Mild and scalable synthesis of a high performance CrFeCoNiRu0.05 high entropy nano-alloy/carbon electrocatalyst for efficient urea production with a chelate-based ionic liquid

Abstract

High-entropy alloys show broad application prospects in electrocatalysis due to their high catalytic activity, conductivity and structural stability. However, achieving their mild and scalable synthesis still remains a great challenge. This paper reports a strategy for the synthesis of CrFeCoNiRu_0.5 high entropy nano-alloy/carbon (termed as CrFeCoNiRu_0.5–HENA/C) using a chelate-based ionic liquid. Cr(III), Fe(III), Co(II), Ni(II) and Ru(III) were coordinated with salicylic acid ionic liquid to form a viscous metal complex solution, followed by low temperature carbonization and subsequent high temperature annealing. The resulting CrFeCoNiRu_0.5–HENA/C consists of a three-dimensional carbon framework and CrFeCoNiRu_0.5–HENA nanocrystal. The carbon framework offers high ion/electron conductivity and good affinity with NO₃⁻ and CO₂ due to the presence of hydrophilic oxygen-containing groups and highly electronegative nitrogen atoms. The CrFeCoNiRu_0.5–HENA nanocrystal has a small size of 52.5 ± 1.2 nm, good element homogeneity and high crystallinity. Such a unique structure improves the adsorption capacity towards NO₃⁻ and CO₂ and the electrocatalytic activity towards the C–N coupling reaction. The CrFeCoNiRu_0.5–HENA/C electrocatalyst exhibits a high urea yield of 35.57 ± 0.81 mmol g_catalyst⁻¹ h⁻¹ with a high faradaic efficiency of 21.02 ± 0.77%, which is much better than that of multi-component nano-alloys from Cr, Fe, Co, Ni and Ru. This study also provides an approach for the construction of high-entropy nano-alloys in catalysis, sensing and energy storage and conversion.