Supporting Information for A sea anemone-like CuO / Co 3 O 4 composite : an effective catalyst for electrochemical water splitting

Experimental details Chemicals: Cobalt nitrate (Wako, Japan) and copper nitrate (Wako, Japan) with analytical grade are used as chemicals for the preparation of pure CuO, Co3O4 and CuO/Co3O4 composite catalysts. Potassium hydroxide (Sigma-Aldrich, Japan) is dissolved in deionized water as electrolyte solution for electrochemical characterization of electrodes. Carbon rods (CR, φ 5mm) are provided by C-task company, Japan.