Phthalocyanine catalysts have well-defined
active site structures that allow reaction-based mechanism exploration. In this
regard, the actual behaviors of metal ions in the phthalocyanine catalysts have
aroused considerable attention. Operando high-energy resolution fluorescence
detected X-ray absorption (HERFD-XANES) can be employed in the practical
situation of electrocatalysis to realize the interfacial interaction between
metal ions and the reactants, offering a unique insight into the active site
geometry and structural evolution during CO2 reduction. In this
work, the CO2RR to CO dominates over the HER with Faradaic
efficiency reaching the maximum value of 89% at 0.85 V versus RHE. The results
demonstrate the atomically dispersed, low-valent Ni(I) centres with high
intrinsic CO2 reduction activity.
The severe burning of fossil fuels brings about a worsening energy
crisis and environmental issues which aroused global concern. Electrocatalysis
and photocatalysis are promising approaches to store intermittent renewable
solar and wind energy in fuels and chemicals, leading to reduced anthropogenic
environmental damage. However, the sluggish kinetics of electrocatalysis and
photocatalysis is a huge obstacle to the overall efficiency improvement of
energy devices. There is still a knotty problem to rational designing
high-performance catalysts, which largely depends on a deep understanding of
the interface microenvironment and dynamic structure evolution of catalysts
during the reaction.
In
transitional metal (TM) layered oxide cathode materials, the energy storage
relies on Li-ion intercalation/de-intercalation in the Li layers. To achieve
higher energy density, lithium- and manganese-rich (LMR) layered oxides are
developed by enabling Li-storage in TM layers. Nevertheless, this process
involves structural evolution (e.g., oxygen release) of cathode materials that
might eventually lead to performance degradation. Typically, LMR materials
contain two structures (i.e., LiTMO2 and Li2MnO3)
that exhibit different electrochemical behaviors during charging/discharging
(Figure 1). Limited by characterization techniques, this process is difficult
to observe, leaving the relevant mechanism study a challenge.
A comprehensive understanding of the microscopic reaction mechanisms at the gas-solid-liquid electrochemical
interfaces is urgently required for the development of advanced
electrocatalysts applied in burgeoning sustainable energy conversion systems.
In-situ synchrotron radiation Fourier transform infrared (SR-FTIR) spectroscopy
is one of the most powerful techniques for investigating the evolving dynamics
of reactive intermediates during electrocatalytic reactions. In this review, we
methodically summarize the recent progress in the research of dynamic
mechanisms for valuable electrocatalytic reactions based on in-situ SR-FTIR
methodology. Moreover, the merits and drawbacks of SR-FTIR spectroscopy, the
design principles of infrared beam setups and in-situ cells, as well as
the in-situ measurement criteria are also discussed in detail. Lastly, the potential challenges and
opportunities in this field are prudently stated. This review is expected to
stimulate a broad interest in the material science and electrochemistry
communities for exploring the dynamic mechanisms of prominent catalysis at
the atomic/molecular level by using SR-based spectroscopy.
Photo/electrocatalytic water splitting has been considered as one of the
most promising approaches for the clean hydrogen production. Among various
photo/electrocatalysts, 2D nanomaterials exhibit great potential because of
their conspicuous properties. Meanwhile, synchrotron-based
soft X-ray absorption spectroscopy (XAS) as a powerful and element-specific
technique has been widely used to explore the electronic structure of 2D
photo/electrocatalysts to comprehensively understand their working mechanism
for the development of high-performance catalysts. In this work, the recent developments of soft XAS techniques applied in
2D photo/ electrocatalysts have been reviewed, mainly focusing on identifying
the surface active sites, elucidating the location of heteroatoms, and
unraveling the interfacial interaction in the composite. The challenges and
outlook in this research field have also been emphasized. The present review
provides an in-depth understanding on how soft XAS techniques unravel the
correlations between structure and performance in 2D photo/electrocatalysts,
which could guide the rational design of highly efficient catalysts for
photo/electrocatalytic water splitting.
Heterogeneous catalysis taking place at solid interfaces plays a crucial role not only in industrial chemical production, energy conversion but also in fundamental research. The dynamic evolution of surface morphology and composition requires full understanding especially under realistic reaction conditions. To this end, conventional scanning tunneling microscopy (STM) has been integrated with high pressure cell and electrochemical cell, forming high pressure (HP) STM and electrochemical (EC) STM for the in-situ/operando characterization at solid-gas and solid-liquid interfaces with atomic resolution, respectively. In this review, we attempt to give a brief introduction to the development and working principle of these two techniques and subsequently summarize several representative progresses in recent days. The dynamic changes in active sites, surface reconstruction, absorbates alteration and products formation are directly characterized in a combination with other surface sensitive technologies. The correlation between surface structures and catalytic performance as well as the underlying mechanism can thus be unraveled, which provides insights into the rational design and optimization of catalysts.
High-resolution magic angle
spinning (MAS) NMR can afford both qualitative and quantitative information of
the solid, liquid and gas phase at atomic level, and such information obtained at in situ/operando conditions is of vital importance for understanding
the crystallization process of material as well as the reaction mechanism of
catalysis. To meet the requirement of experimental conditions for material
synthesis and catalytic reactions, in situ MAS NMR techniques have been continuously developed for using at
higher temperatures and pressures with high sensitivity. Herein, we will
briefly outline the development of this technology and discuss its detailed
applications in understanding material synthesis and heterogeneous catalysis.
An in-depth understanding of the catalytic reaction mechanism is the key to designing efficient and stable catalysts. In situ transmission electron microscope (TEM) is the most powerful tool to visualize and analyze the microstructures of catalysts during catalysis. In situ TEM combined with three-dimensional (3D) electron tomography (ET) reconstruction technique enables interrogations of catalysts' structural dynamics and chemical changes in high temporal and spatial dimensions. In this review, we discuss and summarize the recent advances in in situ TEM together with 3D ET for catalyst studies. Topics include the latest research progress of in situ TEM imaging as well as 3D visualization and quantitative analysis of catalysts. We also pay particular attention to artificial intelligence (AI)-enhanced smart 3D ET. These include deep learning (DL)-based data compression and storage for the analysis of large TEM data, recovery of wedge-shaped information lost in 3D ET reconstructions, and DL models for reducing residual artifacts in 3D reconstructed images. Finally, the challenges and development prospects of current in situ TEM and 3D ET research are discussed.
The roles of temperature
change in surface-enhanced Raman scattering (SERS) hotspots are important for
understanding the plasmon-mediated selective oxidation of p-aminothiophenol
in a SERS measurement. Here, we demonstrate that the temperature change in
hotspots seriously influences the conversion of p-aminothiophenol on Au
by employing variable-temperature SERS measurements. The conversion steadily
and irreversibly increased when the temperature increased from 100 to 360 K.
But the conversion decreased above 360 K, because this conversion was
exothermic. This temperature-dependence conversion suggests that the
temperature change in hotspots originated from the photothermal effect should
be coupled to the hot-electron effect in promoting the selective oxidation of p-aminothiophenol.
Understanding
the atomic and electronic changes of active sites promotes the whole new sight
into electrochemical carbon dioxide reduction reaction (CO2RR),
which provides a feasible strategy to achieve carbon neutrality. Here we employ operando high-energy resolution fluorescence-detected X-ray absorption
spectroscopy (HERFD-XAS) to track the structural evolution of Ni(II)
phthalocyanine (NiPc), considered as the model catalysts with uniform Ni-N4-C8 moiety, during the CO2RR. The HERFD-XAS method is in favor of elucidating
the interaction of the reactant/catalyst interface from the atomic electronic
structure dimension, facilitating the establishment of the catalytic mechanism
and the dynamic structure changes. Based on operando measurement, surface
sensitive difference spectra (∆µ) and spectroscopy simulation, the interfacial
interactions between the active sites of NiPc and reactants are monitored and
the Ni species gradually reduced by increasing the applied potential is
discovered. HERFD-XAS method offers an advanced and powerful tool for
elucidating the complex catalytic mechanism in further various systems.