Quantitative Unraveling\nof Exsolved Heteroboundaries\nfor High-Temperature Electrocatalysis

The application of perovskite oxide for high-temperature\nelectrocatalysis\nis hindered by its limited activity. Exsolution is a smart strategy\nthat allows the enrichment of the perovskite’s surface with\nhighly reactive phases, yielding heteroboundaries. However, the identification\nof the exact catalytic role of this complex architecture is still\nelusive. Here we presented a quantitative analysis of the CO<sub>2</sub> electroreduction reactivity of a series of perovskite thin film\nplatforms (La<sub>0.4</sub>Ca<sub>0.4</sub>Ti<sub>0.94</sub>Ni<sub>0.06</sub>O<sub>3</sub>, LCTN) boosted by exsolved heteropical nanoparticles\n(particularly for Ni and NiO). The cross-scale electrochemical characterizations,\ntogether with density functional theory (DFT) modelings, have shown\nclear evidence that the boundary length of the NP/perovskite interface\nis strictly correlated with the CO<sub>2</sub>RR activity. The intrinsic\nreaction rate per active site at the NiO/LCTN boundary demonstrates\na highest turnover frequency (TOF) of 7.05 ± 0.75 × 104\ns<sup>–1</sup> at 800 °C, which is 2.5 times and 4 orders\nof magnitude better than that of Ni/LCTN and LCTN, respectively. The\nab initio molecular dynamics (AIMD) proves that the CO<sub>2</sub> absorption at the NiO/LCTN boundary leverages a bidentate carbonate\nmodality with a reduced dissociation energy barrier. Moreover, a multifold\nenhancement in oxygen exchange rate was confirmed, which correlated\nto the facilitated oxygen ion hopping between adjacent TiO<sub>6</sub> octahedrons. Further near-ambient pressure X-ray photoelectron spectroscopy\n(NAP-XPS) during CO<sub>2</sub> electrolysis on model electrolyzers\nreveals the crucial role of the NiO/LCTN boundary in stabilizing oxidized\ncarbon intermediates, raising the onset potential threshold of adventitious\ncarbon as well as preventing its build-up.