Earth-abundant transition metal oxides, such as those of Co and Ni, are proven alternatives to replace noble metal catalysts in alkaline electrochemical water splitting. In particular, the potential for making nanostructured catalysts with a mixed composition of e.g. Co-Fe and Ni-Fe is strong for the oxygen evolution reaction (OER), but the long-term stability and understanding of the mixed oxide phase is still limited. A key problem is the missing fundamental insight on how the morphology and interface structure of mixed oxides ultimately regulate electrocatalytic properties.<br/><br/>To develop a better understanding of mixed oxides as OER catalysts, we use scanning tunneling microscopy (STM) and photoemission spectroscopy techniques (XPS) to characterize the structure and chemical composition of well-defined Co and mixed Fe/CoO oxide nanoislands on Au(111) surface [1]. Atom-resolved STM images directly show where single Fe dopants preferentially locate within the Co oxide. Starting from a series of well-defined Co oxide nanoislands with a variable Fe content, we can therefore compare how the oxide surface structure and chemical composition develops after the sample has been used as the working electrode in an in situ electrochemical cell for OER [2]. Our OER activity measurements confirm the expected increased activity for Co-oxides mixed with Fe, which however depends in a highly non-linear way on the actual Fe content. Combining insight from STM, XPS and ambient pressure XPS we can follow the formation of the active Co(Fe) oxyhydroxide (CoOOH) phase from the initial oxide. Based on this information and theoretical modelling (A. Vojvodic, University of Pennesylvania) we propose a model where the main effect of Fe doping in Co oxide is that of a structural stabilizer that acts to preserve smaller particles with more active sites residing on the edges of CoOOH layers [3].

Mixed Co/Fe oxides on Au(111) in the electrocatalytic oxygen evolution

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.