Anchoring Single Copper Atoms to Microporous Carbon Spheres as High‐Performance Electrocatalyst for Oxygen Reduction Reaction

Abstract

Although the carbon-supported single-atom (SA) electrocatalysts (SAECs) have emerged as a new form of highly efficient oxygen reduction reaction (ORR) electrocatalysts, the preferable sites of carbon support for anchoring SAs are somewhat elusive. Here, a KOH activation approach is reported to create abundant defects/vacancies on the porous graphitic carbon nanosphere (CNS) with selective adsorption capability toward transition-metal (TM) ions and innovatively utilize the created defects/ vacancies to controllably anchor TM-SAs on the activated CNS via TMN x coordination bonds. The synthesized TM-based SAECs (TM-SAs@N-CNS, TM: Cu, Fe, Co, and Ni) possess superior ORR electrocatalytic activities. The Cu-SAs@N-CNS demonstrates excellent ORR and oxygen evolution reaction (OER) bifunctional electrocatalytic activities and is successfully applied as a highly efficient air cathode material for the Zn-air battery. Importantly, it is proposed and validated that the N-terminated vacancies on graphitic carbons are the preferable sites to anchor Cu-SAs via a Cu(NC 2 ) 3 (NC) coordination configuration with an excellent promotional effect toward ORR. This synthetic approach exemplifies the expediency of suitable defects/vacancies creation for the fabrication of high-performance TM-based SAECs, which can be implemented for the synthesis of other carbon-supported SAECs.

Deciphering the Precursor–Performance Relationship of Single‐Atom Iron Oxygen Electroreduction Catalysts via Isomer Engineering

“…No peaks associated with crystalline Fe were observed for the samples (Figure S11, Supporting Information), and only one broad peak in the range of 20-30 degree, correspond to the (002) plane of graphite carbon. [45][46][47] This result further supports the conclusions of TEM and HAADF-STEM that the Fe in the Fe-PpPD-800 exists as single atom. Notably, XRD analysis of Fe-PpPD-T at different treatment temperatures showed that the characteristic peaks of iron-based species appeared when the temperature increased to 900 °C or higher (Figure S12, Supporting Information), indicating the Fe aggregates into crystalline species rather than atomically dispersed species under high temperature conditions.…”

“…Moreover, no diffraction spots were detected in the corresponding selected area electron diffraction (SAED) pattern, further confirming the no iron-based nanoparticles were formed in FePpPD-800 (see inset in Figure 1c). Furthermore, the high-resolution TEM image (Figure 1d) only observed a 0.34 nm lattice spacing fringe, attributed to the (002) plane reflection of the graphitic carbon, [44,45] again confirming the absence of iron particles. Similarly, no iron-based nanoparticles were observed for the samples Fe-PoPD-800 and Fe-PmPD-800 (Figure S10, Supporting Information).…”

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects

“…Among them, Cu-SAs@N-CNS exhibits the best ORR performance, with an E 1/2 of 0.90 V ( vs. RHE) and a limiting diffusion current density of −5.50 mA cm −2 in 0.1 M KOH solution. 136 The as-prepared nanofibers are treated with N 2 plasma to increase the number of defects and the N doping amount in the carbon substrate (Fig. 10b).…”

Modulation of Ligand Fields in a Single-Atom Site by the Molten Salt Strategy for Enhanced Oxygen Bifunctional Activity for Zinc-Air Batteries

“…Generally, increasing the number of active sites and optimizing the electronic structure of active site are two effective strategies to boost the catalytic activity of electrocatalysts. − However, increasing the number of active sites of SACs by increasing the metal atomic load remains a challenge since metal atoms tend to agglomerate into nanoparticles during pyrolysis, which is detrimental to their electrocatalytic performance . Based on SACs that are formed by dispersed metal atoms immobilized on the substrate, the size and morphology of the substrate material will significantly affect the exposure of the catalytically active sites of SACs. , Substrate materials with relatively thick dimensions result in a large number of metal active sites being buried inside of the carbon matrix, which cannot be fully utilized. For this reason, under a fixed metal atom load, achieving sufficient exposure of metal active centers will further improve the intrinsic catalytic activity of SACs.…”

“…23 Based on SACs that are formed by dispersed metal atoms immobilized on the substrate, the size and morphology of the substrate material will significantly affect the exposure of the catalytically active sites of SACs. 24,25 Substrate materials with relatively thick dimensions result in a large number of metal active sites being buried inside of the carbon matrix, which cannot be fully utilized. For this reason, under a fixed metal atom load, achieving sufficient exposure of metal active centers will further improve the intrinsic catalytic activity of SACs.…”