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• A composite of g-C 3 N 4 and Vulcan Carbon (VC) is synthesized. • The composite materials were used as a support of Ni "Ni(OH) 2 " catalyst. • Ni/(g-C 3 N 4 (1)/VC(2)) has high roughness and low charge transfer resistivity. • Ni/(g-C 3 N 4 (1)/VC(2)) demonstrated superior urea oxidation activity. • The composite materials demonstrated superior stability during urea oxidation. A g-C 3 N 4 /VC composite material comprising of graphitic carbon nitride (g-C 3 N 4) and Vulcan carbon (VC) with different ratios, i.e., 2:1, 1:1, and 1:2 were prepared through hydrothermal method without using any additives. These composite materials were further utilized as a support for Ni(OH) 2 nanoparticles. These materials formed new type of Ni/(g-C 3 N 4 /VC) composite materials. The SEM images show the sheet-like structure of the graphitic carbon nitride. Although Ni nanoparticles' electrochemical activity over the surface for graphitic carbon nitride was slightly more compared to Ni supported on the Vulcan carbon, the Ni supported on the different composite supports demonstrated an outstanding activity compared with that over the single supports. Among the different composite ratios of the graphitic carbon nitride to the Vulcan carbon, the one with high Vulcan carbon, i.e., 2:1, exhibited the best performance that is nine-times the current density in comparison to that of Ni over Vulcan carbon at 0.5 V using 2 M urea in 1 M potassium hydroxide. The stability for the prepared Ni over the composite support was high, where the degradation in the current density for more than 2 hours was negligible. [ABSTRACT FROM AUTHOR]

One of the main challenges facing the development of urea fuel cells is the low catalytic activity of the anode. Ni decorated carbon nano-fiber is a promising anode catalyst in urea fuel cells. In this study, we have investigated the effect of Cd doping of Ni decorated carbon nano-fiber on catalytic activity for urea oxidation. The catalyst was prepared by heat treatment of electrospun nano-fibers containing different percentages of Ni and Cd acetates in poly(vinyl alcohol) under an inert atmosphere at 850 °C. The initial percentages of the Cd acetate to Ni acetate in the polymer solution was set at 5, 10, 30, 50 and 70 wt.%. The introduction of Cd significantly improved the electro-catalytic activity for urea oxidation. The sample that was prepared with initial 50 wt.% Cd acetate showed the best activity for urea oxidation activity using different urea concentrations, 0.33 M–3 M. The introduction of Cd improved both the quality and the number of active sites for the urea oxidation as seen from the shift of the anodic peak potential and anodic peak current density, respectively. [ABSTRACT FROM AUTHOR]

In this work, Cu 2 O nanoparticles were successfully prepared onto the surface of two-dimensional graphitic carbon nitride (g-C 3 N 4) by using a simple solution chemistry approach. An environment-friendly reducing agent, glucose, was used for the synthesis of Cu 2 O NPs onto the surface of g-C 3 N 4 without using any surfactant or additives. The surface composition, crystalline structure, morphology, as well as other properties have been investigated using XPS, XRD, SEM, FTIR, FESEM, EDS, etc. The electrochemical measurements of the prepared materials demonstrated that Cu 2 O exhibited a weak oxidation activity towards urea, while g-C 3 N 4 has no activity towards urea oxidation. The Cu 2 O supported on the surface of g-C 3 N 4 (Cu 2 O-g-C 3 N 4) demonstrated a significant activity towards urea oxidation that reached two times that of the unsupported one. The significant increase in the performance was related to the synergetic effect between the Cu 2 O and g-C 3 N 4 support. The prepared composite materials demonstrated high stability towards urea oxidation as confirmed from the stable current discharge for around 3 h without any noticeable degradation performance. • Cu 2 O nanoparticles with graphitic carbon nitride was synthesized. • The composite is utilized as efficient electrocatalyst for the oxidation of Urea. • The Cu 2 O-g-C 3 N 4 composite showed high catalytic activity. [ABSTRACT FROM AUTHOR]

Nafion membrane is a commercial type of electrolyte membrane that is widely used in low-temperature fuel cells. Nafion membrane is expensive and allows fuel to crossover from anode to cathode. Therefore, it decreases fuel utilization and results in mixed potential at the cathode. Modifying the Nafion membrane and/or replacing it with non-Nafion-based materials has shown promising results in solving these problems. Graphene is a two-dimensional material with exceptional properties that positively affect the performance of several energy conversion/storage devices. With its large surface functional groups, graphene oxide exhibits considerable ionic conductivity with low fuel crossover. This paper reviews and discusses the recent progress in utilizing graphene or its derivatives as a blend with Nafion and non-Nafion based membranes as well as a standalone membrane in low-temperature fuel cells. Graphene or its derivatives possess a high potential as a standalone membrane or a composite membrane in the various low temperature fuel cells applications in terms of high ionic conductivity at low humidity and relevant high temperature, high thermal, mechanical, and chemical stabilities. This work summarizes the recent progress in utilizing graphene and its derivatives (graphene oxide and other doped graphene) in different types of fuel cells, whether as a standalone or as a modifier of the Nafion and non-Nafion based membranes. The review covers the usage of graphene and its derivatives in PEMFCs, DMFCs, anion exchange DMFCs, and MFCs. Furthermore, it elaborates on the science and the engineering aspects of utilizing graphene and its derivatives in different fuel cells. This work demonstrates the importance of the graphene and its derivatives in improving the performance of low temperature fuel cells. • GO promoted high water retention of the fuel cell's membrane. • GO has excellent mechanical, chemical, and thermal stability, and thus its polymer blends gain these properties. • The blends of the electrolyte polymer with GO decreases the fuel crossover. • Applying of graphene as a standalone membrane in PEMFC was summarized. • The performance of Nafion-based and non Nafion-based membranes modified with graphene in fuel cells was summarized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co dendrites of 20 nm wall thickness was prepared. • The surface area of the Co dendrites is three times that of Co nanoparticles. • An onset potential of 0 V compared to 0.35 V in case of Ni is reported. • A complete passive DUFC is successfully operated using the Co dendrites anode. • A power density of 21 mWcm-2 is obtained at 20 °C. Mesoporous Co dendrites prepared by electroplating have a surface area of 145 m2g−1, which is three times that of Co nanoparticles. The Co dendrites demonstrate superior urea oxidation activity compared to Ni or Co nanoparticles prepared using chemical reduction. The onset potential with Co dendrites is around 0 V "vs. Ag/AgCl" using 2 M urea, that is remarkably lower than 0.35 V "vs. Ag/AgCl" for Ni catalyst at optimum urea concentration of 0.5 M. The current produced in case of the Co dendrites using 2 M urea at 0.5 V "vs. Ag/AgCl" was six times that obtained using Ni. The in-situ measurements using Co dendrites on the Ni foam as anode and Prussian blue as cathode catalyst demonstrated a 21 mWcm−2 at 20 °C. These are the first reported results for a complete Ni-free nonprecious anode and cathode catalysts under real fuel cell operation with high performance comparable to those obtained using precious catalyst under same conditions. [ABSTRACT FROM AUTHOR]

Abstract Direct urea fuel cell (DUFC) is an attractive and inexpensive method for the simultaneous wastewater treatment (urine and urea-contaminated water) and electricity generation. Many efforts have been made to increase the catalytic activity of Ni-based DUFC anodic catalyst toward urea oxidation, which is considered to be the best non-precious catalyst in alkaline media so far. Alloying Ni with other metals and/or non-metals, and increasing its surface area demonstrated a power of up to 26.9 mW cm−2 at room temperature, which is comparable to that obtained in direct alcoholic fuel cells using high loading of precious catalyst. However, this is still viewed as low-performance. This review presents a comprehensive picture of the mechanism of urea oxidation on Ni-based catalysts, the poisoning effect of catalysts and its possible remedies, as well as the different approaches in preparing highly active catalysts. We also analyze the performance and associated issues of DUFC using newly applied strategies to increase its open-circuit voltage and power output via alternative oxidants and re-designed chemical conditions in the cell. [ABSTRACT FROM AUTHOR]

Metal chalcogenides have received significant attention as electro-catalysts in different applications, due to their superior electrical conductivity and good thermal and mechanical stabilities. In this work, the optimum monocrystalline Ni-P and Ni-C, C (Se, S, O) nanosheet (NS), prepared on nickel foam as standalone anodes for urea fuel cells was introduced. The activity was investigated ex-situ and in-situ the cell. The results demonstrated that the non-oxide metal forms, i.e., Ni–P, Ni–S, and Ni–Se, have superior oxidation activity than the Ni layered double hydroxide (Ni-LDH) and Ni–O. In addition, Ni–Se showed the most superior urea oxidation activity among all prepared catalysts. Although the onset potential of all the samples was around 0.35 V vs Ag/AgCl, a steady current of 195 mAcm−2 was recorded after 120 min using Ni–Se, which is two times higher than that of Ni–S, five times higher than Ni–O, and ten times higher than Ni-LDH. The superior activity of the Ni–Se was related to its unique crystalline structure and the high porous morphology. The performance of Ni–Se electrode under actual direct urea fuel cell (DUFC) operation using a nonprecious a Prussian blue cathode revealed 33 mWcm−2 power, which is, one of the highest power outputs in DUFCs equipped with Ni-based anodes at room temperature, as far as the authors know. • Optimum monocrystalline Ni-M, M (Se, S, P, O) nanosheet was prepared on Ni foam. • The oxidation activity towards urea examined ex-situ and in-situ the fuel cell. • Ni–Se demonstrated superior urea oxidation activity. • Using Ni–Se and Prussian blue electrodes, a power output of 33 mWcm−2 is obtained. [ABSTRACT FROM AUTHOR]

The harmful effect of carbon pollution leads to depletion of the ozone layer, which is one of the main challenges confronting the world. Although progress is made in developing different carbon dioxide (CO 2) capturing methods, these methods are still expensive and face several technical challenges. Fuel cells (FCs) are efficient energy converting devices that produce energy via an electrochemical process. Recently varying kinds of fuel cells are considered as an effective method for CO 2 capturing and/or conversion. Among the different types of fuel cells, solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), and microbial fuel cells (MFCs) demonstrated promising results in this regard. High-temperature fuel cells such as SOFCs and MCFCs are effectively used for CO 2 capturing through their electrolyte and have shown promising results in combination with power plants or industrial effluents. An algae-based microbial fuel cell is an electrochemical device used to capture and convert carbon dioxide through the photosynthesis process using algae strains to organic matters and simultaneously power generation. This review present a brief background about carbon capture and storage techniques and the technological advancement related to carbon dioxide captured by different fuel cells, including molten carbonate fuel cells, solid oxide fuel cells, and algae-based fuel cells. Unlabelled Image • Carbon capture and storage technologies are discussed. • The application of Fuel cell in CO 2 capture is evaluated. • Challenges associated with CO 2 capture using fuel cell is discussed. • Prospects of fuel cells in CO 2 capture is discussed. [ABSTRACT FROM AUTHOR]