Encapsulation of Iron Nitride by Fe–N–C Shell Enabling Highly Efficient Electroreduction of CO₂ to CO

Abstract

The conversion of CO 2 into valuable chemicals has captured extensive attention for its significance in energy storage and greenhouse gas alleviation, but the development of cost-effective electrocatalysts with high activity and selectivity remains the bottleneck. Herein, we designed a Fe−N−C nanofiber catalyst featuring a core−shell structure consisting of iron nitride nanoparticles encapsulated within Fe and N codoped carbon layers that can efficiently catalyze CO 2 to CO with nearly 100% selectivity, high faradic efficiency (∼95%), and remarkable durability at −0.53 V versus reversible hydrogen electrode. Theoretical calculations reveal that the introduction of an iron nitride core can facilitate the CO intermediate desorption from the Fe and N codoped shell, thus enhancing the catalytic performance of CO 2 reduction. This work presents an ideal approach to rationally design and develop transitionmetal and N codoped carbon materials for efficient CO 2 reduction.C O 2 electroreduction reaction (CO 2 RR) is a promising strategy to convert CO 2 into multifarious valuable chemicals and synthetic fuels. The ultimate feasibility of this conversion, however, is currently impeded by the high overpotential, poor selectivity, and structural instability. Research efforts have been devoted to developing highperformance CO 2 RR electrocatalysts, primarily focused on the metallic electrodes, such as metal, 1 metal oxides, 2 or metal alloys. 3 Through control of the morphology of the electrode, 4 particle size, 5 geometry of the metallic surface, 6,7 and working electrolyte, 8,9 CO 2 can be converted into different products, such as CO, CH 4 , HCOOH, and other hydrocarbons. 10,11 These products are always yielded at a high overpotential, leading to unsatisfactory energy efficiency. Simultaneously, the hydrogen evolution reaction (HER) happens in the company of the CO 2 RR, thus resulting in the poor selectivity for the target product. Recently, the noble metals, such as Ag 12 or Au, 13,14 were found to efficiently catalyze the electroreduction of CO 2 to CO with high selectivity. Nevertheless, their prohibitive cost and high overpotential make this approach economically challenging.

A Disquisition on the Active Sites of Heterogeneous Catalysts for Electrochemical Reduction of CO2 to Value‐Added Chemicals and Fuel

“…For instance, atomically dispersed Fe on N‐doped graphene (Fe‐NG) with Fe‐N 4 sites (as revealed by XAS studies and HRTEM) exhibited a FE CO of 80% at an applied potential of −0.5 V, compared to metallic Fe nanoparticles supported on same N‐doped graphene, which demonstrated a FE CO of merely 12% at the sample applied potential . Similarly, atomic Fe dispersed on CNT embedded Fe nanoparticles were also recently reported to be highly active for CO 2 RR to CO with a FE CO > 95% . In fact, as indicated in Figure 15 , the introduction of a iron nitride core facilitates CO desorption from the Fe–N x –C sites and this allows the attainment of high selectivity, stability and moderate j during long term CO 2 RR.…”

“…The DFT calculations indicate a much lower free energy barrier for *CO desorption from Fe–N 4 –C/Fe 2 –N and this allows the attainment of high CO selectivity during long‐term CO 2 RR. Reproduced with permission . Copyright 2018, American Chemical Society.…”

Supported Single Atoms as New Class of Catalysts for Electrochemical Reduction of Carbon Dioxide

“…These systems involve the Fe–N x and/or Fe–C x single‐atom active sites along with heteroatom doped (N–C x ) active sites, Fe/FeO x /FeC NPs and NCs . Cheng et al synthesized a Fe–N–C nanofiber catalyst with iron nitride NPs confined within Fe and N codoped carbon shell, showing a high catalytic activity for CO 2 RR with nearly 100% selectivity and ≈95% FE at −0.53 V for CO production . DFT calculations disclosed that the desorption of CO* intermediate from the Fe, N shell is much easier when incorporated with the iron nitride core .…”

“…Cheng et al synthesized a Fe–N–C nanofiber catalyst with iron nitride NPs confined within Fe and N codoped carbon shell, showing a high catalytic activity for CO 2 RR with nearly 100% selectivity and ≈95% FE at −0.53 V for CO production . DFT calculations disclosed that the desorption of CO* intermediate from the Fe, N shell is much easier when incorporated with the iron nitride core . Li et al proposed that the Fe 3 C is much more active than the Fe–N x centers, while the activity of Fe–N x centers is even lower than the N–C based centers .…”

Transition Metal (Fe, Co and Ni)−Carbide−Nitride (M−C−N) Nanocatalysts: Structure and Electrocatalytic Applications

“…With the increased consumption of fossil fuels, a lot of greenhouse gas, such as CO 2 , NO x , have been generated . Therefore, many researches have been designed to solve this problem, for example CO 2 RR to directly convert CO 2 into some complex carbon‐based fuels and chemical compounds . In general, the process about the electrochemical reduction of CO 2 usually occurs in the aqueous solutions .…”