Infopack #3: Catalyst Optimization

1 INFO-PACK #3 • CATALYST OPTIMIZATION Next-Generation Catalysts for Ammonia Cracking: catalytic performance and durability of Ni-BZCY electrodes Introduction Catalyst Optimization Ni-based electrodes have been widely validated for Solid Oxide Fuel Cell (SOFC) applications, but their limited stability under NH₃ remains a major drawback. Protonic ceramic electrochemical reactors (PCERs) allow the operation at lower temperatures, which reduces the catalytic activity of the electrodes. Our goal is the enhancement of both the catalytic activity at low temperatures (below 700 ºC) and the long-term stability of Ni-BZCY electrodes under NH₃. To reach this goal, several strategies were employed in the SINGLE project, including metal infiltration, galvanic replacement, and morphological modification. The developed electrodes were evaluated through catalytic activity tests and structural and morphological characterization to understand the mechanisms responsible of the improved performance. ABSTRACT The potential of ammonia for hydrogen storage makes the NH₃ cracking (Ammonia Dehydrogenation reaction) a key step for H₂ production and several researches have focused on the study and development of effective catalysts for this process. PCERs offer a one-step solution by combining ammonia dehydrogenation with hydrogen separation and compression. State-ofthe-art PCERs use a proton-conducting electrolyte based on BZCY and one of the electrodes typically consists of a Ni-BZCY composite. The Ni particles present in this electrode exhibit high catalytic activity towards the ammonia dehydrogenation. The work performed in the SINGLE project aims to improve both the catalytic performance and long-term stability of the Ni-BZCY electrode under NH3. To reach these objectives, the optimization of the Ni-BZCY electrode has been carried out via metal infiltration, galvanic replacement, and morphological modifications, being these different strategies compatible with the existing PCERs manufacturing process. Key points • The catalytic performance of the Ni-BZCY electrodes has been improved for NH₃ cracking. • The long-term stability of Ni-BZCY electrodes under NH₃ exposure has been enhanced. • The strategies employed to enhance the electrode performance are compatible with the existing PCER manufacturing process chain. INFO-PACK #3 2 INFO-PACK #3 • CATALYST OPTIMIZATION Ammonia dehydrogenation (ADH) to produce hydrogen is an endothermic reaction (ΔH° = 45.9 kJ/mol at 25 °C) that can be catalytically driven. Several metals have been studied as catalyst for this reaction, including Ru, Ni, Rh and Ni, among others. Ruthenium (Ru)-based catalysts are the most active reported to date; however, their high cost and limited availability hinder large-scale implementation. In contrast, although nickel (Ni)-based catalysts are less active, they offer a cost-effective and scalable alternative, making them attractive for industrial applications. For example, Ni supported on alumina (Ni/Al₂O₃) is currently employed in the metallurgical industry to generate controlled atmospheres via ammonia dehydrogenation. PCERs offer the possibility to couple hydrogen production via ADH with its simultaneous separation and compression in a single step. The PCERs developed in the SINGLE project by CTMS consist of a dense proton-conducting electrolyte based on BZCY and two electrodes (anode and cathode), both made of a Ni-BZCY composite. The Ni-BZCY anode has three different roles: (1) mechanical support for the tubular cell, (2) electrochemical anode for hydrogen oxidation to protons, and (3) catalysis of the ammonia dehydrogenation reaction. While proof-of-principle tests in single cells have demonstrated nearly 100% NH₃ conversion at 650 °C, the SINGLE project aims to operate PCERs under high ammonia pressure and reduced temperatures (below 600 ºC). Under these conditions, Ni-BZCY catalyst may experience kinetic limitations which results in the need of improvements in catalytic performance to enable efficient operation at lower temperatures. Additionally, previous studies have revealed interactions between Ni and NH₃ affecting catalyst stability, highlighting the need of further optimization. To overcome these challenges, the SINGLE project focuses on improving the catalytic activity and long-term stability of the Ni-BZCY anode using promoters and modifications to the Ni-BZCY ceramic support. Previous studies report that CeO₂, Y₂O₃, and alkali-promoted Ni/Al₂O₃ catalysts achieve higher ammonia conversion below 600 °C. Other elements, such as Fe and Co can also act as effective promoters. These promoters will be introduced via metal infiltration or atomic galvanic replacement techniques. Furthermore, since Ni–NH₃ interactions may degrade catalyst performance over time, structural modifications of the BZCY support, such as adjusting porosity and composition, have been also explored. 3 INFO-PACK #3 • CATALYST OPTIMIZATION Then, three main strategies have been employed to achieve the abovementioned objectives: metal infiltration, galvanic replacement and morphological modifications of the anode. The figure below shows the improved catalytic activity of one of the optimized anodes developed in the SINGLE project, compared to the performance of the standard Ni-BZCY anode. The SINGLE project will optimize catalyst performance at low temperatures and durability through structural and material modifications. PCERs offer a promising approach for efficient hydrogen production via ammonia decomposition at high NH₃ pressures and moderate temperatures (below 600 °C). However, operating at these lower temperatures can hinder the catalytic activity and long-term stability of the Ni-BZCY anode. To address these challenges, the SINGLE project explored three strategies: metal infiltration, galvanic replacement, and morphological modification of the Ni-BZCY anode. The introduction of promoters, along with morphological modifications, enabled the optimization of both the catalytic performance and the durability of the anode. Catalytic tests confirmed enhanced ammonia conversion and improved stability under operating conditions. Overall, the optimized Ni-BZCY electrodes demonstrated superior performance and long-term reliability, while remaining compatible with existing PCER manufacturing processes. These results support the development of efficient, low-temperature ammonia-to-hydrogen systems for industrial applications. Conclusions 4 INFO-PACK #3 • CATALYST OPTIMIZATION Authors Bibliography Selene Hernández Morejudo Research Director at CoorsTek Membrane Science AS [email protected] Sonia Escolástico Tenured Scientist at Instituto de Tecnología Química Universitat Politècnica de València, Consejo Superior De Investigaciones Científi ca [email protected] Single-step hydrogen production from NH3, CH4, and biogas in stacked proton ceramic reactors. Daniel Clark et. al. DOI: 10.1126/science.abj3951 Catalytic ammonia decomposition to produce hydrogen: A mini-review. Jung Eun Lee et. al. Chemical Engineering Journal 475 (2023) 146108 Co-funded by the European Union, the Clean Hydrogen Partnership and its members Hydrogen Europe and Hydrogen Europe Research. Views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or Clean Hydrogen Partnership. Neither the European Union nor the granting authority can be held responsible for them.  singleh2.eu  [email protected]  SINGLE H2 PROJECT