A thin layer X-ray absorption spectroelectrochemical cell is described, It is suitable for "in-situ" studies of thin films and has the advantage that both fluorescence and transmission measurements can be made at the same time so as to ensure accurate calibration of the X-ray energy. Use of the cell is demonstrated in a study of the structure of a nickel oxide material anodically deposited on a graphite substrate which contains multivalent nickel states and appears promising for use in the fabrication of ultracapacitors.