Hierarchical CoWO 4 /Ni x Fe y S microspheres bearing crystalline-amorphous interface as a multifunctional platform for outperformed water splitting and sensitive hydrazine sensing

Highly efficient and multifunctional electrocatalysts are of high value in energy transformation and electrochemical sensing. Herein, hierarchically architectured cobalt tungstate/nickel iron sulfide (CoWO 4 /Ni x Fe y S) microspheres with a crystalline-amorphous interface have been prepared on bimetallic substrate of nickel - iron foam (NIF) by a two-step hydrothermal method. Electrochemical characterization shows that CoWO 4 /Ni x Fe y S microspheres can boost the electrocatalytic activity effectively through the synergistic effect on the crystallineamorphous interface. When the CoWO 4 /Ni x Fe y S is applied as the electrocatalysts for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the overpotentials at a high current density of 500 mA cm -2 are only 322.8 mV and 306.5 mV, respectively. The overall water splitting device composed of CoWO 4 /Ni x Fe y S/ NIF couple only needs a cell voltage of 1.80 V to reach a current density of 100 mA cm -2 , and 2.19 V to reach 500 mA cm -2 . The CoWO 4 /Ni x Fe y S/NIF can be also utilized as an effective electrochemical platform for the sensing of toxic hydrazine in a wide range from 50 mu M to 17.3 mM, with a detection limit of 46.4 mu M. All these results display that the CoWO 4 /Ni x Fe y S/NIF can be a high-performance multifunctional material for energy transformation and environmental pollutant monitoring.