الفهرس 
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Abstract
Our globe is changing due to climate change, which also significantly affects food output, disturbs animal habitats, and causes extreme weather events. Carbon dioxide emission from automobiles and industrial plants is considered the main cause behind the climate change because it leads to increase the average climate temperature. Increase the average world temperature results in occurring extreme global disasters including tropical storms, wildfires, protracted droughts, and heat waves. Moreover, according to NASA, increasing carbon dioxide concentration in the air will both harm and benefit crops. For instance, high carbon dioxide levels can improve water-use efficiency in crops and mitigate yield losses due to climate change, but the high levels can also lead to have a big disturbance in nitrogen/carbon balance that results in a reduction in the amount of essential elements like iron, zinc, and protein that crops need to grow.
Fuel cells are promising devices to replace the fossil fuels as sustainable energy devices. However, alcohols-based fuel cells emit carbon dioxide. Therefore, because only water vapor is the discharge gas, hydrogen-based fuel cells are the optimum devices from environmental and renewable points of view; the safety considerations and device handling constrains constrain. The wide application of hydrogen-based fuel cells unfortunately. Therefore, if a proper hydrogen storage material could be exploited, instead of high pressure hydrogen tanks, this will be highly beneficial for wide spreading of hydrogen-based fuel cells.
Ammonium phosphates are promising hydrogen storage material candidate. Beside the low cost and availability, the commercially available compounds contain huge amounts of hydrogen (5.22, 6.82 and 8.05 wt% for mono, di- and tri-ammonium phosphate, respectively). The embedded hydrogen in these compounds could be successfully extracted using Ni-based photo catalysts under visible light radiation. The aim of this work is to development new catalysts to electrochemically extract the hydrogen from ammonium phosphates. Consequently, these electrocatalysts can be exploited as anodes in ammonium phosphate fuel cells. In this regard, different and effective Ni-based nanostructures are introduced as effective electrocatalysts for ammonium phosphate compounds in this study.
The electro-oxidation of tri(ammonium) phosphate utilizing carbon nanotubes coated with nickel was examined in the current study. The catalyst in use was synthesized using a straightforward one-pot synthesis method that involved calcining a composite made of well-mixed nickel acetate and carbon nanotubes at 850 oC in an inert environment. The obtained results showed that when the nickel content was optimized, 1 weight percent metal is the optimal composition, the generated Ni-decorated carbon nanotubes composite is an efficient electro-catalyst for tri(ammonium) phosphate oxidation. Additionally, it was found that, according to the results of the chronoamperometry analysis, the electro-oxidation reaction is independent of the nickel (oxy) hydroxide active layer, giving electrooxidation of ammonium phosphate on the surface of the proposed catalyst a clear advantage over alcohols.
Beside Ni/carbon nanotubes composite, Ni NPs-decorated graphene was synthesized and its electrocatalytic performance toward electro-oxidation of tri(ammonium) phosphate was investigated. The utilized catalyst has been prepared by simple one-pot synthesis procedure; calcination of well mixed nickel acetate/commercial sugar composite. The results showed that the prepared Ni NPs-decorated multiwall graphene composite is an effective electro-catalyst for tri(ammonium) phosphate oxidation when the nickel content is optimized; 3 wt.% metal is the best composition. Furthermore, chronoamperometry analysis results concluded that the active layer did not consume during the electro-oxidation reaction which creates a distinct advantage for this fertilizer over alcohols. Stability of the active layer is attributed to performing Ni(OH)2/Ni(OOH) redox reaction during tri(ammonium) phosphate electro-oxidation process. Overall, the study opens a new avenue for utilizing hydrogen-rich, cheap and available substances for hydrogen generation using continuously-active non-precious electrodes.
Moreover, Ni-incorporated & N-doped reduced graphene oxide was also synthesized to be exploited as an electrocatalyst for ammonium phosphate. The proposed electrocatalyst was prepared by also a simple one-pot synthesis procedure. Typically, well-mixed nickel acetate tertrahydrate/ polyvinylpyrrolidone mixture have been calcined under nitrogen atmosphere at 700 oC. X-ray diffraction (XRD) analyses confirmed formation of zero-valent nickel and reduced graphene oxide because of the clear appearance of the corresponding peaks. Moreover, X-ray photoelectron spectroscopy (XPS) analyses concluded formation of graphene sheets functionalized by oxygenated groups and doped by pyrrolic and prydinic nitrogen; however only pyrrolic nitrogen has been detected in Ni-free samples. Transmission electron microscope (TEM) images indicated formation multilayers reduced graphene oxide. Electrochemical measurements indicated that the prepared composite is an effective electro-catalyst for tri(ammonium) phosphate oxidation when the nickel content is optimized. The electrode containing 31.9 wt% Ni shows the maximum generated current density however clear oxidation peaks were observed with 40.2 wt% formulation.