Self-supported cobalt oxide electrocatalysts with hierarchical chestnut burr-like nanostructure for efficient overall water splitting

The hierarchical nanostructure catalyst on the self-supported electrode with a rational and large-area distribution is essential for high-efficiency overall water splitting. Herein, a novel strategy based on spatially shaped femtosecond laser ablation pretreatment is proposed for constructing self-supported cobalt oxide electrocatalysts with hierarchical chestnut burr-like nanostructures on a copper substrate. The femtosecond laser ablation can create pinning and attachment sites for the growth of nanowires to form stable self-supported structures. Due to the hierarchical three-dimensional fluffy structures and tight adhesion between active materials and substrates, the prepared self-supported electrocatalysts can provide rapid charge transfer, a large surface area with ample active sites, accelerated electrolyte diffusion, effective catalytic components, and high conductivity during the electrocatalytic process. Naturally, the self-supported electrode demonstrated favorable electrocatalytic properties in alkaline solutions (1 M KOH), presenting low overpotentials of 105 and 235 mV at the current density of 10 mA cm⁻² during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Moreover, the constructed electrolyzer system with the self-supported electrocatalysts can facilitate overall water splitting at the low cell voltage of 1.51 V to achieve a current density of 10 mA cm⁻² and exhibits durability for up to 72 h, indicating a high level of activity and stability for water electrolysis. This work presents a novel perspective for the construction of electrocatalysts structures with stable and efficient properties.