Fabrication of a Thermochemical Reactor for Sustainable
Hydrogen Production

As the world shifts toward renewable energy, green hydrogen (H2) has emerged as a promising solution for reducing emissions in sectors that are difficult to electrify. Thermochemical H2 production offers an alternative to electrolytic H2 production by using high-temperature redox cycles. This individual research project focuses on the improvement of the fabrication methods and eventual fabrication of a Labyrinth Reactor (LR) for thermochemically producing H2. The LR is a compact system that uses a metal oxide, e.g. cerium oxide, to produce H2 through a two-step metal oxide redox cycle. This cycle involves first reducing a metal oxide at high temperatures to release oxygen. In the second step, the reduced metal oxide reacts with steam at a lower temperature to be reoxidized, producing H2. Unlike many reactors that conduct this cycle in one reaction zone, the LR physically separates this cycle into the reduction, heat recovery, and water splitting zones. These zones are contained within an insulating firebrick cavity, where the metal oxide weaves through a narrow path to each zone. This novel configuration fits a typically long path into a small reactor volume. This allows for a compact design with a cyclical path, which improves thermal efficiency and maximizes power density for a cost-effective H2 yield. The reactor utilizes a firebrick insulating cavity with a path separating the three distinct zones. This firebrick cavity required fabrication as it comprised of multiple layers of firebrick, each with a distinct geometry, and additional firebrick components placed within the layers. The layers and components were fabricated using a computer numerical control (CNC) milling machine. The method for fabrication involved multiple steps; cutting the firebricks down to the desired size, polishing the sides to be level, establishing the zero in the software used to control the CNC machine, using various grinding bits to carve out the necessary path of each firebrick layer, and assembling the layers to ensure they fit together securely. Throughout the fabrication process, ii several challenges were encountered, including uneven polishing, coordinate loss during CNC operations, and deviations during grinding. These issues were addressed by optimizing spindle speeds, shortening G-code runs, and reducing human error where possible. Additionally, CNC processes were refined to improve accuracy. The LR was developed from insights gained from teams around the world working on thermochemical reactor systems. In particular, the LR design stems from the work done by Sandia National Laboratories on the CR5 and Cascading Pressure Reactor. The first iteration, version 1, of the LR was built and tested in ASU LightWorks® Laboratory. The testing resulted in significant fractures within the firebrick layers and components. This led to the second iteration, version 2, which involved a redesign of the firebrick layers to prevent these structural damages. The focus of this research involves the fabrication process of version 2 of the LR. The fabricationprocess was improved through technique refinements, and design elements that made fabrication difficult were identified for future redesign. Ultimately, due to the complexity of certain firebrick components, version 2 of the LR was not completed. Given the lengthy process, it was decided that shifting focus to designing and fabricating a new LR iteration would be more valuable. The constructed layers of version 2 were used for various testing. The lessons learned through the fabrication process influenced the design of the third iteration of the LR, version 3. Also, this project serves as a guide for best practices for future fabrication efforts. Version 3 is far simpler in terms of layer geometry to expedite the fabrication process. Also, the new iteration is larger, has more reactive material, and has the goal of producing 1g/hour of H2. Version 3 is currently being fabricated by the ASU LightWorks® Laboratory and will then go on to be tested. Overall, this work contributes to LightWorks® Laboratory’s aim for the advancement of a thermochemical reactor for scalable green H2 production.