New electrocatalysts designed for environmentally friendly ammonia production

Schematic diagram of ammonia synthesis by electrocatalysis with Fe–Co bimetallic monoatomic catalyst. Author: Shenbo Zhang

Scientists have demonstrated the use of controlled synthesized single-[{” attribute=””>atom catalysts (SACs) to depict the relationship between electrocatalytic nitrogen reduction reaction (NRR) performance and single-atom (SA) loading.

Conducted by researchers from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, the study will be published today (November 14) in the journal Nature Sustainability.

Electrosynthesis of ammonia from NRR at ambient conditions has been widely regarded as a “green ammonia synthesis” technology to replace the traditional energy- and capital-intensive Haber-Bosch process.

Scientists agree that the intriguing features of SACs may create a new catalytic paradigm. However, one of the key challenges hindering the rational design and development of SACs is the lack of insight into the relationship between performance and SA loading, due mainly to the inability to precisely control the synthesis of SACs with desired SA loading densities and active site coordination forms.

Atomically Dispersed Bimetallic Iron–Cobalt Electrocatalysts for Green Production of Ammonia

(a) HAADF-STEM images. (b) Plots of the loaded Fe and Co SAs against [Fe3+] and [Co2+]. (c) EXAFS fitting curves of the Fe and Co K edge. (d) Co K edge XANES spectra. (e) Solid-state 13C NMR spectra. (F) RNH3 and FE of the corresponding catalysts. (G) Effect of catalyst loading density on geometric domain activity. (h) DFT-optimized configurations. (i) DFT optimized configurations after the initial NRR electrocatalytic cycle. Author: Shenbo Zhang

In this study, the researchers demonstrated an adsorption-controlled synthetic method that uses bacterial cellulose as an adsorption regulator to control Fe3+/Co2+ saturation of bacterial cellulose by carbothermal reduction. Fe-Co SAs were then fixed to carbon derived from bacterial cellulose using bimetallic [(O–C2)3Fe–Co(O–C2)3] coordination.

What is important is that scientists have uncovered a set of relationships which quantify Fe3+/Co2+ distribution between bacterial cellulose and adsorption solution and percent conversion of impregnated Fe3+/Co2+ on bacterial cellulose to Fe/Co SA on carbon derived from bacterial cellulose. They then demonstrated the use of such quantitative relationships to control the controlled synthesis of bimetallic Fe–Co SACs with desired Fe/Co contents and atomic ratios.

They showed that controllably synthesized SACs could display the electrocatalytic relationship between NRR performance and SA loading. Fe/Co single atom electrocatalysts (SAECs) have the highest node density and NRR performance for bimetallic Fe–Co SAs, making them capable of achieving superior ammonia yields with exceptional faraday efficiency.

The catalytic activity of SACs, unlike other types of catalysts, is determined by the nature of the SA, the physicochemical properties of the support, and importantly, the coordination bonds that attach the SA to the support.

Under electrocatalytic NRR conditions, [(O–C2)3Fe–Co(O–C2)3] in the synthesized bimetallic Fe-Co SAECs is rapidly transformed into a more stable coordination configuration [(O–C2)3Fe–Co(O–C)C2]thus promoting and sustaining NRR performance.

The researchers believe that these new findings will be of great interest to the wider catalysis community.

Reference: “Atomically Dispersed Bimetallic Fe–Co Electrocatalysts for Environmentally Friendly Ammonia Production” 14 Nov 2022 Sustainability of nature.
DOI: 10.1038/s41893-022-00993-7 New electrocatalysts designed for environmentally friendly ammonia production

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