Ru Perovskites with Enhanced Activity and Durability for the OER in Acid Media
Authors: Rodriguez Garcia Isabel , Gómez de la Fuente José Luis , Galyamin Dmitry , Kayser Paula , Abdel Salam Mohamed , Mokthar Mohamed , Alonso José Antonio , Retuerto Maria , Rojas Sergio 
Published: February 2024

Iridium- and Ruthenium based catalysts are the only feasible ones for the oxygen evolution reaction (OER) in acidic media. The high price and scarcity of Ir is a major hurdle to realize electrolysis in the GW-scale. Ru-based catalysts can be suitable candidates to replace Ir, since they are more active for the OER than Ir. However, Ru catalysts lack sufficient stability during the OER. This is because, Ru tends to form soluble upper oxides e.g. RuO4 at high voltages (> 1.4 V). Previous studies reveal that Na- or K-doping can increase Ru’s durability during the OER.1,2 However, recent studies demonstrate that Ru’s activity and stability depends on the structure and composition of the Ru-based catalyst.3

In this work, we report a series of Ru double perovskites, namely R2NiRuO6 (R = Pr, Nd, Tb, Dy, Y, Ho and Er)4 with low ruthenium content and high OER activity in acidic electrolyte. The oxides have been synthesized by wet-chemistry and thoroughly characterized by XRD (Rietveld refinement), TEM and XPS.

The OER was studied in the rotating ring disk (RDE) configuration in 0.1 M HClO4. Due to the absence of Sr or alkali metals in their structure, in addition to displaying high initial OER activity, the perovskites are stable during OER cycles between 1.1 and 1.7 V, with Dy2NiRuO6 being stable at least during 500 consecutive cycles (see Figures 1a and 1b).

Characterization results reveal that Ru-O distances in the perovskites follow the order Dy<Er<Y<Ho<Tb<Nd<Pr. As shown in Figure 1c, the OER activity, i.e., the potential recorded at 10 mA·cm-2, follows the same trend. Also, the durability of the catalysts follows the same trend.

The smaller Ru-O distance indicates a higher oxidation state of Ru atoms in Dy2NiRuO6. In addition, the gives symmetry and order to the structure. perovskite, making it more stable

XPS and TEM-EDS post-mortem studies of Dy2NiRuO6 reveal a loss of Ni after 500 OER cycles and the presence of Ru3+ cations, being the main cause of the loss of OER activity.

The R2NiRuO6 double perovskites reported in this work are the first example of highly active and stable Ru-based perovskites for the OER in acidic electrolyte that can opens the way for the replacement of Ir from state of the art PEMWEs.

(1) Retuerto, M.; Pascual, L.; Calle-Vallejo, F.; Ferrer, P.; Gianolio, D.; Pereira, A. G.; García, Á.; Torrero, J.; Fernández-Díaz, M. T.; Bencok, P.; Peña, M. A.; Fierro, J. L. G.; Rojas, S. Na-Doped Ruthenium Perovskite Electrocatalysts with Improved Oxygen Evolution Activity and Durability in Acidic Media. Nat. Commun.
2019, 10 (1), 2041. https://doi.org/10.1038/s41467-019-09791-w.

(2) Rodríguez-García, I.; Galyamin, D.; Pascual, L.; Ferrer, P.; Peña, M. A.; Grinter, D.; Held, G.; Abdel Salam, M.; Mokhtar, M.; Narasimharao, K.; Retuerto, M.; Rojas, S. Enhanced Stability of SrRuO3 Mixed Oxide via Monovalent Doping in Sr1-XKxRuO3 for the Oxygen Evolution Reaction. J. Power Sources
2022, 521, 230950. https://doi.org/10.1016/j.jpowsour.2021.230950.

(3) Paoli, E. A.; Masini, F.; Frydendal, R.; Deiana, D.; Malacrida, P.; Hansen, T. W.; Chorkendorff, I.; Stephens, I. E. L. Fine-Tuning the Activity of Oxygen Evolution Catalysts: The Effect of Oxidation Pre-Treatment on Size-Selected Ru Nanoparticles. Catal. Today
2016, 262, 57–64. https://doi.org/10.1016/j.cattod.2015.10.005.

(4) Kayser, P.; Alonso, J. A.; Muñoz, A.; Fernández-Díaz, M. T. Structural and Magnetic Characterization of the Double Perovskites R2NiRuO6 (R = Pr-Er): A Neutron Diffraction Study. Acta Mater.
2017, 126, 114–123. https://doi.org/10.1016/j.actamat.2016.12.024.

Figure 1