TY - JOUR A1 - Pu, Y. A1 - Celorrio, V. A1 - Stockmann, Jörg M. A1 - Sobol, Oded A1 - Sun, Z. A1 - Wang, W. A1 - Lawrence, M. J. A1 - Radnik, Jörg A1 - Russel, A. E. A1 - Hodoroaba, Vasile-Dan A1 - Huang, L. A1 - Rodriguez, P. T1 - Surface galvanic formation of Co-OH on Birnessite and its catalytic activity for the oxygen evolution reaction JF - Journal of Catalysis N2 - Low-cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earthabundant metal oxides. In this work, surface galvanic formation of Co-OH on K0.45MnO2 (KMO) was achieved via the redox reaction of hydrated Co2+ with crystalline Mn4+. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, such as chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoOxHy deposited on the KMO and its electronic structure strongly depend on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl- favors the formation of Co-OH, changing the rate-determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media. KW - Nanoparticles KW - Oxygen evolution reaction (OER) KW - Catalysis KW - ToF-SIMS KW - XPS KW - K-rich Birnessite (K0.45MnO2) PY - 2021 DO - https://doi.org/10.1016/j.jcat.2021.02.025 VL - 396 SP - 304 EP - 314 PB - Elsevier Inc. AN - OPUS4-52328 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wahl, S. A1 - El-Refaei, S. M. A1 - de Oliveira Guilherme Buzanich, Ana A1 - Amsalem, P. A1 - Lee, K.-S. A1 - Koch, N. A1 - Doublet, M.-L. A1 - Pinna, N. T1 - Zn0.35Co0.65O – A Stable and highly active oxygen evolution catalyst formed by zinc leaching and tetrahedral coordinated cobalt in wurtzite structure JF - Advanced Energy Materials N2 - To arrive to sustainable hydrogen-based energy solutions, the understanding of water-splitting catalysts plays the most crucial role. Herein, state-of-the-art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth-abundant cobalt and zinc oxides. The precursor catalyst Zn0.35Co0.65O is synthesized via a fast microwaveassisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ-Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic Performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm−2 ηinitial = 306 mV, η98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today’s literature, clear structureactivity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER. KW - Oxygen Evolution Catalyst KW - XAFS KW - Oxygen evolution reaction (OER) KW - Cobalt and zinc oxides PY - 2019 DO - https://doi.org/10.1002/aenm.201900328 SN - 1614-6832 SN - 1614-6840 VL - 9 IS - 20 SP - 1900328,1 EP - 10 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-48200 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -