Photochemically synthesized cobalt oxide hydroxide (PCOH) under UV light has been successfully achieved without the addition of surfactants, templates, or organic solvents at ambient temperatures. PCOH samples can be converted to spinel cobalt oxide (PCO) after the calcination at 500 degrees C. The in-situ growth of hierarchical nanostructures was demonstrated with a three-stage mechanism in the photochemical preparation. The development of nanostructures and elemental condensation under different irradiation time governs the bifunctional-sensing performance of the cobalt oxide products. The formation of nanostructured cobalt oxides involves a free-radical oxidation mechanism in the acidic condition. We further demonstrate that the preparation of sensor-active cobalt oxides under nature sunlight (Solar-2H) is feasible. Compared to the multi-component bifunctional electrocatalysts comprised of enzymes and noble metals, our greenly prepared electrocatalysts, as the single-species sensor, achieve bifunctional hydrogen peroxide detection effectively. The as-produced electrocatalysts utilize electro-oxidative and electro-reductive signals together as bifunctional sensor, maximizing the wide detection range of 0.005-35 mM, a low detection limit of 0.7 mu M, selective H2O2 detection, and similar to 3000-time higher sensitivity than commercial cobalt oxides. (C) 2015 Elsevier Ltd. All rights reserved.