Electrochemical ammonia synthesis

The superiority and peculiarity of electrochemical ammonia synthesis. Ammonia synthesis reaction is an exothermic reaction accompan3dng volume reduction. In... 

Fig. 10.7 Schematic diagram of electrochemical ammonia synthesis using gas diffusion electrode in aqueous solution...

The above ammonia synthesis processes take place in nonaqueous solution. Their chemical environment is very different from that of biological nitrogen fixation. They are not true electrochemical ammonia synthesis because the electrochemical method is used for regeneration of precursor of complex only. 

In 1989, Huruyanagai and Kichihaneshou at University of Yamanashi reported an electrochemical ammonia synthesis method at normal temperature and atmospheric pressure in aqueous solution.The gas diffusion electrode supported Fe-Phthalocyanine catalyst was used and the experimental instrument was shown in Fig. 10.7. ... 

Therefore, how to enhance the catalytic efficiency of catalyst in water solution and prevent catalyst from poison are important factors in increasing the cmrent efficiency and stability of electrode in the electrochemical ammonia synthesis. The use of solid electrol de is one of ways to solve these problems. 

The new challenge on the theory is about the prediction of biomimetic ammonia-synthesis path at room temperature and atmospheric pressure. There are some reports on the study of photocatalytic, bio-catalytic and electrochemical ammonia synthesis catalysts. The latter should be achieved preferably by electrochemical processes with efficiency similar to the synthesis strategies that are available today. 

Ammonia may also be produced from renewable energy sources like solar and wind-power by use of the generated (excess) electricity to drive the electrochemical reaction at certain overpotential, i.e., the excess potential needed to drive the reaction. This framework could potentially decouple the energy consmnption from the renewable production of energy. The main challenge for ammonia s)mthesis is to find the optimal catalyst. The electrochemical ammonia synthesis process takes place at the cathode side of the electrochemical cell following the overall reaction ... 

C.G. Yiokari, G.E. Pitselis, D.G. Polydoros, A.D. Katsaounis, and C.G. Vayenas, High pressure electrochemical promotion of ammonia synthesis over an industrial iron catalyst, /. Phys. Chem. 104, 10600-10602 (2000). 

Proton conductors ammonia synthesis, 468 conductivity, 93 ethylene oxidation, 470 hydrogen oxidation, 457 list of electrochemically promoted reactions, 146... 

Formally, ammonia synthesis is closely related to Fischer-Tropsch synthesis. Industrial operation involves the use of an iron catalyst promoted with calcium and potassium oxides. However, the reason we consider this process here is not directly in connection with alkali promotion of the catalyst. We are concerned with a remarkable achievement reported by Yiokari et al. [15], who use a ton-conducting electrolyte to achieve electrochemical promotion of a fully promoted ammonia synthesis catalyst operated at elevated pressure. Specifically, they make use of a fully promoted industrial catalyst that was interfaced with the proton conductor CaIno.iZro.903-a operated at 700K and 50 bar in a multipellet configuration. It was shown that under EP the catalytic rate could be increased by a factor of 13 when... 

Concluding from previous works, the key factor for electrocatalytic ammonia synthesis could be the number of TPB sites at the cathode to facilitate the reaction between protons from the electrolyte, N2 from gas phase, and electrons from external power source. Therefore, the big challenge on the electrochemical synthesis of ammonia is the low formation rates thus more efficient catalysts need to be identified. 

Murakami, T., Nishikiori, T., Nohira, T., Ito, Y. (2005). Investigation of anodic reaction of electrolytic ammonia synthesis in molten salts imder atmospheric pressure. Journal of the Electrochemical Society, 152(5), D75—D78. 

Wang ID, Xie YH, Zhang ZF, Liu RQ, Li ZJ (2005) Protonic conduction in Ca -doped La M O (M = Ce, Zr) with its application to ammonia synthesis electrochemically. Mater Res Bull 40 1294-1302 Wang DY, Symons WT, Farhat RJ, Valdes CA, Briggs EM, Polikarpus KK, Kupe J (2006a) Ammonia gas sensors. US Patent 7,074,319 B2... 

Electrolytic ammonia s mthesis in a molten salt under atmospheric pressure. In 2005, Murakami et al proposed an electrolytic ammonia synthesis process from water and nitrogen gas in molten salt under atmospheric pressure and at lower temperature. In this process, water vapor and was electrolyzed via electrochemical reaction to form ammonia gas and ions in molten salt. Nitride ions were formed on metallic cathode and oxygen ions were removed from metallic anode during electrolysis. The electrolyte was alkaline metallic chloride containing The principle is showed in Fig. 10.9. 

Figure 10.13(a) shows the ammonia synthesis rates (mol H-s ) at constant voltage and inlet Ph2/Pn2 =0.82. Reaction rate increases from 6.9 x 10 mol H-s to 1.35 X 10 mol H s as increasing of reaction time. p = r/vo is defined as enhancement coefficient in this figure and its value is 2. A = Ar/(—I/F) is defined as inductive efficiency, reflecting the influence of electrochemical proton transfer to catalyst. This parameter is used to differentiate the inductive and non-inductive efficiency. The A is 0.6 in Fig. 10.13(a), indicating that 60% of proton transfers to... 

Molten Salt Electrochemical Processes Directed Toward a Low Carbon Society 525 Table 7.1.1 Comparison of energy required for ammonia synthesis... 

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