Na-modified La(CrMnFeCoNi)_1/5O₃ high entropy perovskite oxides with B-site valence fluctuations for excellent OER performance electrocatalysts

High-entropy perovskite oxides, an emerging electrocatalytic electrode material, integrates the distinctive features of high-entropy materials and perovskites, offering significant potential in electrocatalysis. While adjusting the B-site elements has been a widely adopted approach for modulating the electrocatalytic activity of HEPs, there was a notable lack of systematic investigations into the role of A-site ions in regulating their electrocatalytic performance. To overcome this deficiency, in the present study, La1-xNax(CrMnFeCoNi)(1/5)O-3 HEPs were synthesized using carbon nanotubes-based sacrificial template method. It was found that the Na substitution at the A-site not only significantly reduced the synthesis temperature but also facilitated the preservation of carbon nanotubes. This retention contributed to the formation of a three-dimensional network structure, exposing a greater number of active sites. The Na modification induced significant valence fluctuations at the B-site and tailored the oxygen vacancy concentrations, enhancing the synergistic "cocktail effect" among the various metal atoms. Furthermore, the introduction of Na stimulated the formation of surface M-OOH species, which serve as active intermediates to enhance OER activity. As a result, the Na-modified HEPs demonstrated exceptional OER performance compared to their parent phases. Among these, La0.6Na0.4(CrMnFeCoNi)(1/5)O-3 (L6N4-5M) sample exhibited a lower overpotential of 313 mV at a current density of 10 mA cm(-2) and a Tafel slope of 47.4 mV dec(-1). Additionally, the A-site Na modification strategy and the in-depth investigation of the OER mechanism provide valuable insights for the future design and development of high-performance HEP electrocatalysts.