Substituent Effects in Iron Porphyrin Catalysts for the Hydrogen Evolution Reaction. Issue 10 (5th January 2023)

• Record Type: Journal Article
• Authors: Heppe, Nils; Gallenkamp, Charlotte; Paul, Stephen; Segura‐Salas, Nicole; von Rhein, Niklas; Kaiser, Bernhard; Jaegermann, Wolfram; Jafari, Atefeh; Sergueev, Ilya; Krewald, Vera; Kramm, Ulrike I.
• Is Part Of: Chemistry. Volume 29:Issue 10(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-01-05
• Subjects: density functional theory -- electrochemistry -- heterogeneous catalysis -- hydrogen -- molecular electrochemistry -- renewable resources; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202202465
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: For a future hydrogen economy, non‐precious metal catalysts for the water splitting reactions are needed that can be implemented on a global scale. Metal‐nitrogen‐carbon (MNC) catalysts with active sites constituting a metal center with fourfold coordination of nitrogen (MN4 ) show promising performance, but an optimization rooted in structure‐property relationships has been hampered by their low structural definition. Porphyrin model complexes are studied to transfer insights from well‐defined molecules to MNC systems. This work combines experiment and theory to evaluate the influence of porphyrin substituents on the electronic and electrocatalytic properties of MN4 centers with respect to the hydrogen evolution reaction (HER) in aqueous electrolyte. We found that the choice of substituent affects their utilization on the carbon support and their electrocatalytic performance. We propose an HER mechanism for supported iron porphyrin complexes involving a [Fe II (P⋅)] − radical anion intermediate, in which a porphinic nitrogen atom acts as an internal base. While this work focuses on the HER, the limited influence of a simultaneous interaction with the support and an aqueous electrolyte will likely be transferrable to other catalytic applications. Abstract : The comparison of differently substituted iron porphyrins in their as‐prepared state and after immobilization on carbon indicates no or only a weak interaction with the carbon support. Hydrogen evolution catalysis of the supported systems is improved by electron donating groups that destabilize an Fe(II) intermediate, presumably by assisting in the formation of a radical anion.