CO₂ gas sensing is of great importance because of the impact of CO₂ on global climate change. Here, utilizing an inverse opal hydrogel, we describe a CO₂ gas sensing method that allows highly sensitive and selective detection over a wide concentration range. The CO₂ sensor is specific, quantitative, interference tolerant and without the need for special instruments.

Taking Cu²⁺, Pb²⁺ and Ag⁺ as examples of target cations, we describe a general strategy for constructing photonic metal ion sensing hydrogels that allow highly sensitive and selective detection via visual color changes. The sensors consist of heavy metal ion sensitive hydrogels with inverse opal structure. The presence of target cations causes shrinkage of the hydrogels and blue shift of the refraction peak wavelength with a detection limit lower than 1 nM. The interconnected macropores and the preorganized ligands makes these sensors sensitive and selective to the target ions without significant interference from pH, while the response mechanism based on the release of water of hydration after coordination prevents interference from ionic strength and anions. With this sensory system, direct, sensitive, rapid and selective detection of heavy metal ions with a broad dynamic range is achieved without expensive instruments, providing general methods for designing colorimetric metal ion sensing materials.

Electrochemical energy storage devices play a vital role in human life, and the requirements for their sustainability and environmental friendliness have been increasing in recent years. Electropolymerization, as a convenient method for polymer synthesis, has attracted increasing attentions in applications in the field of energy storage and conversion. It is not only commonly employed for the fabrication of various self‐supporting electrodes, but also is one of the most promising preparation strategies for organic electrode materials, internal interlayers within electrodes, functional protective layers, and current collector surface modifications. Previously published works have confirmed that the introduction of electropolymerization can effectively improve the electrochemical performance of various energy storage devices. However, there are still challenges in the universality of the synthesis route, in‐depth understanding of interface chemical behavior, and scaled‐up production. This mini review summarizes the main components in electropolymerization, material synthesis mechanisms, and their application principles in batteries and supercapacitors. Additionally, the current challenges and future development directions of electropolymerization have been discussed, offering some perspectives for further exploration.