Vacancy Rich TiB₂ Nanosheets Promote Electrochemical Ammonia Synthesis

The ability to exfoliate transition metal diborides has led to a renewed interest in their prospect to be applied as catalysts for electrochemical reactions. This is due to an enhanced access to the unprecedented interfaces these nanomaterials offer. In this work, we show that nanosheets exfoliated from TiB₂ exhibit vacancies that facilitate an excellent interface for catalyzing nitrogen reduction reaction (NRR). We found that these nanosheets demonstrate a high selectivity toward NH₃ because of their abiity to preferentially chemisorb and activate N₂. These nanosheets exhibit a superlative NH₃ yield of 318 μg h^-1 cm^-2 at -0.2 V versus RHE with a faradaic efficiency of 57%. We also found how the relative ratios of Ti and B atoms in these nanosheets can affect the NH₃ yield and faradaic efficiency. We supplement these results with DFT studies that indicate that it is the creation of frustrated Lewis pairs along with the Ti-B synergy that induces a push-and-pull effect; this in turn favors N₂ activation and lowers the energy barrier for NRR. Furthermore, we explored B-exposed and Ti-exposed surfaces to understand how different surfaces affect the reaction yield and efficiency and found that Ti-exposed surfaces with boron divacancy have the highest propensity for NRR. The maiden insights presented in this study on the role of transition metal-boron synergy and interfaces present significant additions to the fast-expanding knowledge on nanoscaled metal borides.