Atomically precise (AgPd)27 nanoclusters for nitrate electroreduction to NH3: Modulating the metal core by a ligand induced strategy

Abstract

Electrochemical nitrate reduction reaction (eNO3–RR) to synthesize NH3 is a sustainable method to convert environmental contaminants into valuables. Pd based bimetallic nanocatalysts have demonstrated great promise as efficient catalysts, yet modulating the composition and configuration to improve the catalytic performance and achieve comprehensive mechanistic understanding remains challenging. Herein, by employing two ligands with different electron functional groups, we successfully prepared two atomically precise (AgPd)27 bimetallic clusters of Ag18Pd9(C8H4F)24 (Ag18Pd9) and Ag22Pd5(C9H10O2)26 (Ag22Pd5). The two clusters possess markedly different metal core composition and configuration, where Ag18Pd9 has a sandwich metal core structure with 9 Pd atoms located in the middle layer and Ag22Pd5 has a rod-shaped metal core structure composed of the M13 configuration with 5 Pd atoms located at the center and vertices of the M13 configuration. Unexpectedly, Ag22Pd5 exhibited remarkably superior eNO−3RR performance than Ag18Pd9. Specifically, the highest Faradaic efficiency of NH3 (FENH3) and its yield rate can reach 94.42 ​% and 1.41 ​mmol ​h−1 ​mg−1 ​at −0.6 ​V vs. RHE for Ag22Pd5, but the largest FENH3 and NH3 yield rate is only 43.86 ​% and 0.41 ​mmol ​h−1 ​mg−1 ​at −0.5 ​V vs. RHE for Ag18Pd9. The in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) test provides the experimental evidence of the reaction intermediates hence revealing the reaction pathway, also shows that Ag22Pd5 has stronger capability for NO−3 adsorption and NH3 desorption than that of Ag18Pd9. Theoretical calculations indicate that the de-ligated clusters can expose the available AgPd bimetallic sites, synergistically serving as effective active sites and the different configurations result in significantly different catalytic activities, where the active sites in Ag22Pd5 are more favorable for NO−3 adsorption and NH3 desorption to accelerate the catalytic process.