Electrochemical wet-cell fabrication for in situ soft X-ray hyperspectral imaging of real-life ORR electrocatalysts

Over the past decade, electrochemical in situ imaging and spectral imaging with soft X-ray probes have evolved from a high-risk pioneering challenge to established techniques that now receive substantial beamtime at synchrotron imaging beamlines. Despite a growing body of literature and near-commercial solutions, setting up wet electrochemical cells for these experiments remains challenging and non-routine. Moreover, most published studies revolve around bona fide model materials or environments rather than systems mimicking real in operando conditions. Thus, the concrete impact of these potentially extraordinarily informative approaches remains questionable outside the community of method specialists. In this context, this study aims to lay the foundation for the development of real-life electrocatalysts under electrochemical control. Since these materials are typically fabricated in powder form, their transfer and fixation onto the electrode system of the in situ cell, simultaneously ensuring an appropriate optical density for a high signal-to-noise ratio and maintaining electrochemical activity, remains an open question. The approach is general in nature, but, in this study, we specifically concentrate on α-MnO2 nanowires, a widely employed oxygen reduction reaction (ORR) electrocatalyst for alkaline metal-air batteries, and describe: (i) the methodology for particle attachment and electrochemical activity assessment; (ii) the fabrication of electrochemical wet cells compatible with these materials; and (iii) the preliminary feasibility of spectral scanning transmission X-ray microscopy (STXM) results at the Mn L-edge.