Reinforced photocatalytic reduction of CO₂ to CO by a ternary metal oxide NiCo₂O₄

The work reported herein was the facile preparation of uniform urchin-like NiCo₂O₄ microspheres, and their use as an efficient and stable cocatalyst for photocatalytic CO₂ reduction catalysis. A combined solvothermal-calcination strategy was applied to synthesize the NiCo₂O₄ material that was systematically characterized by physical and chemical measurements (e.g. SEM, TEM, XRD, XPS, EDX, elemental mapping and N₂ physisorption analysis). By cooperation with a visible light photosensitizer, the NiCo₂O₄ material effectively promoted the deoxygenative reduction of CO₂ to CO by more than twenty times under mild reaction conditions. The carbon origin of CO evolution was validated by ¹³CO₂ isotope tracer experiments. Various reaction parameters were examined and optimized, and a possible reaction mechanism was proposed. Furthermore, the stability and reusability of NiCo₂O₄ cocatalysts were firmly confirmed.