Strategic regulation of nitrogen-containing intermediates for enhanced nitrate reduction over Co3O4/SiC catalyst having multiple active centers

Abstract

Regulating the intermediates involved in the electrocatalytic nitrate reduction reaction (NO₃RR) is crucial for the enhancement of reaction efficiency. However, it remains a great challenge to regulate the reaction intermediates through active site manipulation on the surface of the catalyst. Here, a family of n%-Co₃O₄/SiC (n = 5, 8, 12, 20) catalysts with a delicate percentage of Co²⁺ and Co³⁺ were prepared for NO₃RR. We found that Co³⁺ primarily acts as the active site for NO₃⁻ reduction to NO₂⁻, while Co²⁺ is responsible for the conversion of NO₂⁻ to NH₃. Moreover, the conversion of these intermediates over the active sites is autonomous and separately controllable. Both processes synergistically accomplish the reduction of nitrate ions to synthesize ammonia. Combining the experimental studies and density functional theory (DFT) calculations, it is discovered the pathway (*NHO→*NHOH→*NH₂OH→*NH₂→*NH₃) is more favorable due to the lower ΔG value (0.25 eV) for the rate-limiting step (*NO→*NHO). The NH₃ yield rate of 8%-Co₃O₄/SiC reached 1.08 mmol/(cm² h) with a Faradaic efficiency of 96.4% at −0.89 V versus the reversible hydrogen electrode (RHE), surpassing those of most reported non-noble NO₃RR catalysts. This strategy not only provides an efficient catalyst for NO₃RR but also serves as an illustrative model for the regulation of multi-step reaction intermediates through the design of distinct active sites, thereby presenting a new approach to enhance the efficiency of intricate reactions.