Ceria nanorods as highly stable free radical scavengers for highly durable proton exchange membranes

Unveiling CeZnOx Bimetallic Oxide: A Promising Material to Develop Composite SPPO Membranes for Enhanced Oxidative Stability and Fuel Cell Performance

The incorporation of cerium-zinc bimetallic oxide (CeZnOx) nanostructures in sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membranes holds promise in an enhanced and durable fuel cell performance. This investigation delves into the durability and efficiency of SPPO membranes intercalated with CeZnOx nanostructures by varying the filler loading of 1, 2, and 3% (w/w). The successful synthesis of CeZnOx nanostructures by the alkali-aided deposition method is confirmed by wide-angle X-ray diffraction spectroscopy (WAXS), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses. CeZnOx@SPPO nanocomposite membranes are fabricated using a solution casting method. The intricate interplay of interfacial adhesion and coupling configuration between three-dimensional CeZnOx and sulfonic moieties of the SPPO backbone yields an enhancement in the bound water content within the proton exchange membranes (PEMs). This constructs simultaneously an extensive hydrogen bonding network intertwined with the proton transport channels, thereby elevating the proton conductivity (Km). The orchestrated reversible redox cycling involving Ce3+/Ce4+ enhances the quenching of aggressive radicals, aided by Zn2+, promoting oxygen deficiency and Ce3+ concentration. This synergistic efficacy ultimately translates into composite PEMs characterized by a mere 4% mass loss and a nominal 6% decrease in Km after rigorous exposure to Fenton's solution. Remarkably, an improved power density of 403.2 mW/cm2 and a maximum current density of 1260.6 mA/cm2 were achieved with 2% loading of CeZnOx (SPZ-2) at 75 °C and 100% RH. The fuel cell performance of SPZ-2 is 74% higher than its corresponding pristine SPPO membrane.

Effective Atomic N Doping on CeO2 Nanoparticles by Environmentally Benign Urea Thermolysis and Its Significant Effects on the Scavenging of Reactive Oxygen Radicals

Atomic nitrogen doping on CeO₂ nanoparticles (NPs) by an efficient and environmentally benign urea thermolysis approach is first studied, and its effects on the intrinsic scavenging activity of the CeO₂ NPs for reactive oxygen radicals are investigated. The N-doped CeO₂ (N-CeO₂) NPs, characterized by X-ray photoelectron and Raman spectroscopy analyses, showed considerably high levels of N atomic doping (2.3-11.6%), accompanying with an order of magnitude increase of the lattice oxygen vacancies on the CeO₂ crystal surface. The radical scavenging properties of the N-CeO₂ NPs are characterized by applying Fenton's reaction with collective and quantitative kinetic analysis. The results revealed that the significant increase of surface oxygen vacancies is the leading cause for the enhancements of radical scavenging properties by the N doping of CeO₂ NPs. Enriched with abundant surface oxygen vacancies, the N-CeO₂ NPs prepared by urea thermolysis provided about 1.4-2.5 times greater radical scavenging properties than the pristine CeO₂. The collective kinetic analysis revealed that the surface-area-normalized intrinsic radical scavenging activity of the N-CeO₂ NPs is about 6- to 8-fold greater than that of the pristine CeO₂ NPs. The results suggest the high effectiveness of the N doping of CeO₂ by the environmentally benign urea thermolysis approach to enhance the radical scavenging activity of CeO₂ NPs for extensive applications such as that in polymer electrolyte membrane fuel cells.

Comparative Studies on Effects of Metal Cation (La) and Non-Metal Anion (N) Doping on CeO2 Nanoparticles for Regenerative Scavenging of Reactive Oxygen Radicals

The intrinsic effects of metal cation (La) and non-metallic anion (N) doping of CeO2 nanoparticles (NPs) for regenerative scavenging of reactive oxygen radicals were studied. La-doped CeO2 NPs were prepared by the conventional impregnation method at various La doping levels. N-doped CeO2 NPs were prepared by urea thermolysis with two different methods: (i) direct thermolysis of urea after physical mixing with CeO2 NPs and (ii) wet impregnation of CeO2 NPs with urea followed by thermolysis under inert N2 atmosphere. Physicochemical properties of samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and N2 sorption measurement. Radical scavenging properties of the samples were characterized by applying Fenton’s reaction. Results indicated that atomic N doping on CeO2 NPs significantly enhanced radical scavenging properties of CeO2 NPs, resulting in an activity of N-doped CeO2 about 3.6 times greater than the pristine CeO2 NPs and 1.6 times higher than the La-doped CeO2 NPs. This result suggests that anionic N doping of CeO2 NPs is highly effective in enhancing radical scavenging properties of CeO2 NPs, whereas such modifications have been typically practiced by hetero-metal doping with rare earth metal elements. A collective structure–property correlation analysis suggested that enhancement of radical scavenging properties of heteroatom-doped CeO2 NPs was largely attributed to an increase in surface oxygen vacancies on CeO2 NPs due to heteroatom doping.

Electrochemical detection of hydrogen peroxide using micro and nanoporous CeO2 catalysts

In this research work, focus has been made on a glassy carbon electrode (GCE) modified commercial micro and synthesized nano-CeO₂ for the detection of hydrogen peroxide (H₂O₂). Firstly, CeO₂ nanoleaves were prepared by solvothermal route. Both commercially available micro CeO₂ and synthesized nano-CeO₂ structures were analyzed by different characterization techniques. The Raman spectra of synthesized nano CeO₂ has more oxygen vacancies than micro CeO₂. SEM images revealed that the synthesized CeO₂ acquired leaf-like morphology. The catalyst nano CeO₂ offered mesoporosity from nitrogen adsorption-desorption isotherms with massive sites of activation for increasing efficiency. Experiments on determining H₂O₂ using micro CeO₂ or nano-CeO₂/GCE was conducted using cyclic voltammetry (CV) and amperometry. Enhanced H₂O₂ reduction peak current with lower potential was observed in nano-CeO₂/GCE. The influence of scan rate and H₂O₂ concentration on the performance of nano-CeO₂/GCE were also studied. The obtained results have indicated that nano-CeO₂/GCE showed improved electrochemical sensing behavior towards the reduction of H₂O₂ than micro-CeO₂/GCE and bare GCE. A linear relationship was obtained over 0.001 μM-0.125 μM concentration of H₂O₂, with good sensitivity 141.96 μA μM^-1 and low detection limit of 0.4 nM. Hence, the present nano-CeO₂ system will have a great potential with solvothermal synthesis approach in the development of electrochemical sensors.