Rational design of hollow core-double shells hybrid nanoboxes and nanopipes composed of hierarchical Cu-Ni-Co selenides anchored on nitrogen-doped carbon skeletons as efficient and stable bifunctional electrocatalysts for overall water splitting

It is of prime importance to develop efficient nonprecious noble-metal-free water splitting bifunctional electrocatalysts for both H-2 and O-2 evolution reactions (HER and OER), which remains a grand challenge. However, the design of hollow nanostructured based on di- and tri-metal selenides, particularly non-spherical hollow nanostructures, is scarcely reported. Herein, for the first time, novel tri-metal selenides based on hollow Cu0.4Ni0.3Co0.3Se2 mesoporous nanosheet double shell were successfully designed on hollow N-doped carbon nanoboxes (Cu0.4Ni0.3Co0.3Se2@N-C n-box) and nanopipes (Cu0.4Ni0.3Co0.3Se2@N-C n-pipe). The hollow N-C n-box and N-C n- pipe skeletons were obtained from the related Fe2O3 nanocubes and nanorods templates that have prepared with completely different morphologies via only a minor change in synthesis step. Remarkably, benefiting from the special electronic structure engineering and unique hollow hierarchical design with high surface areas, open channels for effective gas releasing, fast electron/mass transport, the resulting advanced electrocatalysts provide outstanding OER activity as well as desirable HER performance in the alkaline medium. Moreover, an overall water splitting device is assembled using two symmetrical Cu0.4Ni0.3Co0.3Se2@N-C n-box electrodes as anode and cathode, which can deliver a current density of 10 mA cm(-2) at a cell voltage as low as 1.53 V. More significantly, in addition to extraordinary operational stability of the electrolyzer, it can achieve high current density of 100 mA cm(-2) with only cell voltage of 1.79 V, respectively, which are very useful for practical application. This work offers a rational strategy for the structure engineering of advanced hollow hybrid nanostructures as a nonprecious noble-metal-free water splitting bifunctional electrocatalyst, which can push forward the development of high efficient and low cost H-2 production.