Key Takeaways & Executive Findings
- •• Provides an overview of the principles, capabilities, advantages, and limitations of various advanced in situ characterization techniques. • Reviews in situ studies of fuel cells, water electrolysis, CO2 reduction reaction, and lithium batteries across multiple scales, from materials to surroundings. • Highlights dynamic tracking of chemical and structural evolution of overall reaction systems, including materials, intermediates, products, and surroundings during operation. • Proposes future integration of multimodal in situ/operando approaches with artificial intelligence for real-time monitoring at practical scales.
Abstract
Escalating global energy demands and climate urgency necessitate advanced electrochemical energy conversion and storage technologies (EECSTs) like electrocatalysis and rechargeable batteries. Improving their performance relies on elucidating reaction mechanisms and structure-performance relationships via in situ studies. This review summarizes recent in situ studies of EECSTs through a variety of advanced characterization techniques aiming at mapping reaction pathways for the rational design of overall high-performance reaction systems. We outline the principles, capabilities, advantages, and limitations of various in situ techniques. Their applications in in situ studies of fuel cells, water/CO2 electrolysis, and lithium batteries are highlighted with representative examples. These studies enable dynamic tracking of chemical and structural evolution of overall reaction systems, including materials, intermediates, products, and surroundings during operation, providing insights critical to rational system design. Future advancements will involve integrating multimodal in situ/operando approaches with artificial intelligence to enable real-time monitoring at practical scales. Such integration promises precise mechanistic insights and robust structure-performance correlations, ultimately accelerating the development of high-performance EECSTs aligned with sustainability and market requirements.
1. Introduction
Rising global energy demands, fossil fuel depletion, and environmental crises [1–3] urgently call for sustainable electrochemical energy conversion and storage technologies (EECSTs), including fuel cells [4–6], water electrolysis [7, 8], CO2 reduction reaction (CO2RR) [9–11], and lithium batteries [12–16]. Enhancing their performance requires rational design of overall reaction systems, including components such as materials, intermediates, products, and surroundings based on mechanistic understanding, particularly the dynamic chemical and structural evolution of these components under operating conditions. Conventional electrochemical methods lack the spatiotemporal resolution to capture transient species or localized reactions at the molecular/atomic level. In contrast, modern advanced in situ characterization techniques enable real-time observation of dynamic changes without extracting samples or interrupting reactions, thereby providing more accurate and reliable insights into reaction pathways.
Current advanced in situ characterization techniques encompass electron microscopy (transmission electron microscope (TEM), scanning electron microscope (SEM), and scanning transmission electron microscopy (STEM)), optical microscopy (laser scanning confocal microscopy (LSCM)), probe characterization techniques (atomic force microscope (AFM), scanning tunneling microscope (STM), scanning electrochemical microscopy (SECM), and atomic probe tomography (APT)), X-ray characterization techniques (X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), resonant elastic X-ray scattering (REXS) and X-ray absorption spectroscopy (XAS)), infrared spectroscopy (IR), Raman spectroscopy (Raman), electrochemical impedance spectroscopy (EIS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), chromatographic techniques (liquid chromatography (LC) and gas chromatography (GC)), mass spectrometry (MS), and sensor, etc. Each technique operates on distinct principles and probes specific energy levels, providing unique spatial and temporal insights. Based on probing depth and target species, these methods can be categorized into four groups: TEM, SEM, STEM, LSCM, AFM, STM, SECM, APT, XPS, XRD, REXS, and EIS for materials characterization; XAS, IR, Raman, and EPR for intermediate species analysis; NMR, LC, GC, and MS for product detection.
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Xing Chen, Yu-Lin Sun, Xiu-Mei Lin, Jin-Chao Dong, Jian-Feng Li (2026). In situ Studies of Electrochemical Energy Conversion and Storage Technologies: From Materials, Intermediates, and Products to Surroundings. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-02014-6
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Frequently Asked Questions
What are the main in situ characterization techniques reviewed in this paper?
The paper reviews advanced in situ techniques including electron microscopy (TEM, SEM, STEM), optical microscopy (LSCM), probe techniques (AFM, STM, SECM, APT), X-ray techniques (XPS, XRD, REXS, XAS), infrared and Raman spectroscopy, EIS, EPR, NMR, chromatography (LC, GC), mass spectrometry, and sensors.
Which electrochemical systems are highlighted in the in situ studies?
The review highlights in situ studies of fuel cells, water electrolysis, CO2 reduction reaction, and lithium batteries.
What is the significance of in situ studies for electrochemical energy technologies?
In situ studies enable real-time tracking of chemical and structural evolution of materials, intermediates, products, and surroundings during operation, providing critical insights for rational design of high-performance reaction systems.
What future directions are proposed for in situ studies?
Future advancements involve integrating multimodal in situ/operando approaches with artificial intelligence to enable real-time monitoring at practical scales, promising precise mechanistic insights and robust structure-performance correlations.
How are in situ techniques categorized in the paper?
The techniques are categorized into four groups based on probing depth and target species: materials characterization (e.g., TEM, XRD), intermediate species analysis (e.g., XAS, Raman), product detection (e.g., NMR, MS), and other techniques.
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