Rethinking the Storage and Conversion of Fuels: Producing Green Hydrogen from Ammonia using Non-Equilibrium Plasma*

Hydrogen provides a promising source of green energy; however, it presents unique energy storage challenges that require novel methods of generating hydrogen from more convenient feedstocks. A potential solution is the utilization of ammonia given its compositional percentage of hydrogen, high energy density, liquid phase at standard conditions, and the vast industrial infrastructure that exists to facilitate its production and distribution. The ammonia-to-hydrogen reaction pathway however suffers from slow kinetics given the presence of the N-H bond. Non-equilibrium plasmas, in tandem with an optimized choice of catalyst, are capable of exciting selectively the vibrational and electronic states of ammonia to reduce the activation barrier. Furthermore, within a gas temperature of 300-500 K, hydrogen and nitrogen products are favored. This work characterizes experimentally the dependence of yield and energy efficiency within an inductively coupled plasma reactor by varying temperature, pressure, flow rate, and choice and positioning of catalyst. The findings display how plasma sources can be tuned in tandem with catalytic surfaces to convert ammonia to hydrogen and provide insights into the fundamentals of plasma catalysis. The catalyst selection is informed by microkinetic modeling, and experimental results will be compared to model expectations. Furthermore, vibrational gas temperatures are measured using spectroscopic methods.