Abstract
The electrocatalytic activity of Ln0.3Sr1.7PdO3 (Ln = La, Nd, or Gd) perovskites prepared by the citrate combustion method for the hydrogen evolution reaction (HER) was examined by electrochemical techniques. The X-ray diffraction data indicate the formation of Sr2PdO3 and SrPd3O4 as primary and secondary phases, respectively, with the LnPd alloy only appearing in the Gd3+-doped sample. Transmission electron microscopy images clearly show the orthorhombic geometry of Sr2PdO3 in all samples, and the particle size decreased and the Brunauer–Emmett–Teller surface area increased as the dopant ionic size decreased. Potentiodynamic cathodic polarization measurements show that lanthanide doping at the Sr2+ site increased the catalytic activity toward the HER compared to that of the undoped binary perovskite, Sr2PdO3, except for the La3+-doped sample. The order of catalytic activity is Gd0.3Sr1.7PdO3 > Nd0.3Sr1.7PdO3 ≈ Sr2PdO3 > La0.3Sr1.7PdO3, which is consistent with the impedance data and activation energy calculations. This order is probably related to the amount of the secondary phase, SrPd3O4, contained in each sample, which not only contributes to the activity but also prevents the catalyst from being deactivated. Of all the prepared ternary perovskites, Ln0.3Sr1.7PdO3 shows considerable operational stability, making it a promising HER catalyst.
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