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The evolution of the Mn charge state, chemical composition, and electronic structure of (LSMO) cathodes during the catalytic activation of solid oxide fuel cell (SOFC) has been studies using X-ray spectroscopy of as-processed, exposed, and activated dense thin LSMO films. Comparison of O-edge and Mn-edge X-ray absorption spectra from the different stages of LSMO cathodes revealed that the largest change after the activation occurred in the Mn charge state with little change in the oxygen environment. Core-level X-ray photoemission spectroscopy and Mn resonant photoemission spectroscopy studies of exposed and as-processed LSMO determined that the SOFC environment (ambient pressure of) alone results in La deficiency (severest near the surface with Sr doping) and a stronger contribution, leading to the increased insulating character of the cathode prior to activation. Meanwhile, O-edge X-ray …