Abstract
It is widely recognized that hydrogen is an appropriate fuel for the sustainable energy system because it can be utilized as an energy storage material of intermittent renewable energy sources, and it generate no environmentally harmful products after combustion. However, in region where green hydrogen production cannot follow the need, import is necessary. In this case, transportation and storage of pure hydrogen can be a problem because of the high cost of maintaining liquefied state and low amount of hydrogen in compressed gas. In this regard, ammonia has received much attention as a hydrogen carrier with advantageous properties of relatively mild condition for liquefaction, high volumetric density of hydrogen, and no carbon content. Electrochemical ammonia oxidation reaction (AOR) to extract the hydrogen has been researched as much less energy is required for electrolysis when replacing oxygen evolution reaction to the AOR in aqueous alkaline condition. But high overpotential even when the most active electrocatalyst, platinum, is used and rapid poisoning by strongly adsorbed N species inhibit the practical application. To deal with these problems, there are a lot of on-going researches with various methods and perspectives. In this study, we investigated the effect of alkali metal cations on electrochemical AOR on polycrystalline platinum electrode. With same concentration but different alkali metal cations, measured the activity of platinum was different for the AOR peak (K+ > Na+ > Li+ ≈ Cs+). The reaction kinetics were also affected, supported by the electrochemical impedance spectroscopy and Tafel slope. Also, we checked that the alkali metal cation promotes the AOR by comparing the cyclic voltammetry results with and without the cation in ammonia solution. These kinds of cation effects are also demonstrated in other electrochemical reactions including the hydrogen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, and oxygen evolution reaction. Mainly, there are two explanations i) the degree of interaction between cations and water structure and reaction intermediates at the interface, ii) the local electric field between electrode and hydrated cation in electric double layer. We will present and discuss the effect of alkali metal cations on the AOR in this point of view and competitive adsorption of water, proton, hydroxide and ammonia on the platinum surface in aqueous alkaline electrolyte.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call