(Invited) Dynamic Reconstruction of Lanthanum Nickelate Catalysts and Activation By Iron during OER

Abstract

Accurate description of activity trends among perovskite oxide oxygen evolution catalysts using electronic descriptors requires that the bulk structure of the catalyst is comparable to that of the surface. Relatively few works thus far have addressed the dynamic nature of the catalyst structure during OER and the implications this has for rationalization of activity. Here the in-situ surface reconstruction of LaNiO3 particles and an analogous Ruddlesden-Popper phase, La2NiO4+ δ, is described using electrochemical and materials characterization techniques. Small, but characteristic redox features were observed during cyclic voltammetry of these materials corresponding to the Ni2+/3+ redox reaction in amorphous NiOxHy. The size of these redox features grow with prolonged cycling and chronoamperometry indicating that increased duration of electrochemical conditioning continuously induces reconstruction. The reconstructed species contributes to an increased surface area as determined by electrochemical impedance spectroscopy. Near doubling of the OER activity after intentional introduction of only 35 ppb Fe species is observed after cycling, consistent with the formation of NiOxHy on the crystalline surface and subsequent adsorption of Fe to form well-known and extremely active NiFeOxHy OER catalysts. This work brings into focus the importance of considering surface amorphization on perovskite catalysts in discussion of their activity.