Graphic of Fuel Cell Chemistry (image) Stanford School of Engineering Caption The large red and white balls are oxygen atoms. The blue balls are hydrogen atoms. The arrow shows the fuel cell storing electricity during the daytime when the water molecule (left) lands its oxygen atom and surrenders two hydrogen atoms (blue balls at end of arrow). At night, the reaction would reverse. The two blue balls would pick up an oxygen atom and release the electricity they stored. The Stanford team discovered that the efficiency of the fuel cell depended on having empty spaces on the fuel cell surface where oxygen atoms could land. Credit SLAC National Accelerator Laboratory Usage Restrictions with attribution Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.