Distortion-Induced Interfacial Charge Transfer at Single Cobalt Atom Secured on Ordered Intermetallic Surface Enhances Pure Oxygen Production

In this work, atomic cobalt (Co) incorporation into the Pd2Ge intermetallic lattice facilitates operando generation of a thin layer of CoO over Co-substituted Pd2Ge, with Co in the CoO surface layer functioning as single metal sites. Hence the catalyst has been titled Co1-CoO-Pd2Ge. High-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy confirm the existence of CoO, with some of the Co bonded to Ge by substitution of Pd sites in the Pd2Ge lattice. The role of the CoO layer in the oxygen evolution reaction (OER) has been verified by its selective removal using argon sputtering and conducting the OER on the etched catalyst. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy demonstrate that CoO gets transformed to CoOOH (Co3+) in operando condition with faster charge transfer through Pd atoms in the core Pd2Ge lattice. In situ Raman spectroscopy depicts the emergence of a CoOOH phase on applying potential and shows that the phase is stable with increasing potential and time without getting converted to CoO2. Density functional theory calculations indicate that the Pd2Ge lattice induces distortion in the CoO phase and generates unpaired spins in a nonmagnetic CoOOH system resulting in an increase in the OER activity and durability. The existence of spin density even after electrocatalysis is verified from electron paramagnetic resonance spectroscopy. We have thus successfully synthesized intermetallic supported CoO during synthesis and rigorously verified the role played by an intermetallic Pd2Ge core in enhancing charge transfer, generating spin density, improving electrochemical durability, and imparting mechanical stability to a thin CoOOH overlayer. Differential electrochemical mass spectrometry has been explored to visualize the instantaneous generation of oxygen gas during the onset of the reaction.

Rational interface engineering of Cu2S-CoOx/CF enhances oxygen evolution reaction activity

Interface engineering is the most direct and efficient way to enhance the oxygen evolution reaction (OER) activity of transition-metal sulfides (TMSs). However, present methods of engineering nano-interfaces remain to be improved. Here, we present a nitrate-pyrolysis method to create a sulfide-oxide interface on Cu2S for the first time. Specifically, a CoOx decorated Cu2S nanowire array on Cu foam (Cu2S-CoOx/CF) is prepared successfully, and the XPS result demonstrates the interfacial connection between Cu2S and CoOx. To afford a current density of 25 mA cm-2, Cu2S-CoOx/CF needs an overpotential of 255 mV, lower than that of Cu2S/CF (354 mV) and CoOx/CC (378 mV). These results indicate that the introduction of the sulfide-oxide interface is an efficient means to enhance the OER activity of Cu2S. And this paper should provide a novel route for more explorations in interface engineering for TMSs.

Highly enhanced bifunctional electrocatalytic activity of mixed copper–copper oxides on nickel foam via composition control

Fabricating Cu₂O–CuO and CuO directly on the conducting nickel foam resulted in highly enhanced OER and HER electrocatalytic activity in an alkaline medium, respectively.