Unveiling the Electrocatalytic Activity of Bifunctional Iron-Niobium Double Perovskites for Overall Water Splitting: A-Site Cation Influence

Abstract

Capitalizing on the electrochemical conversion of water into hydrogen stands as a pivotal strategy in the global transition toward sustainable energy sources. This study investigates the influence of the A-site cation type within A₂FeNbO₆ double perovskites (where A = Ca, Sr, or Ba) on their bifunctional electrocatalytic activities. The electrocatalytic performance is scrutinized in relation to charge transfer resistance, oxygen vacancy concentration, and metal-oxygen covalency. Among the variants, Sr₂FeNbO₆ is distinguished as the optimal catalyst, achieving a current density of 10 mA cm⁻² at overpotentials of 260 mV for the oxygen evolution reaction (OER) and 176 mV for the hydrogen evolution reaction (HER), thus matching the performance of leading metal oxide electrocatalysts. The study reveals pH-dependent kinetics for Sr₂FeNbO₆, indicative of a lattice oxygen evolution mechanism for OER. An electrolyzer employing Sr₂FeNbO₆ electrodes for both the anode and cathode delivers a current density of 10 mA cm⁻² at an efficient cell voltage of 1.76 V for complete alkaline water splitting, while also demonstrating exceptional stability. These insights advance the understanding of material optimization for electrocatalysis and position Sr₂FeNbO₆ as a viable catalyst for the sustainable production of hydrogen.