An international team led by the Spanish National Research Council (CSIC) has developed an efficient sodium-doped ruthenium electrocatalyst with improved oxygen evolution activity and durability in acidic media. An open-access paper on their work is published in Nature Communications.

Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO₆ octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites.

—Retuerto et al.

It will be necessary to incorporate renewable energies and better regulation of the energy sector in the short term. For this it is essential to manage the long-term storage of renewable energies and their storage in hydrogen form is one of the most efficient and viable alternatives to accumulate this type of energy.

—María Retuerto, CSIC, lead author

TheSr_0.95Na_0.05RuO₃ and S_0.90Na_0.10RuO₃ catalysts exhibit very high specific OER activity, with a potential of ~1.35 V (an overpotential of only 120 mV) at 0.5 mA cm⁻²_geo.

The researchers found that substituting Sr by Na increases the stability of the perovskite structure, thus preventing deactivation during repeated cycling. This result is also supported by DFT, demonstrating lower surface energy and higher dissolution potentials for Na-doped perovskites, which slows down the collapse of the perovskite structure.

Our conclusions could help in guiding future research in several ways: (a) other monovalent cations such as Li⁺, K⁺, and Cs⁺ can be tested to ascertain whether they also enhance the activity and/or the stability. (b) If Ru⁵⁺ sites are instrumental for the enhancement of SrRuO₃, then B-site doping with e.g., trivalent cations might as well enhance the activity. (c) Since Sr_0.875Na_0.125RuO₃ is the most active compound … we used the ESSI to determine that its activity can be further optimized if the *OH binding energy is strengthened by −0.16 eV. This is an interesting hypothesis to be verified experimentally in subsequent studies.

—Retuerto et al.

Resources

• María Retuerto et al. (2019) “Na-doped ruthenium perovskite electrocatalysts with improved oxygen evolution activity and durability in acidic media.” Nature Communications doi: 10.1038 / s41467-019-09791-w