Electrochemical nitrogen fixation under mild conditions could save energy and greenhouse gas emissions in industrial nitrogen production. Recently, many pioneering catalysts have been reported. However, a multifunctional N₂ reduction reactions (NRR)/N₂ oxidation reaction (NOR) catalyst with high ammonia yield, large Faradaic efficiency, and excellent stability, which effectively suppresses the side reactions during N₂ fixation, is still missing.

Yongwen Tan, Hunan University, China, and colleagues have designed a nanoporous boron carbide (np-B₁₃C₂) catalyst for electrochemical nitrogen fixation. The team used a chemical etching approach to dissolve an orthorhombic CoB solid solution phase of a Co₃₀B₆₄C₆ precursor. What remains is a B₁₃C₂ skeleton with a bicontinuous nanoporous structure. The researchers found that this np-B₁₃C₂ shows superior catalytic activity and stability to NRR and NOR in aqueous electrolytes compared to most reported electrocatalysts.

Strong coupling between the B–C sites affects the electronic structures of the neighboring B atoms of B₁₃C₂. As a result, the B sites can effectively adsorb and activate chemically inert N₂ molecules. This minimizes the energy required by the potential-determining step. In addition, the introduction of carbon can increase the inherent conductivity and decrease the binding energy of the reactants. As a result, the N₂ fixation performance is improved.

A high NH₃ yield of 91.28 µg h⁻¹mg_cat.⁻¹ and Faradaic efficiency (FE) of 35.53 % at −0.05 V versus the reversible hydrogen electrode were obtained for NRR, as well as long-term stability of up to 70 h. According to the researchers, this means it is among the most active NRR electrocatalysts. The catalyst can also achieve a NO₃⁻ yield of 165.8 µg h⁻¹mg_cat.⁻¹ and a FE of 8.4 % for NOR.

• Nanoporous B₁₃C₂ towards Highly Efficient Electrochemical Nitrogen Fixation,
  Jiao Lan, Min Luo, Jiuhui Han, Ming Peng, Huigao Duan, Yongwen Tan,
  Small 2021.
  https://doi.org/10.1002/smll.202102814