Effect of deposition template on high entropy oxide model systems for the oxygen evolution reaction

High-entropy oxide catalysts are promising candidates for overcoming intrinsic activity limitations in the oxygen evolution reaction (OER), a key bottleneck in electrochemical conversion. Thin-film model systems provide a controlled platform for uncovering the underlying catalytic mechanisms. Here, we develop and compare four deposition templates for LaNi_0.2Co_0.2Fe_0.2Mn_0.2Cr_0.2O₃  model systems: (i) epitaxial films on Nb:SrTiO₃ , (ii) sacrificial-layer-released films transferred to platinized Si wafers, (iii) locally epitaxial films grown on oxide nanosheets, and (iv) films directly grown on platinized Si wafers. These geometries support a wide range of operando techniques while enabling direct comparison of materials grown under identical pulsed laser deposition conditions. Using electrochemical measurements and ex-situ characterization, we evaluate crystallinity, stoichiometry, surface morphology, and OER activity across the different templates. The observed variations highlight the important role of template selection in interpreting catalytic performance. We find that the transferred epitaxial thin film and the film on Nb:SrTiO₃  are comparable in stoichiometry and electrocatalytic activity, while the epitaxial film has higher crystallinity. The films on nanosheets and directly grown on Pt have a reduced crystallinity, broader orientation distribution, different stoichiometry and a lower catalytic activity. Overall, this set of deposition templates facilitates the integration of well-controlled model systems with operando spectroscopy, advancing mechanistic insight and guiding the rational design of next-generation high-entropy OER catalysts.