  Improvement of electrochemical technologies is one of the most popular topics
in the field of renewable energy. However, this process requires a deep
understanding of the electrode electrolyte interface behavior under operando
conditions. X-ray absorption spectroscopy (XAS) is widely employed to
characterize electrode materials, providing element-selective oxidation state
and local structure. Several existing cells allow studies as close as possible
to realistic operating conditions, but most of them rely on the deposition of
the electrodes on conductive and X-ray transparent materials, from where the
radiation impinges the sample. In this work, we present a new electrochemical
flow-cell for operando XAS that can be used with X-ray opaque substrates, since
the signal is effectively detected from the electrode surface, as the radiation
passes through a thin layer of electrolyte. The electrolyte can flow over the
electrode, reducing bubble formation and avoiding strong reactant concentration
gradients. We show that high-quality data can be obtained under operando
conditions, thanks to the high efficiency of the cell from the hard X-ray
regime down to 4 keV. We report as a case study the operando XAS investigation
at the Fe and Ni K-edges on Ni-doped maghemite films, epitaxially grown on Pt
substrates. The effect of the Ni content on the catalytic performances for the
oxygen evolution reaction is discussed.
