So is a lithium-ion battery. Or any other type of battery. A fuel cell is really just another type of battery. All of them produce electricity electrochemically.
If you actually aim to store electricity as electricity, you want a capacitor. Recently, so-called supercapacitors have been developed, which are capable of storing useful amounts of energy, but they're starting to blur the line between electric and chemical storage, e.g., pseudocapacitors.
The navy has developed an experimental way to convert seawater into jet fuel. It looks like it takes more energy in terms of electricity to make the fuel than it releases. However, it does qualify as a pretty simple energy storage device if you could take solar or wind generated electricity and brackish water or seawater to create fuel.