Green synthesis of Ni3S2 nanoparticles from a nontoxic sulfur source for urea electrolysis with high catalytic activity

Urea electrolysis receives great attention due to its capability to tackle with urea−containing wastewater and allow energy–saving hydrogen production simultaneously. Ni3S2 has favorably metallic property due to the short Ni−Ni bonds in its structure and the most abundant nickel content in the stoichiometric formula among nickel sulfides, thus it is considered an effective electrocatalyst for urea oxidation. However, the current Ni3S2−based catalysts usually derived from toxic sulfur sources, posing safety concerns in production. Herein, we reveal Ni3S2 nanoparticles (ca. 10 nm) can be directly deposited onto Ni substrate in a facile hydrothermal reaction from nontoxic L–cysteine sulfur source without any additives. Ni3S2 serves as a highly efficient and reliable electrocatalyst for urea oxidation with high current responses, low Tafel slope, and reduced resistance. Moreover, the apparent activation energy of urea oxidation for the prepared Ni3S2 electrocatalyst is evaluated as 3.2 kJ mol−1, which is much lower than that of Ni(OH)2 (15.7 kJ mol−1). As a result, the obtained Ni3S2 demonstrates remarkable catalytic activity of 280.2 A g–1 outperforming the Ni(OH)2 electrocatalyst (61.1 A g–1). In addition, Ni3S2 exhibits reliable catalytic performance, as examined by chronoamperometric, chronopotentiometric, and multi–current steps analyses.