Understanding the role of Ce sites for boosting PEC-NIRR without externally applied potentials

Abstract

Photoelectrochemical nitrate reduction reaction (PEC-NIRR) is a promising technology of nitrogen fixation, which has the advantages of mild conditions and small carbon footprint. However, due to the low selectivity and competitive hydrogen evolution reaction (HER), PEC-NIRR still faces a critical challenge to achieve the efficient production of NH₃. For the first time, in this study, Ce-doped p-BiVO₄ was fabricated and applied to PEC-NIRR. Ce³⁺ mainly replaced the Bi³⁺ sites in the p-BiVO₄ matrix, and the reversible redox ability of Ce effectively promoted internal carrier migration and surface catalytic kinetics. Without the externally applied potentials (0 V vs. RHE), 1.5% Ce–BiVO₄ showed desirable activity, and the NH₃ yield of 1.5% Ce–BiVO₄ reached 31.54 μg h⁻¹ cm⁻², which is 3.9 times that of p-BiVO₄. The selectivity of NH₃ (relative to NO₂⁻) was enhanced to 24.5 times, compared with that of pristine p-BiVO₄. In addition, ¹H nuclear magnetic resonance (¹H NMR) spectroscopy verified that the source of N was entirely NO₃⁻. Therefore, this work identifies the critical role of Ce sites for tailoring the nature of p-BiVO₄ for efficient PEC-NIRR.