A new solar-to-hydrogen prototype converts solar energy into hydrogen at a rate of 14.2 percent, and has already been run for more than 100 hours straight. [Image: Miguel Modestino / EPFL]
Solar power’s complete integration into the global energy grid has been stifled by the lack of efficient methods for storing the energy to meet demands when the sun isn’t shining. Now, a team of researchers from Switzerland has demonstrated what they say is a scalable device for converting solar energy into storable hydrogen fuel using existing technologies and common materials (J. Electrochem. Soc., doi: 10.1149/2.0541610jes).
Members of the SHINE (Solar Hydrogen Integrated Nano Electrolysis) project, including OSA Fellow Demetri Psaltis and OSA Member Christophe Moser, created and demonstrated a “robust and effective” device that could increase solar-energy storage capacity through the electrochemical production of hydrogen fuel from sunlight, using an advanced interconnection method for joining silicon photovoltaic cells. The team reports that the device achieved a solar-to-hydrogen conversion efficiency (SHE) 44 percent higher than other silicon-based devices, and ran continuously for more than 100 hours without performance degradation.
Shingled solar cells and nickel electrodes
The new device is made up of three “shingled” silicon-heterojunction (SHJ) solar cells. The shingling method enabled the researchers to interconnect the cells without any empty space between them. That lack of empty space enhanced current density, making it possible to fuel the water-splitting unit of the device with only three cells. Co-author Miguel Modestino, École Polytechnique Fédérale de Lausanne, says previous designs that didn’t use shingling required four interconnected SHJ cells to create enough voltage to catalyze the electrochemical process.
The device also makes use of earth-abundant nickel electrocatalysts. Each of the nickel-foam electrodes provided a high active surface area of about 60 cm2 to sustain the current output of the SHJ solar cells.
Device demonstration
During the SHINE device demonstration, the researchers illuminated SHJ modules with a 300-W solar simulator. The modules captured the light and converted it into electricity that powered the water-splitting unit containing nickel-foam electrodes. Water molecules in the unit were oxidized, separating into hydrogen and oxygen atoms. The hydrogen protons were reduced to molecular hydrogen gas, which was collected and stored as fuel.
The researchers observed SHE values between 14.5 and 14.2 percent—a 44 percent efficiency increase compared with the previous silicon-based solar-to-hydrogen device. They also were able to run the device for more than 100 hours straight. That suggests, in the team’s view, that the technology could have the reliability and stability necessary to meet commercial energy needs.