Nano‐Ferric Oxide Embedded in Graphene Oxide: High‐performance Electrocatalyst for Nitrogen Reduction at Ambient Condition

Abstract

Nitrogen (N2) fixation at ambient condition by electrochemical N2 reduction reaction (NRR) is energy‐efficient and eco‐friendly as compared to the traditional Harber–Bosch process, but it is extremely challenging. Development and design of high‐performance NRR electrocatalysts are indispensable to achieve the goal. In this work, a strongly coupled hybrid of nano‐Fe3O4 with reduced graphene oxide (rGO) is synthesized via an in situ redox hydrothermal approach, and the synthesized Fe3O4@rGO hybrid has excellent activity, selectivity, and stability as an NRR catalyst. The NH3 yield rate of 28.01 μg h‐1 mg‐1 at −0.3 V and the Faradaic efficiency (FE) of 19.12% at −0.1 V are obtained in 0.1 M Na2SO4 solutions at ambient conditions. The superior NRR performance is attributed to the chemical coupling effect between rGO and nano‐Fe3O4 particles, which leads to the enhancement of the binding affinity to N2 molecules, improvement of the conductivity, and lowering the free energy of reaction for the limiting reaction step. This work provides a facile route in fabricating hybrid NRR catalysts with superior performance and shed lights on the reaction mechanism with theoretical mechanistic calculations.

Graphene Derivatives and Graphene Composite Electrocatalysts for N2 Reduction Reaction

“…In our previous work, Fe 3 O 4 was strongly coupled with reduced graphene oxide to prepare Fe 3 O 4 @rGO NRR electrocatalyst. [ 42 ] Before and after the NRR process, the X‐ray photoelectron spectroscopy (XPS) Fe 2p spectra (Figure 3b) do not present obvious change, indicating that the electrocatalysts show high component stability.…”

“…Hence, the DFT is commonly used to study the NRR procedures at the atomic scale popularly. [18,42,43] In this part, we will discuss the criteria for NRR electrocatalysts at two aspects: 1) experiments and 2) DFT simulations.…”

“…[23,98] Moreover, the formed located electric field can increase the adsorption for N 2 and decrease the energy barrier at the PDS, leading to a higher NRR catalytic activity and selectivity. [42] It is worth noting that the NRR process is not generally considered to occur on graphene, meaning that the composited graphene acts as the accelerator. However, the used graphene commonly contains intrinsic defects introduced by the procedures of preparation and processing, and the contribution of intrinsic defects of graphene on NRR is ignored directly in Figure 11.…”

“…In Table 3, the graphene-composited NRR electrocatalysts are shown. [42,43,61,73,[99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115][116] It is shown that the oxides and sulfides are commonly composited with graphene as NRR electrocatalyst. Compared with sulfides/graphene composites, the oxides/ graphene composites show a higher NRR performance.…”

“…Among almost all those catalysts with metal elements, they exhibit a low Faraday efficiency (below 13%) due to the fact that the d-orbital electrons in metal elements are beneficial for proton adsorption, Reproduced with permission. [42] Copyright 2020, John Wiley & Sons.…”