Starting in October 2020 the Department of Energy (DOE) created a new laboratory consortium focused on researching and developing hydrogen electrolysis for fuel cells called H2NEW co-led by The National Renewable Energy Laboratory (NREL) and Idaho National Laboratory (INL). The NIST Neutron Imaging Team contributes to the Low Temperature Electrolyte (LTE) portion of this consortium led by NREL in order to image and study proton exchange membrane (PEM) electrolyzers. H2NEW will focus on materials and component integration, manufacturing, and scale-up to help support large industry deployment of durable, efficient, and low-cost electrolyzers for hydrogen production.
PEM Electrolyzers are similar in design to PEM Fuel Cells, which allows for similar imaging methods to be employed. As described elsewhere for fuel cells neutron imaging is an established method to study transport phenomena in PEM electrochemical cells in situ. Neutrons are able to penetrate metallic cell components and still remain sensitive to liquid water or gas bubbles in an electrolysis cell. This method has been used by the TEAM Laboratory at the University of Toronto to image various electrolyzer transport phenomenon in recent years [1-7] . Electrolysis cells are filled with water, but neutrons are still able to penetrate through water and the titanium porous transport layer (PTL) to see the reduction in liquid water due to the presence of gas phases in the cell or the transport of liquid water through the membrane. Neutron imaging will directly visualize and characterize the multiphase flow phenomena at interfaces and how surface treatments improve gas transport through the PTL. To study the interfaces in larger electrolysis cells, we can also use heavy water, which has a cross section that is an order of magnitude lower than light water. NIST has developed a new neutron imaging detector that allows for a limiting spatial resolution of 1.5 micrometers. NIST is also developing a novel neutron microscope based on Wolter optics that will provide 3 micrometer spatial resolution with time resolution of about 1 s, which will enable real-time 3D neutron imaging to capture transient water transport phenomena in the MEA and the porous transport layer (PTL).
 Lee JK, Lee CH, Fahy KF, Kim PJ, LaManna JM, Baltic E, Jacobson DL, Hussey DS, Stiber S, Gago AS, Friedrich KA, Bazylak A. Spatially graded porous transport layers for gas evolving electrochemical energy conversion: High performance polymer electrolyte membrane electrolyzers. Energy Convers Manag 226: 113545, 2020.
 Lee JK, Lee C, Fahy KF, Kim PJ, Krause K, LaManna JM, Baltic E, Jacobson DL, Hussey DS, Bazylak A. Accelerating Bubble Detachment in Porous Transport Layers with Patterned Through-Pores. ACS Appl. Energy Mater. ( September 22, 2020). doi: 10.1021/acsaem.0c01239.
 Lee JK, Lee C, Fahy KF, Zhao B, LaManna JM, Baltic E, Jacobson DL, Hussey DS, Bazylak A. Critical Current Density as a Performance Indicator for Gas-Evolving Electrochemical Devices. Cell Reports Phys Sci 1: 100147, 2020.
 Lee CH, Lee JK, George MG, Fahy KF, LaManna JM, Baltic E, Hussey DS, Jacobson DL, Bazylak A. Reconciling temperature-dependent factors affecting mass transport losses in polymer electrolyte membrane electrolyzers. Energy Convers Manag 213: 112797, 2020.
 Lee CH, Lee JK, Zhao B, Fahy KF, LaManna JM, Baltic E, Hussey DS, Jacobson DL, Schulz VP, Bazylak A. Temperature-dependent gas accumulation in polymer electrolyte membrane electrolyzer porous transport layers. J Power Sources 446, 2020.
 Minnaar C, De Beer F, Bessarabov D, Current Density Distribution of Electrolyzer Flow Fields: In Situ Current Mapping and Neutron Radiography, Energy Fuels 2020, 34, 1, pgs. 1014–1023, 2019, https://doi.org/10.1021/acs.energyfuels.9b03814
 Lee C, Banerjee R, Ge N, Lee JK, Zhao B, Baltic E, LaManna JM, Hussey DS, Jacobson DL, Abouatallah R, Wang R, Bazylak A. The effect of cathode nitrogen purging on cell performance and in operando neutron imaging of a polymer electrolyte membrane electrolyzer. Electrochim Acta 279, 2018.