Leilei Yin,Mingzi Sun,Shuai Zhang,Yongkang Huang,Bolong Huang,Yaping Du
Currently, there are still obstacles to rationally designing the ligand fields to activate rare-earth (RE) elements with satisfactory intrinsic electrocatalytic reactivity. Herein, axial coordination strategies and nanostructure design are applied for the construction of La single atoms (La-Cl SAs/NHPC) with satisfactory oxygen reduction reaction (ORR) activity. The nontrivial LaN 4 Cl 2 motifs configuration and the hierarchical porous carbon substrate that facilitates maximized metal atom utilization ensure high half-wave potential (0.91 V) and significant robustness in alkaline media. The aqueous and flexible Zinc-air battery (ZAB) integrating La-Cl SAs/NHPC as the cathode catalyst exhibits a maximum power density of 260.7 and 68.5 mW cm −2 , representing one of the most impressive RE-based ORR electrocatalysts to date. Theoretical calculations have demonstrated that the Cl coordination evidently modulate the electronic structures of La sites, which promoted electron transfer efficiency by d-p orbital couplings. With enhanced electroactivity of La sites, the adsorptions of key intermediates are optimized to alleviate the energy barriers of the potential-determining step. Importantly, this preparation strategy is also successfully applied to other REs. This work provides perspectives for near-range electronic structure modulation of RE-SAs based on a nonplanar coordination micro-environment for efficient electrocatalysis.
Heteroatom-doping is an effective method for modifying the geometric symmetry of metal–nitrogen–carbon (M–N–C) single-atom catalysts and thereby tuning the electronic structure. Up to now, most of the current reports have concentrated on introducing heteroatoms into the highly symmetrical M–N 4 structure. The coordination-unsaturated M–N 2 structure is more sterically favorable for the insertion of alien atoms to optimize the electronic structure. Herein, a Ni–N 2 catalyst with out-of-plane coordinated chlorine (Cl) atoms (Ni–N 2 Cl/C) is successfully constructed on chlorine-functionalized carbon supports (C–Cl) for an efficient carbon dioxide reduction reaction (CO 2 RR). Density functional theory calculations demonstrate that the prepared Ni–N 2 Cl/C catalyst exhibits a higher capability in balancing COOH* formation and CO* desorption. In addition, in situ Raman spectra confirm that the lower CO binding energy on the Ni–N 2 Cl/C facilitates CO escape, leading to excellent CO 2 RR performance. A high CO Faradaic efficiency (FE CO ) of more than 80% is achieved from −0.6 to −1.2 V versus reversible hydrogen electrode on the Ni–N 2 Cl/C and it exhibits negligible FE CO and current declination over a 40-h stability test. Furthermore, a high turnover frequency (TOF) value of 15 808 h −1 is obtained, which is more than ten times that of Ni–N 2 /C (1476 h −1 ) without coordinated Cl atoms.
The development of oxygen reduction reaction (ORR) catalysts with high activity, stability, and economic applicability plays a decisive role in reducing expenses and enhancing the discharge performance of seawater-based zinc-air batteries (SWZABs). Co- and Fe-based single-atom catalysts (M-N4-C) with metal-N4 structure offer advantages of well-defined active structure and high active site utilizations. However, the oxygen electrocatalytic performance of M-N4-C remains a formidable challenge due to the highly stable centrosymmetric electronic structure. To overcome the dilemma, we develop a Co-N4Cl-C with axial coordination of Cl atoms. The axial coordination drags the Co atoms out of the Co-N4 centrosymmetric configuration. This alters the electronic configuration of Co single-atom sites, resulting in a valence state change from +1.83 to +0.67 and forming a localized negative charge environment. These alternations enhance the electronic orbital overlap between Co single-atom sites and oxygen species, promote the rapid evolution of *OOH intermediates, and inhibit the adsorption of toxic Cl- ions, ensuring the ORR kinetics and stability. Co-N4Cl-C exhibits a high oxygen reduction onset potential of 1.05 mV and a half-wave potential of 0.88 mV vs. the reversible hydrogen electrode. The SWZAB, featuring a Co-N4Cl-C catalyst cathode, Zn anode, and NaCl electrolyte supplemented with KOH, reaches a discharge voltage platform of 1.27 V and a peak power density of 179 mW·cm-2, even at a current density of 10 mA·cm-2. This study sheds important light on advancing single-atom catalysts with superior ORR performance and economic viability.
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