Depth-resolved compositional analysis of W/B4C multilayers using resonant soft X-ray reflectivity

Controllable Exfoliation of MOF-Derived Van Der Waals Superstructure into Ultrathin 2D B/N Co-Doped Porous Carbon Nanosheets: A Superior Catalyst for Ambient Ammonia Electrosynthesis

The electrocatalytic nitrogen reduction reaction (NRR) to synthesize NH₃ under ambient conditions is a promising alternative route to the conventional Haber-Bosch process, but it is still a great challenge to develop electrocatalysts' high Faraday efficiency and ammonia yield. Herein, a facile and efficient exfoliation strategy to synthesize ultrathin 2D boron and nitrogen co-doped porous carbon nanosheets (B/NC NS) via a metal-organic framework (MOF)-derived van der Waals superstructure, is reported. The results of experiments and theoretical calculations show that the doping of boron and nitrogen can modulate the electronic structure of the adjacent carbon atoms; which thus, promotes the competitive adsorption of nitrogen and reduces the energy required for ammonia synthesis. The B/NC NS exhibits excellent catalytic performance and stability in electrocatalytic NRR, with a yield rate of 153.4 µg·h^-1 ·mg^-1 cat and a Faraday efficiency of 33.1%, which is better than most of the reported NRR electrocatalysts. The ammonia yield of B/NC NS can maintain 92.7% of the initial NRR activity after 48 h stability test. The authors' controllable exfoliation strategy using MOF-derived van der Waals superstructure can provide a new insight for the synthesis of other 2D materials.

Nanoporous B13 C2 towards Highly Efficient Electrochemical Nitrogen Fixation

The electrochemical nitrogen fixation under mild conditions is a promising alternative to the current nitrogen industry with high energy consumption and greenhouse gas emission. Here, a nanoporous boron carbide (np-B₁₃ C₂ ) catalyst is reported for electrochemical nitrogen fixation, which is fabricated by the combination of metallurgical alloy design and chemical etching. The resulting np-B₁₃ C₂ exhibits versatile catalytic activities towards N₂ reduction reactions (NRR) and N₂ oxidation reaction (NOR). A high NH₃ yield of 91.28 µg h^-1 mg_cat.^-1 and Faradaic efficiency (FE) of 35.53% at -0.05 V versus the reversible hydrogen electrode are obtained for NRR, as well as long-term stability of up to 70 h, making them among the most active NRR electrocatalysts. This catalyst can also achieve a NO₃^- yield of 165.8 µg h^-1  mg_cat.^-1 and a FE of 8.4% for NOR. In situ Raman spectroscopy and density functional theory calculations reveal that strong coupling between the BC sites modulates the electronic structures of adjacent B atoms of B₁₃ C₂ , which enables the B sites to effectively adsorb and activate chemical inert N₂ molecules, resulting in lowered energy required by the potential-determining step. Besides, the introduction of carbon can increase the inherent conductivity and reduce the binding energy of the reactants, thus improving N₂ fixation performance.