Dynamically Unveiling Metal–Nitrogen Coordination during Thermal Activation to Design High‐Efficient Atomically Dispersed CoN₄ Active Sites

Abstract

We elucidate the structural evolution of CoN4 sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)‐8‐derived carbon host as an ideal model for Co2+ ion adsorption. Subsequent in situ X‐ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co−OH and Co−O species into active CoN4 sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four‐electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal‐induced compressive strain of Co−N bonds in CoN4 active sites formed at 900 °C. Further, we developed a two‐step (i.e., Co ion doping and adsorption) Co‐N‐C catalyst with increased CoN4 site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.

Acid-Stable and Active M–N–C Catalysts for the Oxygen Reduction Reaction: The Role of Local Structure

“…Besides the well-known Fe–N–C catalyst, the Ru–N–C, , Co–N–C, ,,, and Mn–N–C , catalysts have already been synthesized and tested as an ORR catalyst in acid conditions. However, when we compare theoretical and experimental results, we need to keep in mind that the variation in catalyst preparation and different metal precursor can possibly lead to a different configuration of MN y site for different metal atoms.…”

Atomically Dispersed Fe–Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn–Air Batteries

“…Nowadays, the platinum-group-metal (PGM)-based catalysts such as Pt, Ru, and Ir are still the most commonly used for the ORR/OER, but high cost and scarcity restrict their large-scale applications. − Over the last few decades, continuous advancements of PGM-free catalysts are highly in demand to replace the PGM-based ones. , Among them, the atomically dispersed and nitrogen-coordinated single-metal sites embedded in carbon (M–N–C) have emerged as the most promising ORR or OER catalysts due to their maximized atom utilization and dense activity density. − Inspired by pioneering research, the MN 4 moieties in the M–N–C catalysts have been proved by theoretical results and experiments as the ORR and OER active sites. − Plenty of excellent strategies have been reported to improve the electrocatalytic performance by increasing the specific surface area, defect density, nitrogen content, and active site density. ,− Although their encouraging ORR or OER activity has been demonstrated recently, achieving bifunctional ORR/OER activity and stability using a single metal site still remains a grand challenge. , …”

Atomically dispersed Co–N–C electrocatalysts synthesized by a low-speed ball milling method for proton exchange membrane fuel cells

“…Besides, contrasted with Co foil, the intensity maximum at about 6.7 Å -1 attributed to Co-Co coordination was not detected in Co-120 and Co-40. The aforesaid evidences well identified that Co species were atomically dispersed in synthesized samples 38 .…”

“…The results also confirmed the existence of Co-N structure from the side. It can be seen that the ball milling precursors reached the Co doping amount of the traditional adsorption method of monatomic cobalt synthesis method 38 , and has many advantages, such as high yield, green environmental protection and so on. Moreover, it is worth mentioning that Co-120 and Co-40 has a super high nitrogen content of about 7 at.%, and higher N content means more defects, which would provide a broad application space of this material 39 .…”