Improved Stability of Nickel-Iron Based Oxygen Evolution Electrocatalyst By the Immobilization of Tetraphenylporphyrin

Abstract

Anion exchange membrane water electrolysis (AEMWE) is an attractive technology for the production of green hydrogen and has advantages in terms of cost owing to the use of non-precious catalyst materials. NiFe-based materials are the best-in-class electrocatalysts for the alkaline oxygen evolution reaction. Defining the active sites of NiFe-based materials has been a controversial issue over the past decades. Previously, Ni was regarded as an active site; however, active sites, such as Fe or Ni–Fe dual active sites have been considered in recent studies. Despite the complexity of heterogeneous catalysis, with the aid of in situ/operando measurements and density functional theory (DFT) calculations, Fe was selected as the ultimate active site in state-of-the-art materials. However, the electrocatalyst suffers from rapid degradation in Fe-purified KOH. Herein, we report a catalyst/electrolyte interface engineering strategy using tetraphenylporphyrin (TPP) to alleviate the destabilization of NiFe-based catalysts. The online electrochemical flow cell inductively coupled plasma-optical emission spectroscopy proved that thermodynamically unstable Fe liberation was the primary cause of deactivation. TPP acts as a protective layer and suppresses hydrated metal dissolution at the catalyst/electrolyte interface. The stable TPP layer on NiFe elongates the lifetime near the electrode, enhancing the redeposition kinetics of the active site, Fe. As a proof of concept, the role of TPP was validated at the half-cell and 2.4 times suppression of degradation rate in AEMWE scale at a constant current density of 500 mA cm-2. This strategy of using a TPP as a protective layer may serve as a new platform for stable oxygen evolution electrocatalysts.