EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Green hydrogen is produced by water electrolysis using renewable energy. In the electrolyzer, at the cathode occurs the hydrogen evolution while at the anode the oxygen evolution reaction (OER) takes place. The OER is an energetically demanding reaction that requires a high overpotential to occur. Thus, a challenge is the development of new low-price 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 several areas around the world. Hence, the employment of seawater draws attention for hydrogen generation. However, the presence of chlorides implies new challenges, in particular, the simultaneous chlorine evolution reaction (CER) with the OER at the anode.
With the aim of obtaining a selective and electrocatalytic anode, in this work bulk Fe-Mn-Mo anodes with different compositions were produced through powder metallurgy. The effect of composition variations of each electrode is related with the electrocatalytic properties. 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, Tafel slopes and time-dependent potential curves. Finally, the selectivity of the OER was determined through electrolyte titration of chlorine species.
The results showed a homogenous surface with low porosity. The encountered phases were a solid solution of Fe-Mn and MnO. The lowest potential and Tafel slope achieved for the OER was 0.8 V (NHE) at 10 mAcm-2 and 60 mVdec-1, respectively. The highest oxygen evolution efficiency obtained was 99,99%. Taking into account these results, the composition of the developed anodes as well as the production method are a promising way to scale up seawater electrolysis.