| Summary: | Efficient, economical, and environmentally friendly multifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are prerequisites for achieving the development of renewable energy conversion and storage technology. As we know, OER and ORR are reverse reactions, playing a crucial role in achieving efficient water splitting, metal air cells and fuel cells. Many studies have been conducted on catalysts for OER and ORR, among which single atom catalysts (SACs) have become one of the most promising catalysts for studying catalytic mechanisms and achieving efficient catalysis due to their unique coordination mode and high metal utilization rate. This work focuses on the rational design of SACs for electrocatalytic oxygen reactions. The main findings of this thesis could be summarized as follows:
1. SACs are being pursued as economical electrocatalysts. However, their low active-site loading, poor interactions, and unclear catalytic mechanism call for significant advances. In the first work, atomically dispersed Ni/Co dual sites anchored on nitrogen-doped carbon (a-NiCo/NC) hollow prisms are rationally designed and synthesized. Benefiting from the atomically dispersed dual-metal sites and their synergistic interactions, the obtained a-NiCo/NC sample exhibits superior electrocatalytic activity and kinetics towards the OER. Moreover, density functional theory calculations indicate that the strong synergistic interactions from heteronuclear paired Ni/Co dual sites lead to the optimization of the electronic structure and the reduced reaction energy barrier.
2. Manipulating the intrinsic activity for heterogeneous catalysts at the atomic level is an effective strategy to improve the electrocatalytic performances as well but remains challenging. Herein, atomically dispersed Ni anchored on CeO2 particles entrenched on peanut-shaped hollow nitrogen-doped carbon structures (a-Ni/CeO2@NC) are rationally designed and synthesized. The as-prepared a-Ni/CeO2@NC catalyst exhibits substantially boosted intrinsic activity and greatly reduced overpotential for the electrocatalytic OER. Experimental and theoretical results demonstrate that the decoration of isolated Ni species over the CeO2 induces electronic coupling and redistribution, thus resulting in the activation of the adjacent Ce sites around Ni atoms and greatly accelerated OER kinetics.
3. Manipulating the coordination environment and electron distribution for heterogeneous catalysts at the atomic level could improve the electrocatalytic performance effectively. In the third work, atomically dispersed Fe and Co anchored on nitrogen, phosphorus co-doped carbon hollow nanorod structures (FeCo-NPC) are rationally designed and synthesized. The as-prepared FeCo-NPC catalyst exhibits significantly boosted electrocatalytic kinetics and greatly upshifted half-wave potential for the ORR. Furthermore, when utilized as the cathode, the FeCo-NPC catalyst also displays excellent zinc-air battery performance. Experimental and theoretical results demonstrate that the introduction of single Co atoms with Co-N/P coordination around isolated Fe atoms induces asymmetric electron distribution, resulting in the suitable adsorption/desorption ability for oxygen intermediates and the optimized reaction barrier, thereby improving the electrocatalytic activity.
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