High surface area mixed lanthanum nickelate/ferrates (LaNi1−xFexO3) via modified carbon templating coated on nickel in alkaline OER

Abstract

Perovskites have been proven as a highly versatile, tailorable material class, encompassing well-established, highly active oxygen evolution reaction (OER) electrocatalysts based on earth-abundant transition metals. Facile synthesis methods yielding large specific surface areas (SSA) for enhanced catalyst utilization and testing in industrially relevant conditions are crucial for accelerating the large-scale application of alkaline OER, which is regarded as a bottleneck for electrocatalytic water splitting. The synthesis of such perovskites with high SSAs, however, remains challenging. Here, a modified carbon templating method, where metal nitrates are impregnated into activated carbon and subsequently precipitated with an additional KOH impregnation step, is applied to synthesize a solid solution series of lanthanum nickelate/ferrate LaNi_1−xFe_xO₃ perovskite phases. These materials are tested in the alkaline OER as catalyst coatings applied on Ni metal substrates. XRD analysis confirms the formation of perovskites as primary phases, with SEM, elemental analysis, XPS, and Raman spectroscopy substantiating the material characterization. SSAs determined by N₂ physisorption outperform those prepared by comparably facile syntheses. SEM images reveal a less dense coating of LaFeO₃ than LaNiO₃ on Ni substrates, positively affecting the OER activity of higher Fe-content catalysts. The stability of the perovskite-coated electrodes is assessed by XPS and Raman spectroscopy before and after chronopotentiometry, recorded for 24 hours.