Active‐Site Imprinting: Preparation of Fe–N–C Catalysts from Zinc Ion–Templated Ionothermal Nitrogen‐Doped Carbons

Abstract

sales of light electric vehicles (battery electric vehicles and plug-in hybrid electric vehicles) are politically pushed and increasing exponentially. [1] Vehicles based on proton-exchange-membrane fuel cells (PEMFCs) have the potential to surpass the limitations of battery-based ones, especially, regarding the driving range. Unfortunately, the mass commercialization of this technology is hampered by the limited availability and high cost of Pt, which is required to speed up the anodic and cathodic reactions happening in a PEMFC. [2,3] Since ≈4 times more Pt is required on the cathode than at the anode side, the development of cathode materials containing low Pt amount is a promising way to reduce costs. Unfortunately, low-Pt cathode materials suffer from other limitations, such as losses due to mass transport; [4] also, when the Pt content is reduced below 100 µg cm −2 , the cost of other components rises. [3] For these reasons, completely replacing the Pt at the cathode side is a reasonable and promising way to go.In the last 10 years, platinum-group-metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) have drawn the attention of many research groups all over the world. Since it has been shown that bioinspired metal-nitrogen-doped-carbon (M-N-C, M = Fe, Co) catalysts could meet the requirements for Atomically dispersed Fe-N-C catalysts are considered the most promising precious-metal-free alternative to state-of-the-art Pt-based oxygen reduction electrocatalysts for proton-exchange membrane fuel cells. The exceptional progress in the field of research in the last ≈30 years is currently limited by the moderate active site density that can be obtained. Behind this stands the dilemma of metastability of the desired FeN 4 sites at the high temperatures that are believed to be a requirement for their formation. It is herein shown that Zn 2+ ions can be utilized in the novel concept of active-site imprinting based on a pyrolytic template ion reaction throughout the formation of nitrogen-doped carbons. As obtained atomically dispersed Zn-N-Cs comprising ZnN 4 sites as well as metal-free N 4 sites can be utilized for the coordination of Fe 2+ and Fe 3+ ions to form atomically dispersed Fe-N-C with Fe loadings as high as 3.12 wt%. The Fe-N-Cs are active electocatalysts for the oxygen reduction reaction in acidic media with an onset potential of E 0 = 0.85 V versus RHE in 0.1 m HClO 4 . Identical location atomic resolution transmission electron microscopy imaging, as well as in situ electrochemical flow cell coupled to inductively coupled plasma mass spectrometry measurements, is employed to directly prove the concept of the active-site imprinting approach.

Chemical Vapor Deposition of Fe-N-C Oxygen Reduction Catalysts with Full Utilization of Dense Fe-N4 Sites

“…and quadrupole slitting (QS) than those of D3 here were usually observed in Fe-N-C catalysts synthesized using iron chlorides as the Fe precursors (17,36). Due to this observation and the match of IS and QS values of D3 with those of FeCl 2 (37), and even closer match with FeCl 2 -graphite intercalation compounds (38), we assign the D3 component in FeNC-CVD-750 to FeCl 2 .…”

Chemical Vapor Deposition of Fe-N-C Oxygen Reduction Catalysts with Full Utilization of Dense Fe-N4 Sites

“…and quadrupole slitting (QS) than those of D3 here were usually observed in Fe-N-C catalysts synthesized using iron chlorides as the Fe precursors(17,36). Due to this observation and the match of IS and QS values of D3 with those of FeCl 2 (37), and even closer match with FeCl 2 -graphite intercalation compounds (38), we assign the D3 component in FeNC-CVD-750 to FeCl 2 .…”

Recent Progress in Engineering the Atomic and Electronic Structure of Electrocatalysts via Cation Exchange Reactions

“…Recently, the cation exchange strategy has been extended to synthesize single metal catalysts. [85][86][87][88] A combination of the cation exchanged single metal atoms with the well-controlled oxide or sulfide materials may create new and exciting opportunities for achieving unique catalytic performance. 3) Long-term stability evaluation must be explored in details for possible applications.…”

“…Recently, the cation exchange strategy has been extended to synthesize single metal catalysts. [ 85–88 ] A combination of the cation exchanged single metal atoms with the well‐controlled oxide or sulfide materials may create new and exciting opportunities for achieving unique catalytic performance. Long‐term stability evaluation must be explored in details for possible applications. [ 89,90 ] The assessment should be made on a monthly basis and the changes in catalyst composition, the mass of the catalyst, and catalyst surface area should be carefully investigated.…”