Tailoring Nitrogen Chemistry in Boron- and Nitrogen-Codoped Carbon for Enhanced Electrochemical Ammonia Synthesis

The electrocatalytic nitrogen reduction reaction (eNRR) is a promising sustainable solution for ammonia (NH3) production under ambient conditions. Among different electrocatalytic materials, boron-based nonmetallic systems have been identified as potential electrocatalysts for the eNRR because of the unique ability of boron to mimic transition metal d-orbitals to act as active sites for effective nitrogen activation. However, the influence of the local chemical environment of the active boron site, especially nitrogen doping, on eNRR catalytic behavior has been largely overlooked. In this work, we synthesized a series of boron and nitrogen codoped carbon (BNC) catalysts via high-temperature annealing of polyaniline and boric acid mixtures and systematically examined the impact of nitrogen functionalities and hexagonal boron nitride (h-BN) content on eNRR performance. The electronic structure and catalytic behavior of the active boron sites were strongly influenced by the presence of pyridinic nitrogen and h-BN, both of which were highly dependent on the precursor ratio and annealing temperature. From the electrochemical studies it is observed that the BNC-2–1000 catalyst which synthesized from polyanine and boric acid with a ratio of 2:1 annealed at 1000 °C, demonstrated excellent eNRR performance in 0.1 M H2SO4, achieving an ammonia yield of 23.5 μg h–1 mgcat–1 and a Faradaic efficiency (FE) of 18.1% at – 0.2 V vs RHE, surpassing the performance of many of the recently reported metal-free electrocatalytic materials in the similar category. The enhanced performance of BNC-2–1000 emanates from the synergistic effect of the abundant pyridinic-N and B–N moieties, which enhances nitrogen adsorption and activation to effectively weaken the N≡N bond, further supported by its reduced Tafel slope and higher density of accessible active sites. Moreover, boron doping was found to promote nitrogen incorporation via a codoping mechanism and to drive the formation of C–N–B motifs, thereby contributing to carbon matrix modulation. Our study highlights the pivotal influence of nitrogen chemistry, particularly the coordination of pyridinic-N, in optimizing boron-centered active sites to design efficient metal-free electrocatalysts for advancing sustainable ammonia production.