B-terminated (111) polar surfaces of BP and BAs: promising metal-free electrocatalysts with large reaction regions for nitrogen fixation

The nitrogen electroreduction reaction (NRR) in aqueous solutions under ambient conditions represents an attractive prospect to produce ammonia, but the development of long-term stable and low-cost catalysts with high-efficiency and high-selectivity remains a great challenge. Herein, we investigated the potential of a new class of experimentally available boron-containing materials, i.e. , cubic boron phosphide (BP) and boron arsenide (BAs), as metal-free NRR electrocatalysts by means of density functional theory (DFT) calculations. Our results revealed that gas phase N 2 can be sufficiently activated on the B-terminated (111) polar surfaces of BP and BAs, and effectively reduced to NH 3 via an enzymatic pathway with an extremely low limiting potential (−0.12 V on BP and −0.31 V on BAs, respectively). In particular, the two proposed B-terminated (111) surfaces not only have a large active region for N 2 reduction, but also can significantly inhibit the competitive hydrogen evolution reaction, and thus have rather high efficiency and selectivity for the NRR. Therefore, cubic BP or BAs with mainly exposed (111) facets may serve as promising metal-free NRR catalysts with superior performance. Promising metal-free electrocatalysts reduce nitrogen to ammonia under ambient conditions with high-efficiency, high-selectivity and large reaction regions.