Engineering metal-organic frameworks precursors and thermal treatment to achieve high-activity CeO2 oxygen evolution electrocatalysts

Metal–organic frameworks (MOFs) provide a versatile platform for engineering metal oxides with controlled structure and functionality. In this work, two cerium-based MOFs (CeBDC and CeBTC) were synthesized via an ultrasound-assisted route and thermally converted into CeO 2 nanoparticles at different calcination temperatures (350–700 °C). The combined influence of ligand architecture and thermal treatment on the structural, electronic, and electrocatalytic properties was systematically investigated. Structural and surface analyses (XRD, Rietveld refinement, FTIR, UV–Vis, XPS, and electron microscopy) revealed that both parameters strongly modulate crystallite size, defect density, and the Ce 3 + /Ce 4+ surface ratio. Electrochemical measurements toward the oxygen evolution reaction (OER) in alkaline medium (1.0 mol L −1 KOH) demonstrated that catalytic performance is governed by a balance between oxygen vacancies and charge-transfer properties. Among all samples, CeO 2 -D-700 exhibited the best performance, delivering a low overpotential of 316 mV at 10 mA cm −2 , a Tafel slope of 52.8 mV dec −1 , and excellent stability over 24 h, conserving its structural integrity. Electrochemical impedance spectroscopy confirmed its low charge-transfer resistance and enhanced double-layer capacitance, associated with an optimized Ce 3+ /Ce 4+ ratio and defect-mediated active sites. These results demonstrate that ligand-directed MOF precursor engineering combined with thermal modulation enables fine control over defect chemistry and electronic structure, providing an effective strategy to optimize CeO 2 -based electrocatalysts for OER.