High-efficiency Electroreduction of O2 into H2 O2 over ZnCo Bimetallic Triazole Frameworks Promoted by Ligand Activation.

Co-based metal-organic frameworks (MOFs) as electrocatalysts for two-electron oxygen reduction reaction (2e- ORR) are highly promising for H2 O2 production, but suffer from the intrinsic activity-selectivity trade-off. Herein, we report a ZnCo bimetal-triazole framework (ZnCo-MTF) as high-efficiency 2e- ORR electrocatalysts. The experimental and theoretical results demonstrate that the coordination between 1,2,3-triazole and Co increases the antibonding-orbital occupancy on the Co-N bond, promoting the activation of Co center. Besides, the adjacent Zn-Co sites on 1,2,3-triazole enable an asymmetric "side-on" adsorption mode of O2 , favoring the reduction of O2 molecules and desorption of OOH* intermediate. By virtue of the unique ligand effect, the ZnCo-MTF exhibits a 2e- ORR selectivity of ≈100 %, onset potential of 0.614 V and H2 O2 production rate of 5.55 mol gcat -1 h-1 , superior to the state-of-the-art zeolite imidazole frameworks. Our work paves the way for the design of 2e- ORR electrocatalysts with desirable coordination and electronic structure.

Understanding Catalyst Surfaces during Catalysis through Near Ambient Pressure X-ray Photoelectron Spectroscopy.

Heterogeneous catalysis occurs on the surface of a catalyst particle in a gas or liquid environment of reactants. The surface of the catalyst particle acts as an active chemical agent directly participating in a chemical reaction performed at a solid-gas or solid-liquid interface. Thus, authentic surface chemistry and the structure of a catalyst particle during catalysis are key descriptors for understanding catalytic performance of this catalyst. However, identification of the authentic surface of a catalyst particle during catalysis is not a simple task. We are far from knowing the fact. Photoelectron spectroscopy is one of the main techniques for characterizing surface of a catalyst since it's a surface sensitive technique. When used to track the surface of a catalyst particle at relatively high temperature in gas phase in the torr pressure range, it is called near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) or AP-XPS for simplicity. In the last several years, AP-XPS has been used to observe surface chemistry of catalysts of single crystals and nanoparticles of metal, metal oxide, and carbide. In this review, instrumentation of the near ambient pressure X-ray photoelectron spectrometers and observation of catalyst surfaces in gases phase under reaction conditions and during catalysis with AP-XPS are discussed with the following objectives: (1) to present how the surface of a catalyst particle can be characterized in gas phase, (2) to interpret how surface chemistries observed during catalysis are correlated with measured catalytic performances, (3) to demonstrate how the uncovered correlations between surface structures and catalytic performances help to understand catalytic mechanisms at a molecular level, and (4) to discuss challenges and prospects of using AP-XPS to explore the authentic surface of a catalyst under a condition near to an industrial catalytic condition. This review focuses on the application of AP-XPS to studies of catalysis and how the insights gained from AP-XPS studies can be used to achieve fundamental understanding of the catalytic mechanism at a molecular level.