Elucidating the Hydrogen Evolution Reaction Mechanism of Immobilized Iron Porphyrin Electrocatalysts

Abstract

Based on global warming our society need to change towards CO2 free or neutral options of energy supply. The hydrogen economy plays an important role in providing and utilizing green hydrogen. While platinum is the best-known catalysts for the hydrogen evolution reaction (HER), alternatives are required that are sustainable and free of platinum group metals (PGMs).Metal-nitrogen-carbon (MNC) catalysts have shown promising activity for the HER [1], however, often beside catalytically active MN4 centers they contain side phases that hinder mechanistic insights. The inhomogeneity in composition is based on the usual preparation approaches, that involve in minimum one pyrolysis or heat-treatment step. To avoid side phases, we focused on immobilized iron porphyrin model complexes and explored there the HER.In this work, I will present our results associated with a substituent variation [2] and in-depth characterization by post-mortem and in situ approaches using different nuclear resonance techniques [3]. On the basis of this, we identified different species associated with the reaction cycle and the rate limiting step.The knowledge on this will help further improvement of the porphyrinic system for HER and validation to what extent a similar mechanism applies after the pyrolysis.