NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements, operando X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γphases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure MM centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.

Efficient and active catalysts with high selectivity for hydrocarbons and other valuable chemicals during stable operation are crucial. We have taken advantage of low-pressure oxygen plasmas to modify dendritic Cu catalysts and were able to achieve enhanced selectivity toward C2 and C3 products. Utilizing operando spectroscopic methods such as X-ray absorption fine-structure spectroscopy (XAFS) and quasi in situ X-ray photoelectron spectroscopy (XPS), we observed that the initial presence of oxides in these catalysts before the reaction plays an inferior role in determining their catalytic performance as compared to the overall catalyst morphology. This is assigned to the poor stability of the CuxO species in these materials under the conditions of electrocatalytic conversion of CO2 (CO2RR). Our findings shed light into the strong structure/chemical state-selectivity correlation in CO2RR and open venues for the rational design of more effective catalysts through plasma pretreatments.

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