Topotactic transformation of Ni-based layered double hydroxide film to layered metal oxide and hydroxide

•LDH film can be prepared on Ti metal substrate by reflux or hydrothermal treatment.•The LDH can topotactically transformed by hydrothermal treatment.•The transformed NiCo-LDH was examined for their crystal structure by synchrotron XRD.

Topotactic transformation of film-shaped samples comprising a layered double hydroxide (LDH) to a metal oxide phase was performed by a hydrothermal or heat treatment. The degree of transformation was examined by X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray diffraction (SXRD). The LDH film prepared as a raw material by a reflux process with urea was composed of plate-shaped particles that were partially perpendicular to the substrate. For the transformation, the LDH powder and film were treated hydrothermally at 90, 120, and 200 °C in a LiOH aqueous solution or heated to 400, 600, and 800 °C with a LiOH·H2O contact. The film shape and morphology of the LDH particles were retained after the hydrothermal treatment at 120 °C. XPS and SXRD confirmed that two types of LDH with different compositions, Ni:Co = 62:38 and 90:10, were formed in the as-prepared LDH. In the case of the sample treated hydrothermally, metal hydroxide with no intercalated anion within the interlayer space was observed and the metal oxyhydroxide formed with a ratio of approximately 15%. For the heated samples, the transformation to LiNi1-xCoxO2-related materials was carried out by heating to 600 or 800 °C.