One of the most important chemical reactions for renewable energy technologies such as fuel cells and metal-air batteries today is oxygen reduction. Due to the relatively sluggish reaction kinetics, catalysts are necessary to generate high power output. The most common catalyst for this reaction is platinum, but its scarcity and derived high price have raised the search for abundant nonprecious metal catalysts. Inspired from enzymatic processes which are known to catalyze oxygen reduction reaction efficiently, employing transition metal complexes as their catalytic centers, many are working on the development of bioinspired and biomimetic catalysts of this class. This research news article gives a glimpse of the recent progress on the development of bioinspired molecular catalyst for oxygen reduction, highlighting the importance of the molecular structure of the catalysts, from advancements in porphyrins and phthalocyanines to the most recent work on corroles, and 3D networks such as metal-organic frameworks and polymeric networks, all with nonpyrolyzed, well-defined molecular catalysts for oxygen reduction reaction.
Platinum group metal (PGM)‐free catalysts for oxygen reduction reaction have shown high oxygen reduction reaction activity in alkaline media. In order to further increase the power density of anion‐exchange membrane fuel cells (AEMFCs), PGM‐free catalysts need to have a high site density to reach high current densities. Herein, synthesis, characterization, and utilization of heat‐treated iron porphyrin aerogels are reported as cathode catalysts in AEMFCs. The heat treatment effect is thoroughly studied and characterized using several techniques, and the best performing aerogel is studied in AEMFC, showing excellent performance, reaching a peak power density of 580 mW cm−2 and a limiting current density of as high as 2.0 A cm−2, which can be considered the state‐of‐the‐art for PGM‐free based AEMFCs.
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Aerogels offer a great platform for heterogeneous electrocatalysis owing to their high surface area and porosity. Atomically dispersed transition metal ions can be imbedded in these platforms at ultra‐high site density to make them catalytically active for various reactions. Herein, the synthesis of a new class of conjugated microporous organic aerogels that are used as covalent 3D frameworks for the electrocatalysis of oxygen reduction reaction (ORR) is reported. Modified aerogels functionalized with bipyridine ligands enable copper ion complexation in a single‐step synthesis. The aerogels’ structures are fully characterized using a wide array of spectroscopic and microscopic methods, and heat‐treated in order to make them electronically conductive. After heat treatment at 600 °C, the aerogels maintained their macrostructure and became active ORR catalysts in alkaline environment, showing high mass activity and ultra‐high site density.
Bioinspired transition-metal complexes may serve as efficient
and low-cost potential catalysts for oxygen reduction reaction (ORR)
in fuel cells, instead of precious group metal-free (PGM-free) materials.
Herein, we present a study of the ORR electrocatalytic activity of
different mesosubstituted Co-corroles with varying electronegativity
using both experimental and theoretical methods. Specifically, we
studied the influence of different mesosubstituted Co-corroles on
catalytic activity. Using density functional theory (DFT), we computed
lowest unoccupied molecular orbital (LUMO) energies, vertical excitation
energies, electrostatic potentials, and O2 adsorption energies
and compared them with the ORR catalytic activity obtained from cyclic
voltammetry and rotating ring-disk electrode measurements. We found
that the first one-electron reduction for all the corroles occurs
at the Co-center based on computed LUMOs, and that this is a necessary
step for the ORR mechanism to take place. The ORR reduction potential
trends observed from theory and experiments are in good agreement.
Based on this work, we conclude that the role of the substituents
is significant and an important factor that affects the overpotential
required for the ORR.
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