Bioinspired Transition‐Metal Complexes as Electrocatalysts for the Oxygen Reduction Reaction

Abstract

The oxygen reduction reaction (ORR) is one of the most important reactions in life processes and energy conversion systems. To alleviate global warming and the energy crisis, the development of high-performance electrocatalysts for ORR for their application in energy conversion and storage devices such as metal-air batteries and fuel cells is highly desirable. Inspired by the biological oxygen activation/reduction process associated with heme- and multicopper-containing metalloenzymes, iron and copper-based transition metal complexes have been extensively explored as ORR electrocatalysts. This review outlines recent progress on non-precious-metal electrocatalysts for ORR that do not require pyrolysis treatment, which is regarded as desirable from the viewpoint of bio-inspired molecular catalyst design, focusing on iron/cobalt macrocycles (porphyrins, phthalocyanines, and corroles) and copper complexes in which the ORR activity is tuned by ligand variation/substitution, the method of catalyst immobilization, and the underlying supporting materials. Current challenges and exciting imminent developments in bio-inspired ORR electrocatalysts are summarized and proposed.

Synthesis and Active Site Identification of Fe−N−C Single‐Atom Catalysts for the Oxygen Reduction Reaction

“…Inspired from enzymatic processes, grafting macrocyclic compounds to a conductive substrate is developed to prepare catalysts with well-defined active-site structures. [46] Liu and co-workers reported a bio-inspired ORR electrocatalyst by covalently grafting iron porphyrin to multiwalled carbon nanotubes (MWCNTs) mimicking the active site of heme-containing O 2 -activating enzymes ( Figure 6A). [47] This non-pyrolyzed catalyst exhibited remarkably higher ORR activity, superior stability, and excellent methanol tolerance in comparison to the commercial Pt/C catalyst in both acid and alkaline.…”

Carbon Nanotube‐Based Non‐Precious Metal Electrode Catalysts for Fuel Cells, Water Splitting and Zinc‐Air Batteries

“…Certain organic molecules with promising oxygen reduction reaction (ORR) activities have been attracting attentions since Jasinski found transition metal‐N 4 chelates were active for the ORR for the first time . To date, a variety of organic molecules have been explored as the ORR catalysts of which the metal porphyrins and phthalocyanines are the most promising candidates .…”

“…In order to further elevated the valence of centered iron ions, Cao et al. used pyridine‐functionalized single‐walled carbon nanotubes (Py−CNTs) as the support for FePc, in which an axial ligand was provided for the centered Fe ions in the FePc molecules, in which the half‐wave potential of the resultant FePc−Py−CNTs reached 0.915 V vs. RHE and did not decrease even after 1000 cycles of cyclic voltammetry.…”

Cu(I) Coordination Complex Precursor for Randomized CuOx Microarray Loaded on Carbon Nanofiber with Excellent Electrocatalytic Performance for Electrochemical Glucose Detection

“…Indeed, they can be used both as immobilization matrixes for metal/metal oxides and as transducers due to their electrochemical signal [24][25][26].Recently, the construction of micro-/nano-structures assembly-based electrode compositions containing copper/copper oxides has been studied for enhancing the electrocatalytic properties and implicit, the electroanalytical performance for the non-enzymatic detection of glucose through the one-pot solvothermal method [8] and the copper-based metal-organic framework [1].Copper coordination complexes represent one of the largest classes containing copper with relevant photochemical and photophysical properties [27]. Inspired by the important role of copper in biological systems, biomimetic materials that were based on copper coordination complexes were obtained and reported as good catalysts for water oxidation [28] or oxygen reduction in fuel cells [29][30][31][32]. Cu(I) coordination complexes with chelating NˆN ligands show appropriate photophysical and redox properties, being proposed as successful cheap and nontoxic alternatives in Light Emitting Devices (LEDs) instead of rare earth and noble metals [33] or Dye Sensitized Solar Cells (DSSCs) instead of Ru(II) [34].…”

“…Copper coordination complexes represent one of the largest classes containing copper with relevant photochemical and photophysical properties [27]. Inspired by the important role of copper in biological systems, biomimetic materials that were based on copper coordination complexes were obtained and reported as good catalysts for water oxidation [28] or oxygen reduction in fuel cells [29][30][31][32]. Cu(I) coordination complexes with chelating NˆN ligands show appropriate photophysical and redox properties, being proposed as successful cheap and nontoxic alternatives in Light Emitting Devices (LEDs) instead of rare earth and noble metals [33] or Dye Sensitized Solar Cells (DSSCs) instead of Ru(II) [34].…”