Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits excellent activity which is thought to be related to dynamic reconstruction at the flexible perovskite surface due to accommodation of large amount of oxygen vacancies. By studying the local structure and chemistry of BSCF surfaces, in detail, via a range of transmission electron microscopy (TEM) methods, we show that the surfaces of the as-synthesized BSCF particles are Co/Fe rich, and remarkably, adopt a spinel-like structure with a reduced valence of Co ions. Post-mortem and identical location TEM analyses reveal that the Co/Fe spinel-like surface retains a stable chemical environment of the Co/Fe ions, although its structure weakens after electrochemical processing. Further, it is verified that prior to the onset of OER, the Co/Fe spinel-like surface promotes the formation of the highly active Co­(Fe)­OOH phase, which enhances the OER electrocatalytic properties of the underlying conductive BSCF perovskite. This study provides a detailed understanding of the fundamental transformations that oxide catalysts undergo during electrochemical processes and can aid in the development of novel oxide catalysts with enhanced activity.

sequestrated. Recently, electrochemical CO 2 reduction reactions (CO 2 RR) enabled by renewable energy have been suggested as a promising strategy to solve these problems, sequestrating discharged CO 2 into chemical feedstocks, and downscaling the use of fossil fuels in the chemical production industry. In addition, CO 2 RR is an efficient way to store electricity generated from intermittent renewable energies in the form of liquid fuels for transport and other applications. [3][4][5] Copper-based materials are the most investigated class of catalysts for CO 2 RR due to their unique ability to reduce CO 2 molecules to carbonaceous compounds containing more than two carbon atoms (C 2+ products). However, the high overpotential required and the low product selectivity over the pristine Cu surface have motivated researchers to develop more efficient strategies to overcome these challenges. Most previous publications have focused on engineering the properties of Cu-based catalysts, such as optimizing the size and shape of Cu nanomaterials, [6][7][8][9][10] introducing grain boundaries, [11] and creating alloys with other metals [12][13][14][15] to increase the number of active sites and/or to improve the intrinsic catalytic activities of Cu toward the desired products. Despite the tremendous progress that has been made, CO 2 RR is still not viable at an industrial scale.The activity and selectivity of the electrochemical CO 2 reduction reaction (CO 2 RR) are often hindered by the limited access of CO 2 to the catalyst surface and overtaken by the competing hydrogen evolution reaction. Herein, it is revealed that polymers used as catalyst binders can effectively modulate the accessibility of CO 2 relative to H 2 O at the vicinity of the catalyst and thus the performance of CO 2 RR. Three polymers with different hydrophilicities (i.e., polyacrylic acid (PAA), Nafion, and fluorinated ethylene propylene (FEP)) are selected as binders for Cu catalysts. At a thickness of only ≈1.2 nm, these binders strongly affect the activity and selectivity toward multi-carbon (C 2+ ) products. The FEP coated catalyst exhibits a C 2+ partial current density of over 600 mA cm −2 with ≈77% faradaic efficiency at −0.76 V versus RHE. This high performance is attributed to the hydrophobic (aerophilic) properties of FEP, which reduces the local concentration of H 2 O and enhances that of the reactant (i.e., CO 2 ) and the reaction intermediates (i.e., CO). These findings suggest that tuning the hydrophobicity of electrocatalysts with polymer binders can be a promising way to regulate the performance of electrochemical reactions involving gas-solid-liquid interfaces.

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Cu-based bimetallic catalysts have attracted great attention for the reverse water gas shift (RWGS) reaction due to their high activity and selectivity. This work reports the application of Cu−In bimetallic catalysts for the RWGS reaction and demonstrates that the promotion effect of In on Cu is support sensitive. The Cu−In/ZrO 2 catalyst exhibited significantly higher CO 2 conversion than the Cu/ZrO 2 catalyst, whereas the CO 2 conversion over Cu−In/CeO 2 was much lower than that of Cu/CeO 2 . The reasons of the support-dependent RWGS activity was revealed by systematic characterizations. On the ZrO 2 support, Cu and In formed Cu−In alloys and promoted the activation of CO 2 by the oxygen vacancies from partially reduced In 2 O 3 . On the CeO 2 support, Cu and In were in the form of metallic Cu and In 2 O 3 , respectively. The dispersion of Cu and the formation of oxygen vacancies on CeO 2 were obstructed by the introduction of In, leading to decreased RWGS activity. Among these catalysts, Cu/CeO 2 showed the best RWGS activity because of the strong CO 2 activation ability of the partially reduced CeO 2 support and the highly active Cu/CeO 2−x interfaces. These results provide new insights into the design and understanding of supported bimetallic catalysts for CO 2 hydrogenation.