Co₂P–Ni₃S₂ Heterostructured Nanocrystals as Catalysts for Urea Electrooxidation and Urea-Assisted Water Splitting

Abstract

In order to realize efficient hydrogen production with low energy consumption, the urea oxidation reaction (UOR) is used as a substitute for the oxygen evolution reaction (OER) to reduce the thermodynamic potential of water electrolysis. Highly efficient and stable nonprecious metal electrocatalysts are desired to resolve the slow kinetics resulted from the six-electron transfer process inherent in UOR. Here, the heterostructured nanocrystals of Co2P–Ni3S2 were constructed through deposition of Ni salt on acetylene black coated with CoP species (Co2P–Ni3S2/C) and subsequent vulcanization. Compared with single component CoP/C and Ni3S2/C, the Co2P–Ni3S2/C with optimal ratio of Co2P and Ni3S2 shows lower potential (1.338 V) to reach 10 mA·cm–2, which also realizes good long-term stability for nearly 100 h in chronoamperometry test. The X-ray photoelectron spectroscopy and UOR results together revealed that Ni3+ is the main site to form active intermediates, which is formed by the electron transfer from Ni3S2 to Co2P through a heterostructured interface. Inspired by the excellent UOR activity of Co2P–Ni3S2/C, as an anode in electrolyte for hydrogen evolution through urea-assisted water splitting, the current density of 10 mA·cm–2 can be achieved at a potential of only 1.389 V. Therefore, the construction of two component heterostructure is conducive to electron transfer and active site regulation, so as to realize the development of effective UOR catalyst and promote the UOR application for energy-saving hydrogen production.