Higher reduction is required, depending on the operating temperatures in the SOFC stack, and for automotive applications such as SOFC APU’s. Hexavalent chromium at end of life is a hazardeous waste, and might complicate the recycling strategy for used vehicles.

The design and performance of a Chromium Getter is presented: this component captures hexavalent chromium, as released by a cathode air preheater or another steel component. The Getter is a catalyst: it reduces hexavalent chromium to trivalent chromium, which is stored on a Ti/TiO2 surface in the component.

Lab tests were executed during 1000 h, at 750°C, 4 g/s mass flow, 3% moisture. The source of the hexavalent chromium is a plate heat exchanger, with contains 0.6 m² heat exchanging walls, consisting of austenitic alloy. These walls were kept at 780°C overall. This was done for accelerated testing. Chromium was analyzed at 7 collection runs, each taking 20h. During the collection runs, the outflowing hot gas was cooled in a Liebig cooler. The Liebig coolers were rinsed with acid, and the total chromium amount in the acid was measured using ICP-OES. The hexavalent fraction was determined by photometry after derivatization.

The concentration of hexavalent chromium species at the outlet of the Chromium Getter is below the analytical detection limit during the 1000h test. This corresponds to a conversion by a factor 650 or higher, as compared to measurements on heat exchangers without chromium getter.

Post mortem analysis shows that the chromium stored on the active surface is trivalent chromium, as desired. Therefore, the component can be recycled as regular metal at the end of life. The storage capacity of the component is calculated for a 1.2 kWe SOFC system, using a Chromium Getter with 0.17 l volume.