Study On Ammonia Hydrogen Production By Decomposition Of Electrochemical Method

With energy and environmental issues become increasingly prominent, the development of sustainable alternative energy sources is imminent. As a clean energy source, hydrogen energy are attracting more and more attention. However, we must firstly solve the problem of hydrogen sources in order to realize the development and utilization of hydrogen energy. Ammonia, with a 17.65 wt% hydrogen content, is an excellent hydrogen carrier. Compared with pure hydrogen, ammonia is more easily stored and transported. It is easily liquefied by compression under 1.0 MPa at ambient temperature. Synthesis of NH3 is already one of the largest industrial processes worldwide via the Haber-Bosch process, and as a result, the infrastructure for the storage and transport of NH3 already exists. Hydrogen originating from ammonia decomposition does not contain COX species, On the other hand, NH3 itself could potentially be used in direct ammonia fuel cells. Essentially, the ammonia economy can achieve the same benefits of a hydrogen economy.In this paper, liquid ammonia electrolysis to generate hydrogen has been studied. We establish a scientific and rational electrolysis experiments and analysis system, choose safe and inexpensive electrolytes, optimization of the electrode catalyst material so as to realize the high efficiency electrolytsis of liquid ammonia. The main research content of this article are as follows:1. Establish a three-electrode liquid ammonia electrolytic cell and analysis systemOn the basis of the previous studies, a stainless steel three-electrode electrolytic cell was designed for the purpose of electrolysis of liquid ammonia. And through to the construction of the experimental apparatus, the selection of lining materials and reference electrode built a relatively complete system of liquid ammonia electrolytic experiment. The experimental device consists of three parts, of ammonia guide way system, electrolytic experiment system and qualitative and quantitative analysis system. The qualitative analysis of the product was carried out by retention time, and the standard curve method was used for quantitative analysis. A scientific and rational electrolysis experiments and analysis system has been established.2. Influence of different ammonium salt electrolytes on the electrolysis of liquid ammonia and current efficiencyWe systematically studied the effect of alkaline metal amides (KNH2, NaNH2), acidic ammonium salt (NH4I, NH4Br, NH4Cl, NH4NO3) and neutral potassium salt (KPF6) as the supporting electrolyte on system resistance, electrolytic efficiency and the rate of hydrogen generate of liquid ammonia system. It was found that under different environment liquid ammonia electrolytic process has a different reaction mechanism. A minimum electrolysis voltage (Emin) of ca.1.3 V is required when using Pt foil as the anode and cathode.Compared to KNH2, NaNH2 and KPF6, the electrolytes containing NH4+ exhibit the predominant role in increasing the current density and reducing the system resistance, which is probably determined by the ionic molar conductivity and solubility of each electrolyte in NH3 (l). Only by adding 1 M ammonium salt as a supporting electrolyte, the electrolysis of NH3 (l) exhibit>80% current efficiency and 0.7-0.8 mL/min average rate of hydrogen generation during the chronopotentiometry tests at 120 mA/cm2 for 3 h. And after taking into account many factors, NH4Cl are proved to be the most appropriate supporting electrolyte for electrolysis of NH3 (l).3. Influence of different electrocatalysts on the electrocatalytic activity of liquid ammonia systemAiming to decrease the overpotential of electrode reaction, five kinds of electrocatalysts, i.e. Pt black, Rh, Pt-Ir, Rh-Pt and Ph-Pt-Ir alloys were prepared and characterized, and were further electrochemically tested in the presence of NH4CI. Explores the influence of different electrocatalysts on the electrocatalytic activity and electrochemical stability. It is shown that trimetallic Rh-Pt-Ir and bimetallic Pt-Ir, Rh:Pt (1:1) alloy electrodes exhibit the combined benefit of a better activity and minimized deactivation. The Rh-Pt-Ir alloy anode shows the best electrocatalytic activity with lowest Emin of ca.0.47 V and highest current density of 46.9 mA/cm2 at 2.0 V. In comparison to that of Pt foil anode, the mininum electrolysis voltage is reduced by two-thirds and the current density is increased by twice. Besides, it exhibits much lower anode potential of 0.22 V at 1 mA/cm2 current density and 1.76 V at 210 mA/cm2, and it has the best electrochemical stability under the different current density.