Recent Advances in In Situ/Operando Surface/Interface Characterization Techniques for the Study of Artificial Photosynthesis

Abstract

(Photo-)electrocatalytic artificial photosynthesis driven by electrical and/or solar energy that converts water (H2O) and carbon dioxide (CO2) into hydrogen (H2), carbohydrates and oxygen (O2), has proven to be a promising and effective route for producing clean alternatives to fossil fuels, as well as for storing intermittent renewable energy, and thus to solve the energy crisis and climate change issues that we are facing today. Basic (photo-)electrocatalysis consists of three main processes: (1) light absorption, (2) the separation and transport of photogenerated charge carriers, and (3) the transfer of photogenerated charge carriers at the interfaces. With further research, scientists have found that these three steps are significantly affected by surface and interface properties (e.g., defect, dangling bonds, adsorption/desorption, surface recombination, electric double layer (EDL), surface dipole). Therefore, the catalytic performance, which to a great extent is determined by the physicochemical properties of surfaces and interfaces between catalyst and reactant, can be changed dramatically under working conditions. Common approaches for investigating these phenomena include X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning probe microscopy (SPM), wide angle X-ray diffraction (WAXRD), auger electron spectroscopy (AES), transmission electron microscope (TEM), etc. Generally, these techniques can only be applied under ex situ conditions and cannot fully recover the changes of catalysts in real chemical reactions. How to identify and track alterations of the catalysts, and thus provide further insight into the complex mechanisms behind them, has become a major research topic in this field. The application of in situ/operando characterization techniques enables real-time monitoring and analysis of dynamic changes. Therefore, researchers can obtain physical and/or chemical information during the reaction (e.g., morphology, chemical bonding, valence state, photocurrent distribution, surface potential variation, surface reconstruction), or even by the combination of these techniques as a suite (e.g., atomic force microscopy-based infrared spectroscopy (AFM-IR), or near-ambient-pressure STM/XPS combined system (NAP STM-XPS)) to correlate the various properties simultaneously, so as to further reveal the reaction mechanisms. In this review, we briefly describe the working principles of in situ/operando surface/interface characterization technologies (i.e., SPM and X-ray spectroscopy) and discuss the recent progress in monitoring relevant surface/interface changes during water splitting and CO2 reduction reactions (CO2RR). We hope that this review will provide our readers with some ideas and guidance about how these in situ/operando characterization techniques can help us investigate the changes in catalyst surfaces/interfaces, and further promote the development of (photo-)electrocatalytic surface and interface engineering.

The Recent Progresses of Electrodes and Electrolysers for Seawater Electrolysis

“…2.4 Å, which is consistent with Ru−Ru bonds of metallic Ru. These operando characterizations were applied to the study of the changes in catalyst surfaces/interfaces [58][59][60]. Except for Pt-group elements as shown in Figure 1d, nonprecious TMs are also ideal substituted catalysts with lower cost.…”

Tailoring Interfacial Physicochemical Properties in Cu2O-TiO2@rGO Heterojunction: Insights from EXAFS and Electron Trap Distribution Analysis

“…EXAFS provides insights into bond lengths, coordination numbers, and the presence of defects or disorder, all of which profoundly influence the electronic properties of the heterojunction. 30 Moreover, reverse double-beam photoacoustic spectroscopy (RDB-PAS) proves to be exceptionally useful in the study of charge carrier dynamics within semiconductor heterojunctions. It can provide a detailed picture of the electronic and acoustic responses at the heterojunction interface, crucial for understanding the efficiency and kinetics of charge carriers, which are pivotal factors in the performance of semiconductor heterojunctions, particularly those involved in energy conversion applications.…”

“…Extended X-ray absorption fine structure (EXAFS) analysis enables us to investigate the local atomic structure and bonding environment of specific elements within the heterojunction. EXAFS provides insights into bond lengths, coordination numbers, and the presence of defects or disorder, all of which profoundly influence the electronic properties of the heterojunction . Moreover, reverse double-beam photoacoustic spectroscopy (RDB-PAS) proves to be exceptionally useful in the study of charge carrier dynamics within semiconductor heterojunctions.…”