Highly active atomically dispersed CoN₄ fuel cell cathode catalysts derived from surfactant-assisted MOFs: carbon-shell confinement strategy

Abstract

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction are essential for affordable fuel cells.

Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

“…The conclusion on this matter could also be a sort of a middle way. In a detailed work, He et al present experimental support for the presence of a slightly different active site, which they refer to as Co–N 2+2 in line with earlier theoretical studies . By using a surfactant (Pluronic F127 block copolymer) assisted approach in combination with zeolitic imidazolate framework they achieved highly dispersed single Co‐atomic sites.…”

“…It is interesting to note however that Sun et al propose that Co–N 4 and Co–N 2 sites are complementing each other in the ORR, in such way that the dissociation of O 2 only proceeds until the adsorption of HOOH on the Co–N 4 site and that the further dissociation of HOOH only proceeds on neighboring Co–N 2 sites . Other studies indicate however that ORR could proceed with good efficiency from start to beginning (from (I) to (IV) in Equation on both Co–N 4 and Co–N 2 sites . The conclusion on this matter could also be a sort of a middle way.…”

“…Theoretical calculations show that both Co–N 4 , and Co–N 2 moieties embedded in a carbon matrix are thermodynamically stable . From the reports available at present date, only few experimental support for Co–N 2 moieties are however reported in all other cases EXAFS is shown to give a Co–N coordination close to four, although some reports identify their active centers as Co–N x . For most of the Co–N x reports, there is however, a lack of XAFS, and the x should rather be seen as being a value not fully determined.…”

A Phthalocyanine‐Based Layered Two‐Dimensional Conjugated Metal–Organic Framework as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction

“…[13,14,[16][17][18][19][20][21][22][23][24] In particular,s uch MOFs can provide an ideal platform for the investigation of the mechanism of the ORR process,w hich is essential for the rational design of electrocatalysts. [17] Apart from M-N x sites, [28] the catalytic activity of M-O x sites with unique electronic structures is intrinsically high for electrocatalytic ORR. The2 D porous structure ensures fast mass transport while the defined active sites (Ni-N 4 )e ffectively catalyze the ORR.…”

“…[27][28][29] Theas-prepared PcCu-O 8 -Co,hybridized with carbon nanotubes (PcCu-O 8 -Co/CNTs), affords superior ORR activity (E 1/2 = 0.83 Vv s. RHE, n = 3.93, j L = 5.3 mA cm À2 )i n alkaline media compared to that of other reported intrinsic MOF catalysts due to the high coverage of electrochemically active Co sites,high conductivity,and porous structure.Insitu Raman spectroscopy was employed to probe the Co-O 4 centers and their interaction with oxygen intermediates during the ORR process,v erifying that the Co-O units act as catalytic active sites.F inally,w ee mployed PcCu-O 8 -Co in the zinc-air batteries,w hich exhibited promising discharge performance and capacity,s uperior to commercial Pt/C electrocatalysts. This 2D PcCu-O 8 -Co MOF features ah ighly crystalline structure and optimized spin state of the cobalt node,w herein the unpaired electron in the s*antibonding orbital (e g = 1) in the cobalt node leads to Co-O 4 centers with high ORR activity.…”