Nickel-constructing interfaces of multiheterostructure on self-supporting electrode for efficient overall urea-water splitting

Water splitting is an environmentally friendly strategy for producing hydrogen but is constrained by the high theoretical potential of the oxygen evolution reaction (OER) at the anode. It is possible to save energy by substituting the OER with the urea oxidation reaction (UOR) with a low theoretical potential. In particular, developing bifunctional catalysts (hydrogen evolution reactions (HER)/UOR) and exploring their catalytic mechanisms and active sites are highly desirable with the rapid development of the hydrogen economy. Herein, the combination of electrodeposition and immersion methods to grow a well-aligned MOF on a graphene-like material (MXene) is reported. Specifically, Ni3S2 species were formed on the hexahedral structure of cobalt-based MOF (CoMOF) by electrodeposition. The resultant M/CM/Ni3S2/NF demonstrates good electrocatalytic capabilities toward the HER and UOR, with overpotentials and potentials of 0.174 and 1.392 V required to reach 100 mA cm−2, respectively. DFT results established that the coupling of MXene, CoMOF, and Ni3S2 can optimize the free energy of hydrogen adsorption on the catalyst surface. Furthermore, in situ XRD revealed that the (1 1 1), (2¯ 11) and (2 2 0) crystal planes resulted in good stability of the material. This work provides an innovative and novel route for designing high-activity bifunctional catalysts for various electrochemical energy applications.