Electricity from seawater: New method efficiently produces hydrogen peroxide for fuel cells
In their recently published paper, the scientists said solar energy is an important alternative to fossil fuels, yet there are still limitations to the technology, namely that solar power systems aren’t as reliable at night. Certain technology sidesteps this problem by using hydrogen, H2, to store solar energy “in the form of chemical energy“. This allows fuel cells to produce electricity at all hours of the day. But H2 comes with its own issues: typically it has to be compressed or cooled to a liquid state to be stored efficiently.
Scientists have used sunlight to turn seawater (H2O) into hydrogen peroxide (H2O2), which can then be used in fuel cells to generate electricity. It is the first photocatalytic method of H2O2 production that achieves a high enough efficiency so that the H2O2 can be used in a fuel cell.
"The most earth-abundant resource, seawater, is utilized to produce a solar fuel that is H2O2," Fukuzumi told Phys.org.
In the new study, the researchers developed a new photoelectrochemical cell, which is basically a solar cell that produces H2O2. When sunlight illuminates the photocatalyst, the photocatalyst absorbs photons and uses the energy to initiate chemical reactions (seawater oxidation and the reduction of O2) in a way that ultimately produces H2O2.
After illuminating the cell for 24 hours, the concentration of H2O2 in the seawater reached about 48 mM, which greatly exceeds previous reported values of about 2 mM in pure water. Investigating the reason for this big difference, the researchers found that the negatively charged chlorine in seawater is mainly responsible for enhancing the photocatalytic activity and yielding the higher concentration.
Overall, the system has a total solar-to-electricity efficiency of 0.28%. (The photocatalytic production of H2O2 from seawater has an efficiency of 0.55%, and the fuel cell has an efficiency of 50%.)
"In the future, we plan to work on developing a method for the low-cost, large-scale production of H2O2 from seawater," Fukuzumi said. "This may replace the current high-cost production of H2O2 from H2 (from mainly natural gas) and O2."