NiS-NiS2 heterostructure for efficient electrocatalytic overall urea splitting

Heterogeneous catalysts possess many advantages over single-phase catalysts. However, how to tune the heterogeneous interface state and density in heterostructures to optimize their electrocatalytic performance is still a challenge. Here, we propose a method for the preparation of NiS-NiS2 heterostructure by vulcanization of nickel foam at high temperature, which can effectively tune the weight ratio of NiS to NiS2 in heterostructure and their corresponding electrocatalytic urea oxidation reaction (UOR), hydrogen evolution reaction (HER) and overall urea splitting performance. The electrocatalytic activity show a trend of volcano curve with the increase of the ratio of NiS to NiS2, and the best electrocatalytic activity was obtained at the ratio of 6.74, in which the potentials at current density of 10 mA cm-2 of UOR, HER and overall urea splitting are 1.28 V, -49.5 mV and 1.34 V versus reversible hydrogen electrode (vs. RHE), and the Tafel slopes are 21.7, 74.1 and 90.9 mV dec-1, respectively. Furthermore, it also demonstrates excellent electrocatalytic stability. This work provides an effective way to tune the interfacial structure of heterogeneous electrocatalysts while significantly improving their electrocatalytic performance, which is beneficial to the development of efficient heterostructure and expand their applications.