Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

Abstract

Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)‐supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (>70 mV) anodic shift of the half‐wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn‐air batteries, which exhibited equal performance to that with Pt‐based materials.

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

“…As disclosed by Figure 3b, Cu‐SAs@N‐CNS possesses a Tafel slope of 66 mV dec −1 , which is considerably smaller than those of Pt/C (76 mV dec −1 ) and N‐CNS (94 mV dec −1 ), further evidencing the faster reaction kinetics of ORR on Cu‐SAs@N‐CNS. [ 5d,e,23 ] Additionally, an average transferred electron number of 3.98 can be determined from the Koutecký–Levich (K–L) plots derived from the corresponding LSV curves of Cu‐SAs@N‐CNS (Figure 3c), signifying a four‐electron ORR pathway. Within the potential range of 0.2–0.9 V versus RHE, the transferred electron number derived from the RRDE measurements (Figure 3d; Figure S19, Supporting Information) is found to be between 3.8 and 4.0, which agrees well with that measured by the K–L plot method.…”

Highly Curved Nanostructure‐Coated Co, N‐Doped Carbon Materials for Oxygen Electrocatalysis

“…For the rechargeable Zn‐air battery, bifunctional electrocatalysts on air electrode for oxygen reduction/evolution reaction (ORR/OER) are urgently needed due to current drawbacks. Precious metal based catalysts (such as Pt/C and RuO 2 ) are expensive, while low‐cost transition‐metal‐based catalysts still does not meet commercial requirements [11–17] . Recently, materials with highly curved surface have been applied in energy‐related small molecule activation reactions due to the tensile strain effect and local electric field enhancement [18–23] .…”

Highly Curved Nanostructure‐Coated Co, N‐Doped Carbon Materials for Oxygen Electrocatalysis

“…For the rechargeable Zn‐air battery, bifunctional electrocatalysts on air electrode for oxygen reduction/evolution reaction (ORR/OER) are urgently needed due to current drawbacks. Precious metal based catalysts (such as Pt/C and RuO 2 ) are expensive, while low‐cost transition‐metal‐based catalysts still does not meet commercial requirements [11–17] . Recently, materials with highly curved surface have been applied in energy‐related small molecule activation reactions due to the tensile strain effect and local electric field enhancement [18–23] .…”