Is there any chance for bismuth to catalyse E-NRR in Aqueous media? Noemi Pirrone 1 , Sara Garcia Ballesteros, 1 Simelys Hernández, 2 and Federico Bella 1 1 Politecnico di Torino, Italy, 2 CREST group, Italy Electrochemical nitrogen reduction reaction (E-NRR) for ammonia production represents an environmental- friendly alternative to the highly polluting Haber-Bosh process, being one of the major sources of carbon dioxide emissions in the atmosphere. In this field, the synthesis of a catalyst able to make nitrogen triple bond react with protons represents the crucial step. Indeed, the competing hydrogen evolution reaction (HER) is favoured due to its lower activation energy. Theoretical calculations have shown that bismuth can activate nitrogen to produce ammonia thanks to the interaction of bismuth 6p band with nitrogen 2p orbitals. 1 In particular, bismuth nanocrystals obtained through solvothermal synthesis have reached 66% Faradaic efficiency (FE) and 200 mmol g -1 h -1 yield in an H-cell type, using potassium sulfate as electrolyte. 2 However, the attempt to replicate this outstanding material, slavishly following the synthesis procedure, did not produce the expected results. 3 Having this in mind, our study aims at replicating the bismuth nanocrystals synthesis and to test its performances in a less studied flow cell system, equipped with a gas diffusion electrode (GDE) on which the catalyst is immobilized through air-brushing technique. Flow cell configuration could allow the achievement of even greater ammonia production, due to the higher nitrogen mass transport on the catalyst layer compared to the H-cell, in which a larger gas flow rate is needed to guarantee enough nitrogen supply. 4 Unfortunately, even if XRD analysis confirmed the presence of metallic bismuth, all the tests performed using bismuth catalyst in the GDE flow cell did not lead to the expected results. In our opinion, even considering the differences between our work and the one presented by Hao et al. , it is inquisitive that we were not able to obtain even low amounts of ammonia, especially knowing that GDE flow-cell configuration should affect positively the performance of the catalyst, improving the overall efficiency, thanks to the optimized solid-liquid-gas interface. Trying to analyse all parameters that could affect negatively ammonia production, we concluded that the possible weaknesses of our procedure are: i) the impossibility to carry out catalyst deposition on carbon support under argon atmosphere using the air-brushing technique, favouring the transformation of metallic bismuth into bismuth oxides, ii) the scale-up of the synthesis procedure, that can affect final catalyst morphology and iii) the different deposition technique, that is air-brushing on carbon paper instead of drop-casting on glassy carbon. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 948769, project title: SuN 2 rise). References 1. W. P. Utomo et al. , Adv Funct Mater , 2022, 32 , 2106713. 2. Y.-C. Hao et al. , Nat Catal , 2019, 2 , 448–456. 3. J. Choi et al. , Nat Catal 2022 5:5 , 2022, 5 , 382–384. 4. M. Kolen et al. , ACS Catal , 2022, 5726–5735.
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