Phosphorus doped carbon nitride with rich nitrogen vacancy to enhance the electrocatalytic activity for nitrogen reduction reaction

It is very significant to explore the metal-free electrocatalyst with high activity and good stability for Nitrogen reduction reaction (NRR). Herein, an efficient and stable metal-free NRR electrocatalyst P-NV-C3N4 is synthesized successfully through the P doping in C3N4 combined with the design of nitrogen vacancy (NV) structure. The electrocatalyst has excellent electrocatalytic activity, selectivity and stability (over 20 h) for NRR in neutral electrolyte. Its yield of NH3 is 28.67 μg h−1 mgcat.−1, and the FEs is 22.15% at −0.3 V (vs. RHE), which is considerably better than pristine C3N4, P-C3N4 and NV-C3N4. Structural characterization and Density functional theory calculation (DFT) reveals that P doping can effectively promote water splitting and provide hydrogen source for nitrogen reduction. Meanwhile, the N-vacancy structure can significantly inhibit the formation of HER pathway, hinder the Heyrovsky step (H*→H2), and promote the adsorption and activation of N2. Through the research of different NRR pathway, its optimal reaction pathway (distal pathway) is determined. In addition, P-NV-C3N4 can reduce the energy barrier of potential-determining step (ΔGPDS) in NRR process, and stabilize the reaction intermediates, thus improving its NRR performance.