Modulation effect in adjacent dual metal single atom catalysts for electrochemical nitrogen reduction reaction

Nitrogen reduction reaction (NRR) is a clean mode of energy conversion and the development of highly efficient NRR electrocatalysts under ambient conditions for industrial application is still a big challenge. Metal-nitrogen-carbon (M-N-C) has emerged as a class of single atom catalyst due to the unique geometric structure, high catalytic activity, and clear selectivity. Herein, we designed a series of dual metal single atom catalysts containing adjacent M-N-C dual active centers (MN_(4)/M'N_(4)-C) as NRR electrocatalysts to uncover the structure-activity relationship. By evaluating structural stability, catalytic activity, and selectivity using density functional theory (DFT) calculations, 5 catalysts, such as CrN_(4)/M'N_(4)-C (M’ = Cr, Mn, Fe, Cu and Zn), were determined to exhibit the best NRR catalytic performance with the limiting potential ranging from -0.64 V to -0.62 V. The CrN_(4) center acted as the main catalytic site and the adjacent M'N_(4) center could enhance the NRR catalytic activity by modulation effect based on the analysis of the electronic properties including the charge density difference, partial density of states (PDOS), and Bader charge variation. This study offers useful insights on understanding the structure-activity relationship of dual metal single atom catalysts for electrochemical NRR.

Evolution of Zn(Ⅱ) single atom catalyst sites during the pyrolysis-induced transformation of ZIF-8 to N-doped carbons

The pyrolysis of zeolitic imidazolate frameworks(ZIFs) is becoming a popular approach for the synthesis of catalysts comprising porphyrin-like metal single atom catalysts(SACs) on N-doped carbons(M-N-C).Understanding the structural evolution of M-N-C as a function of ZIF pyrolysis temperature is important for realizing high performance catalysts.Herein,we report a detailed investigation of the evolution of Zn single atom catalyst sites during the pyrolysis of ZIF-8 at temperatures ranging from 500 to 900℃.Results from Zn L-edge and Zn K-edge X-ray absorption spectroscopy studies reveal that tetrahedral ZnN4 centers in ZIF-8 transform to porphyrin-like ZnN4 centers supported on N-doped carbon at temperatures as low as 600℃.As the pyrolysis temperature increased in the range 600-900℃,the Zn atoms moved closer to the N4 coordination plane.This subtle geometry change in the ZnN4 sites alters the electron density on the Zn atoms(formally Zn2+),strongly impacting the catalytic performance for the peroxidase-like decomposition of H2 O2.The catalyst obtained at 800℃(Zn-N-C-800) offered the best performance for H2 O2 decomposition.This work provides valuable new insights about the evolution of porphyrin-like single metal sites on N-doped carbons from ZIF precursors and the factors influencing SAC activity.

Electrocatalytic H_(2)O_(2)generation for disinfection

Epidemics are threatening public health and social development.Emerging as a green disinfectant,H_(2)O_(2)can prevent the breakout of epidemics in migration.Electrochemical H_(2)O_(2)production powered by renewable electricity provides a clean and decentralized solution for on-site disinfection.This review firstly discussed the efficacy of H_(2)O_(2)in disinfection.Then necessary fundamental principles are summarized to gain insight into electrochemical H_(2)O_(2)production.The focus is on exploring pathways to realize a highly efficient H_(2)O_(2)production.Progress in advanced electrocatalysts,typically single-atom catalysts for the two-electron oxygen reduction reaction(2e−ORR),are highlighted to provide high H_(2)O_(2)selectivity design strategies.Finally,a rational design of electrode and electrolytic cells is outlined to realize the on-site disinfection.Overall,this critical review contributes to exploiting the potentials and constraints of electrochemical H_(2)O_(2)generation in disinfection and pinpoints future research directions required for implementation.