Templated synthesis of porous single atom electrocatalysts with high atomic utilization Jesús Barrio 1, 2 , Angus Pedersen 1, 2 , Alexander Bagger 3 , Saurav, Ch. Sarma 2 , Mengjun Gong 4 , Anthony Kucernak 4 , Maria-Magdalena Titirici 2 , Ifan E.L. Stephens 1 1 Department of Materials, Royal School of Mines, Imperial College London, UK, 2 Department of Chemical Engineering, Imperial College London, UK, 3 Department of Chemistry, University of Copenhagen, Denmark, 4 Department of Chemistry, Molecular Sciences Research Hub, Imperial College London,UK Fe single atoms in nitrogen doped carbon materials (Fe-NC) have attracted plenty of attention during the last decades in the field of electrocatalysis for oxygen reduction and carbon dioxide conversion amongst others. In the cathode of proton exchange membrane fuel cells Fe-NC are the most promising solution to scarce and expensive Platinum-group-metal catalysts; [1] In CO 2 reduction, they have achieved similar performance to that of nanostructured Au and Ag. However, their controlled synthesis and stability for practical applications remains challenging. Approaches to enhance their catalytic performance include increasing the loading of Fe single atoms, for example by decoupling high temperature pyrolysis and Fe coordination atoms, or enhancing the intrinsic activity of the FeN x sites through engineering of the coordination environment or by creation of dual atom catalysts. [2,3] Currently, the utilization of Fe within these materials remains very low owing to the lack of C-N scaffolds that combine adequate micro- and mesoporosity. In this work we employ inexpensive 2,4,6-Triaminopyrimidine (TAP) with MgCl 2 .6H 2 O as porogen to prepare a highly porous N-doped carbon material. [4] The hydrogen bonding between nitrogen moieties of TAP and the water molecules of the Mg salt allows an optimal interaction during pyrolysis that leads to remarkable porosity in the nitrogen-doped material (~3300 m 2 g -1 ) and very available N sites for Fe coordination. The subsequent low temperature Fe coordination results in a highly active O 2 reduction to electrocatalyst with a mass activity 4.0 A g -1 at 0.8 V RHE in acid electrolyte. Additionally, the material shows near 100% Faradaic Efficiency for the CO 2 reduction to CO (FE co = 93.5% at -0.55 V vs RHE) with one of the highest TOF reported up to date (4.5 s -1 ) Aberration corrected high-angle annular dark field scanning transmission electron microscopy with energy dispersive x-ray spectroscopy of the catalyst confirms the solely atomic Fe and N distribution pre- and post- accelerated degradation tests. In-situ nitrite stripping reveals a high active site density of 2.54×10 19 sites g -1 ; the remarkable porosity of the graphitic material and hierarchal structure ensures remarkably high electrochemical active site utilisation of 42%. Ex-situ X-ray absorption extended fine structure suggests the presence of penta- coordinated FeN 5 sites, potentially enabling the stability of the active site for O 2 and CO 2 reduction. References 1. F. Jaouen, D. Jones, N. Coutard, V. Artero, P. Strasser, A. Kucernak, Johnson Matthey Technol. Rev. 2018, 62, 231 2. J. Barrio, A. Pedersen, et. al., J. Mater. Chem. A 2022, 10, 6023-6030.
3. A. Mehmood, et. al., Nat. Catal. 2022, 5, 311. 4. J. Pampel, et. al., Mater. Horizons 2017, 4, 493.
E01
Made with FlippingBook Learn more on our blog