Synchrotron X-ray Radiography Research Articles

Synchrotron X-Ray radiography of vanadium redox flow batteries – Time and spatial resolved electrolyte flow in porous carbon electrodes

A porous carbon electrode fully saturated with electrolyte is one crucial aspect of vanadium redox flow battery efficiency. It determines the electrochemically active surface area, provides more active sites for the reaction during operation, and prevents local degradation due to inhomogeneities in electrolyte distribution. We investigate the electrolyte invasion and distribution at open-circuit potential in heat-treated carbon felt electrodes at varying compression ratios and flow field configurations, using synchrotron X-ray radiography. The quantitative analysis yields time-resolved saturation values of the injection and resolves local changes in saturation to detect areas of lower electrolyte accessibility. Compression ratios of 50% and above lead to a high electrode utilization with more than 97% saturation over the felt thickness. In contrast, carbon felts at 25% and 17% compression only reach 49% and 15% saturation near the flow fields. However, increasing the flow velocity after the injection causes the boundary area next to the flow field to fill even at low compressions. This area is especially critical for the electrode utilization since it is invaded after the bulk. Depending on the compression level, it does not reach full saturation.

In-situ visualisation of dynamic fracture and fragmentation of an L-type ordinary chondrite by combined synchrotron X-ray radiography and microtomography

The relationship between the dynamic mechanical properties of stony meteorites and their microstructures was investigated in-situ for an L-type ordinary chondrite using a split-Hopkinson pressure bar apparatus and ultra-high speed phase-contrast X-ray radiography at the European Synchrotron Radiation Facility (ESRF). Synchrotron X-ray microtomography (μCT) was performed both prior to and immediately following dynamic compression to correlate key structural features between the initial microstructure and recovered fragments as well as to identify the leading mechanisms for fracture and fragmentation. Real-time visualisation of damage evolution in the specimens revealed the very first cracks to be initiated at the sites of FeNi-metal nodules. These cracks propagated rapidly through the largest group of chondrules (the porphyritic olivine type chondrules) along the loading direction, which led to the formation of column-like fragments. μCT analysis of the collected fragments confirmed the dominant mode of fracture to be transgranular with a clear link between FeNi-metal nodule statistics and the size distribution of fragments, emphasising their role in mechanical failure and fragmentation process. The resulting fragmentation was used to validate the predictions of brittle fragmentation models, and found to be in good agreement with the laboratory-scale impacts. In turn, these models can help unravel the consequences of impact-induced fragmentation processes that have helped shape the solar system.

Effects of Ni on the nucleation and growth behavior of Cu6Sn5 in Sn–8.5Cu alloy: An in situ observation

Cu6Sn5 and Cu3Sn are important intermetallic compounds, greatly influencing the reliability of the Sn-Cu solder system. Micro-alloying Ni has been proved to be effective in suppressing Cu3Sn, but its influence on the formation of Cu6Sn5 is still unclear. In this paper, the nucleation and growth behavior of Cu6Sn5 in Sn-8.5Cu-xNi (x = 0, 0.05, 0.1, 0.5, 1) alloys are in situ investigated using synchrotron X-ray radiography, X-ray diffraction, and electron probe micro-analyzer. The results show that Ni can significantly increase the nucleation temperature of (Cu, Ni)6Sn5 since (Cu, Ni)6Sn5 has a more negative heat of formation. When Ni ≥ 0.05 wt%, the nucleation temperature of (Cu, Ni)6Sn5 will be higher than that of Cu3Sn. As a result, the peritectic reaction Cu3Sn + L → Cu6Sn5 doesn't occur and instead (Cu, Ni)6Sn5 nucleates from the melt before cooling down to the nucleation temperature of Cu3Sn. During the nucleation and growth of (Cu, Ni)6Sn5, Ni-rich clusters preferentially form stable crystal nuclei, and then low Ni parts grow on them. Raising Ni content increases the number of Ni-rich clusters, so the grain density of (Cu, Ni)6Sn5 increases with Ni addition. With the growth of (Cu, Ni)6Sn5, some Ni-rich clusters are in contact with (Cu, Ni)6Sn5-liquid interface and promote the rapid growth of (Cu, Ni)6Sn5 around the newly formed Ni-rich region. The excessively enlarged parts break down at the weak points because of gravity, further refine the grain. The results based on this study provide an opportunity to optimize the structure of Cu6Sn5 in the Sn-Cu system.

4D micro-scale, phase-contrast X-ray imaging and computed tomography of HMX-based polymer-bonded explosives during thermal runaway

High-resolution synchrotron x-ray radiography with computed tomography is used to observe the evolution of porosity created by thermal exposure in two HMX-based polymer-bonded explosive compositions; LX-04 and BX-63. The measurements were made in situ, over an extended period of time, during which the samples were heated on a slow-rate thermal trajectory. The tests ended with thermal-runaway to ignition after which the samples were consumed by combustion. The primary means of damage appears to be from mechanical debonding of the HMX-binder interface with secondary contribution from chemical decomposition. Confinement and binder properties affect the amount of porosity and permeability that develops. Additionally, observations were made describing the emergence and structure of an internal ignition volume, the formation and transport of a pre-ignition melt layer, and how the early stages of combustion were affected by material morphology, mechanical confinement and melt. The contact angle between molten HMX and the fluoropolymer, Viton A, is also presented. For the first time we have time-resolved x-ray images of ignition in sufficient detail to verify the mechanism of cookoff in polymer-bonded explosive compositions.

In-situ studies and simulation of equiaxed solidification in Al–20Cu alloy

The equiaxed solidification of Al–20Cu alloy under different cooling rates was investigated using in-situ synchrotron X-ray radiography. The results showed that mean grain size increases rapidly at the early stage of solidification, then reaches the final grain size gradually. And the change of final mean grain size with cooling rate follows d = 4132.3 × R −0.86. In addition, the evolution of grain size in Al–20Cu alloy was also simulated by ProCAST software. The experimental and simulation results indicated that, in the range of the cooling rate (5.0–7.5 K min−1), the major factor influencing the final grain size is the maximum nucleation density, while the nucleation undercooling has an insignificant effect on the final grain size.

Revealing the Nucleation and Growth Mechanisms of Fe-Rich Phases in Al-Cu-Fe(-Si) Alloys Under the Influence of Al-Ti-B

Al-5Ti-1B is commonly added to the Al alloys for grain refinement, which also affects the type, size, morphology, and formation sequence of Fe-rich intermetallic phases. The underlying nucleation and growth mechanism of Fe-rich phases under the influence of Al-5Ti-1B during the solidification of Al-Cu-Fe(-Si) alloys were systematically studied by thermodynamic calculation, and with scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), focused ion beam (FIB) coupled with transmission electron microscopy (TEM), and in-situ synchrotron X-ray radiography. The SEM and in-situ synchrotron X-ray radiography experiments revealed that the Al-5Ti-1B addition significantly reduced the size and number of primary Al3(CuFe) phases. and refined the size of α-Fe in Al-Cu-Fe-Si alloy without changing their type. This was caused by Ti solute atoms in Al melts, which limiting the nucleation and growth of primary Al3(CuFe) phases during solidification. The FIB and TEM results showed that the prior formed TiB2 particles or/and newly-formed aluminium oxide were nucleate sites for Al6(CuFe) phase and α-Fe phase in Al-Cu-Fe alloy and Al-Cu-Fe-Si alloy, respectively. The Edge-to-Edge model and orientation relationship further confirmed the experimental results. In addition, V diffusion into TiB2 particles in the Al melts to form (TiV)B2 particles and lowering the interfacial energy enhance the heterogenous nucleation for Fe-rich phases.

In situ electrical resistivity and viscosity measurements of iron alloys under pressure using synchrotron X-ray radiography

ABSTRACT We have developed a new type of experimental setup utilizing a multi-anvil large volume press and designed for simultaneous measurements of structure-sensitive thermophysical properties (diffraction, electrical resistivity, viscosity). This multi-probe capability was tested on iron alloys at 2 GPa and up to 1750 K. Phase transitions as detected by X-ray diffraction patterns are clearly associated with changes in the electrical response of the samples. In Fe-S liquids, viscosity measurements in the molten state indicate an increase in viscosity with increasing the amount of alloying agent. A correlation between electrical resistivity and viscosity from our data and previous works is observed. This multi-probe measurement capability improves the detection of solid-state transformations and solid-melt transitions, relates structural and electrical properties of geomaterials, and allows constraining the mobility of melts using viscosity data. This new setup advances research about melt distribution and mobility at conditions relevant to planetary interiors.

Observing Oxygen Transport in Polymer Electrolyte Water Electrolysis Via Operando X-Ray Tomographic Microscopy

The power-to-gas process using polymer electrolyte water electrolysis (PEWE) to produce hydrogen, is increasingly attracting interest as a mean to store the surplus electricity generated from intermittent renewable sources. However, high capital and operational costs limit the widespread implementation of the PEWE technology in the current energy system. The operational costs are dominated by electricity prices and therefore improving PEWE efficiency is crucial. In PEWE cells, water is supplied at the anode side and it is distributed to the active electrode (catalyst layer, CL) through a porous transport layer (PTL). During operation, oxygen is produced at the anodic CL and it is discharged at the flow channel. However, the undesired accumulation of oxygen in the anodic porous transport layer (PTL) may interfere with the transport of water to the active sites, contributing to efficiency losses, especially for high current density operations.The evolution and transport of oxygen in PEWE leads to a complex two-phase flow regime that is governed by a complex interplay of viscous and capillary forces in the PTL microstructure. To date, the precise relationship between current density, PTL morphology (pore dimensions, shape) and oxygen pathways is largely unknown. Furthermore, the overall influence of the water/gas transport on the mass transport losses in PEWE is still largely debated.In the past decade, many studies have been conducted to directly observe the oxygen transport within operating PEWE cells. Neutron radiography has been employed to compute the average water-gas saturation in PTLs for different current densities, temperature, or operating pressures [1, 2]. Furthermore, X-ray radiography was used to examine bubble formation and growth in the flow channel [3]. However, radiographic studies can only provide average information on the gas-water distribution in PTLs and a spatially-resolved description of the oxygen pathways at the microscale is crucially needed.In this work, we present the first operando X-ray tomographic microscopy (XTM) experiment where oxygen pathways inside a representative PTL material are imaged in three dimensions. The shape, dimension, and connectivity of oxygen pathways in the PTL microstructure are described for current densities ranging from 0.1 to 2.5 Acm-2. Furthermore, a precise measure of oxygen saturation in the PTL porosity is discussed in terms of current density and distance from the catalyst layer. Finally, the differences in oxygen saturation between regions under the channel and rib are also presented. We believe that these results will represent a step forward in the understanding of two-phase flow in PEWE cells, paving the way for a more rational design of better performing PTL materials.[1] Zlobinski, M., et al., 2020. Transient and steady state two-phase flow in anodic porous transport layer of proton exchange membrane water electrolyzer. Journal of the Electrochemical Society[2] Selamet, O.F., et al., 2013. Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging. International Journal of Hydrogen Energy 38, 5823–5835.[3] Hoeh, M.A., et al., 2015. In operando synchrotron X-ray radiography studies of polymer electrolyte membrane water electrolyzers. Electrochemistry Communications 55, 55–59 Figure 1

In-situ X-ray radiography of primary Fe-rich intermetallic compound formation

The formation of primary Fe-rich intermetallic compound crystals and the effect of TiB2 and TiC inoculation during solidification of a hypereutectic Al-Fe alloy has been investigated. Both horizontal, near isothermal conditions and vertical, directional thermal gradient conditions were studied using laboratory and synchrotron X-ray radiography. TiB2 and TiC inoculation enhanced formation of Fe-rich intermetallics under all experimental conditions. Near isothermal solidification resulted in the highest intermetallic number density and average formation rate, whilst increasing the thermal gradient reduced both. A model for intermetallic crystal formation is proposed to explain the effect of thermal gradient and cooling rate on the intermetallic number density and average formation rate.

Synchrotron X-ray Radiography and Tomography of Vanadium Redox Flow Batteries-Cell Design, Electrolyte Flow Geometry, and Gas Bubble Formation.

The wetting behavior and affinity to side reactions of carbon‐based electrodes in vanadium redox flow batteries (VRFBs) are highly dependent on the physical and chemical surface structures of the material, as well as on the cell design itself. To investigate these properties, a new cell design was proposed to facilitate synchrotron X‐ray imaging. Three different flow geometries were studied to understand the impact on the flow dynamics, and the formation of hydrogen bubbles. By electrolyte injection experiments, it was shown that the maximum saturation of carbon felt was achieved by a flat flow field after the first injection and by a serpentine flow field after continuous flow. Furthermore, the average saturation of the carbon felt was correlated to the cyclic voltammetry current response, and the hydrogen gas evolution was visualized in 3D by X‐ray tomography. The capabilities of this cell design and experiments were outlined, which are essential for the evaluation and optimization of cell components of VRFBs.

Research progress on solidification structure of alloys by synchrotron X-ray radiography: A review

Abstract The synchrotron radiation technology has recently emerged as a powerful tool to characterize the real-time microstructure evolution during solidification of alloys. Compared with other methods, the synchrotron radiation technology, along with its unique advantages of strong brightness, high energy, excellent resolution, and good monochromaticity, allows for capturing the dendrite evolution behavior of alloys in real time and can be dynamically coordinated with high-resolution CCD (Charge-coupled Device) imaging systems. This paper briefly reviews the recent advances in developing synchrotron radiation for solidification of alloys with low, medium, and high melting points, and under the external electric, magnetic, and ultrasonic fields. Furthermore, a series of microstructural features and behaviors such as dendrite morphology, growth orientation, dendrite fracture, and rotation are described in detail. Finally, the development trends and application prospects of synchrotron radiation technology in alloy solidification are forecasted.

Capturing Marangoni flow via synchrotron imaging of selective laser melting

Marangoni flow has a substantial influence on the quality of components fabricated via laser powder bed fusion (LPBF). However, Marangoni flow in melt pools is rarely quantified due to the opacity of liquid metals and the necessity for in situ evaluation. Here we report the findings of high-temporal-resolution synchrotron x-ray radiography experiments tracking the flow in the melt-pool. Dense, highly attenuating tungsten carbide particles are seeded within an elemental powder blend of aluminium and copper of varying composition. Due to the extremely high temporal resolution of greater than 50 kfps at the 31-ID-B beamline at the Advanced Photon Source, USA, we can track the position of tracer particles from frame to frame. This data provides valuable process guidance for optimising mixing and informs the development and validation of multiphysics models.

Electroless nickel plating and spontaneous infiltration behavior of woven carbon fibers

The effects of electroless Ni plating on the interaction between molten aluminium and carbon fibers was studied to investigate the fabrication of woven carbon fiber-reinforced Al-matrix composites by liquid processing. An appropriate electroless plating method for coating carbon fibers in woven form was developed. The uniform and compact coatings could be generated stably at a temperature of 70 °C and pH 4.0, and the addition of a disperser improved the deep plating ability and promoted bidirectional plating. More than 80% of the coated woven fibers exhibited excellent coating properties, which offered sufficient fixation and protection of the fibers for subsequent processing. A synchrotron X-ray radiography analysis indicated that the spontaneous infiltration behavior mainly stemmed from the chemical reaction between Al and Ni, rather than the simple physical filling of the fiber interspaces with molten aluminium. The infiltration process could be divided into three typical periods, namely the slow infiltration, rapid infiltration, and stable infiltration periods. Moreover, the coated fibers oriented in the direction perpendicular to the infiltration direction were more easily infiltrated than those oriented in the direction parallel to the infiltration direction.

Grain nucleation and growth behavior of (Cu, Ni)6Sn5 in Sn–10Cu–1Ni alloy under pulse current: An in situ observation

In situ synchrotron X-ray radiography is used to study the effect of pulse current on the nucleation and growth of (Cu, Ni)6Sn5 intermetallic compounds (IMCs) during the solidification of Sn–10Cu–1Ni (wt.%) alloy. The synchrotron tomography analysis reveals that the (Cu, Ni)6Sn5 exhibits a six-fold snowflake-like 3D morphology. As the density of pulse current increases from 0 to 200 A/cm2, (Cu, Ni)6Sn5 gradually exhibits a direction-dependent morphology and the “self-poisoning” phenomenon caused by gravity segregation is weakened. The competitive growth between the neighboring grains is directly observed. In addition, the Boltzmann function is used as a model for fitting the grain density versus temperature at four different current densities where R2 ≥ 0.995 confirms a good correlation of the model with experimental data. The initial nucleation temperature increases with the increasing current density “j” from 0 to 50 A/cm2, while decreases from 50 A/cm2 to 200 A/cm2. Besides, the maximum nucleation rate Imax monotonically increases with the increasing current density; while the final grain density with j = 200 A/cm2 is less than that with j = 50 A/cm2 because of the short nucleation duration. The results of this study provide an opportunity to achieve the active control of (Cu, Ni)6Sn5 morphology by imposing pulse current.

Carbon felt electrodes for redox flow battery: Impact of compression on transport properties

In a flow battery setup, carbon felt materials are compressed to obtain higher performance from the battery. In this work, a commercially available carbon felt material, commonly used as electrodes in Vanadium Redox Flow Battery setups was evaluated for the transport properties (diffusivity, permeability, pressure drop required for maintaining flow, among others) while under seven set levels of compression, using an image analysis coupled with pore network modeling approach. X-ray computed tomography has been used to obtain the microstructure of a commercially available electrode under compressed conditions. An open-source pore network modeling tool, OpenPNM has been used to investigate the transport properties of the porous felt material at each of the set compression levels. The results from the modeling are compared against experimentally obtained electrolyte transport patterns visualized using synchrotron X-ray radiography. The electrical resistance of the carbon felt electrode was measured experimentally using a four-probe method. The compression resulted in a 58% reduction in permeability, and a 25% reduction in single-phase diffusion. This combination of ex-situ characterization of the electrical and fluid transport through the electrodes provides valuable data for modeling flow battery systems, and validating hypothesis from in situ testing.

Coupling in situ synchrotron X-ray radiography and phase-field simulation to study the effect of low cooling rates on dendrite morphology during directional solidification in Mg–Gd alloys

The effect of low cooling rate with a fixed temperature gradient during directional solidification of Mg–Gd alloys is investigated by coupling in situ X-ray synchrotron radiography and phase-field method. Results show that the primary dendrite spacing decreases with the increase of cooling rates, and the relationship between the logarithm of primary dendrite arm spacing and the logarithm of cooling rate is linear. After fitting, the slope of primary dendrite arm spacing is −0.71, while that of phase field simulation is −0.74, which indicates the experimental statistics are basically consistent with that of phase field simulation. The simulation thoroughly studies the kinetic transition process of seaweed-like morphology and the evolution of solute distribution for dendrites, both the solid volume fraction and the velocity of liquid-solid interface increase with the increase of cooling rate. The simulation is in good agreement with experimental results.

Detecting cathode corrosion in polymer electrolyte membrane fuel cells in dead-ended anode mode via alternating current impedance

In this work, an in-operando alternating current (AC) impedance-based method is developed to detect cathode corrosion in a polymer electrolyte membrane (PEM) fuel cell operating in dead-ended anode (DEA) mode. Polarization resistances are measured over a 2.0 s sampling time with this method, exhibiting a 10 times higher temporal resolution than conventional electrochemical impedance spectroscopy methods. The performance characteristics of a PEM fuel cell in DEA mode are investigated with both a pristine membrane electrode assembly (MEA) and a corroded MEA, and the sudden rise in the cathode polarization resistance accompanied by a uniform anode polarization resistance is identified as a new indicator for a corroded cathode. The accumulation of nitrogen in the corroded cathode leads to a rise in cathode polarization resistance. This elevated cathode polarization resistance leads to a dehydrated catalyst-coated membrane (CCM) evident through a reduction of the liquid water saturation at the CCM—microporous layer interface (observed using synchrotron X-ray radiography).

Visualization of electrolyte flow in vanadium redox flow batteries using synchrotron X-ray radiography and tomography – Impact of electrolyte species and electrode compression

The electrolyte distribution inside the porous electrodes of vanadium redox flow batteries is critical to the performance, as it determines the electrochemically active surface area. Herein, the influence of thermal activation, compression, and the injected electrolyte species on the pressure drop and the wetting is investigated by means of synchrotron X-ray radiation. The saturation versus the through-plane position is quantitatively displayed as a function of time to resolve the wetting process. The initial state after the imbibition is then quantitatively compared to the saturation after flow-through conditions. It was concluded that thermal activation plays a major role in the wetting, resulting in an up to six times higher saturation. Only a minor increase in saturation between the initial wetting state and after flow-through was observed. Additionally, there are only minor differences in the wetting behavior between the vanadium species in the electrolyte, the V(III) electrolyte shows the highest saturation. Increasing compression leads to a higher pressure drop and the saturation decreases only at compression ratios higher than 50%. Air pocket formation inside the liquid column was observed and the displacement and re-emergence of air pockets after flow-through is displayed.

Analysis of Apparent Diffusion Coefficient in Composite Electrode of Solid State Battery Using Ag-Ion

All-solid-state rechargeable batteries are expected to be used widely owing to their safety, long lifecycles, and high energy densities. However, it remains a challenge to exceed the performance of a liquid-type lithium-ion battery, primarily because of poor optimization of the processes of fabrication of the composite electrode structures and cell stacks used in all-solid-state batteries. For the development of all-solid-state batteries at the cell level, it is crucial to not only enhance the ionic conductivity of the solid electrolyte but to also clarify the reaction mechanisms peculiar to the solid electrolyte and composite electrode of an all-solid-state battery. Regarding the unique mechanism of the battery cell, the inhomogeneous concentration distribution of the carrier ion occurs in electrolytes and composite electrodes in conventional lithium-ion batteries that employ a liquid electrolyte. Under charge-discharge in a high-rate condition, resistance distribution in the perpendicular direction becomes remarkable, and a reaction distribution occurs, which leads to a decrease of utilization for active materials. 1) In the case of all-solid-state rechargeable batteries, the situation should differ drastically. Since the transport number of lithium-ion in a lithium-ion solid conductor is almost 1.0, the distribution of carrier ion concentration does not exist in principle because only the lithium-ion can move in a solid electrolyte. However, to our knowledge, there is no report on the direct measurement of carrier ion concentration distribution in solid electrolytes during the charge-discharge of all-solid-state batteries in the literature. This status is because direct observation is difficult owing to the lightness of the lithium ion. To detect the macroscopic diffusion phenomena occurring in an all-solid-state battery, we applied synchrotron X-ray radiography to an all-solid-state battery system with a silver-ion solid electrolyte. Because silver is a considerably heavier element than lithium, its diffusion behaviors in the electrolyte and electrode can be visualized based on changes in the transmittance of X-rays. This study examines whether we detect the concentration distribution of the carrier ion in the solid electrolyte and composite electrode of an all-solid-state rechargeable battery. In addition, the apparent diffusion coefficient is evaluated by using time-dependent concentration change of silver-ion in composite electrode. In the solid electrolyte, no change in the concentration of carrier ions is detected. By contrast, in the composite electrode, a preferential reaction at the electrode/electrolyte interface is confirmed in the initial stages of charge and discharge. 2) Although a change in the concentration of the solid electrolyte would be an advantage, reaction distribution in the composite electrode is one of the critical issues from the viewpoint of practical application of high-energy-density, all-solid-state rechargeable batteries. 1). Y. Orikasa, Y. Gogyo, H. Yamashige, M. Katayama, K. Z. Chen, T. Mori, K. Yamamoto, T. Masese, Y. Inada, T. Ohta, Z. Siroma, S. Kato, H. Kinoshita, H. Arai, Z. Ogumi and Y. Uchimoto, Sci. Rep., 6, 26382 (2016). 2). K. Kandori, H. Yamashige, N. Furuta, T. Nonaka and Y. Orikasa, Electrochemistry, in press.

In-Operando Changes of the Cation Exchange Membrane in CO2 electrolyzers

CO2 electrolysis provides a promising solution for reducing CO2 concentration levels in the atmosphere and for decarbonizing current CO2 sources. Through CO2 electrolysis, we can synthesize syngas, formic acid, and other useful hydrocarbon feedstocks [1] for carbon-neutral fuels, creating a cyclic consumption of hydrocarbons. A critical limitation of industrializing current CO2 electrolyzer designs is understanding the mass and ionic transport effects of the reactants and products across the membrane-electrode assembly [1,2]. These effects are directly dependent on the operating conditions and reduce cell performance [1]. Membrane hydration is an important parameter that significantly affects cell performance and optimum performance can be achieved by supplying humidified CO2 gas supply at the cathode, as evident in fuel cell technologies [3]. In this study, we investigated the impact of humidified CO2 gas supply on cell performance and correlated it with mass transport effects causing changes in the cation exchange membrane (CEM). We operated a CEM CO2 electrolyzer with varied cathode gas inlet relative humidity (RH) to study the performance change at various current densities while simultaneously using synchrotron X-ray radiography to quantify membrane hydration changes and water dynamics. These results were coupled with electrochemical impedance spectroscopy (EIS) data, which gave us the high frequency resistance (HFR) highlighting the ohmic losses present in the membrane at various RH conditions. Similar work on other electrochemical devices (fuel cells [4] and water electrolyzers [5]) has shown the relationship between cell performance and changes in membrane hydration and transport resistance. Significant improvement in cell performance was observed as the cathode inlet RH increased. This improvement is a direct result of increased membrane hydration. Furthermore, EIS data exhibited a significant decrease in HFR as RH increased, indicative of lower ionic transport resistance across the membrane. As the electrolyzer is operated at various current densities, the through plane visualizations of the CEM provide insight into the relative changes in the membrane. Mass transport phenomena have a significant effect on cell performance at elevated current densities, which is evident by in-operando membrane hydration changes and membrane ohmic losses. From our observations, the humidification of CO2 gas supply has a significant effect on cell performance. We believe this knowledge can be translated into substantially improving the performance of CO2 electrolyzers for industrial-scale implementation.