Electric Field Aided Low-Temp Conversion of Ammonia to Hydrogen

A breakthrough method using electric field-aided surface protonics allows the conversion of ammonia to hydrogen at low temperatures. This innovative approach could enhance hydrogen production efficiency while reducing energy consumption. Ammonia, being a hydrogen-rich compound, presents a cleaner and more sustainable fuel option, and this new technique offers a promising solution for future energy needs. The process has significant potential for renewable energy applications.

The on-demand conversion of ammonia to green hydrogen gas occurs at low temperatures. This process uses a Ru/CeO2 catalyst to facilitate the reaction. Additionally, an electric field is applied to enhance the efficiency of the conversion.

Ammonia (NH₃) can be decomposed to produce hydrogen gas without emitting CO₂, making it a valuable option for the green energy industry due to its ease of transport and high hydrogen density. However, the challenge with using ammonia lies in its requirement for very high temperatures for decomposition reactions. In a collaborative effort between a university and industry, a team of Japanese researchers introduced a surface protonics-assisted method to produce green hydrogen from ammonia on demand using an electric field and Ru/CeO₂ catalyst.

Hydrogen gas is attracting significant attention as a potential energy source for a green and sustainable future, thanks to its high energy density and carbon-free nature. Although hydrogen is the most abundant element in the universe, it is typically found in bound forms, such as ammonia, metal hydrides, and other hydrogenated compounds.

Among hydrogen carriers, ammonia stands out due to its widespread availability, high hydrogen content (with hydrogen comprising 17.6% of its mass), and ease of liquefaction and transport. However, a significant drawback of ammonia is the need for extremely high temperatures (greater than 773K) for its decomposition. Efficient hydrogen production for fuel cells and internal combustion engines demands high ammonia conversion rates at lower temperatures.

To address this issue, Professor Yasushi Sekine of Waseda University, along with his team, including Yukino Ofuchi and Sae Doi from Waseda University and Kenta Mitarai from Yanmar Holdings, developed a new compact process capable of operating at lower temperatures. They demonstrated an experimental setup that achieved high rates of ammonia-to-hydrogen conversion at significantly lower temperatures by applying an electric field in the presence of a highly active and easily producible Ru/CeO₂ catalyst. Their research was published in Chemical Science on August 27, 2024.

Professor Sekine emphasized the collaborative nature of the project, stating that it involved Waseda University and Yanmar Holdings, a leader in ammonia utilization. Their goal was to develop a process that would exploit ammonia’s potential to generate hydrogen on-demand. Sekine explained that they initially investigated conventional thermal catalytic systems, where the reaction involves N and H adsorbate formation through N-H bond dissociation, followed by recombination of the adsorbates to form N₂ and H₂ gases.

The researchers observed that on active metal Ru, the rate-limiting step was nitrogen desorption at low temperatures and N-H bond dissociation at high temperatures. To overcome this, they turned to electric field-assisted catalytic reactions, which enhanced proton conduction on the catalyst surface, reduced the activation energy, and lowered the reaction temperatures for more efficient ammonia conversion.

Using this information, the team developed a novel thermal catalytic system for the low-temperature decomposition of ammonia into hydrogen, using the Ru/CeO₂ catalyst and a DC electric field. They discovered that their method efficiently decomposed ammonia at temperatures as low as 473 K, achieving a 100% conversion rate at 398 K given sufficient contact time between the ammonia and the catalyst. This success was attributed to the electric field's ability to promote surface protonics—proton hopping on the catalyst surface facilitated by the DC electric field, which lowered the apparent activation energies for ammonia conversion.

In contrast, without the electric field, nitrogen desorption slowed dramatically, causing the ammonia decomposition reaction to eventually stop. The importance of surface protonics in improving ammonia conversion rates was further supported by experimental data and density functional theory (DFT) calculations.

This innovative approach demonstrated that green hydrogen could be produced from ammonia at low temperatures via an irreversible pathway, achieving near-100% conversion rates with high reaction efficiency. Sekine concluded that this method could accelerate the adoption of clean alternative fuels by simplifying the on-demand synthesis of CO₂-free hydrogen.

For questions or comments write to writers@bostonbrandmedia.com

Source: sciencedaily‍