Electrocatalytic oxygen evolution reaction (OER) is a core reaction responsible for converting renewable electricity into storable fuels; yet, it is kinetically challenging, because of the complex proton-coupled multielectron transfer process. Transition-metal-based electrocatalysts, which provide the possibility for the realization of low-cost, high-activity, and stable OER in alkaline solution, therefore have attracted significant research interest in recent years. A fundamental understanding of composition–structure–activity relationships for these electrocatalysts is essential to guide the design of practical electrocatalysts for industrial applications. With more advanced ex situ and in situ techniques to determine the active sites, there has been increasing evidence revealing the critical role of Fe in the high performance of Fe-containing transition metal-based electrocatalysts. Here, we present a critical review of recent progress in Fe-containing electrocatalysts for OER, highlighting the significant role of Fe in enhancing the OER activity. We outline the historical development of the Fe-containing electrocatalysts, summarize the conflicting viewpoints on catalytic active sites, and offer guidelines for more rigorous identification. The synthesis techniques and the major challenges in improving the intrinsic catalytic activity and stability are discussed. Finally, a perspective regarding emerging issues yet to be explored for developing OER electrocatalysts for practical applications are also provided.

Since the first report of all-inorganic perovskite solar cells (PSCs) in 2014, more than 200 research articles have been published on this topic, reporting the enhancement in the stabilized power conversion efficiency (PCE) up to 18.4%. Allinorganic PSCs have become one of the most astonishing research domains in the field of perovskite-based photovoltaics. In this Review, significant improvements in all-inorganic PSCs are analytically reviewed, with some insight into the kinetics of intrinsic phase, light, and thermal stability of all-inorganic perovskites. Theoretical calculations specify that there is still a large capacity for further enhancement of device parameters. The critical challenges and the possible elucidations concerning improving the performance of all-inorganic PSCs are also discussed. Our focus is on the assessment of all-inorganic perovskite materials' properties and the recapitulation of the latest approaches of improving the PCE of corresponding devices in order to introduce new horizons toward commercialization.

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The sensor can detect H2S gas with a concentration as low as 0.5 ppm. The frequency shift of sensor is derived from the change of mass loading on films. The responses became much faster and stronger with the increase of RH.