Rhodium Substituted La0.85Sr0.15CoO3: An Active Oxygen Evolution Electrocatalyst Based upon Ionic Rhodium

Nanocrystalline La<inf>0.85</inf>Sr<inf>0.15</inf>CoO<inf>3</inf> (LSCO) as well as a series of metal substituted La<inf>0.85</inf>Sr<inf>0.15</inf>M<inf>0.05</inf>Co<inf>0.95</inf>O<inf>3</inf> (M = Rh, Pt, Ru, Pd) compounds were prepared and a detailed characterization and electrochemical studies was carried out. Rh substituted La<inf>0.85</inf>Sr<inf>0.15</inf>CoO<inf>3</inf> showed the best activity with respect to current density. Thereafter, a series of Rhodium substituted LSCO catalysts were synthesized varying the concentration of Rh and were then fully characterized. XRD showed a pure nanocrystalline phase of La<inf>0.85</inf>Sr<inf>0.15</inf>CoO<inf>3</inf> having no Rh or Rh-oxide related peaks, confirming that Rh does not exist as a separated phase and is well substituted in the perovskite lattice. Electrochemical oxygen evolution reaction (OER) studies performed in neutral, as well as basic conditions show that Rh substitution has the most profound effect on the OER activity. Variation in the Rh concentration indicates that the OER activity peaks at 2.5% Rh substituted LSCO catalyst (La<inf>0.85</inf>Sr<inf>0.15</inf>Rh<inf>0.025</inf>Co<inf>0.975</inf>O<inf>3</inf>) and decreases thereafter. Electrochemical surface area study and Tafel slope measurements for all Rh substituted LSCO indicated a profound increment in the electrocatalytic activity because of the presence of ionic Rh in the La<inf>0.85</inf>Sr<inf>0.15</inf>CoO<inf>3</inf> lattice in comparison to pure LSCO. X-ray photoelectron spectroscopy of the postcharacterized sample confirmed that Rh³⁺ is the active center for the reaction.