Development of a methodology for ferrites evaluation by WDXRF

MFe2O4 (M: metal) (ferrites) are compounds widely employed in many industrial areas. The thermochemical water-splitting cycles, one of the most popular applications of these materials, have a significant potential to efficiently produce green hydrogen employing renewable energy resources. These thermochemical cycles can employ ferrites with spinel crystal structure. These cycles are known as “ferrite cycles” [1, 2].

Spinel ferrites are considered appropriate candidates for two-step water splitting processes. In these cycles, the starting ferrite is reduced in the endothermic first step (activation), releasing oxygen, and then reacted with water (hydrolysis) to produce hydrogen and the pristine ferrite. These spinel ferrites are subsequently recycled to the first step and can be used in several hydrogen production cycles. This is a green hydrogen production process as it uses H2O as a starting product and the final products obtained are H2 and O2.

In terms of cost, synthetic ferrites could be interesting candidates for scalable production. Different approaches of synthesis have been proposed, although co-precipitation method can be considered an easy and economical method for preparation of spinel ferrites [3]. In this study, cobalt ferrite was synthetized by co-precipitation method using stoichiometric amounts of metal nitrates [4, 5]. To evaluate the performance of this method of synthesis is important the characterization of the as-prepared materials. Elemental characterization is mandatory, in this case, to determine the amount of each element in the final compound and Wavelength Dispersive X-ray Fluorescence (WDXRF) is an appropriated instrumentation for this evaluation. A methodology was developed and validated using WDXRF technique, for the evaluation of ferrites substituted with different metals (cobalt and nickel). An analysis of the sources of analytical uncertainty was also performed.