Pilot-scale in situ water electrolyzer with an improved fluid flow and modified electrodes for upscaling hybrid biological–inorganic systems

Anthropogenic emissions of CO₂ and other greenhouse gases have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever. In this scope, hybrid biological–inorganic systems represent a sustainable and versatile chemical synthesis platform using CO₂ as a feedstock which realizes the idea of ’Cleaner Production’. Practical implementation of hybrid biological–inorganic systems for the production of value-added chemical products requires development of scalable and robust electrobioreactors with a high energy efficiency and an adequate size. This work reports an in situ water electrolyzer stack design as part of an electrobioreactor system required for the pilot-scale operation of the hybrid biological–inorganic process approaching the aforementioned requirements. The electrolyzer is designed by applying fluid dynamics simulation tools to model the electrolyte flow. The design takes into consideration the problem of leakage currents, reported in the previous works, which is tackled by applying an electrically insulating coating. Different electrode surface modification approaches, such as coating with electrocatalysts and etching, are used to further enhance the performance and energy efficiency of the electrolyzer. The performance of the electrolyzer stack was evaluated in a pH-neutral solution required for the hybrid biological–inorganic processes. The in situ water electrolyzer developed in this study showed a high Faraday efficiency close to 90% and acceptable specific energy consumption below 90 kWh kg_H2⁻¹. The obtained energy-efficiency values are the highest reported for similar applications with a similar scale which emphasizes the successful design of the in situ water electrolyzer stack. All data collected during experimental work might be applied to further investigation, simulation, and optimization of electrobioreactors operating at neutral pH. Overall, the results achieved in this study are promising and represent a crucial step toward the industrial implementation of hybrid biological–inorganic systems.