Fluorine-doped Nickel Cobalt Oxide Spinel As Efficiently Bifunctional Catalyst for Overall Water Splitting

Exploring highly active, low cost, and robust electrocatalysts for overall water splitting remains a great challenge. Herein, a fluorine-doped nickel cobaltate spinel (NiCo2O4) is derived from the bimetallic nickel/cobalt metal-organic framework (CoNi-MOF) by a facile solvothermal approach and followed by an annealing process. It displays that the proposed NiCo2O4 nanostructure is combined with electro-catalytic active NiO and CoF2 nanoparticles. All of these nanoparticles are embedded homogeneously within the mesoporous carbon matrix to form abundant catalytic sites, leading to a strong synergetic effect with ionic/semi-ionic F and N atoms (denoted as NiCo2O4/NiO/CoF2@mC). It shows that the NiCo2O4/NiO/CoF2@mC hybrid obtained under 700 degrees C (denoted as NiCo2O4/NiO/CoF2@mC(700)) can be employed as efficiently bifunctional catalysts for hydrogen evolution (HER) and oxygen evolution reactions (OER) in alkaline solution. The NiCo2O4/NiO/CoF2@mC(700) hybrid presents the faster and more efficient charge transfer, thus displaying an excellent electrocatalytic activity with low overpotentials of -45.3 mV and 1.47 V to reach a current density of 10 mAcm(-2) and Tafel slopes of 29 and 78 mV dec(-1) for the HER and OER, respectively. A two-electrode electrolyzer based on the NiCo2O4/NiO/CoF2@mC(700) catalyst as both the anode and cathode exhibits outstanding stability for sustained water splitting with a cell voltage of only 1.56 V at 10 mA cm(-2). This study not only opens a new avenue for designing efficient and flexible catalysts but also extends the application of metal organic frameworks in renewable energy resources. (C) 2019 Elsevier Ltd. All rights reserved.