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  1. >24% screen printed Cu contacted n-TOPCon solar cells with successful implementation of LECO process

    Ok, Young-Woo ; Zhong, Ruohan ; Upadhyaya, Vijaykumar ; ... - Solar Energy Materials and Solar Cells
    In this paper, we report the successful fabrication of >24.0 % efficiency n-TOPCon Si solar cells with screen-printed, fire-through Cu contact to n-TOPCon on the rear side and Ag contacted boron emitter on the front side by implementing optimized firing and LECO conditions. The highest efficiency (24.3%) Cu contacted n-TOPCon cell in this study showed excellent cell performance parameters with Voc >730 mV, Jsc of 41.1 mA/cm2 and FF of 80.8%, resulting in an absolute efficiency gap of 0.2% between Cu-contacted and fully Ag contacted n-TOPCon cells (24.5%). The mini-module fabricated with the Cu contacted n-TOPCon cell showed excellent reliabilitymore » and durability of open-circuit voltage (Voc), pseudo fill factor (pFF) and efficiency after prolonged damp-heat tests. Such high efficiency screen printed Cu contacted n-TOPCon cells provide unique opportunity to replace very expensive Ag contact on n-TOPCon with cheaper screen printable Cu metal pastes.« less

  2. In Situ Studies of Ru-CeO2–TiO2 Catalysts for Selective CO2 Hydrogenation to Methane: Importance of Metal ↔ Oxide–Oxide Interactions

    Barba-Nieto, Irene ; Fernández-García, Marcos ; Reddy, Kasala Prabhakar ; ... - ACS Catalysis
    Here, this work investigates Ru-CeO2-TiO2 catalysts for the CO2 methanation reaction and compares their performance with previously studied Ru-CeO2 systems. Despite the lower Ru loading, the TiO2-containing catalysts exhibit significantly higher activity. To understand this behavior, in situ X-ray absorption spectroscopy (XAS) was carried out at the Ru K-edge and Ce L3-edge. Unlike Ru-CeO2, which displays reversible redox behavior of Ru, the Ru-CeO2-TiO2 catalysts show irreversible Ru reduction and a substantially higher fraction of Ce3+ species under all tested conditions (H2, CO2, H2/CO2). The stabilization of metallic Ru during methanation, together with the enhanced formation of Ce3+ promoted by TiO2more » through interfacial electronic transfer, accounts for their superior performance. Complementary in situ DRIFTS measurements reveal the formation and rapid consumption of bidentate carbonates and formates. These species act as a key intermediate in methane formation. Overall, these findings highlight the crucial role of the mixed CeO2-TiO2 oxide in tuning the surface chemistry of the catalysts by stabilizing metallic Ru, enhancing ceria reducibility, and promoting efficient reaction pathways for CO2 methanation. The manipulation of metal↔oxide-oxide interactions can be a very useful tool when dealing with the valorization of CO2.« less

  3. Transient Studies of CO2 Adsorption over CeO2 Nanostructures with In Situ DRIFTS and Modulation Excitation

    Wang, Yuxi ; Moncada, Jorge ; Sahoo, Sanjubala ; ... - Journal of Physical Chemistry. C
    Experiments of in-situ DRIFTS combined with modulation excitation (ME) spectroscopy showed a rich surface chemistry associated with the adsorption of CO2 on nanocubes and nanospheres of ceria. The nanocubes exposed faces with a (100) orientation, with the edges and corners displaying (110) and (111) orientations, respectively. Here, the nanospheres mainly contained ceria (111) and (110) planes. DFT calculations showed that CO2 is a multidentate adsorbate on ceria that can undergo changes in its bonding configuration depending on the chemical environment. At 250 °C, a temperature typically used for the conversion of CO2 into oxygenates, alkanes and olefins, CO2 reacted withmore » O centers or OH groups present on the nanocubes and nanospheres to yield bi- and tri-dentate carbonates, hydroxycarbonates, and formates. Both nanostructures were highly reactive and a dynamic equilibrium was established: carbonate species were rapidly generated upon the injection of CO2 and they decomposed upon the removal of CO2 from the gas phase. In the case of the ceria nanocubes, the adsorption/desorption processes were essentially reversible, opening the door to catalytic transformations. A larger concentration of defects in the ceria nanospheres led to strongly bound carbonates and formates that may be spectators, site blockers, or surface modifiers in catalytic processes. In the ME studies, additional intermediates were detected, and it was clear that the response of surface species to the presence/absence of CO2 was highly dependent on the morphology of the ceria nanostructures.« less

  4. Activity and selectivity for CO2 methanation of clusters and nanoplates of ruthenium dispersed on ceria: In-situ studies with XAFS and DRIFTS

    Barba-Nieto, Irene ; Fernández-García, Marcos ; Moncada, Jorge ; ... - Catalysis Today
    The performance of Ru/CeO2 catalysts under CO2 hydrogenation conditions was studied using in situ X-ray absorption fine structure (XAFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to understand the structural evolution and chemical nature of each component under reaction conditions. The catalysts were prepared using a reverse microemulsion method that maximized the dispersion of RuOx particles on ceria. A RuOx → Ru transformation was observed upon exposure of the RuOx/CeO2 systems to H2 at 250 °C. For a sample with 5% molar Ru, two-dimensional clusters (2-4 atoms) of Ru formed on top of the ceria support. An increase inmore » the loading of ruthenium to 20% molar led to the formation of nanoplates of the metal 2-3 atomic layers thick. Both Ru structures were highly dispersed on ceria. They were oxidized after exposure to CO2 at 250 °C. However, under CO2/H2 mixture, they remained in a metallic state as two-dimensional clusters and nanoplates. In situ DRIFTS studies, the 5% and 20% Ru/CeO2 catalysts showed distinct reaction intermediates when exposed to CO2 or CO2/H2 (1/4) reaction mixtures. Normalized to the Ru molar percentage, the 5% Ru/CeO2 system was the most active catalyst exhibiting a selectivity of ~ 60% CH4 and 40% CO at 250 °C. On the other hand, under the same reaction conditions, the 20% Ru/CeO2 system was less active but had a CH4 selectivity close to 80%. In conclusion, these results highlight the importance of the structure of the metallic Ru particles as a factor that determines the catalytic performance.« less

  5. Visualizing Size-Dependent Dynamics of CeO2-δ{100}-Supported CoOx Nanoparticles Under CO2 Hydrogenation Conditions

    Deng, Kaixi ; Wang, Yuxi ; Pérez-Bailac, Patricia ; ... - Journal of the American Chemical Society
    Carbon dioxide is a major greenhouse gas. In order to optimize processes focused on its chemical valorization, one needs detailed information about the effects of CO2 and/or CO2/H2 mixtures on the structure and morphology of metal/oxide catalysts. Here, in this study, the evolution of a catalyst with cobalt supported on CeO2-cube nanostructures under CO2 hydrogenation conditions was investigated by using a set of in situ characterization techniques (X-ray absorption fine structure, X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, and environmental transmission electron microscopy (TEM)). The {100} facets of the ceria support displayed an unexpectedly high stability due to strongmore » interactions with the aggregates of cobalt oxide. A significant influence of interfacial bonding between CoOx and CeO2-δ {100} is evident through a clear preference in the orientation of CoOx nanoparticles (NPs) with respect to the substrate. For initially reduced Co/CeO2-cube nanostructures, a kinetically controlled oxidation of cobalt upon the introduction of CO2 was observed during the early stages of CO2 hydrogenation. Environmental TEM revealed the size-dependent morphological behavior of cobalt oxide NPs due to strong interactions with the CeO2 {100} surface. When the environment was switched from H2 to a mixture of H2 and CO2 at 250 °C, small CoOx NPs (in the largest dimension < 2.5 nm) rapidly transformed from a pyramidal three-dimensional (3D) form to a planar, monatomic layer attached to the concurrently oxidized CeO2-δ {100} surface. This maximizes the number of sites available for the binding of CO2 or reaction intermediates. The shape transformation reflected the oxophilic character of cobalt and strong metal–support interactions. The removal of CO2 from the gas phase led to a reduction of the cobalt oxide NPs by hydrogen and a reversible two-dimensional → 3D transformation. In contrast, no significant morphological changes, apart from further oxidation, were observed for big CoOx NPs (in the largest dimension > 3 nm). These trends are not seen for nanoparticles of noble metals. The observed morphological and structural changes in the small CoOx NPs affected the stability of reaction intermediates and modified the selectivity of the CoOx/CeO2 catalyst system for methane production.« less

  6. Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O2−δ Nanoparticles

    Zhang, Sipei ; Fang, Zhengwu ; Chi, Miaofang ; ... - ACS Applied Materials and Interfaces
    Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. Here, in this work, Pr0.2Ce0.8O2−δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strainmore » and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO2 (1 to 10–4 atm O2). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO2. STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.« less

  7. Prediction of the Cu Oxidation State from EELS and XAS Spectra Using Supervised Machine Learning

    Gleason, Samuel P. ; Carbone, Matthew R. ; Lu, Deyu ; ... - Microscopy and Microanalysis
    Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) provide detailed information about distributions and locations of atoms, their coordination numbers and oxidation states, and the bonding characteristics [1]. However, analysis of XAS/EELS data often relies on matching the spectra of an unknown experimental sample to a series of simulated or experimental spectra of standard samples. Here, this limits analysis throughput and the ability to extract quantitative information from a sample.

  8. Butene-Rich Alkene Formation from 2,3-Butanediol through Dioxolane Intermediates

    Cordon, Michael J. ; Li, Meijun ; Yang, Xiaokun ; ... - ACS Sustainable Chemistry & Engineering
    The cost-effective production of sustainable aviation fuels (SAF) remains a major challenge within the energy sector. One approach to address this is the fermentation of biomass feedstocks into oxygenates followed by catalytic conversion to alkenes or other oligomerization precursors. 2,3-Butanediol (BDO) is a promising fermentation product due to its four-carbon nature, its decreased microorganism toxicity and associated higher maximum fermentation titers relative to other alcohols and oxygenates, and its capacity to be readily converted into butene isomers and longer chain alkenes. BDO conversion is currently constrained by separation challenges for BDO isolation due to its high boiling point and hydrophilicity.more » Here, this work expands upon previous BDO reactive separation via dioxolane formation over a solid acid catalyst by investigating the conversion of dioxolanes into alkene mixtures. Dioxolanes were formed from a range of aldehydes and subsequently converted over a Cu/ZSM-5 catalyst (448–523 K) via an ether cleavage, hydrogenation, and dehydration reaction network to form alkene-rich product mixtures (96% C3+ alkene yield, 523 K). This selectivity is greater than that of direct BDO conversion to alkenes over an identical catalyst (89%, 523 K). C3+ alkene selectivity is maximized between 498 and 523 K at complete dioxolane conversion without significant alkene hydrogenation to alkanes. The alkene product distributions can be tailored via both aldehyde selection during dioxolane formation and the dioxolane conversion reaction temperature. Alkene mixtures from dioxolane conversion predominantly reflect the carbon chain length and stereochemistry of BDO and the initial aldehyde at or below 498 K, yet higher reaction temperatures yield alkene mixtures of similar carbon chain distributions, regardless of initial aldehyde selection. Deactivation of the Cu/ZSM-5 catalyst is observed for multiple steps of the overall reaction network but can be minimized by facilitating the complete dioxolane-to-alkene reaction network at temperatures of at least 498 K.« less

  9. Structural and Chemical Evolution of an Inverse CeOx/Cu Catalyst under CO2 Hydrogenation: Tunning Oxide Morphology to Improve Activity and Selectivity

    Moncada, Jorge ; Chen, Xiaobo ; Deng, Kaixi ; ... - ACS Catalysis
    Small nanoparticles of ceria deposited on a powder of CuO display a very high selectivity for the production of methanol via CO2 hydrogenation. CeO2/CuO catalysts with ceria loadings of 5%, 20%, and 50% were investigated. Among these, the system with 5% CeOx showed the best catalytic performance at temperatures between 200 and 350 °C. The evolution of this system under reaction conditions was studied using a combination of environmental transmission electron microscopy (E-TEM), in situ X-ray absorption spectroscopy (XAS), and time-resolved X-ray diffraction (TR-XRD). For 5% CeOx/Cu, the in situ studies pointed to a full conversion of CuO into metallicmore » copper, with a complete transformation of Ce4+ into Ce3+. Images from E-TEM showed drastic changes in the morphology of the catalyst when it was exposed to H2, CO2, and CO2/H2 mixtures. Under a CO2/H2 feed, there was a redispersion of the ceria particles that was detected by E-TEM and in situ TR-XRD. Finally, these morphological changes were made possible by the inverse oxide/metal configuration and facilitate the binding and selective conversion of CO2 to methanol.« less

  10. Beneficial effect of copper on pitting resistance of Ni-Cr-Fe alloys

    Hariharan, Karthikeyan ; Li, Sirui ; Taylor, Christopher D. ; ... - Electrochimica Acta
    This study examines the effect of copper alloying on pitting resistance in a model solid solution FCC Ni-13%Cr-10%Fe alloy through potentiodynamic and potentiostatic polarization in 0.1 M NaCl in conjunction with an analysis using first-principles competitive electro-chemisorption modeling. The pitting potential increased with increasing Cu content in the alloy. Furthermore, the extent of metastable pit growth was suppressed and the incubation time for metastable to stable pit transition increased with Cu content. The first-principles competitive adsorption calculations suggested that Cu alloying suppresses chloride ion adsorption on the alloy surface in a simulated pit environment, which inhibits active dissolution at themore » pit bottom, enhances proton adsorption, and thereby increases the local pH at the pit bottom. In conclusion, we propose that these two effects of Cu in solid solution combine to reduce pit stability and may act in addition to the enrichment of Cu on the corroding pit surface.« less
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