Bimetallic M/N/C catalysts prepared from π-expanded metal salen precursors toward an efficient oxygen reduction reaction

Abstract

Bimetallic metal and nitrogen-containing carbon (M/N/C) catalysts were prepared by pyrolysis of a mixture of carbon support and π-expanded Fe(salen) and Cu(salen) precursors. The bimetallic catalyst promotes efficient four-electron reduction of dioxygen.

Impact of Heterometallic Cooperativity of Iron and Copper Active Sites on Electrocatalytic Oxygen Reduction Kinetics

“…Thus, (Cu,Fe)–N–CNT showed higher ORR activity than Cu–N–CNT and Fe–N–CNT. Similar synergistic effects on the ORR activity were also reported for (Cu,Fe)–N–C electrocatalysts. − …”

“…The C c O utilizes a binuclear complex containing a heme and a copper ion as the active center. , The selectivity toward the 4e – reduction for the ORR reaches >99% for C c O. , Inspired by the active site structure of C c O, molecular-based C c O mimics have been synthesized to understand the mechanistic insights into the enzymatic ORR. Electrochemical studies of these synthetic models suggest that the Cu site acts as the initial O 2 binding site to form bridging heme–peroxo–Cu intermediates and suppresses the release of reactive oxygen species. ,− Cu-doped Fe–N–C, (Cu,Fe)–N–C, electrocatalysts have also been synthesized for the ORR and synergistic effects of the copresence of iron and copper active sites on the ORR activity have been found. − Furthermore, the suppression of the H 2 O 2 production was also observed for (Cu,Fe)–N–C electrocatalysts, compared with the corresponding Cu–N–C and Fe–N–C catalysts . However, heterobimetallic effects of Cu and Fe active sites on the ORR kinetics remain unclear although intensive kinetic studies have been done for single metallic M–N–C catalysts such as Fe–N–C. − …”

“…Low product selectivity of ORR electrocatalysts is believed to contribute to the degradation of the catalyst and/or ionomer and proton-exchange membranes in PEFCs through Fenton-type side reactions, which generate radical species particularly from Fe ion species and H 2 O 2 (Fe 2+ /H 2 O 2 → Fe 3+ / • OH/OH – , Fe 3+ /H 2 O 2 → Fe 2+ / • OOH/H + ). − , The improvement of the 4e – selectivity is crucial for developing practical non-PGM catalysts. To improve the ORR activity and selectivity of Fe–N–C, heterometal-doped Fe–N–C catalysts of (M,Fe)–N–C (M = Mn, Co, , Ni, or Cu − ) have been synthesized. , …”

Thermally Controlled Construction of Fe–Nx Active Sites on the Edge of a Graphene Nanoribbon for an Electrocatalytic Oxygen Reduction Reaction

“…The Fe/N/C electrocatalysts were prepared from the precursors using two methods A and B (Figure ). In method A, precursors 1 – 8 , the iron source, and carbon black (VC) were combined and the mixture was pyrolyzed according to our previously reported method. , The pyrolysis temperature was optimized (Figure S5). Then, Fe/ 1 @VC, Fe/ 2 @VC, Fe/ 3 @VC, Fe/ 4 @VC, Fe/ 5 @VC, Fe/ 6 @VC, Fe/ 7 @VC, or Fe/ 8 @VC was obtained.…”

“…Precursors 1–8 (0.1 mmol for the unit structure of polymer precursors 1 – 4 ), FeCl 2 ·4H 2 O (19.8 mg, 0.1 mmol), and Vulcan XC-72R (33.3 mg) (VC, Cabot) were mixed for the preparation of the Fe/N/C catalysts according to the method described in our previous reports. , …”