Effect of oxygen and titanium contents on the stability of nanocrystallineTi-Ru-Fe-O cathode materials for chlorate electrolysis

Electrodes made from nanocrystalline Ti:Ru:Fe (2 - y:1 + y/2:1 + y/2), with y varying from 0 to 1 by step of 0.25, and Ti:Ru:Fe:O (2:1:1:w), with w va rying from 0 to 2 by step of 0.5, were prepared and tested as activated cat hodes for the hydrogen evolution reaction in typical chlorate electrolysis conditions. These electrodes were subjected to an accelerated aging test, c onsisting of a succession of cycles of hydrogen discharge (HER) and open-ci rcuit (OCP) conditions. In addition to monitoring the cathodic overpotentia l value during the aging test, visual inspection and mass loss measurements were performed on the electrodes at the end of the test to assess their st ability. In the case of Ti:Ru:Fe (2:1:1), a large increase of the cathodic overpotential value is observed after 20 cycles. Adding O to the formulatio n causes a remarkable improvement of the long-term stability of the electro des. As little as [O] = 10 at.% in nanocrystalline Ti:Ru:Fe:O (2:1:1:w) mat erials is sufficient for the electrode to show absolutely no sign of degrad ation after 50 cycles of HER/OCP, the longest accelerated test conducted. A dding more O to the formulation of the material does not lead to further st ability improvement. A better stability under the conditions of the acceler ated aging test can also be observed for nanocrystalline Ti:Ru:Fe (2 - y:1 + y/2:1 + y/2) materials with y > 0. In that case however, the level of imp rovement is dependent on the value of y. The best results are obtained for y = 0.75. A hypothesis is proposed to explain the improved stability obtain ed by lowering the Ti content and/or by adding O. The similarity and differ ence between both ways of improving the stability of the nanocrystalline Ti :Ru:Fe materials are also discussed.