Manipulating electron redistribution of active sites by in situ engineering B-S-V bond in VS2 catalyst for stable nitrogen fixation

[Display omitted] •The reduction of V4+ to V2+ in deactivated VS2 can be restrained by B-doping.•We used in situ tests to trace the evolution of V and analyze the NRR process.•In situ engineering B-S-V bond facilitates the electron transfer from V to B. VS2 is a promising NRR electrocatalyst, however, it remains a challenge to stabilize the V4+ active sites to retain the activity of VS2 under long term electrolysis. Herein, we report the synthesis of boron doped VS2 (B-VS2) as an advanced NRR electrocatalyst with stable V4+ for efficient catalytic performance. X-ray absorption spectroscopy (XAS) proves that B-doping virtually induces the formation of B-S-V bonding configuration in the resultant B-VS2. Importantly, we used quasi in situ X-ray photoelectron spectrometer (XPS), in situ Raman and in situ Fourier transform infrared (FTIR) spectra to dynamically trace the evolution of V valence state and analyze the accumulation of NN and NN species during NRR process. The significantly enhanced NRR performance of B-VS2 is attributed to the in situ engineering B-S-V bond which can stabilize V4+ active sites by manipulating electron redistribution. Density functional theory calculations show that the newly formed B-S-V bond facilitates the electron transfer from V atoms to B atoms, in which S atoms act as the electron transfer bridges, thus generating electron-rich B sites and electron-deficient V sites. Such an electron redistribution substantially stabilizes the V4+ active sites, which suppresses the reduction of V4+ to V2+ at extremely low overpotential. This work not only provides powerful guidelines for improving the NRR performance of VS2 based electrocatalysts, but also offers a deep understanding of relationship between the valence state of active sites and the catalytic activity.