Typically, a battery contains four components: the cathode (positive), the anode (negative), a conductive chemical called the electrolyte that flows in between, and a separator that keeps the cathode and anode apart. Amazingly, the battery uses an engineered...

of two half reactions: At the cathode, protons (positively charged hydrogen ions) are reduced to hydrogen, whereas the oxidation of water produces oxygen at the anode. Sunlight and photocatalysts are believed to hold one key to jumpstart this process. The scientists...