Catalytic electrolysis of ammonia on platinum in alkaline solution for hydrogen generation

Abstract

Catalytic electrolysis of ammonia provides a promising technique for generation of hydrogen and, simultaneously, maintenance of environmental sustainability. In this work, the electro-oxidation of ammonia on platinum (Pt) electrode was systematically studied in alkaline solution by cyclic voltammetry. The effects of operating conditions and the electrochemical test parameters, such as ammonia concentration, KOH concentration, electrode rotating speed, temperature, upper switch potential, potential sweep rate and cyclic number, on the ammonia oxidation and hydrogen evolution were investigated. The ammonia oxidation on Pt electrode is controlled by mass-transfer process of ammonia towards the electrode surface. However, the adsorption and desorption of N x H y intermediates play important roles in ammonia oxidation and hydrogen evolution. Determination of the ammonia electro-oxidation kinetics depends on a comprehensive consideration of mass-transfer and adsorption/desorption processes. There is an optimal ammonia concentration and KOH concentration to maximize the ammonia oxidation and hydrogen evolution simultaneously. The ammonia electro-oxidation current decreases with the increasing electrode rotating speed, and increases with the elevated temperature. The cell efficiency for ammonia electrolysis on Pt electrode can be up to 45%. Increasing ammonia and KOH concentrations could increase the electrolytic cell efficiency slightly.