Construction of nickel and sulfur co-doped carbon nanotubes derived from hydrogen-bonded organic frameworks for efficient biomass electrooxidation

The electrochemical conversion of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA), powered by renewable electricity, provides an efficient strategy for upgrading biomass to produce high value-added products. In this work, sulfur-doped hollow metal–organic framework (MOF) nanotubes were synthesized in a scalable and controllable manner by using hydrogen-bonded organic frameworks (HOFs) as the template and precursor. Interestingly, sulfur doping of the catalysts could be simply achieved by replacing nickel nitrate with nickel sulfate at the synthesis stage, and the designed sulfur-doped catalysts demonstrated excellent electrocatalytic activity in the HMFOR and remarkable durability, achieving nearly 100% conversion of HMF and high FDCA faradaic efficiency. Moreover, the HMFOR activity could be further enhanced by additional sulfur doping of the prepared catalyst, while maintaining its unique tubular morphology. The combination of sulfur doping with hollow nanotubes greatly increases the electrochemically active surface area and improves electron transport. In situ Raman and electrochemical impedance spectroscopy disclose that the continuously generated Ni3+ active species act as intermediates to promote HMF oxidation. In addition, this facile fabrication method is more environmentally friendly and significantly expands the scope of preparing non-precious metal-based nanotubes for electrocatalytic applications.