The near-infrared radiation (NIR) absorbers are of fundamental significance in several fields of applications in optical sensors, photothermal energy converter, imaging, NIR stealth cloak, and smart windows.

Hydrogen energy is considered as the most promising renewable sources of energy to substitute fossil fuels. It has the advantages of zero-greenhouse emission, abundant resources, and high energy density. The electrocatalytic hydrogen evolution reaction (HER) using water splitting has received intense interest as an environmental-friendly technology consisting of HER and water oxidation reaction (WOR). Although the HER is a clean technology, it requires a high electric energy consumption and a high energetic efficiency. Thus, increasing the photocatalytic efficiency of HER is significantly necessary.

Nitrogen dioxide (NO2) gas is a kind of toxic gas, which is mainly produced by the exhaust gas of burning fossil fuel. Breathing air with a high concentration of NO2 can irritate airways in the human respiratory system. It is reported that the short-term exposure limit of NO2 gas for human body is 1 ppm for 15 min. Thus, gas sensing detection of NO2 gas is very important to protect environment and protect human health. There are drawbacks of low sensing response and low decetion efficiency within common sensors.

Ammonia (NH3) is a colorless and toxic gas, which has a pungent odor. which has a pungent odor. This compound has been widely used in agriculture, fertilizer, factories, food processing, power plants, refrigeration systems, medical treatments, and living environments. Inhalation of ammonia may cause various acute respiratory diseases. It is proved that exposure to ammonia above 50 ppm can irritate the eyes, nose, throat and skin, and extended exposure to ammonia above 200 ppm may even cause chemical burns of skin and permanent lung damage. Thus, the development of ammonia sensors is very significant in the applications of environmental monitoring, industrial process control, and food industry and medical diagnostics. The sensing materials of resistant-type ammonia sensors mainly include semiconducting metal oxides, carbon nanomaterials and conducting polymers.