Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State, Geometric Structure, and Catalytic Selectivity using Operando Spectroscopy.

The direct electrochemical conversion of carbon dioxide (CO2 ) into multi-carbon (C2+ ) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2 O nanocubes during operation in low-current H-Cells and in high-current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time-resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu-seeds during the surprisingly slow reduction of bulk Cu2 O. The initially (100)-rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide-derived generation of under-coordinated lattice defects, can support the high C2+ product yields.

Phenol-Catalyzed Discharge in the Aprotic Lithium-Oxygen Battery.

Discharge in the lithium-O2 battery is known to occur either by a solution mechanism, which enables high capacity and rates, or a surface mechanism, which passivates the electrode surface and limits performance. The development of strategies to promote solution-phase discharge in stable electrolyte solutions is a central challenge for development of the lithium-O2 battery. Here we show that the introduction of the protic additive phenol to ethers can promote a solution-phase discharge mechanism. Phenol acts as a phase-transfer catalyst, dissolving the product Li2 O2 , avoiding electrode passivation and forming large particles of Li2 O2 product-vital requirements for high performance. As a result, we demonstrate capacities of over 9 mAh cm-2areal , which is a 35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li2 O2 .

The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO2 electroreduction.

This communication examines the effect of the surface morphology of polycrystalline copper on electroreduction of CO(2). We find that a copper nanoparticle covered electrode shows better selectivity towards hydrocarbons compared with the two other studied surfaces, an electropolished copper electrode and an argon sputtered copper electrode. Density functional theory calculations provide insight into the surface morphology effect.

Electrodeposited AgCu Foam Catalysts for Enhanced Reduction of CO2 to CO.

Selective electrochemical reduction of CO2 is an emerging field which needs more active and stable catalysts for its practicability. In this work, we have studied the influence of Ag metal incorporation into Cu dendritic structures on the product distribution and selectivity of CO2 electroreduction. Bimetallic AgCu foams prepared by hydrogen bubble templated electrodeposition shift the potentials of CO production to more positive values compared to bulk silver. The presence of Ag during the electrodeposition significantly changed the size and the shape of the dendrites in the pore walls of AgCu foams compared to Cu foam. The CO adsorption characteristics are studied by operando Raman spectroscopy. In the presence of Ag, the maximum CO adsorption is observed at a more positive potential. As a result, an improved selectivity for CO is obtained for AgCu foam catalysts at lower overpotentials compared to Cu foam catalyst, evidencing a synergistic effect between the bimetallic components. We were successful in increasing the CO mass activity with respect to the total Ag amount. AgCu foams are found to retain the CO selectivity during long-term operation, and with their easily scalable electrodeposition synthesis they possess high potential for industrial application.

Structure, Activity, and Faradaic Efficiency of Nitrogen-Doped Porous Carbon Catalysts for Direct Electrochemical Hydrogen Peroxide Production.

Carbon materials doped with nitrogen are active catalysts for the electrochemical two-electron oxygen reduction reaction (ORR) to hydrogen peroxide. Insights into the individual role of the various chemical nitrogen functionalities in the H2 O2 production, however, have remained scarce. Here, we explore a catalytically very active family of nitrogen-doped porous carbon materials, prepared by direct pyrolysis of ordered mesoporous carbon (CMK-3) with polyethylenimine (PEI). Voltammetric rotating ring-disk analysis in combination with chronoamperometric bulk electrolysis measurements in electrolysis cells demonstrate a pronounced effect of the applied potentials, current densities, and electrolyte pH on the H2 O2 selectivity and absolute production rates. H2 O2 selectivity up to 95.3 % was achieved in acidic environment, whereas the largest H2 O2 production rate of 570.1 mmol g-1 catalyst h-1 was observed in neutral solution. X-ray photoemission spectroscopy (XPS) analysis suggests a key mechanistic role of pyridinic-N in the catalytic process in acid, whereas graphitic-N groups appear to be catalytically active moieties in neutral and alkaline conditions. Our results contribute to the understanding and aid the rational design of efficient carbon-based H2 O2 production catalysts.

Reactivity Determinants in Electrodeposited Cu Foams for Electrochemical CO2 Reduction.

CO2 reduction is of significant interest for the production of nonfossil fuels. The reactivity of eight Cu foams with substantially different morphologies was comprehensively investigated by analysis of the product spectrum and in situ electrochemical spectroscopies (X-ray absorption near edge structure, extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and Raman spectroscopy). The approach provided new insight into the reactivity determinants: The morphology, stable Cu oxide phases, and *CO poisoning of the H2 formation reaction are not decisive; the electrochemically active surface area influences the reactivity trends; macroscopic diffusion limits the proton supply, resulting in pronounced alkalization at the CuCat surfaces (operando Raman spectroscopy). H2 and CH4 formation was suppressed by macroscopic buffer alkalization, whereas CO and C2 H4 formation still proceeded through a largely pH-independent mechanism. C2 H4 was formed from two CO precursor species, namely adsorbed *CO and dissolved CO present in the foam cavities.