cell for electro-oxidation of urea. It is observed that the morphology of the calcined NiCr catalyst, which has a higher specific surface area, is identical to that of the electrospun NiCr catalyst fiber. Cr-doping at 40% (Cr/Ni) significantly increases the oxidation peak current of the urea oxidation reaction. The addition of carbon nanotubes also considerably enhances the catalytic activity. A direct urea/H 2 O 2 fuel cell, which utilizes the synthesized catalyst (NiCr-CNT@C) as a free-standing anode, exhibits excellent performance with a maximum power density of 48.1 mW cm−2 and an open-circuit voltage of 0.92 V at 80 °C. Thus, the highly porous free-standing NiCr-CNT@C catalyst mat can be employed as an efficient anode material for urea oxidation in urea fuel cells. Image 1 • A freestanding NiCr catalyst mat was synthesized by electrospinning technique. • NiCr bimetal nanoparticles were uniformly embedded in the carbon nanofibers. • The NiCr catalyst featured excellent electro-catalytic activity for urea oxidation. • A urea fuel cell with NiCr catalyst exhibited a power density of 48.1 mW cm−2. [ABSTRACT FROM AUTHOR]