## 3 Sample Environments
### Devices  
Given the high penetration power of neutrons in combination with the possibility of highlighting different parts of a material or the distribution of water via the use of deuteration, one would guess that neutron scattering techniques would be a prime tool for the investigation of devices, like batteries, liquid/gas separating membranes under operando conditions, and soot formation by combustion of hydrocarbons in engines, to name a few. However, this kind of research does not currently have a widespread following. This might be due to a combination of the relatively low neutron fluxes available currently and a certain bias that neutron facilities are somewhat inaccessible to the general user. However, there are examples of the above-mentioned systems studied with neutrons. There also is somewhat of a bias against more engineering-oriented or applied applications that can be found in many beam line access panels. Most of the experiments using simulated devices can be found in energy storage and generation-related materials. The device that was studied using neutron scattering and imaging techniques was a polymer-electrolyte fuel cell [130]. The interest here is the distribution and transport in the fuel cell and the two techniques, SANS and imaging, were combined in a single experiment where the neutron imaging system could be moved out of the beam during the acquisition of the SANS data. This is particularly interesting since the two techniques might not give the same type of information, but the accessible length scales are complementary, and relevant information over length scales from nano- to milli-meters can be obtained in a single experiment. It can be pointed out that this cell was a realistic model where metal components were illuminated by the neutron beam. Using SAXS experiments, where the electron densities of H2O and polymers are not sufficiently different to generate a contrast that can make aluminum, H2O and polymer all visible, no information about the distribution of water can be obtained. Importantly, the above-mentioned experiment emphasizes the ability to study materials under operando conditions. It is noteworthy that data acquisition time for SANS was 80 s/frame and for imaging 210 s/frame. In a  
Figure 14: A load frame with U-shaped load beams that allow the sample to be deformed, whilst being completely immersed in water. The temperature-controlled reservoir containing H2O/D2O can be placed around the sample (reproduced with permission from [129], AIP Publishing, 2013). later publication, infrared spectroscopic data were also used to evaluate the physical and chemical events inside the fuel cell [131; 132]. Another energy-related application is the study of Li-ion batteries. The concentration of Li-salt and the type of electrode material used has consequences for the operation of the battery and its longevity. By using a half-cell, i.e., a single electrode surrounded by an electrolyte solution, it enables one to follow the events at the solid-electrolyte interface. In the case where one uses an ordered mesoporous carbon electrode, mesoporous events take place in the range where small angle scattering (SAXS/SANS) can yield information. Here again there is a lack of electron density contrast between the Carbon and the Li compared to the pores, which indicates that neutron scattering is better suited to gain insights into the effects of the use of different Li-salts and concentrations during the duty cycle for in-operando cycling/discharging [133]. Similar experiments, but with greater emphasis on the analysis of the scattering results and the role of the scattering contrast in the analysis of the data, were also published [134]. Supercapacitors, hybrid devices with characteristics between a capacitor and a battery, rely on a high internal surface for redox reactions to take place.