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We employed operando soft X-ray absorption spectroscopy (XAS) to monitor the changes in the valence states and spin properties of LaMn 1- x Co x O 3 catalysts subjected to a mixture of CO and O 2 at ambient pressure. Guided by simulations based on charge transfer multiplet theory, we quantitatively analyze the Mn and Co 2p XAS as well as the oxygen K-edge XAS spectra during the reaction process. The Mn sites are particularly sensitive to the catalytic reaction, displaying dynamics in their oxidation state. When Co doping is introduced ( x ≤ 0.5), Mn oxidizes from Mn 2+ to Mn 3+ and Mn 4+ , while Co largely maintains a valence state of Co 2+ . In the case of LaCoO 3 , we identify high-spin and low-spin Co 3+ species combined with Co 2+ . Our investigation underscores the importance to consider the spin and valence states of catalyst materials under operando conditions., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Steering the selectivity of electrocatalysts toward the desired product is crucial in the electrochemical reduction of CO 2 . A promising approach is the electronic modification of the catalyst's active phase. In this work, we report on the electronic modification effects on CuO-ZnO-derived electrocatalysts synthesized via hydrothermal synthesis. Although the synthesis method yields spatially separated ZnO nanorods and distinct CuO particles, strong restructuring and intimate atomic mixing occur under the reaction conditions. This leads to interactions that have a profound effect on the catalytic performance. Specifically, all of the bimetallic electrodes outperformed the monometallic ones (ZnO and CuO) in terms of activity for CO production. Surprisingly, on the other hand, the presence of ZnO suppresses the formation of ethylene on Cu, while the presence of Cu improves CO production of ZnO. In situ X-ray absorption spectroscopy studies revealed that this catalytic effect is due to enhanced reducibility of ZnO by Cu and stabilization of cationic Cu species by the intimate contact with partially reduced ZnO. This suppresses ethylene formation while favoring the production of H 2 and CO on Cu. These results show that using mixed metal oxides with different reducibilities is a promising approach to alter the electronic properties of electrocatalysts (via stabilization of cationic species), thereby tuning the electrocatalytic CO 2 reduction reaction performance., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We study the electrocatalytic oxygen evolution reaction using in situ X-ray absorption spectroscopy (XAS) to track the dynamics of the valence state and the covalence of the metal ions of LaFeO 3 and LaFeO 3 /LaNiO 3 thin films. The active materials are 8 unit cells grown epitaxially on 100 nm conductive La 0.67 Sr 0.33 MnO 3 layers using pulsed laser deposition (PLD). The perovskite layers are supported on monolayer Ca 2 Nb 3 O 10 nanosheet-buffered 100 nm SiN x membranes. The in situ Fe and Ni K-edges XAS spectra were measured from the backside of the SiN x membrane using fluorescence yield detection under electrocatalytic reaction conditions. The XAS spectra show significant spectral changes, which indicate that (1) the metal (co)valencies increase, and (2) the number of 3d electrons remains constant with applied potential. We find that the whole 8 unit cells react to the potential changes, including the buried LaNiO 3 film., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)