Cecile S. Bonifacio

Bio: Cecile S. Bonifacio is an academic researcher from University of Pittsburgh. The author has contributed to research in topics: Ion milling machine & Transmission electron microscopy. The author has an hindex of 16, co-authored 67 publications receiving 1436 citations. Previous affiliations of Cecile S. Bonifacio include University of California, Davis.

Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene

Abstract: There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper(+) species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper(+) is key for lowering the onset potential and enhancing ethylene selectivity.

Enhanced Carbon Dioxide Electroreduction to Carbon Monoxide over Defect-Rich Plasma-Activated Silver Catalysts

Abstract: Efficient, stable catalysts with high selectivity for a single product are essential to making the electroreduction of CO2 a viable route to the synthesis of industrial feedstocks and fuels. We reveal how a plasma oxidation pre-treatment can lead to an enhanced content of low-coordinated active sites which dramatically lower the overpotential and increase the activity of CO2 electroreduction to CO. At -0.6 V vs. RHE, more than 90% Faradaic efficiency towards CO could be achieved on a pre-oxidized silver foil. While transmission electron microscopy and operando X-ray absorption spectroscopy showed that oxygen species can survive in the bulk of the catalyst during the reaction, in situ X-ray photoelectron spectroscopy showed that the surface is metallic under reaction conditions. DFT calculations show how the defect-rich surface of the plasma-oxidized silver foils in the presence of local electric fields results in a drastic decrease in the overpotential for the electroreduction of CO2.

Oxygen Reduction Reaction on Classically Immiscible Bimetallics: A Case Study of RhAu

Abstract: The catalytic properties of bulk-immiscible alloys are less explored than their bulk-miscible counterparts due to inherent difficulties in their synthesis and stabilization. The development of alternative synthetic methods can, however, provide routes toward bulk-immiscible nanoparticles with metastable randomly alloyed structures. In this study, we combine computational screening and a microwave-based synthesis method to target bulk-immiscible alloys that show enhanced reactivity over pure metals for the oxygen reduction reaction (ORR). A number of systems are identified theoretically as promising ORR catalysts. The theoretical predictions are experimentally verified for the RhAu system, for which a specific surface ensemble is identified as being highly active in the ORR.

Thermal Stability of Core–Shell Nanoparticles: A Combined in Situ Study by XPS and TEM

Abstract: In situ techniques of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the thermal stability of Ni–Co core–shell nanoparticles (NPs). The morphological, structural, and chemical changes involved in the core–shell reconfiguration were studied during in situ annealing through simultaneous imaging and acquisition of elemental maps in the TEM, and acquisition of O 1s, Ni 3p, and Co 3p XP spectra. The core–shell reconfiguration occurred in a stepwise process of surface oxide removal and metal segregation. Reduction of the stabilizing surface oxide occurred from 320 to 440 °C, initiating the core–shell reconfiguration. Above 440 °C, the core–shell structure was disrupted through Ni migration from the core to the shell. This resulted in the formation of a homogeneous Ni–Co mixed alloy at 600 °C. This study provides a mechanistic description of the alteration in the core–shell structures of NPs under vacuum conditions and increasing annealing temperature, ...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte

Abstract: To date, copper is the only heterogeneous catalyst that has shown a propensity to produce valuable hydrocarbons and alcohols, such as ethylene and ethanol, from electrochemical CO2 reduction (CO2R). There are variety of factors that impact CO2R activity and selectivity, including the catalyst surface structure, morphology, composition, the choice of electrolyte ions and pH, and the electrochemical cell design. Many of these factors are often intertwined, which can complicate catalyst discovery and design efforts. Here we take a broad and historical view of these different aspects and their complex interplay in CO2R catalysis on Cu, with the purpose of providing new insights, critical evaluations, and guidance to the field with regard to research directions and best practices. First, we describe the various experimental probes and complementary theoretical methods that have been used to discern the mechanisms by which products are formed, and next we present our current understanding of the complex reaction networks for CO2R on Cu. We then analyze two key methods that have been used in attempts to alter the activity and selectivity of Cu: nanostructuring and the formation of bimetallic electrodes. Finally, we offer some perspectives on the future outlook for electrochemical CO2R.

CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface

Abstract: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

Advances and challenges in understanding the electrocatalytic conversion of carbon dioxide to fuels

Abstract: The electrocatalytic reduction of carbon dioxide is a promising approach for storing (excess) renewable electricity as chemical energy in fuels. Here, we review recent advances and challenges in the understanding of electrochemical CO2 reduction. We discuss existing models for the initial activation of CO2 on the electrocatalyst and their importance for understanding selectivity. Carbon–carbon bond formation is also a key mechanistic step in CO2 electroreduction to high-density and high-value fuels. We show that both the initial CO2 activation and C–C bond formation are influenced by an intricate interplay between surface structure (both on the nano- and on the mesoscale), electrolyte effects (pH, buffer strength, ion effects) and mass transport conditions. This complex interplay is currently still far from being completely understood. In addition, we discuss recent progress in in situ spectroscopic techniques and computational techniques for mechanistic work. Finally, we identify some challenges in furthering our understanding of these themes. Electrocatalytic reduction of CO2 to fuels could be used as an approach to store renewable energy in the form of chemical energy. Here, Birdja et al. review current understanding of electrocatalytic systems and reaction pathways for these conversions.