Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

Ambient-Pressure X-ray Photoelectron Spectroscopy to Characterize the Solid/Liquid Interface: Probing the Electrochemical Double Layer

Ambient-pressure X-ray photoelectron spectroscopy (APXPS) has contributed greatly to a wide range of research fields, including environmental science [1 H. Bluhm, Journal of Electron Spectroscopy and Related Phenomena 177, 71–84 (2010).[Crossref], [Web of Science ®] , [Google Scholar]], catalysis [2 D.E. Starr et al., Chemical Society Reviews 42, 5833–5857 (2013).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], and electrochemistry [3 E.J. Crumlin, H. Bluhm, and Z. Liu, Journal of Electron Spectroscopy and Related Phenomena 190, 84–92 (2013).[Crossref], [Web of Science ®] , [Google Scholar]], to name a few. The use of this technique at synchrotron facilities primarily focused on probing the solid/gas interface; however, it quickly advanced to the probing of liquid/vapor interfaces [4 D.E. Starr et al., Physical Chemistry Chemical Physics 10, 3093–3098 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 5 M.A. Brown et al., Physical Chemistry Chemical Physics 10, 4778–4784 (2008).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]] and solid/liquid interfaces through an X-ray-transparent window [6 J. Kraus et al., Nanoscale 6, 14394–14403 (2014).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]–8 T. Masuda et al., Appl Phys Lett 103 (2013).[Crossref], [Web of Science ®] , [Google Scholar]]. Most recently, combining APXPS with “Tender” X-rays (~2.5 keV to 8 keV) on beamline 9.3.1 at the Advanced Light Source in Lawrence Berkeley National Laboratory (which can generate photoelectrons with much longer inelastic mean free paths) has enabled us to probe the solid/liquid interface without needing a window [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. This innovation allows us to probe interfacial chemistries of electrochemically controlled solid/liquid interfaces undergoing charge transfer reactions [9 S. Axnanda et al., Scientific Reports 5 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]]. These advancements have transitioned APXPS from a traditional surface science tool to an essential interface science technique.     

An Advanced Materials Beamline for Energy Research (AMBER)

Detailed mapping of the electronic structure is a crucial part of explaining the behavior of materials. It is the electronic structure that determines the conductivity and thermal properties. It is the electronic structure that determines chemical properties. Knowledge about the electronic structure can help in determining the atomic structure of molecules.     

In-Situ and In-Operando Experiments

How do we learn about the electronic and atomic characteristics of novel materials for efficient solar energy conversion (photovoltaics and water-splitting), energy storage (Li-ion batteries and multivalent-ion batteries), and efficient catalytic activity and selectivity in catalysis? The fundamental scientific problems that we plan to understand and ultimately control are: (1) efficient absorption-induced electron-hole pair formation and its separation at the complex interfaces; (2) bandgap, band levels, and band structure of earth abundant materials that are of crucial importance in electrochemical and photocatalytic applications.     

Fe-N-modified multi-walled carbon nanotubes for oxygen reduction reaction in acid

We report a facile synthesis of Fe-N-C catalysts based on the surface functionalization of multi-walled carbon nanotubes (MWCNTs), which show high activity and stability for oxygen reduction reaction (ORR) in acid. Fe-N-MWCNT catalysts, whose ORR mass activities could vary by 3-4 times depending on the choice of Fe precursors, were found to have considerably higher ORR mass activity and higher stability than N-modified MWCNTs (N-MWCNTs). The Fe-N-MWCNT catalyst with a dominant Fe-N(x) moiety (with x ≈ 4) and a surface Fe/C ratio of ～0.004 exhibits the highest ORR mass activity in acid (～0.7 mA mg(-1)(Fe-N-MWCNT) at 0.8 V vs. RHE), where the lower mass activity of other Fe-N-MWCNT catalysts can be attributed to lower Fe/C ratios and Fe-N(x) moieties (with x smaller than 4) as revealed from X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Moreover, the enhanced stability of Fe-N-MWCNTs in comparison to N-MWCNTs can be attributed to less H(2)O(2) production during ORR as determined from rotating ring disk electrode (RRDE) measurements, and higher activity for H(2)O(2) electro-reduction by rotating disk electrode (RDE) measurements. The large surface Fe/C ratio and Fe-N(x) moiety corresponding to high ORR activity and stability of Fe-N-MWCNTs demonstrate that surface functionalization can be very helpful to graft active catalytic sites onto carbon nanostructures, and to provide insights into the ORR mechanism of non-noble metal catalysts (NNMCs) for proton exchange membrane fuel cells (PEMFCs).