Regulating the High Entropy Component of Double Perovskite for High-Temperature Oxygen Evolution Reaction

Solid oxide electrolysis cells (SOECs) could convert CO 2 to CO powered by clean electricity with low overpotential, high Faradaic efficiency, and high current density . Since the performance of SOEC is affected by sluggish oxygen evolution reaction (OER) kinetics at the anodes, the modification of anode materials is crucial for the further application of SOEC. Perovskites with high configurational entropy exhibit high catalytic activity in many reactions, but are rarely reported in SOECs. Herein, two kinds of high entropy perovskites (HEPs), with formulas of (Pr 0.2 La 0.2 Sm 0.2 Nd 0.2 Gd 0.2 )BaCo 2 O 6− δ (A-HEP) and Pr(Ba 0.2 Sr 0.2 Ca 0.2 Na 0.2 K 0.2 ) Co 2 O 6− δ (A′-HEP), are synthesized by doping different rare earth metal , and alkaline metal or alkaline earth metal ions into A-site and A′-site of the double perovskites. Rietveld refinement of X-ray diffraction patterns and elemental maps of scanning electron microscope images confirm the successful synthesis of the two samples. The tetragonal double perovskite structure of A-HEP and the transformation to orthorhombic structure of A′-HEP due to the difference in average atomic radii and oxidation states of the doped ions are also detected. Co 2 p X-ray photoelectron spectroscopy (XPS) and O K -edge X-ray absorption spectroscopy reveal that the average oxidation state of Co is lifted from +3.23 in A’-HEP to +3.39 in A-HEP, and the hybridization of Co 2 p and O 1 s orbitals is also enhanced in A-HEP, which increase the electron transfer pathway and reduce the transfer barrier. Therefore, the electrical conductivity of A-HEP at 800 °C is higher than that of A’-HEP. Moreover, the increased absorption oxygen species concentration of A-HEP in O 1 s XPS and O 2 -temperature programmed desorption results indicates more surface oxygen vacancies , thus increasing active sites for the anodic OER. Consequently, the anodic polarization resistances related to oxygen transportation, electron transfer and surface reaction processes are decreased remarkably in A-HEP, resulting in a high current density of 1.76 A·cm −2 at 800 °C and a stability of 200 h. This work presents a new method for designing high-performance HEPs as SOEC anode materials . Download: Download high-res image (130KB) Download: Download full-size image