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.