Electrochemically enhanced oxygen evolution and urea oxidation reactions with advanced high-entropy LDH nanoneedles†

Abstract

This study describes the synthesis of innovative high-entropy layered double hydroxide (HE-LDH) nanoneedles, achieved through a straightforward hydrothermal method using a combination of cost-effective active non-noble transition elements, Fe, Co, Cr, Mn, and Zn (denoted as FCCMZ), for electrocatalysis. The structure and elemental composition of the synthesised HE-FCCMZ LDH were characterised by FE-SEM, FE-TEM, XRD, XPS, and ICP-OES. The electrocatalytic activity for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) was analysed by LSV, CV, chronopotentiometry, and EIS methods. The resulting HE-FCCMZ LDH, exhibited superior performance in the electrocatalytic OER and UOR in alkaline medium. Specifically, the optimized HE-FCCMZ LDH sample demonstrated a low overpotential of 185 mV vs. RHE to achieve a current density of 10 mA cm⁻², with a minimal Tafel slope of 49.7 mV dec⁻¹. It is superior to other ternary and quaternary LDHs. For the UOR, HE-FCCMZ LDH demonstrated a very low potential of 250 mV vs. Hg/HgO. The HE-FCCMZ LDH demonstrated remarkable electrocatalytic OER performance, as evidenced by its high intrinsic activity, including the turnover frequency (TOF). Moreover, HE-FCCMZ LDH electrocatalysts showcased exceptional stability for 60 hours and hold potential for practical industrial use as OER catalysts.