MAX Phase (Nb 4 AlC 3 ) For Electrocatalysis Applications.

In search for novel materials to replace noble metal-based electrocatalysts in electrochemical energy conversion and storage devices, special attention is given to a distinct class of materials, MAX phase that combines advantages of ceramic and metallic properties. Herein, Nb 4 AlC 3 MAX phase is prepared by a solid-state mixing reaction and characterized morphologically and structurally by transmission and scanning electron microscopy with energy-dispersive X-ray spectroscopy, nitrogen-sorption, X-ray diffraction analysis, X-ray photoelectron and Raman spectroscopy. Electrochemical performance of Nb 4 AlC 3 in terms of capacitance as well as for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is evaluated in different electrolytes. The specific capacitance C s of 66.4, 55.0, and 46.0 F g -1 at 5 mV s -1 is determined for acidic, neutral and alkaline medium, respectively. Continuous cycling reveals high capacitance retention in three electrolyte media; moreover, increase of capacitance is observed in acidic and neutral media. The electrochemical impedance spectroscopy showed a low charge transfer resistance of 64.76 Ω cm 2 that resulted in better performance for HER in acidic medium (Tafel slope of 60 mV dec -1 ). In alkaline media, the charge storage value in the double layer is 360 mF cm -2 (0.7 V versus reversible hydrogen electrode) and the best ORR performance of the Nb 4 AlC 3 is achieved in this medium (Tafel slope of 126 mV dec -1 ).