Self-sorting multimetal–organic gel electrocatalysts for a highly efficient oxygen evolution reaction

Abstract

Developing nonprecious electrocatalysts toward the oxygen evolution reaction (OER) remains one of the main challenges for large-scale electrocatalytic water splitting. Metal–organic gels (MOGs) have recently emerged as promising nonprecious electrocatalysts for the OER, which have the advantages of high surface areas, hierarchical porosity, good compatibility, and open metal active sites for electrocatalysis. Herein, multimetallic metal–organic aerogel electrocatalysts (MG–FeNiCo) are assembled from 1,3,5-benzenetricarboxylic acid and Fe³⁺, Co²⁺, and Ni²⁺ nitrates via a facile one-pot method. In this way, multiple metal ions react with 1,3,5-benzenetricarboxylic acid to yield a multimetallic metal–organic gel. The multimetal–organic gel is a self-sorting system rather than a co-assembled one, exhibiting mixed nanoparticle and tape morphology. The bimetallic and multimetallic metal–organic gels exhibit a partially amorphous structure together with regular nanoscale metal–organic framework phases. It is noted that the MG–FeNiCo aerogel shows thermoreversible stimulus-response and a low density of 52.8 mg cm⁻³, and can support about 770 times its weight. MG–FeNiCo exhibits excellent OER performance with a low overpotential of 248 mV and 272 mV at a current density of 20 mA cm⁻² and 50 mA cm⁻², respectively, and a small Tafel slope of 49 mV dec⁻¹. Chronopotentiometry experiments revealed that MG–FeNiCo can retain a current density of 10 mA cm⁻² for 48 h with only a ∼2.1% increase, indicating the excellent activity and stability of MG–FeNiCo in the OER. The excellent performance is attributed to the synergistic effect of multiple metal ions to obtain more abundant active sites, and there is more electron movement in the oxidation and reduction state transformation of multiple metal ions (Fe³⁺/Fe²⁺ and Ni³⁺/Ni²⁺). Additionally, a conductive substance (graphene oxide) was doped into the gel network to form MG–FeNiCo-xGO aerogels. MG–FeNiCo–xGO aerogels show improved OER performance and good stability and durability. This strategy provides a simple and efficient method to explore multimetallic electrocatalysts.