Lattice Expansion in Optimally Doped Manganese Oxide: An Effective Structural Parameter for Enhanced Thermochemical Water Splitting

Abstract

Earth abundant transition-metal oxides have attracted broad interest for thermochemical production of renewable fuels and other gaseous commodities. Despite progress, a major challenge remains in achieving fast and reversible redox kinetics as well as large oxygen exchange capacities. Here, we present insights on the optimal doping of manganese oxide nanocrystals for their efficient and stable utilization as redox material for thermochemical water splitting. The detailed investigation of the evolution of the material properties over a broad range of possible Ce–Mn compounds reveals a single key structural parameter affecting the thermochemical performance. We observe that the expansion of the MnO lattice is essential for activating its reduction from oxide to carbide and thus for H2O splitting during its subsequent reoxidation. This is optimally achieved for a very narrow window of dopant concentration peaking at 3% Ce content, which provides the largest distortion of the manganese oxide crystal lattice. In contrast, smaller or higher Ce amounts of 1 and 5%, respectively, result in significantly smaller lattice expansions either due to an insufficient dopant amount or to the segregation of Ce in large CeO2 domains. We use these findings to propose a mechanism for the enhancement of the redox kinetics of this metal oxide, which may provide guidance for the design of a family of future materials for thermochemistry.

Boosting methane partial oxidation on ceria through exsolution of robust Ru nanoparticles

“…In order to overcome this problem, doping with other cations, 4 such as Zr 14 or La 5 , has been employed in order to increase the reducibility of cerium oxides and, subsequently, the fuel yields obtained by H 2 O and/or CO 2 splitting. Morphological modifications 15 or combinations in the form of composites with other metal oxides such as perovksites 16 or binary oxides 17,18 have been also successfully tested. Additionally, during the methane partial oxidation (MPO) step, most literature reports show syngas selectivity far from 100%, 6 which results from the combustion of CH 4 with readily available oxygen anions at the CeO 2 surface producing CO 2 and H 2 O.…”

Concentration-Dependent Solar Thermochemical CO 2 /H 2 O Splitting Performance by Vanadia–Ceria Multiphase Metal Oxide Systems

“…Oxygen-carrier-mediated solar thermochemical reductionoxidation (redox) cycling is a promising approach to produce renewable fuels utilizing solar energy [1][2][3][4][5][6][7][8]. A typical solar-thermochemical redox cycle consists of two steps: (1) reduction of the oxygen carrier under an inert or reducing gas atmosphere (Reaction (1)) and (2) reoxidation of the reduced oxygen carrier by CO 2 (Reaction (2)) and H 2 O (Reaction (3)).…”

Iron-based energy storage materials from carbon dioxide and scrap metal

“…40 The relative intensity of the O-C-O to C-C peaks decreases as a function of the heat-treatment temperature, indicating that the samples treated at higher temperatures suffer a larger loss of O-C-O groups. The spectra of F4N and F3A, correspond to the C1s lineshape typical of physisorbed impurities on nominally carbon-free samples, 45 indicating a complete loss of oxalate. These results are in line with Raman spectra, where the G and D peak (attributed to C-C bonds in the carbonaceous residue) can only be observed for F4N and, more faintly, in F3N.…”