Facile molten salt synthesis of bimetallic NiFe-Ti3C2Tx MXene nano-hybrid as an efficient oxygen evolution electrocatalyst

Non-precious metal OER electrocatalysts are critical for developing efficient electrochemical hydrogen production. Recently, MXenes have increasingly been applied as conductive electrocatalyst support materials. Here, an HF-free and scalable one-step synthesis, based on Lewis acid molten salt (LAMS) etching of Ti3AlC2 MAX phase, is employed, varying the Ni/Fe ratio, to optimize a series of bimetallic NixFey-Ti3C2Clx nano-hybrids as precatalysts for OER electrocatalysis. The best performing sample, Ni1Fe1-Ti3C2Clx, has a Ni:Fe ratio of 1:1, with an overpotential at 10 mA cm-2 of 310 mV, and a Tafel slope of 48 mV dec−1. Cyclic voltammetry reveals the surface availability of both Ni and Fe species, with the OER activity correlated to the Ni(III)/Ni(II) redox potential. Advanced characterization confirms the formation of nano-structured Ni-Fe alloy intimately bound to the Ti3C2Clx support, as the Fm3̅m or Im3̅m phases, depending on the Ni/Fe ratio employed in the LAMS synthesis. Density functional theory (DFT) calculations suggest that the adsorbate evolution mechanism (AEM) is preferred over the lattice oxygen mechanism (LOM) when either Ni or Fe acts as the active center, with higher activity on the Ni sites. This study demonstrates a facile method for the preparation of nano-structured bimetallic-MXene heterostructures with applications in electrochemical energy conversion.