Methacrylated gelatin-embedded fabrication of 3D graphene-supported Co ₃ O ₄ nanoparticles for water splitting

We developed a general platform for the fabrication of transition metal oxide nanoparticles supported by a graphene foam (GF) by first coating it with a methacrylated gelatin (GelMA) hydrogel, which served as a 3D matrix for nanoparticle dispersion. The engineered GelMA/GF matrix was hydrophilic with good mechanical strength and high conductivity, therefore providing a good platform for the dispersion of a variety of metal/oxide precursors. Due to this platform, well-dispersed Co ₃ O ₄ nanoparticles with the smallest size of 3 nm assembled on the nitrogen-doped graphene foam (Co ₃ O ₄ /NGF). The crystalline transformation from a CoCl ₂ [H ₂ O] ₂ precursor to Co ₃ O ₄ was revealed by in operando X-ray diffraction and absorption techniques. After applying Co ₃ O ₄ /NGF as a free-standing electrocatalyst for water splitting, the nanoparticles of size 3 nm exhibited optimal catalytic activity in alkaline media; the corresponding cell could promote water splitting at a current density of 10 mA cm ^-2 with only 1.63 V and exhibited excellent stability in a 25 h long-term operation. Our results demonstrate that the GelMA hydrogel-coated 3D graphene foam can be a promising platform for the design and fabrication of graphene-based multifunctional materials.