Influência da estrutura cristalina e da temperatura na obtenção de CeO2 derivado de metal-organic frameworks e seu desempenho eletrocatalítico na OER

Abstract

Global energy demand is growing due to economic expansion and population growth, facing climate challenges caused by greenhouse gases (GHG). Hydrogen is a sustainable alternative, especially when produced by water splitting, but this process is energy-intensive. To make green hydrogen production viable, it is necessary to develop cost-effective and efficient electrocatalysts. CeO2 is promising as an electrocatalyst due to its ability to modulate charge and exploit structural defects. Combined with metal-organic frameworks (MOFs), which modulate surface area and porosity, efficient electrocatalysts can be created. This study obtained pure CeO2 particles from two Ce-MOFs based on 1,4-benzenedicarboxylic acid (BDC) and 1,3,5-benzenetricarboxylic acid (BTC) ligands, verified by XRD analysis. Techniques such as X-ray photoelectron spectroscopy and infrared molecular absorption spectroscopy indicated the presence of residual carbon, and thermogravimetric analysis verified the thermal stability of the MOFs until their complete transformation into CeO2. Scanning electron microscopy images showed that the MOFs maintain similar morphologies after heat treatment, although with greater agglomeration. High-resolution transmission electron microscopy verified the nanometric size of the particles. In the oxygen evolution tests, electrochemical tests with linear sweep voltammetry in 1 M KOH show a better overpotential value at a current density of 10 mA cm-2 of 316 mV and a favorable Tafel slope of 52.80 mV dec-1 for CeBTC calcined at a temperature of 700°C. While the kinetic data performed at 1.5 V vs. ERH, through electrochemical impedance spectroscopy, showed electrolytic solution resistance and charge transfer resistance of 0.39 and 18.1 Ω, respectively, and double layer capacitance of 67.8 mF. The results presented in this work indicate a superior efficiency compared to previously reported pure CeO2 materials. In addition, chronopotentiometry demonstrated excellent stability of the oxides over 24 hours.