Tuning oxygen reduction activity on chromia surface via alloying: a DFT study

Economical electro-catalysts for the oxygen reduction reaction (ORR) are highly desirable for a range of advance energy storage technologies. Chromium compounds have been suggested as one possible source of non-precious metal based catalysts for oxygen reduction reaction (ORR), especially chromia (Cr₂ O₃ ) which is the most stable form of Cr oxide at room temperature. Using density functional theory+U calculations, we investigate the 4-electron ORR on the hydroxylated Cr₂ O₃ surfaces alloyed with 17 different transition metals. On the one hand, we find that the ORR overpotential is lower when the Cr₂ O₃ surface alloyed with elements towards the end of both the first and second rows of transition metals. Among these elements, Cd alloyed Cr₂ O₃ surface is found to promote the ORR the most, but due to its high toxicity and price it loses out to Zn as the recommended alloyant. On the other hand, we find that the ORR overpotential is generally higher and less varied on the Cr₂ O₃ surface alloyed with the early-to-mid row transition metal elements (e. g. Zr, Ti). As Cr₂ O₃ is also a major component in the passive film on stainless steels, where a low ORR rate is desirable to reduce the impact of localized corrosion. This implies that alloying with early-to-mid row transition elements could be beneficial to stainless steels. The difference in oxygen reduction activity is attributed to the tendency of forming stable ORR intermediates during the oxygen reduction process.