Page 36 - ILL Annual Report 2019

MATERIALS SCIENCE
Inés Puente Orench. Spanish
Aragón Materials Science Institute, CSIC, Spain
‘Since 2007 I have been co-responsible for CRG-D1B, the powder neutron diffractometer at the ILL. Our research focus is the synthesis and characterisation of multi-metallic organic
frameworks and their derived products. Powder neutron diffraction in combination with single crystal X-rays provides
unique information about preferred co-ordination environments.’
Encoding metal cation arrangements in metal–organic frameworks for programming the composition of electrocatalytically active multi-metal oxides
High-intensity powder diffractometer D1B
Fuel cells are probably one of the best alternative energy sources to fossil fuel. However, the high cost and/or scarcity of some of their components have hindered their commercialisation. In particular, to obtain high oxygen reduction reaction (ORR) activity, a significant amount of platinum is used in cathodes. Spinel-type oxides have recently appeared as alternative electrocatalysts
for this reaction. The activity of these solids strongly depends on their composition, and fine adjustment of the metal component and their ratios could lead to improvement in their performance. However, up until now the incorporation of three or four metal cations at precise atomic ratios in the same solid remains challenging with current synthetic routes.
Figure 1
The multi-metal MOF is formed by the combination of various cations (Zn2+, Co2+, Mn2+ and Ca2+) forming a helical, inorganic SBU, and the organic linker H2hfipbb (left). The helical-shaped inorganic SBUs are formed by alternating tetrahedral and octahedral co-ordination polyhedra. The SBUs contain 2, 3 or 4 different metal elements (right).
AUTHORS
C. Castillo-Blas, N. López-Salas, M.C. Gutiérrez, E. Gutiérrez-Puebla, M. Ángeles Monge, Á. Monge and F. Gándara (CSIC, Madrid, Spain) I. Puente Orench (ILL and CSIC, Madrid, Spain)
ARTICLE FROM
J. Am. Chem. Soc. (2019)—doi: 10.1021/jacs.8b12860
Our study is based on the use of metal–organic frameworks (MOFs) that comprise multiple metal elements as platform materials for incorporating, in a controllable way, desired arrangements of selected metal cations. Post-synthetic transformation of these materials allows multi-metal spinel oxides with compositions that are programmable from the complex MOF precursors to be obtained. Some of these solids exhibit catalytic activity comparable with commercial platinum- based catalysts, in terms of current density and number of transferred electrons.
Metal–organic frameworks (MOF) are crystalline material, formed by the combination of metal clusters with organic linkers to produce extended, periodic structures. We have shown that through a careful combination of inorganic secondary building units (SBUs), network topology and
initial molar ratios it is possible to obtain isoreticular MOFs incorporating up to four different metal cations distributed at specific locations. In particular, starting from an MOF formed by zinc and the organic linker 4,4’-(hexafluoroisopropylidene) bis(benzoic acid) (H2hfipbb), we have successfully incorporated cobalt, manganese and calcium in the same SBU. By taking advantage of differences in the preferential co-ordination environment of selected metal elements, and with judicious adjustment of their initial molar ratios, it is possible to direct the location of these metal cations at specific positions, resulting in the formation of different binary, ternary and quaternary atomic sequences (figure 1).
ANNUAL REPORT 2019