Carbon-supported transition-metal macrocycles

Scherson, D. A.A. Tanaka, S.L. Gupta, D. Tryk, C. Fierro, R. Holze, and E.B. Yeager (1986). Transition metal macrocycles supported on high area carbon Pyrolysis-mass spectrometry studies. Electrochim. Acta 31, 1247-1258. 

Scherson DA, Tanaka A, Gupta SL, Tryk D, Fierro C, Holze R, Yeager EB (1986) Transition metal macrocycles supported on high area carbon pyrolysis-mass spectrometry studies. Electrochim Acta 31 1247-1258... 

Non-precious metal catalyst research covers a broad range of materials. The most promising catalysts investigated thus far are carbon-supported M-N /C materials (M = Co, Fe, Ni, Mn, etc.) formed by pyrolysis of a variety of metal, nitrogen, and carbon precursor materials [106]. Other non-precious metal electrocatalyst materials investigated include non-pyrolyzed transition metal macrocycles [107-122], coti-ductive polymer-based complexes (pyrolyzed and non-pyrolyzed) [123-140], transition metal chalcogenides [141-148], metal oxide/carbide/nitride materials [149-166], as well as carbon-based materials [167-179]. The advances of these types of materials can be found in Chaps. 7-10 and 12-15 of this book. 

On the other hand, phthalocyanines and porphyrins transition metal complexes have been adsorbed on activated carbon fiber nanopouros support in the form of gas diffusion electrodes The loading of the complexes in the support involve the dissolution of the macrocycles in the proper solvent and then the addition of the (activated carbon fibers ACF). The mixtures were stirred on a magnetic stirrer for 3-4 days at room temperature and then vacuum filtered. The ACF with... 

Chapters 7-12 focus on the electrocatalysis of carbon-based non-precious metal catalysts. The unique properties and fuel cell applications of various carbon based catalysts are intensively discussed in these chapters. Chapter 7 summarizes the fundamental studies on the electrocatalytic properties of metallomacrocyclic and other non-macrocyclic complexes. Chapter 8 and 9 review the progress made in the past 5 years of pyrolyzed carbon-supported nitrogen-coordinated transition metal complexes. Chapter 10 gives a comprehensive discussion on the role of transitional metals in the ORR electrocatalysts in acidic medium. Chapter 11 introduces modeling tools such as density functional theory (DPT) and ah initio molecular dynamics (AIMD) simulation for chemical reaction studies. It also presents a theoretical point of view of the ORR mechanisms on Pt-based catalysts, non-Pt metal catalysts, and non-precious metal catalysts. Chapter 12 presents an overview on recent progresses in the development of carbon-based metal-free ORR electrocatalysts, as well as the correlation between catalyst structure and their activities. 

With this respect, the work from Atanasoski and coworkers is promising (compare section Transition Metal Carbides, Nitrides and Chalcogenides ) [35], By performing a heat treatment of their sputtered C-N iFe Aims, the activity was drastically enhanced but still much lower compared to macrocycle-based catalysts. However, when titanium carbide was used as support instead of carbon, a high stability was obtained. The fact that by changing the support, an essentially better durability was obtained is an important result as it shows that even for catalysts based on molecular centers, alternative support materials can be utilized and that the interaction between the support and the catalytic centers might be cmcial for the optimization of those catalysts for a fuel cell application. 

Although heat treatment can destroy the macrocyclic ring, the N4 ring structure in porphyrin and similar macrocycles is still retained. Heat treatment ean also be performed by heat-treating the macrocycles adsorbed on earbon substrates, followed by the addition of transition metal salts. The pyrolyzed maerocycles on carbon supports provide coordination sites, including N4, to bind transition metals such as Fe and Co, forming M-N4 coordination complexes. However, it was also found that the ORR catalytic activity loss of these heat-treated M-N4 eatalysts in long-term operation was due to the loss of the transition metal from the pyrolyzed macrocycle surface. 

Research has been conducted on many metals including Fe, Co, Mn and Pb in order to find an adequate replacement for Pt. Cobalt and iron have attracted the most attention. These two metals are typically combined with tetramethoxyphenylporphyrin (TMPP) or phthalocyanine (Pc) to form metal macrocyclic complexes. Pyrolyzed FePc and CoTMPP complexes have proven the most effective transition metal-based materials. FePc supported on Ketjen black carbon generated a power density of 634 mW m compared to 593 mW produced by a Pt cathode in the same... 

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