Atomically precise nickel-sulfur clusters for efficient electrochemical 2,5-hydroxymethylfurfural oxidation

Nickel sulfide exhibits excellent catalytic activity in the electrochemical 2,5-hydroxymethylfurfural oxidation reaction (HMFOR). However, due to the polydispersity of nanoparticles, it is difficult to establish a clear structure-activity relationship at the atomic level. In this work, we have successfully synthesized atomically precise Ni6(PET)12 and Ni4(PET)8 clusters (PET: 2phenylethanethiol) for HMFOR. Ni2+ and S2- with atomic ratio of 1:2 was mainly existed in Ni6(PET)12 and Ni4(PET)8 to form Ni-S bond. The electrochemical test results have suggested both Ni6(PET)12 and Ni4(PET)8 displayed outstanding electrocatalytic ability for HMFOR. The Ni6(PET)12 exhibited better electrocatalytic ability than Ni4(PET)8 with higher current density, lower overpotential and faster reaction kinetics. The superior electrochemical ability of Ni6(PET)12 may be due to the enhanced adsorption towards HMF molecule with strong interaction towards hydroxyl group and furan ring. Moreover, it found that the Ni2+ species in Ni6(PET)12 could rapidly oxidized into Ni3+ species, which could spontaneously capture electron and proton from HMF for oxidation. The theoretical calculation demonstrated that the Ni6(PET)12 process lower free energy barrier than Ni4(PET)8 to display excellent electrocatalytic performance. This work is of great significance for designing efficient electrocatalysts for HMFOR.