Hyung Chul Yoon

Electrochemical synthesis of ammonia from water and nitrogen catalyzed by nano-Fe2O3 and CoFe2O4 suspended in a molten LiCl-KCl-CsCl electrolyte

Nano-Fe2O3 and CoFe2O4 were suspended in molten salt of alkali-metal chloride (LiCl-KCl-CsCl) and their catalytic activity in electrochemical ammonia synthesis was evaluated from potentiostatic electrolysis at 600 K. The presence of nanoparticle suspension in the molten chloride resulted in improved production of NH3, recording NH3 synthesis rate of 1.78×10−10 mol s−1 cm−2 and 3.00×10−10 mol s−1 cm−2 with CoFe2O4 and Fe2O3, which are 102% and 240% higher than that without the use of a nanocatalyst, respectively. We speculated that the nanoparticles triggered both the electrochemical reduction of nitrogen and also chemical reaction between nitrogen and hydrogen that was produced from water electro-reduction on cathode. The use of nanocatalysts in the form of suspension offers an effective way to overcome the sluggish nature of nitrogen reduction in the molten chloride electrolyte.

Electrochemical Synthesis of Ammonia from Water and Nitrogen: A Lithium-Mediated Approach Using Lithium-Ion Conducting Glass Ceramics

Lithium-mediated reduction of dinitrogen is a promising method to evade electron-stealing hydrogen evolution, a critical challenge which limits faradaic efficiency (FE) and thus hinders the success of traditional protic-solvent-based ammonia electro-synthesis. A viable implementation of the lithium-mediated pathway using lithium-ion conducting glass ceramics involves i) lithium deposition, ii) nitridation, and iii) ammonia formation. Ammonia was successfully synthesized from molecular nitrogen and water, yielding a maximum FE of 52.3 %. With an ammonia synthesis rate comparable to previously reported approaches, the fairly high FE demonstrates the possibility of using this nitrogen fixation strategy as a substitute for firmly established, yet exceedingly complicated and expensive technology, and in so doing represents a next-generation energy storage system.

Hydrogen from Coal-Derived Methanol: Experimental Results

*† This study investigates hydrogen production via steam reformation of coal-derived methanol. The use of coal-derived methanol in fuel cell applications has recently been introduced as a potential energy pathway. However, prior to this study it was unknown if coal-derived methanol obtained from coal gasification is a pure enough feedstock to produce hydrogen for fuel cell applications. As a baseline, a study of fuel cell grade methanol has also been completed. Metrics for comparison are fuel conversion to hydrogen and catalyst degradation. The degradation of the catalyst is evidenced by the decrease in fuel conversion over time at a constant space velocity. The two types of methanol (fuel cell grade and coal-derived) contain different concentrations and types of impurities with different effects on catalyst degradation as evidenced by the performance of the fuel processor. Because of these considerations, different deactivation rates between fuel cell grade and coal-derived methanol were expected. This study shows the practicality of a new hydrogen pathway.

Anion-exchange-membrane-based electrochemical synthesis of ammonia as a carrier of hydrogen energy

With a 17.6 wt% hydrogen content, ammonia is a non-carbon-emitting, easy to store and transport, carrier of hydrogen energy. In this study, an anion-exchange-membrane-based (AEM-based) electrochemical cell was used to electrochemically synthesize ammonia from water and nitrogen under ambient conditions. The electrochemical cell was fabricated by attaching Pt/C to both sides of the AEM, and ammonia was generated by supplying nitrogen gas to the cathodic chamber of the cell. AC impedance and current-voltage (I–V) properties were analyzed in relation to the externally applied voltage, and ammonia-formation rates and faradaic efficiencies were determined. The maximum ammonia-formation rate was 1.96×10−11 mol·s−1·cm−2 at an applied voltage of 2V, with a faradaic efficiency of 0.18%.