Mass transport losses are one of the least understood contributors to the over potential in proton exchange membrane water electrolyzers. In order to explore the possible contribution of porous media two phase flow to these losses, we have used neutron-imaging techniques and took a closer look at water and gas distribution profiles at various current densities, ranging from kinetic to mass transport-governed regions at ambient and elevated pressures. Gas volume and velocity have been computed through quantified neutron images and the two-phase flow regime has been identified. Using sub-second imaging, information on dynamics of gas pathway establishment and re-imbibition during startup and shutdown of electrolyzers has been acquired. Using X-ray tomography and simulated mercury intrusion porosimetry coupled with capillary pressure calculations, the hydrophilicity of the internal surfaces of the porous transport layer material has been determined.

Polymer electrolyte water electrolysis (PEWE) is perceived as a key technology for conversion of renewable electricity in large-scale energy storage applications and deep decarbonization of the traditionally carbon-intensive mobility and chemical industry sectors. Since the price of hydrogen produced by PEWE is dominated by the price of electricity, it is crucial to ensure low degradation rates during the lifetime of a PEWE stack. This study aims to shed light onto the effects of cationic impurities that are responsible for the water impurity related failures of a majority of commercial stacks by employing operando neutron imaging coupled with electrochemical impedance spectroscopy measurements. A detailed overpotential analysis is conducted to elucidate how different voltage losses are triggered depending on the relative position of the cationic contaminant in the catalyst coated membrane. Based on this, a novel, CO 2 -assisted, method for the extraction of cationic impurities from the ionomer of the electrolyzer to recover performance during operation of the cell is presented.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 195.176.113.2 Downloaded on 2019-06-17 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 195.176.113.2 Downloaded on 2019-06-17 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 195.176.113.2 Downloaded on 2019-06-17 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 195.176.113.2 Downloaded on 2019-06-17 to IP

Fast charging is a key requirement for lithium-ion battery (LIBs) technology in a wide range of applications from portable devices to electric vehicles. However, fast charging impose high C-rates and temperature gradients to the system, which cause electrolyte degradation and polymerization, resulting in reduced performance, cycle life, and capacity [1,2]. Therefore, for a safe and efficient implementation of fast charging, it is critical to understand its effect on LIBs components, particularly in the electrolyte.There is a lack of non-invasive methods to elucidate changes in the electrolyte during LIBs operation, and it is commonly studied via post-mortem analysis or ex-situ degradation [3–5]. Neutron imaging (NI) is suitable for studying electrolyte distribution in LIBs, since hydrogen provides high contrast when interacting with the neutron beam, while casing materials like stainless steel or aluminum provide low contrast [6]. Furthermore, the neutron attenuation spectrum of organic molecules depend on the motion of an atom due to molecular vibrations or diffusion, making neutron spectroscopy a suitable tool to identify the chemical composition and aggregation state in batteries. Here, we introduce spectroscopic neutron imaging (SNI) as the new method to study these phenomena in a spatially resolved way.Imaging of electrolyte and solvent samples, performed at the V20 beamline of HZB in Berlin and the IMAT beamline of ISIS in UK (Figure 1-a), show that a liquid binary mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) exhibit similar attenuation spectra – though the different chemical composition and diffusivities result in small variations. On the other hand, solidified species (red region) present a noticeable contrast change due to the reduced molecular diffusion. At 17°C, the organic binary mixture, EC:DEC (1:1 volume ratio), exhibits liquid (EC and DEC) and solid (EC) phases. A similar behavior for solids is observed in the short wavelength (λ<3Ȧ) region of the normalized 1H cross-section spectra, while the curves in the diffusion region (λ>3Ȧ) are bounded to the mobility properties of each molecule (figure 1-b).Additionally, we will present measurements of different electrolytes and organic binary mixtures exposed to temperature-dependent phase changes, obtained via SNI at the ICON beam line of PSI. Setting a lower wavelength resolution requirement allows faster measurements, in order to capture the moment when the sample experiences a phase change. This novel method paves the way for in situ electrolyte behavior analysis, as it allows the detection of fine variations in the electrolyte linked to charge/discharge schemes that negatively affect LIBs performance.Understanding the electrolyte behavior will contribute to the improvement of battery materials to avoid issues in fast charging mechanisms.[1] Y. Liu, Y. Zhu, and Y. Cui, Nature Energy 4, (2019).[2] A. Tomaszewska et al., eTransportation 1, 100011 (2019).[3] G. Gachot et al., Journal of Power Sources 178, 40...

Developments of the porous transport layers (PTLs) in recent years resulted in significant performance improvements in polymer electrolyte water electrolyzers (PEWEs). One of the milestones of the material design was the integration of a microporous layer (MPL) on sintered titanium PTLs. Utilizing high-resolution neutron imaging, the water and gas distribution in the multi-layered porous transport media (ML-PTL) was probed at various current densities (up to 4 A cm −2 ) and pressure conditions up to 8 bar, using a series of four materials, differing in MPL morphology. The water and gas distribution measured is greatly affected by the presence of an MPL. While in the bulk of the PTL, the gas accumulation is increased in the presence of an MPL, in the MPL itself more water is retained. The finer the MPL structure, the higher the liquid saturation. It is observed that the two-phase flow in the MPL has minor influence on the performance of the cell even though the gas accumulation at the CL interface is greatly reduced. The improvements, therefore, appear to be related to the CL and MPL interaction on sub-micron scale and microstructure effect on catalyst area utilization.

The high operation and capital costs of polymer electrolyte water electrolyzers (PEWE) are the major obstacles that have to be tackled for hydrogen to penetrate the market as a solution for renewable energy storage. Commercial stacks often suffer from cationic contamination of catalyst-coated membranes (CCMs) that comes from impure feed water and corrosion of system components, which can result in increasing operation costs and lowered lifetime. This study describes the behavior of the contaminants in the CCMs and their impact on performance under various operating conditions using Gd 3+ as model contaminant imaged with neutron with a combination of high effective temporal (2 s) and spatial (30 μm) resolutions. The presence of electric field directly affects the position of cations in the CCM leading to their accumulation near the cathode catalyst layer. The cationic impurities trigger multiple loss mechanisms, as the ohmic resistance increase does not scale linearly with the amount of occupied exchange groups in the membrane (10% resistance increase caused by 2.5% exchange groups occupation). A model has been developed that predicts the movement of the ions in the CCM under intermittently operating PEWE and was used as a basis to explain the hysteresis observed in the polarization curve of contaminated PEWEs.