Supported cobalt and iron catalysts are important for many catalytic processes. It is believed that combining both elements in a bimetallic catalyst would result in a synergetic catalytic activity during Fischer–Tropsch Synthesis. However, the nature of the interaction between the two elements and its effect on their catalytic properties are not well understood. In the present work, we report the synthesis of carbon-nanotube-supported Co–Fe alloy catalysts using colloidal chemistry methods. The ratios of Co–Fe and their homogeneous distribution in the supported nanoparticles were confirmed using local and bulk characterization techniques. We observed the formation of Co–Fe Janus-like alloy structure and a change of their elemental distribution at the nanoparticle scale upon reduction. The bimetallic catalyst showed reasonable Fischer–Tropsch catalytic activity and selectivity to C5+ hydrocarbons when compared with monometallic iron and cobalt catalysts. Finally, we found that the active phase of the Co–Fe bimetallic species during catalysis depends on the catalytic conditions.

Ultrafast Fe L3 XAS and 2p3d RIXS elucidate the photoexcitation process of hematite.

The role that the α-Fe2O3/NiFeOOH interface plays in dictating the oxygen evolution reaction (OER) mechanism on hematite has been a source of intense debate for decades, but the chemical characteristics of this interface and its function are still ambiguous and subject to speculation. In this study, we employed operando X-ray absorption spectroscopy to investigate the interfacial dynamics at the α-Fe2O3/NiFeOOH interface. We uncovered the spontaneous formation of a FeOOH interfacial layer under (photo)­electrochemical conditions. This FeOOH interfacial layer plays a role in the surface passivation of hematite and in accumulating the (photo)­generated holes upon external potential application. This hole-accumulation process leads to the extraction of more (photo)­generated holes from hematite before releasing them to NiFeOOH to carry out the water-splitting reaction, and it also explains the reason for the delay in the nickel oxidation process. Based on these observations, we propose a model where NiFeOOH acts mainly as an OER catalyst and a facilitator of holes extraction from hematite, while the interfacial FeOOH layer acts as a surface passivation and hole-accumulation overlayer.