A research team from Ulm University and Jena University in Germany has developed a new material that not only efficiently captures and stores solar energy, but also releases hydrogen gas on demand. Even better, this process is completely reversible, and a simple 'pH switch' can restore its vitality, allowing for repeated use. The relevant results have been published in the journal Nature Communications. Green hydrogen, as a key component of future energy transition, typically relies on the photocatalytic process of sunlight for its preparation. But the intermittency of sunlight has always been a barrier to its large-scale application. Now, scientists have for the first time combined the two functions of energy storage and hydrogen release. The team has developed a water-soluble intelligent polymer material - a large molecular framework constructed from different organic units, which also has special redox functions. Experimental data shows that the "charging" efficiency of this material exceeds 80%, and the energy can be stably stored for several days. When hydrogen gas is needed, simply add acid and catalyst to the system, and the stored electrons will immediately combine with protons to generate hydrogen gas, with an efficiency of up to 72%. All of this can be done calmly in a dark room without the need for real-time sunlight exposure. After the reaction is complete, the system can be reset by neutralizing the solution, capturing sunlight again and starting a new cycle of hydrogen storage and release. The team explained that the mystery lies in the fact that the oxidation-reduction reactions occurring in polymer materials are completely reversible, making it easy to achieve the cycle of charging, storing, and discharging. The entire process does not require tedious separation steps, only the pH value of the solution needs to be adjusted. This' pH switch 'is not only practical, but also highly ornamental: when the battery' discharges' to produce hydrogen, the solution will change from purple to yellow; And when it recharges, it will change back from yellow to purple. The team stated that this new model of "on-demand hydrogen supply" is expected to bring new possibilities to energy intensive industries such as steel smelting that require stable green hydrogen sources. This achievement also paves the way for the development of economically efficient and scalable solar energy storage technologies. (New Society)