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.

Two-Dimensional Biphenylene: A Graphene Allotrope with Superior Activity toward Electrochemical Oxygen Reduction Reaction

“…The polarization curves of 2D biphenylene at different pH values can be obtained by solving the rate equations (see the Supporting Information for the computational details). As a validation, the half-wave potentials of Pt(111) were determined to be 0.90 V at pH 1 and 0.87 V at pH 13, consistent with previous experimental studies. − 2D biphenylene exhibits a rather small half-wave potential of 0.53 V at pH 1, which is much lower than that of Pt. Therefore, although 2D biphenylene has a considerably high limiting potential, it would show rather poor ORR performance in acidic environments, which was often ignored by previous theoretical studies.…”

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

“…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][12][13][14][15][16][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][19][20][21][22][23] For example, Guo et al designed a highly curved PdMo bimetallene material, which exhibits excellent bifunctional ORR/OER performance.…”

Meso‐substituted Metalloporphyrin‐based Composites for Electrocatalytic Oxygen Reduction Reactions

“…[65] Liang et al prepared a variety of hybrids by grafting cobalt porphyrin 4 onto the surface of MOF materials and observed quite remarkable ORR activity (Figure 4). [13] He et al prepared several Co porphyrin molecules supported on graphene/Ni (111) substrates with significantly enhanced catalytic oxygen evolution reaction (OER) and ORR performance. The ORR/OER overpotentials were observed to be greatly reduced, in particular that of ORR from 0.6 V to 0.31 V. [66] Besides the reactivity differences between the iron and cobalt porphyrins, the durability of porphyrins with the two metal species has been further investigated.…”

“…[6,7] Research has therefore focused on the design of new relatively inexpensive, environmental friendly and efficient electrocatalysts. [8] Nowadays, there are numerous materials that have been widely investigated as the alternatives to the Pt-based particles, for instance, metal-nitrogen-doped carbon (M-N-C) composites, [9][10][11] organic polymers, [12] metal-organic framework (MOF) [13,14] and covalent-organic framework (COF) materials. [15,16] Whilst many efficient catalytic materials have been inspired/ derived from metalloporphyrin macrocycles, the direct use of porphyrins as the active center hosting the catalytic reactions should be of high interesting and desire deep understanding.…”