Describing perovskite catalysts

ACS Catal. 8, 9567–9578 (2018)

The design of efficient water electrolysers has received a great deal of attention in the past few decades, including significant efforts to develop hydrogen- and oxygen-evolving catalysts. These should exhibit as little thermodynamic penalty as possible to drive the reaction and display high long-term stability, while containing the minimum amounts of precious metals. While the state-of-the-art cathode catalysts have already achieved outstanding performances, more research is required for the oxygen-evolving counterparts. Among these, perovskite oxides are a very interesting class of anode catalysts for use in alkaline electrolytes. One design strategy consists of finding a physicochemical property that correlates with the activity that can then be tuned to find the optimum catalyst. However, this often leads to an over-simplification of a complex scenario where different reaction pathways can occur, meaning that the proposed property lacks generability and cannot be directly transferred between structurally different catalysts.

Now, Emiliana Fabbri and co-workers show that for perovskite oxides, one single descriptor cannot predict the activity towards the oxygen evolution reaction (OER) but rather a combination of descriptors is required. The researchers have investigated a wide range of oxygen-deficient perovskite materials with multiple compositions, including La_1−xSr_xCoO_3−δ (with various x fractions), LaMO_3−δ (where M = Cr, Mn, Fe, Co, Ni), Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ and PrBaCo₂O_6−δ. The descriptors considered are the electronic conductivity, the flat-band potential, and the amount of oxygen vacancies, which were obtained by ex situ and in situ impedance spectroscopy and neutron diffraction, respectively. The single descriptors provide a qualitative estimation of the catalytic activity, although clear outliers are found in all three. On the other hand, the researchers conclude that for a perovskite oxide to be highly active for water oxidation it has to exhibit high electronic conductivity, a high amount of oxygen vacancies and a low flat-band potential.