Fe–N–C electrocatalysts in the oxygen and nitrogen cycles in alkaline media: the role of iron carbide

Abstract

Fe–N–C electrocatalysts hold a great promise for Pt-free energy conversion, driving the electrocatalysis of oxygen reduction and evolution, oxidation of nitrogen fuels, and reduction of N2, CO2, and NOx. Nevertheless,...

Orthogonal Design of Fe−N4 Active Sites and Hierarchical Porosity in Hydrazine Oxidation Electrocatalysts

“…Finally, the carbons are sufficiently graphitic to allow electronic conductivity, as determined by Raman spectroscopy (Figure 6). The ratio of defected (D) to graphitic (G) bands (after deconvolution) is well within the range of typical electrocatalysts [27,50] . Overall, C600 and C800 carbons exhibit very promising properties as electrocatalyst supports: high surface area, hierarchical micro‐/meso‐/macro‐porosity, and sufficient graphitization.…”

“…The ratio of defected (D) to graphitic (G) bands (after deconvolution) is well within the range of typical electrocatalysts. [27,50] Overall, C600 and C800 carbons exhibit very promising properties as electrocatalyst supports: high surface area, hierarchical micro-/meso-/macro-porosity, and sufficient graphitization. In contrast to the commercial carbons typically used for macrocycle support, which are mostly microporous, the richly hierarchical porosity is expected to improve flow of hydrazine and removal of N 2 bubbles, while providing electronic conductivity to the active sites.…”

“…[6][7][8][16][17][18][19][20][21][22] Metal-doped carbon materials -in particular those with atomically dispersed FeÀ N 4 sites -are promising new HzOR electrocatalysts, as they are active, selective, stable, and PGMfree. [20,[25][26][27] They are inspired by FeÀ N 4 macrocycles pioneered by Zagal, reporting in 1980 a carbon-adsorbed iron phthalocyanine (FePc) driving the HzOR in neutral electrolyte. [28] Ever since, HzOR electrocatalysis was reported on many carbon-adsorbed FePcs, across the pH range.…”

Fe3O4 Templated Pyrolyzed Fe−N−C Catalysts. Understanding the role of N‐Functions and Fe3C on the ORR Activity and Mechanism

“…[15,22] The ability of iron containingparticles to resist the leaching treatments using acidic media, usually carried out before a second pyrolysis treatment, has been attributed to their coating by protective graphitic layers and achieved during the thermal treatments. [23,24] For instance, the role in the ORR activity of iron-based carbide particles (Fe 3 C) that are usually formed during the pyrolysis treatments [25] is a controversial matter since, in the literature, they have been described merely as impurities affecting the activity [26,27] and as carbon-coated particles with a significant synergic influence over the active single FeN4 sites. [13,28] Some authors have related their participation in the ORR catalytic performance with promoting the 2 × 2 electron pathway, [22,29] while others have stated that their presence efficiently promotes the 4-electron pathway.…”

Lanthanoid coordination compounds as diverse self-templating agents towards hierarchically porous Fe–N–C electrocatalysts

“…24,[38][39][40][41][42][43][44][45] Surprisingly, few elements are known to be self-templating in carbons: the alkaline earths, 24,[38][39][40][41][42][43][44][45] a handful of post-transition metals, 46,47 lanthanum, 48,49 and several transition metals (which are often catalytic, thus convoluting structural and catalytic effects). [50][51][52][53][54] To expand the utility of the self-templating pore design strategy, the range of templating elements must be extended, and the templating process must be better understood. The self-templating strategy can be enhanced even further with the simultaneous imprinting of catalytic sites, following the Fellinger method (Figure 1).…”