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The scarcity of fuels, high pollution levels, climate change, and other major environmental issues are critical challenges that modern societies are facing, mostly originating from fossil fuels-based economies. These challenges can be addressed by developing green, eco-friendly, inexpensive energy sources and energy storage devices. Electrochemical energy storage materials possess high capacitance and superior power density. To engineer highly efficient next-generation electrochemical energy storage devices, the mechanisms of electrochemical reactions and redox behavior must be probed in operational environments. They can be studied by investigating atomic and electronic structures using in situ x-ray absorption spectroscopy (XAS) analysis. Such a technique has attracted substantial research and development interest in the field of energy science for over a decade. The mechanisms of charge/discharge, carrier transport, and ion intercalation/deintercalation can be elucidated. Supercapacitors generally store energy by two specific mechanisms—pseudocapacitance and electrochemical double-layer capacitance. In situ XAS is a powerful tool for probing and understanding these mechanisms. In this Review, both soft and hard x rays are used for the in situ XAS analysis of various representative electrochemical energy storage systems. This Review also showcases some of the highly efficient energy and power density candidates. Furthermore, the importance of synchrotron-based x-ray spectroscopy characterization techniques is enlightened. The impact of the electronic structure, local atomic structure, and electronically active elements/sites of the typical electrochemical energy storage candidates in operational conditions is elucidated. Regarding electrochemical energy storage mechanisms in their respective working environments, the unknown valence states and reversible/irreversible nature of elements, local hybridization, delocalized d-electrons spin states, participation of coordination shells, disorder, and faradaic/non-faradaic behavior are thoroughly discussed. Finally, the future direction of in situ XAS analysis combined with spatial chemical mapping from operando scanning transmission x-ray microscopy and other emerging characterization techniques is presented and discussed. [ABSTRACT FROM AUTHOR]

Photoelectrodes nanoscale interface design has become a key factor to enhancing their photoelectrochemical performance for water splitting by reducing the photogenerated charge recombination, thus ensuring their efficient separation, transport, and collection. In this work, hematite (α‐Fe2O3) photoanodes were prepared from a simple and scalable methodology capable of synergistically mitigating the charge loss and recombination at all interfaces (i.e., fluorine‐doped tin oxide/hematite, hematite/hematite, and hematite/electrolyte) and achieving overall efficiency of ∼50% for the water oxidation reaction compared to pristine photoelectrodes. The external quantum efficiency at 1.23 V versus reversible hydrogen electrode of pristine hematite was enhanced 6.7 times with the modifications of the three interfaces (Al2O3/NbH/NiFeOx). Electrochemical impedance spectroscopy and intensity‐modulated photocurrent spectroscopies were applied to probe and monitor the photogenerated charge carrier dynamics revealing a substantial improvement in charge separation and collection at the back‐contact interface as well as a partial mitigation of the surface states at the hematite–electrolyte interface. [ABSTRACT FROM AUTHOR]

Halide perovskites have shown high potential for developing self‐driven filterless narrowband photodetectors with the advantages of excellent color recognition, low cost, and simple design. Among the various perovskites, all‐inorganic perovskites are most promising for optoelectronic devices due to their unmatched thermal stability, but they are often more difficult to be fabricated into a phase‐pure form with large grain sizes. Herein, for the first time, a self‐driven all‐inorganic perovskite narrowband photodetector (PNPD) fabricated by a scalable postripening aerosol–liquid–solid deposition method in ambient conditions is reported. Significantly, simply applying a short thermal stress to a pristine film with heterogeneous phases and small grain sizes triggers Ostwald ripening and leads to more than tenfold enlarged grains of phase‐pure CsPbBr3 with considerably improved optoelectronic properties. The self‐driven CsPbBr3‐based all‐inorganic PNPD shows a narrowband response, with a peak responsivity of 106.6 mA W−1, specific detectivity of 2.2 × 1012 Jones at 535 nm, and a narrow full width at half maximum of only 15 nm, placing it among the best of its kind. The PNPD is also fast (trise/tfall = 3.9/3.21 ms) and stable (above 10 000 on/off switches). This work opens the path of tapping all‐inorganic perovskites for next‐generation optoelectronics with high performance and reliability. [ABSTRACT FROM AUTHOR]