S-species-stimulated deep reconstruction of ultra-homogeneous CuS nanosheets for efficient HMF electrooxidation

RESEARCH

The massive consumption of fossil fuels in human society has led to increasingly severe resource crises and environmental pollution, and the efficient utilization of renewable biomass resources is one of the feasible approaches to addressing these issues. The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to produce 2,5-furandicarboxylic acid (FDCA) is expected to reduce the excessive reliance on fossil resource-derived terephthalic acid (PTA), a petroleum-based platform molecule. However, the development of high-performance and low-cost electrocatalysts for the efficient HMF oxidation reaction (HMFOR) remains a significant challenge. 

Now, a team at the Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry and the Institute of Advanced Carbon Conversion Technology, Huaqiao University has developed a coordination-pyrolysis strategy to fabricate a highly dispersed copper sulfide (CuS) nanosheets supported on N-doped porous carbon precatalyst (CuS@NC). The covalent S species trigger the deep-reconstruction of CuS nanosheets, and the in-situ generated SO₄^2- not only promotes the formation of Cu^2+δ species but also facilitates the cleavage of α–C–H and –O–H bonds in HMF. The optimized CuS@NC achieved a high current density of 335 mA cm^-2 at 1.5 V vs. RHE, representing a remarkable 628% enhancement over the control catalyst.

“The conversion of HMF to FDCA via traditional thermocatalytic methods is limited by harsh reaction conditions such as high temperature and high pressure.” said lead author Kui Wang. “Electrocatalysis drives the oxidation process using the directional flow of electrons as the energy injection mode, which not only features mild reaction conditions but also enables the effective utilization of unstable clean electricity (e.g., wind energy, hydropower, tidal energy, etc).”

Theoretical prediction and catalyst design

The electro-oxidation valorization process of HMF involves two sequential steps and the oxidation of HMF is a post-reaction after the oxidation of active species on the electrodes: (1) the electrochemical oxidation of the electrodes; (2) the ​spontaneous abstraction​ of H from the aldehyde and hydroxymethyl groups of HMF by reactive species on the oxidized electrode surface via a proton-coupled electron transfer (PCET) process. In the study, based on the predictions from DFT calculations and AIMD simulations, the researchers designed a precatalyst comprising highly dispersed copper sulfide (CuS) nanosheets supported on nitrogen-doped porous carbon (CuS@NC) via a coordination-pyrolysis strategy, and successfully constructed efficient HMFOR sites of SO₄^2-|Cu(OH)₂ through its in-situ reconstruction, achieving the simultaneous promotion of these two processes. And quasi-in-situ X-ray diffraction (XRD), in-situ Raman, and in-situ electrochemical impedance (EIS) spectroscopy demonstrated the crucial role of S species in promoting the deep-reconstruction of the CuS@NC electrode and improving the utilization efficiency of active sites in HMFOR.

A scalable catalyst design strategy

This study combines theoretical predictions with experimental research to systematically clarify the crucial role of sulfur (S) species in promoting the deep reconstruction of CuS nanosheets and enhancing HMFOR performance. It also proposes a scalable strategy for preparing ultra-uniform transition metal sulfide precatalysts, providing a feasible approach for the development of high-efficiency and low-cost HMFOR catalysts. This method exhibits strong adaptability: by simply controlling the type and ratio of added metals or regulating the subsequent sulfidation process, ultra-uniform porous carbon-supported bimetallic, multimetallic catalysts as well as their sulfides, phosphides, nitrides, etc., can be obtained. These catalysts can match various electrocatalytic reactions including HMFOR, facilitating the construction of efficient electrocatalytic systems.

Sources: https://spj.science.org/doi/10.34133/research.0925