Parahydrogen (p-H2)-based techniques are known to drastically enhance NMR signals but are usually limited by p-H2 supply. This work reports p-H2-based SABRE hyperpolarization at p-H2 pressures of hundreds of bar, far beyond the typical ten bar currently reported in the literature. A recently designed high-pressure setup was utilized to compress p-H2 gas up to 200 bar. The measurements were conducted using a sapphire high-pressure NMR tube and a 43 MHz benchtop NMR spectrometer. In standard methanol solutions, it could be shown that the signal intensities increased with pressure until they eventually reached a plateau. A polarization of about 2%, equal to a molar polarization of 1.2 mmol L−1, could be achieved for the sample with the highest substrate concentration. While the signal plateaued, the H2 solubility increased linearly with pressure from 1 to 200 bar, indicating that p-H2 availability is not the limiting factor in signal enhancement beyond a certain pressure, depending on sample composition. Furthermore, the possibility of using liquefied ethane and compressed CO2 as removable solvents for hyperpolarization was demonstrated. The use of high pressures together with quickly removable organic/non-organic solvents represents an important breakthrough in the field of hyperpolarization, advancing SABRE as a promising tool for materials science, biophysics, and molecular imaging.
Acceptor-doped BaZrO 3 is known for its high proton conductivity, making it an advanced energy material for various applications, for example, electrolyzers, fuel cells, or methane-conversion cells. [1][2][3][4][5] For this reason, many groups are investigating proton migration in acceptor-doped BaZrO 3 from the past to the present day. [2,[6][7][8] Recently, we could show that proton motion in yttrium-doped BaZrO 3 is determined by two phenomena: proton trapping by yttrium ions and the formation of nanoscale percolation pathways of yttrium ions. [9] A single yttrium dopant traps protons on firstand second-nearest neighbor sites, and at low dopant fractions, where the dopants are isolated from each other, trapping results in a decrease in average proton mobility. With increasing dopant fractions there are, however, local structures containing several Y ions in firstand second-nearest neighborhood. Within these nanoscale structures, the trapping zones of all Y ions overlap, and due to the low proton migration energies inside of these local structures, protons can move very fast within them. This phenomenon leads to a strong increase in proton mobility and proton conductivity with increasing dopant fraction, and thus, we named it in our previous publication [9] nanoscale percolation. We emphasize that these nanoscale structures are not necessarily connected, and they do not necessarily cross the whole sample, as in classical percolation, but they can be isolated local structures with fast proton transport, depending on the dopant fraction.In this article, we will investigate the impact of nanoscale percolation in yttrium-doped BaZrO 3 on its oxygen ion conductivity. Although it is known that at low temperatures the oxygen ion conductivity is much smaller than the proton conductivity, there are three reasons for this theoretical study. 1) Oxygen ions are mobile by means of oxygen vacancies, that will be trapped by Y ions, similar to protons. However, there seems to be no detailed theoretical study on the influence of defect interactions on the mobility of oxygen vacancies in Y-doped BaZrO 3 , although BaZrO 3 can be regarded as a prototype perovskite-structured oxide; 2) It is a priori unclear whether the phenomenon of
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