Electro-oxidation of 5-hydroxymethylfurfural by a catalyst containing copper nanoparticles and single copper atoms

Atomic-site electrocatalysts are being considered as potential alternative catalysts due to their exceptionally high atom utilization efficiencies, well-defined active sites and high selectivities. However, the presence of nanoparticles in the single-atom catalysts may affect the catalytic performance. Herein, single-copper-atoms and copper nanoparticles co-embedded in nitrogen-doped carbon nanosheets (CuNPs@Cu/NCNSs) were synthesized and used for 5-hydroxymethylfurfural electro-oxidation. Single copper atoms supported on nitrogen-doped carbon nanosheets (Cu/NCNSs) and copper nanoparticles supported on carbon (CuNPs/C) were also synthesized for comparison. The CuNPs/C exhibited high efficiency in electro-oxidation of HMF to 2,5-furandicarboxylic acid (FDCA) at a low potential of 1.42 V. However, the CuNPs@Cu/NCNSs showed a high 5-formyl-2-furancarboxylic acid (FFCA) selectivity of 86.7%. Oxalic acid (OA) treatment experiments showed that single copper atoms significantly influence the oxidation of HMF to FFCA. Cu(OH)2 active species generated by electrochemical oxidation were demonstrated as the primary catalytic sites for HMF oxidation on the CuNPs/C. In-situ Raman spectra results demonstrated that HMF oxidation on the CuNPs/C followed the path to 5-hydroxymethyl-2-furancarboxylic acid (HFCA), while on the CuNPs@Cu/NCNSs and Cu/NCNSs, HMF was oxidized along the 5-diformylfuran (DFF) pathway.