Prospects for Aerobic Photocatalytic Nitrogen Fixation

Decarbonized ammonia production through photocatalytic nitrogen fixation is appealing, as it may allow for farm-scale fertilizer production using earth-abundant feedstocks, energy, and catalysts. Yet, the viability of decentralized ammonia production systems is largely dependent on the cost of a complete photocatalytic system reaching a Haber-Bosch parity point. Here, we demonstrate that an air separation unit for a farm-scale low-cost photocatalytic ammonia synthesis system can account for 70% of the total system cost. This high cost depends on the type of air separation unit and the purity of nitrogen. This promotes the need for a catalyst, which can tolerate trace oxygen or can even operate under aerobic conditions to attain Haber-Bosch cost parity. We further demonstrate the change in catalytic activity of prototypical undoped and metal-doped titania photocatalysts under aerobic and anaerobic conditions. Among various metal-doped titania photocatalyst, vanadium- and ruthenium-doped titania demonstrated no performance decline under aerobic conditions.

Automated summary

The production of decarbonized ammonia through photocatalytic nitrogen fixation has the potential to revolutionize farm-scale fertilizer production. However, the cost of a complete photocatalytic system remains a critical factor. In this study, we found that the air separation unit accounts for a significant portion of the total system cost. Therefore, it is crucial to develop catalysts that can tolerate trace oxygen or operate under aerobic conditions to achieve cost parity with the traditional Haber-Bosch process. Among the various metal-doped titania photocatalysts, vanadium- and ruthenium-doped titania demonstrated consistent performance under aerobic conditions.