Blue energy fuels: converting ocean wave energy to carbon-based liquid fuels via CO2 reduction

Sequestering CO2 in the form of carbon-based liquid fuels would provide both a convenient and sustainable form of energy for practical use as well as mitigate the effects of global warming and climate change. Ocean wave energy is an abundant and relatively stable source of renewable energy, which would be highly desirable for the conversion of CO2 to conveniently stored and transported liquid fuels. In this work, we demonstrate a wave-energy-driven electrochemical CO2 reduction system, consisting of triboelectric nanogenerators, a supercapacitor and a CO2 reduction reactor, that converts ocean wave energy to chemical energy in the form of formic acid, a liquid fuel. We optimize the energy storage component of the system and operation voltage of the electrochemical cell to achieve efficient energy storage and maximize the production of formic acid. Under simulated waves, the system can produce 2.798 μmol of formic acid per day via the wave energy harvested from a water surface area of 0.04 m2. Moreover, we have performed field tests in the Red Sea to demonstrate the practicality of such an electrochemical CO2 reduction system. Finally, we present design guidelines for achieving a cost-effective, efficient, and large-scale wave-energy-driven CO2 reduction system for liquid fuel production.