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.