Length Ultrathin polycrystalline Co3O4 nanosheets with enriched oxygen vacancies for efficient electrochemical oxygen evolution and 5-hydroxymethylfurfural oxidation

Surfactant-free, freestanding, and hierarchical two-dimensional (2D) polycrystalline cobalt oxide (Co3O4) nanosheets with enriched oxygen vacancies (Co3O4-VO) were synthesized by a topotactic conversion via rapid calcination of the solvothermally synthesized ultrathin cobalt oxide hydrate (CoOxHy) nanosheets. The topochemically transformed Co3O4-VO outperforms the as-synthesized P123-encapsulated CoOxHy nanosheets and their conventionally calcined Co3O4 counterpart for both electrochemical oxygen evolution and 5-hydroxymethylfurfural (HMF) oxidation to 2,5-furandicarboxylic acid (FDCA), owing to their largely preserved 2D structure and elimination of P123 for abundant exposed surface active sites. More importantly, the strain-induced oxygen vacancies at grain boundaries of Co3O4 nanocrystallines are also proposed to be responsible for the improved electrooxidation performance. Furthermore, Co3O4-VO exhibits remarkable long-term stability during the chronoamperometric test in 1 M KOH.

Automated summary

Surfactant-free, freestanding, and hierarchical two-dimensional polycrystalline cobalt oxide nanosheets with enriched oxygen vacancies (Co3O4-VO) were synthesized. These Co3O4-VO nanosheets outperformed the original nanosheets and conventionally calcined Co3O4 in electrochemical oxygen evolution and HMF oxidation to FDCA due to their preserved 2D structure and elimination of surfactant, exposing abundant active sites. The strain-induced oxygen vacancies at grain boundaries of Co3O4 nanocrystallines were also proposed to contribute to the improved electrooxidation performance. Furthermore, Co3O4-VO showed remarkable long-term stability in 1 M KOH chronoamperometric test.