Prospects of using high entropy oxides as catalysts for the oxygen evolution reaction

High entropy oxides (HEOs), containing five or more different metal atoms in addition to oxygen, present a large composition space with rich opportunity to optimise the material properties towards specific applications. Here, the potential of HEOs as electrocatalysts for the oxygen evolution reaction is reviewed. Using rutile oxides as an example, it is demonstrated how the balance between different reaction pathways can be modified by alloying, affecting both activity and stability. Furthermore, alloying leads to changes in the electronic structure, including changes in conductivity and charge transfer between elements. For rutile oxides, the charge transfer improves the activity of the less active elements; however, it correlates with a favourable enthalpy of mixing that may hamper the formation of a randomly ordered crystal. Although these insights may be used to narrow the field of candidate materials, the complementary development of experimental and theoretical models capable of identifying relevant compositions remains important. • The potential advantages of using high entropy oxides (HEOs) as catalysts for the oxygen evolution reaction are summarised. • Different reaction pathways are possible on the oxide surface and the energetic balance between them is modified by alloying. • When different metals are mixed in an oxide, charge can be transferred between them, affecting their catalytic activity. • Experimental and theoretical approaches to identify the optimum composition within the composition space are being developed.