Direct urea fuel cells (DUFCs) are proven as environmentally benign energy generation devices and hold superior potential to meet the booming energy demand with the use of waste‐water containing urea/urine as a fuel. Despite the high theoretical gravimetric energy density, DUFC's experimentally projected value is substantially lower, due to the sluggish electrokinetics of urea oxidation reaction (UOR). The key to realizing high performance, durable DUFCs is reliant upon the advancement of electrode materials encompassing electrochemically active and stable UOR nanocatalysts. Furthermore, an in‐depth electromechanistic understanding of UOR and the use of human urine as a fuel are of great importance to the scale‐up objectives of DUFCs. Herein, the comprehensive portrayal of these salient aspects along with the scientific breakthroughs of UOR catalysts applicable to DUFCs is essential for the practical augmentation of DUFCs. Accordingly, a comprehensive portrayal of background overview, operating principles, UOR mechanism, and recent advances made on UOR catalysts, with the fundamental aspects of electrochemistry and fuel cells, as well as the critical challenges of existing UOR catalysts is presented. Also, the research and scale‐up challenges of UOR catalysts‐equipped DUFCs are outlined with futuristic perspectives to enhance their viability in sustainable energy generation.
Binder-less, self-standing, disposable, and costeffective sensing probes are crucial for the development of nextgeneration nonenzymatic urea sensors (NEUSs). In the present study, three-dimensional (3D) coral-like NiFe-based layered double hydroxide (NF-LDH) microstructures were grown over the naturally inherited porous microchannels of nitrogen-doped carbonized wood (NCW). The microstructural details and chemical composition of the fabricated electrodes were examined by microscopic and spectral methods. The formation of novel 3D coral-like microarchitectures with uniformly enveloped nanoflakes was evidenced from the scanning electron microscopy measurements. Interestingly, NF-LDH exhibited a voltammetric response for urea due to the unique 3D architecture and synergistic influence between catalytically active Ni 3+ sites and doped Fe 3+ centers. Here, NCW serves as a catalyst-docking platform and electronconducting medium. Such direct anchoring of catalytically active structures on conductive scaffolds eliminates the electron transfer resistance provoked by stereotypical insulating binders. Furthermore, the growth of the NF-LDH catalyst on NCW was varied with respect to the mole ratio of Ni 3+ and Fe 3+ . Among the different mole ratios, the NF-LDH catalyst modified with Ni/Fe-0.75:0.25 showed the best sensing performance toward urea with a sensitivity of 53 μA mM −1 cm −2 , a wide linear range from 0.5 to 8 mM, and a limit of detection of 0.114 mM (S/N = 3) in addition to exceptional stability and reproducibility.
The fabrication of proficient anodes for urea oxidation
reaction
(UOR) with the inherent traits including competent catalytic activity,
enhanced electronic conductivity, sound durability, and low cost are
the inevitable criteria for the advancement and practical implementation
of green energy conversion devices, such as direct urea/urine fuel
cells. Herein we are reporting the decoration of biomass-derived nitrogen-doped
carbon fiber aerogel (NCFA) with three-dimensional (3D) flower-like
NiCo2S4 (NCS) architectures fabricated via the
one-step hydrothermal method and exploited as a binder-free anode
for UOR. With concrete operational stability, the constructed NCS@NCFA
(1:2) anode delivered an excellent current density of 166 mA cm–2 and 79 mA cm–2 in urea and human
urine, respectively. This remarkable UOR activity of the NCS@NCFA
(1:2) electrode is chiefly ascribed to the unique 3D open morphological
feature, which triggers the maximum adsorption and momentous electrooxidation
of urea. Moreover, the densely interconnected graphitized fibers not
only inhabit the catalytic active structures but also facilitate the
elevated anolyte transfer characteristics by their conductive open
framework.
The rational design and construction of highly active, inexpensive, environmentally benign, and easily disposable urea-detecting probes is an appealing idea for the dynamic advancement and extensive practical application of enzyme-free...
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