X-ray computed tomography (CT) is a promising technique for three-dimensional imaging of batteries, electrolyzers and fuel cells. Operando techniques rely significantly on reactor design, where the operando cell should approximate the actual device. Furthermore, nano- and micro-scale hierarchical materials are used to convert or store electrochemical energy. Imaging with the single scale or synchrotron beamline provides only sliver of information needed. Carbon and ionomer materials that are used as bulk materials in the electrochemical devices are soft and phase-contrast imaging is required.
We present our micro- and nano-X-ray CT reactors designs for polymer electrolyte fuel cells (PEFCs), electrolyzers, and micro X-ray CT operando pouch cell for battery. With the PEFC hardware we control temperature, relative humidity, pressure of gasses, as well as current density. By imaging the PEFCs at various current densities we are able to observe physical phenomena of membrane swelling with relative humidity increase and formation and removal of liquid water from the cell. With nano X-ray CT we are able to combine morphology with x-ray absorption near edge structure (XANES) to elucidate the oxidation state of the catalyst within the active porous layer. Using phase-contrast we are able to distinguish between liquid water and carbon phases. For electrolyzers, understanding formation and removal of oxygen bubbles, which is sub-second transport phenomena is critical. We combine X-ray CT with sub-second X-ray radiography to understand this transient process. For the batteries, we have developed a high throughput pouch cell design for x-ray CT imaging featuring 1 cm diameter active area.