Composite interconnects and nanostructured electrodes for proton conducting membrane reactors

Today's dominating process for production of hydrogen requires large industrial plants to minimize energy losses and is not suitable for small scale on-site production. CIEPRO has focused on a novel catalytic membrane reactor based on a ceramic proton-conducting electrolyte that fully integrates steam methane reforming, water-gas shift, heat management as well as separation and compression of hydrogen in one single reactor. This results in a highly efficient process with near-zero energy loss as well as a pure CO2-capturable waste stream. The main objective of the project was to establish the science and the technology for cost-effective fabrication of such reactors. To scale-up the process, the individual proton-conducting ceramic cells must be electrically joined at operating temperatures using a novel glass-ceramic composite. CIEPRO has developed a metal-glass-ceramic composite with high electrical conductivity that can be used as an interconnect, and integrated it into a manifold allowing parallel and serial electrical connection of several cells. Throughout the project, this interconnect has both improved significantly in robustness and reliability, and also reduced electrical resistance from 35 mohm to less than 10 mohm (project-end target of 50 mohm). The electrocatalytic electrodes have been improved to a total resistance of less than 0.3 ohm cm2 (target 0.3) under steam methane reforming conditions. The total electric resistance of the hydrogen electrode has been reduced by application of a current collector with a resistance of about 10 mohm cm-1, and a strategy that prevents unwanted coarsening (causing gas diffusion problems) of the current collector has been experimentally confirmed. In addition, a paste enabling electrical connection between the hydrogen electrode and interconnect as well as serving as a secondary current collector has been developed. To improve the long-term durability of the hydrogen electrode, an alternative fabrication procedure has been researched. The procedure results in a higher density of triple phase boundaries, which is beneficial for the electrochemical performance. While achieving full methane conversion and removal of 99% of the formed hydrogen, the membrane has also been simultaneously compressed electrochemically up to 50 bar; demonstrating commercially-relevant energy efficiencies for on-site hydrogen production. Combining the interconnects, sealing technology and high-performance membranes, a six tube segment-in-series reactor (target was three cells) was fabricated and tested, demonstrating a 0.16 kg day-1 production capacity and validating the manufacturability and scalability of this technology. The results from CIEPRO justify further research and development of this hydrogen production technology in new projects, both looking at fundamental aspects as well as further scale-up.

An electrochemically driven protonic membrane reformer enables extraction of hydrogen from the reaction chamber to reach nearly-full equilibrium shift of reforming and water-gas shift reactions, and produces two separate gas products (high-purity hydrogen and wet CO2). The project has focused on the development of the interconnect and electrodes of the protonic membrane reformer, and lab testing has confirmed commercial performance levels for key parameters (catalytic activity, cell resistance, hydrogen flux). The practical implications can be summarized as: -simple, compact and modular system -high energy efficiency -minimization of CO2 emissions A more technical description of the impact of the results was published in Nature Energy (Malerød-Fjeld et al., Nature Energy 2 923 (2017)).

Ceramic proton conductors have the potential to become an essential part of future clean energy systems - from fuel cells to steam electrolysers and catalytic membrane reactors. The project gathers world-leading industry (CoorsTek), high research excellence institute (SINTEF) and university (UiO FASE) to develop innovative segmented-in-series proton conducting ceramic cells integrating novel composite glass-ceramic interconnects and nanostructured electrodes for stable operation of highly efficient steam methane reforming reactors. To tackle this ambitious objective, the project builds on the core expertise of the partners and addresses two distinct research activities underpinning the development of these novel reactors: hierarchically porous electrodes with a nanostructured porous network for improved catalytic activity confined in a macroporous network ensuring fast mass transport; and development of an integrated composite interconnect and seal ensuring dual functions of gas tightness and current collection between cells. The experimental approach will be based on advanced protocols combining soft-chemistry with ceramic processing routes. The resulting segmented-in-series cells will be tested in various operating conditions to define rate limiting factors and establish transport theory in these novel architectures operating in steam methane reforming conditions. The project runs for 3 years, trains 1 postdoctoral research fellow, fosters international collaboration with CSIC University in Spain and CoorsTek in Golden, USA, aims to establish new intellectual properties in various fields (manufacturing of nanostructured electrodes, sealing technology, reactor design) and will broadly disseminate the results of the project in high impact journals and at international conferences.