Atomically Dispersed Iron–Nitrogen Sites on Hierarchically Mesoporous Carbon Nanotube and Graphene Nanoribbon Networks for CO₂ Reduction

Abstract

Atomically dispersed metal and nitrogen co-doped carbon (M-N/C) catalysts hold great promise for electrochemical CO2 conversion. However, there is a lack of cost-effective synthesis approaches to meet the goal of economic mass production of single-atom M-N/C with desirable carbon support architecture for efficient CO2 reduction. Herein, we report facile transformation of commercial carbon nanotube (CNT) into isolated Fe–N4 sites anchored on carbon nanotube and graphene nanoribbon (GNR) networks (Fe-N/CNT@GNR). The oxidization-induced partial unzipping of CNT results in the generation of GNR nanolayers attached to the remaining fibrous CNT frameworks, which reticulates a hierarchically mesoporous complex and thus enables a high electrochemical active surface area and smooth mass transport. The Fe residues originating from CNT growth seeds serve as Fe sources to form isolated Fe–N4 moieties located at the CNT and GNR basal plane and edges with high intrinsic capability of activating CO2 and suppressing hydrogen evolution. The Fe-N/CNT@GNR delivers a stable CO Faradaic efficiency of 96% with a partial current density of 22.6 mA cm–2 at a low overpotential of 650 mV, making it one of the most active M-N/C catalysts reported. This work presents an effective strategy to fabricate advanced atomistic catalysts and highlights the key roles of support architecture in single-atom electrocatalysis.

Carbon‐Supported Single Metal Site Catalysts for Electrochemical CO2 Reduction to CO and Beyond

“…[62] Pan et al reported FeN 4 sites' synthesis on carbon frameworks with graphene nanoribbon attached to the fibrous CNT, achieving high electrochemically active surface area and smooth mass transport. [63] This carbon structure was synthesized through controllable partial unzipping of CNT using KMNO 4 /H 2 SO 4 as oxidants. In contrast, the Fe residues in CNTs synthesized by chemical vapor deposition (CVD) method can be directly used as a Fe source to grow FeN 4 sites.…”

From CO2 to Value-Added Products: A Review about Carbon-Based Materials for Electro-Chemical CO2 Conversion

“…Having nanotubes as a matrix facilitates mass diffusion and provides good conductivity, which was reflected in the high activity of the catalysts towards the reduction of CO 2 with an FE close to 100% in a wide potential of −0.6 V to −1.0 V vs. RHE, current density of 34.3% at −1.0 V, and stability of 20 h maintaining a percentage of 98% of its initial activity. Pan and co-workers [128] also obtained high electrochemical activity using commercial carbon nanotubes (C-CNT) in the synthesis of the catalysts. C-CNT were oxidized to obtain graphene nanoribbons attached to the outer walls of the remaining nanotubes, which had isolated Fe-N 4 active sites.…”

Inside‐and‐Out Semiconductor Engineering for CO2 Photoreduction: From Recent Advances to New Trends

“…[ 154–157 ] 5) A series of new photocatalytic systems are developed for CO 2 photoreduction, such as metal organic frameworks (MOFs), [ 158–163 ] covalent organic frameworks (COFs), [ 164–169 ] semiconductor biohybrids systems, [ 170–172 ] and single atom. [ 173–177 ] These systems have different chemical affinities to CO 2 molecules, and thus may change the redox reaction pathways during CO 2 reduction process. Meanwhile, polarity enhancement and creation of spatially separated active sites as new strategies for enhancing charge separation and optimizing reactive catalytic sites attracts intense attentions.…”