Mo₂CT_xMXene supported nickel-iron alloy: an efficient and stable heterostructure to boost oxygen evolution reaction

Abstract

A polyol-assisted solvothermal route is used to synthesize NixFey nanoalloys supported on a highly electron conductive 2D transition metal Mo2CTx MXene. Structural, morphological and chemical characteristics of the materials are determined using several physicochemical techniques. The MXene support allows not only the formation of a nanostructured metallic NixFey nanoalloys, but also favors the interfacial charge transfer for the OER. The NixFey@Mo2CTx material with a Ni/Fe ratio of 2.66 leads to the outstanding activity for the OER with an amazingly low Tafel slope value of 34 mV dec-1 and a current density of 10 mA.cm-2 at a potential of only 1.50 V vs. RHE. In situ Raman experiments show that β-NiOOH formed by oxidation of the nanoalloys under positive scan, likely containing a very small amount of Fe, is the active phase for the OER. This material exhibits also an excellent stability over 168 h in a 5 M KOH electrolyte. TEM-EELS analyses after 100 voltammetric cycles between 0.2 to 1.55 V vs. RHE evidence for the first time that the MXene support is not fully oxidized in the first cycle. Also, oxyhydroxide layer formed in the OER potential region at the surface of the NixFey nanoparticles can be reversibly reduced.