WEB Electrochemical oxidation of Mn-Mo-Fe anodes for use in seawater electrolysisWednesday (23.09.2020) 15:40 - 15:55 F: Functional Materials, Surfaces, and Devices 1 Part of:
The use of H2 as energy vector, best known as hydrogen economy, is considered for several countries as the most promising clean energy technology. However, H2 production still remains dependent on fossil fuels; only a 4% is obtained without pollutants generation, through water electrolysis.
In the electrolyzer, at the cathode occurs the H2 evolution, while in the anode the oxygen evolution reaction (OER) takes place. The OER is an energetically demanding reaction that requires a high overpotential to occur. Thus, the main challenge is the development of new anode materials capable to decrease this potential. In spite of the advantages of water electrolysis, global water crisis cannot be ignored, which highly restricts the use of this technology in many places. Hence, the employment of seawater draws attention for H2 generation. However, the presence of chlorides implies new challenges, in particular, the simultaneous chlorine evolution reaction (CER) with the OER at the anode, i.e. extra energy consumption. In the literature, the use of Mn oxides produced by anodic electrodeposition have been studied due to their high selectivity to produce the OER above the CER, but this production method also involves Ir electrodeposition i.e. high price.
With the aim of produce a selective and electrocatalytic anode, in this work bulk Mn-Mo-Fe anodes with different compositions were produced through powder metallurgy. Then, their surfaces were electrochemically oxidized to obtain suitable phases. In order to study the appropriate oxidizing parameters, polarization curves of Mn-Mo-Fe electrodes were recorded and analyzed. Morphological and microstructural characteristics of the samples were studied by scanning electron microscopy and x-ray diffraction, respectively. The electrocatalytic behavior of the samples was analyzed by voltammetric curves. Finally, the selectivity of the OER was determined through electrolyte titration of chlorine species. The results showed a porous structure in all the samples which provides a larger surface area to allow the OER. A lower overpotential to evolve O2 was found, which is attributed to the phases formed during anodization. Additionally, the analysis of the reactions in the time, concerning to oxygen evolution efficiency, showed that the Mn-Mo-Fe anodes possess a great ability to evolve O2 over Cl2. Hence, the composition of the developed anodes as well as the production method are a promising way to scale up this technology.