Abstract
Ammonia is an essential chemical used various fields including agriculture and chemical engineering. It is also considered as one of the candidates for carbon-free hydrogen storage. Electrochemical nitrogen reduction reaction (ENRR) has been studied as an alternative to current energy-intensive and greenhouse gas emitting Habor-Bosch process. Lithium mediated nitrogen reduction reaction (Li-NRR), in which organic compounds replace water as the proton shuttle, is currently considered as the most promising route in terms of ammonia production rate. However, ethanol (EtOH), acommon proton shuttle in Li-NRR, has a limited electrochemical stability because it is prone to oxidation at the anode or can be consumed by forming byproducts at the cathode. Therefore, it is highly desirable to search for alternative proton shuttles. In this study, two different ylides—namely, tetrabutylphosphonium chloride (TBPCl) and tetrabutylammonium chloride (TBNCl)—were selected as the proton shuttle in place of EtOH. Both compounds showed spontaneous reaction with lithium nitride by forming ammonia. Both TBPCl and TBNCl showed a higher ammonia production rate and faradaic efficiency than EtOH. Interestingly, tetrabutylammonium chloride showed higher ammonia production rate than tetrabutylphosphonium chloride which may originate from the difference of the acidity. This work demonstrates the possibility of using ylides as an effective proton shuttle and points out the important role of the center atom of the ylides in Li-NRR.
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